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ACI 345R-91(Reapproved 1997)

GUIDE FOR CONCRETE HIGHWAYBRIDGE DECK CONSTRUCTION

Reported by ACI Committee 345

John L. CarratoChairman

John H. Allen Allan C. Harwood

Ralph K. Banks Mark R. Hein

Paul D. Carter Paul Klieger

Ralph L Duncan Surinder K. LakhanpalRobert V. GeveckerRobert J. Gulyas

Paul F. McHale

Jack D. NorbergHarry L. PattersonOrrin RileyWilliam F. SchoenVirendra K. Varma

The durabiliy and maintenance costs of concrete highway bridge decks arehighly dependent upon the care exercised during the construction phase,including attendant activities during the preconstruction and post-construction periods. Recommendations relative to these periods arepresented, covering the areas of design considerations, inspection, pre-construction planning, falsework and formwork, reinforcement, concretematerials and properties, measuring and mixing, placing and consolidation,finishing, curing, postconstruction care, and the use of overlays.

Keywords: admixtures; aggregates; air entrainment; bleeding(concrete); bridge decks; cements;concrete construction; concretefinishing (fresh concrete); concretes; consolidation; cover; cracking(fracturing); curing; drainage; durability; epoxy resins; falsework;formwork (construction); inspection; maintenance; mixing; placing;protective coatings; proportioning;reinforced concrete; reinforcingsteels; resurfacing; scaling; shrinkage; skid resistance; spalling;specifications; structural design; surface roughness; texture; vibration;workability.

CONTENTS

Chapter 1 -- Introduction, p. 345R-11.1 -- General1.2 -- Roughness1.3 -- Cracking1.4 -- Spalling1.5 -- Scaling1.6 -- Slipperiness1.7 -- Summary

ACI Committee Reports, Guides, Standard Practices andCommentaries are intended for guidance in designing,planning, executing or inspecting construction, and inpreparing specifications. Reference to these documentsshall not be made in the Project Documents; they shouldbe phrased in mandatory language and incorporated intothe Project Documents.

34

Chapter 2 -- Design considerations, p. 345R-52.1 -- General2.2 -- Drainage2.3 -- Deck thickness2.4 -- Cover2.5 -- Arrangement of reinforcement2.6 -- Positive protective systems2.7 -- Skid resistance and surface texture2.8 -- Joint-forming materials

Chapter 3 -- Inspection, p. 345R-83.1 -- General3.2 -- Inspection personnel3.3 -- Inspection functions

Chapter 4 -- Preconstruction planning, p. 345R-94.1 -- Construction schedules4.2 -- Coordination of construction and inspection4.3 -- Review of construction method4.4 -- Manpower requirements and qualifications4.5 -- Equipment requirements4.6 -- Specialty concretes

Chapter 5 -- Falsework and formwork, p. 345R-105.1 -- General considerations5.2 -- Consideration for type of form5.3 -- Materials

ACI 345R-91 became effective Sept. 1,199l and replaces ACI 345-82 which waswithdrawn as an ACI standard in 1991.

Copyright 0 1991, American Concrete Institute.All rights reserved including rights of reproduction and use in any form or by

any means, including the making of copies by any photo process, or by anyelectronic or mechanical device, printed or written or oral, or recording for soundor visual reproduction or for use in any knowledge or retrieval system or device,unless permission in writing is obtained from the copyright proprietors.

5R-1

ACI COMMITTEE REPORT

5.4 -- Removal5.5 -- Workmanship

Chapter 6 -- Reinforcement, p. 345R-126.1 -- General considerations6.2 -- Arrangement6.3 -- Reinforcement support and ties6.4 -- Cover over steel6.5 -- Cleanliness6.6 -- Epoxy-coated reinforcing steel

Chapter 7 -- Concrete materials and properties,p. 345R-137.1 -- General7.2 -- Materials7.3 -- Properties of concrete

Chapter 8 -- Measuring and mixing, p. 345R-178.1 -- General8.2 -- Reference documents8.3 -- Measuring materials8.4 -- Charging and mixing8.5 -- Control of mixing water and delivery8.6 -- Communication

Chapter 9 -- Placing and consolidating, p. 345R-209.1 -- General considerations9.2 -- Transportation9.3 -- Rate of delivery9.4 -- Placing equipment9.5 -- Vibration and consolidation9.6 -- Sequence of placing9.7 -- Manpower requirements and qualifications9.8 -- Reinforcement -- Special care during placing9.9 -- Reference documents

Chapter 10 -- Finishing, p. 345R-2310.1 -- General10.2 -- Timing of operations10.3 -- Manual methods10.4 -- Finishing aids10.5 -- Mechanical equipment10.6 -- Texturing10.7. -- Correction of defects

Chapter 11 -- Curing, p. 345R-2711.1 -- General considerations11.2 -- Curing methods11.3 -- Time of application11.4 -- Duration11.5 -- Related information

Chapter 12 -- Postconstruction care, p. 345R-2812.1 - General12.2 - During Continuing Construction12.3 - Construction Associated Preventive

Maintenance

Chapter 13 -- Overlays, p. 345-2913.1 -- Scope13.2 -- Need for overlays13.3 -- Required properties of overlays13.4 -- Types of overlays13.5 -- Design considerations13.6 -- Construction considerations13.7 -- Other considerations

Chapter 14 -- References, p. 345R-3314.1 -- Recommended references14.2 -- Cited references

Appendix A

Chapter 1 -- Introduction

1.1 GeneralThe riding surface of a highway bridge deck should

provide a continuation of the pavement segments whichit connects. The surface should be free from character-istics or profile deviations which impart objectionable orunsafe riding qualities. The desirable qualities shouldpersist with minimum maintenance throughout the pro-jected service life of the structure.

Many decks remain smooth and free from surface de-terioration and retain skid resistance for many years,attesting to satisfactory attention to the many detailsinfluencing such performance. When deficiencies dooccur, they usually take one of the forms described inthis chapter. Subsequent chapters of this report discussthe contribution of various aspects of deck constructionto such defects, and present guidelines based on theoryand experience which should reduce the probability ofoccurrence to an acceptable level.

1.2 RoughnessRoughness can be periodic, varying in wave length,

or it may occur as discrete discontinuities. Excessive sagor camber are deficiencies which cause long wave lengthroughness. Roughness with short wave length, or “wash-boarding,” can appear early and result from inadequatecover over reinforcement, other construction practices, ordevelop subsequently with surface deterioration. Suchshort wave length roughness may be periodic or randomdepending on its cause. Discontinuities at joints or nearabutment backwalls result in sudden “bumps.”

1.3 CrackingCracks may be classified according to their orien-

tation in relation to the direction of traffic as longi-tudinal, transverse, diagonal, or random. In addition, theterms “pattern cracking” and “crazing” are used to referto characteristic defects as defined in ACI 201.1R. Theseverity of cracking is conventionally expressed qualita-tively as fine, medium, and wide, based on crack width.

CONCRETE HIGHWAY BRIDGE DECK CONSTRUCTION 345R-3

Fig. 1.2--Diagonal cracking

ACI 201.1R defines cracking severity as:

a. Fine -- Generally less than lmm wide.b. Medium -- Between lmm and 2mm wide.c. Wide -- Over 2mm wide.

Examples of several types of cracking are shown inFig. 1.1 through 1.4.

Fig. 1.3--Random cracking

Fig. 1.4--Pattern cracking

A compressive survey1 of randomly selected bridgedecks in eight states provides some insights as to fre-quency and causes of various categories of cracking,recognizing that most cracks are caused by a number ofinteracting factors. This survey found comparatively littlelongitudinal and diagonal cracking. Findings from thesurvey are described in Sections 1.3.1 through 1.3.4.

1.3.1 -- The most prevalent longitudinal cracking oc-curred as “reflective” cracks in thin concrete wearingcourses over longitudinal joints of precast, prestressed

box girder spans, or in areas where resistance to sub-sidence was offered by longitudinal reinforcement, voidtubes, or other obstructions.

1.3.2 -- Diagonal cracking occurred most often in theacute angle corner near abutments of skewed bridges, orover single-column piers of concrete box girder, deckgirder, or hollow slab bridges.

1.3.3 -- Transverse cracking was observed on aboutone-half of the 2300 spans inspected. No one factor canbe singled out as the cause of transverse cracking.Among the more important factors were (1) external andinternal restraint on the early and long-term shrinkage ofthe slab and (2) combination of dead-load and live-loadstresses in negative moment regions. In general, theobserved crack pattern suggests that live-load stressesalone play a relatively minor role in transverse cracking.

1.3.4 -- Pattern and random cracking were usuallyshallow and may be related to early or long-term drying.

345R-4 MANUAL OF CONCRETE PRACTICE

Fig. 1.5--Surface spalling

Fig. 1.6--Surface scaling

Fig. 1.7--Polished coarse aggregate contributes to low skidresistance

This minor cracking was a common defect. Occasionally,severe cases were encountered in which the probablecauses were severe early drying (plastic shrinkagecracking2) or unstable conditions associated with reactiveaggregates3.

1.4 SpallingSurface spalls are depressions resulting from sepa-

ration of a portion of the surface by excessive internalpressure resulting from a combination of forces. Anexample is shown in Fig. 1.5. Spalling exposes rein-forcement, decreases deck thickness, and subjects thethinned section to impact. Joint spa11 is used to designatespalls adjacent to various types of joints. The incidenceof spalling varies considerably among the states,’ butwhere it occurs it is a serious and troublesome problem.It is related to the use of deicing chemicals, corrosion ofreinforcement, traffic column, and quantity and quality ofconcrete cover.

1.5 ScalingScaling, such as that shown in Fig. 1.6, is loss of sur-

face mortar, usually associated with the use of deicerchemicals. Severity is normally expressed qualitatively byterms such as light, medium, heavy, or severe. Gradualloss of surface by abrasion is sometimes difficult to dis-tinguish from scaling. Scaling can be locally severe but, inthe absence of studded tires, generally is not a seriousproblem if accepted concreting practices are followed.

1.6 SlipperinessSurface friction measurements of highway pavements

in the United States are typically made using a locked-wheel skid trailer that meets the requirements of ASTME 274. This procedure measures the frictional force on alocked test wheel as it is dragged over a wet pavementsurface under constant load and at a constant speed, withits major plane parallel to the direction of motion andperpendicular to the pavement. The standard referencespeed is usually 40 mph, and the results are expressed asa friction number (FN). Well-textured new pavementswill have friction numbers above 60 when tested at aspeed of 40 mph.

The FN of the bridge deck surface should not differsubstantially from the pavement segments that it con-nects, and should have and retain the minimum valueestablished for pavement surfaces. Published data forbridge decks are meager, but those available for pave-ments indicate that low skid resistance or slipperiness canbe influenced by materials and construction practices,and by subsequently applied coatings. An example of asurface polished by heavy traffic is shown in Fig. 1.7.

1.7 SummaryRoughness, cracking, spalling, scaling, and

slipperiness are the major defects which result when themany details which influence their occurrence are notgiven sufficient attention. Recognition of the interaction


Fig 2.1--Surface sealing promoted by poor drainage

of design, materials, and construction practices, as well asenvironmental factors, is the important first step inachieving smooth and durable decks.

Chapter 2 -- Design considerations

2.1 GeneralThe main purpose of this chapter is to emphasize

those design factors which may affect the resistance of abridge deck to the severe exposure condition broughtabout by the action of deicing chemicals. Hence, thedesign considerations of this chapter are not concerned,for the most part, with the structural analysis of thebridge deck. The items discussed in this chapter, how-ever, are generally within the purview of the bridgedesigner.

2.2 Drainage2.2.1 -- It is vital to establish grades that will insure

proper drainage. In addition to provision for storm waterremoval, attention should be given to the problem ofdraining the small quantities of water from melting snowand brine from deicing chemicals. The shallow slopes andcrowns sometimes found on bridge decks, the small inac-curacies in finish of the wearing surface, the confiningeffect on the curb or barrier, and the accumulation of

Fig. 2.2-Drainage pipe directs wnter front decks to ditch

Fig. 2.3--Lack of adequate drainage facilities results indeterioration of pier

dirt in the gutter often prevent a deck from drainingcompletely. An example is shown in Fig. 2.1. This pond-ing of water and brine on an inadequately drained deckis a basic cause of bridge deck deterioration.

2.2.2 -- Drains should be designed for size andlocation so that drain water may be removed quickly andwill not be emptied on to, or blown against, the concreteor steel below. An acceptable arrangement is shown inFig. 2.2, and an unsuitable one is shown in Fig. 2.3. Anadequate number of small deck drains should be pro-vided in flat surface areas. Metals used in drains should


T O P O F S L A B TO STRINGER+,

Typical Variation

-1Mln,mum size Distribution Steel

------rMmlmum size Distribution Steel

Minimum s u e Main Reinforcement i

B O T T O M O F S L A B

Fig. 2.4--Typical dimensions and tolerance for location ofreinforcing steel in concrete bridge decks

Fig. 2.5--Comparison of bridge deck thickness requirementsfor conventional wood forms and corrugated steel stay-in-place forms

be able to withstand the corrosive effect of deicingchemicals.

2.2.3 -- Inlets should be sized to prohibit large

particles, such as beverage cans, from lodging in thedrain conduit and causing stoppages. Sharp angle turnsshould not be used in drainage conduits, and outfallsshould be readily accessible to facilitate cleaning.

2.3 Deck thickness2.3.1 -- Bridge design agencies usually establish

standard details specifying deck thickness and reinforce-ment arrangement for different bridge deck spans. Anominal minimum deck thickness of 8 in. is recommend-ed (see Fig. 2.5).

2.3.2 -- The high quality of deck concrete that isneeded to achieve durability usually results in muchhigher concrete strengths than needed for the structuralcapacity of the deck. The advent of higher strengthgrades of reinforcing steel also necessitates a reevaluationof established standard details. The temptation exists touse thinner deck slabs and thus use these materials moreefficiently. However, Committee 345 believes that a con-servative approach should be taken in this matter. Whilethere is no direct evidence that deterioration is morelikely to occur in thinner, more flexible decks than inthicker, stiffer decks, there is evidence that once deter-ioration has started, it is likely to progress more rapidlyin the thinner decks. Thinner decks also result in greatercongestion of reinforcement, and the problems associatedwith that condition.

2.3.3 -- As with all construction, tolerances must beallowed in design dimensions to insure achieving all crit-ical minimum values. Recent reports confirm that theplacing of top deck reinforcement often varies widely.4

Average cover has been found to be typically equal tothe design or “plan” cover, with a standard deviation ofabout 0.3 in. Thus, to insure that 97 percent of the rein-forcement has at least the minimum 2.0-in. cover re-quired in Section 2.4, an average and plan cover of
2.6 in. would be required. When these tolerances areadded to the thickness occupied by the reinforcing barsand to the required clearances between bars and slabfaces, the required minimum thickness is close to 8 in.Fig. 2.4 shows the relationship of the several componentdimensions to the total deck thickness assuming the barsizes most commonly used.
If corrugated metal stay-in-place forms are used,slight additional slab thicknesses are required even whentransverse bars are located in the valleys of the cor-rugations. The profile positions of the layers of rein-forcing bars and the minimum cover over the steel mustbe maintained. Fig. 2.5 shows one type of deck designwhere the use of corrugated forms results in an add-itional 3/8-in. of concrete and a second design with anadditional 1 in. of concrete. This design simplifies formplacement, particularly on radial structures.

2.3.4 -- Adequate provision for deck haunches (orfillets) is a design feature associated with deck thickness.The designer should select bearing elevations so that thesteel or precast concrete girder does not penetrate intothe deck slab thickness at any point along its length. The

CONCRETE HIGHWAY BRIDGE DECK CONSTRUCTION

2.4 Cover2.4.1 -- A most important consideration in bridge

deck design is the thickness of protective concrete coverover the top reinforcement. It is recommended that 2 in.of concrete, measured from top of bar, be the minimumamount of protective cover over the uppermost reinforce-ment in bridge decks.5 The reader is directed to ACI 117,Section 3.4, for construction tolerances. Spalling generallyoccurs readily on decks having inadequate cover over thebars. Similar requirements for top, bottom, and side facesfor reinforcing bar cover should be considered for coastalenvironments.

designer must consider the differences between the road-way profile and the girder profile -- including the pos-sible deviations from expected girder camber -- at variouspoints along the girder length. Small concrete haunchesare formed in that portion of the deck where the top sur-face of the girder is lower than the bottom of the slab.On the other hand, slab thickness is reduced and theplacement of reinforcement can be affected where thegirder projects into the slab.

Clearly, deviations from the specified cover, as dis-cussed in Section 2.3.3, should be expected to occur inconstruction. The designer should try to anticipate con-ditions that could make accurate steel placement moredifficult, or where the desired concrete surface might be“undercut” by the action of the strikeoff, as at nonuni-form sections of complicated geometrical transitions, andcompensate with an increased cover requirement.

2.5 Arrangement of reinforcement2.5.1 -- In the most common type of bridge deck --

the slab-on-beam bridge using a 7% to 9 in. thick slabspanning between longitudinal girders -- the primaryreinforcement is placed transverse to the girders. To usethis reinforcement most effectively from a structuralpoint of view, current practice places the reinforcementclosest to the top and bottom slab surfaces. TheMSHTO Standard Specifications for Highway Bridgesprovides simple empirical equations to represent theWestergaard analysis of bridge deck behavior. The pri-mary reinforcement is selected on the basis of one-wayslab action and pure flexure. Shear, bond, and fatigue arenot considered in the procedure. None of the bridge deckdurability studies has indicated any structural deficienciesin the deck design procedure with the level of stressesgenerally permitted. The primary slab reinforcement gen-erally consists of No. 5 or No. 6 bars placed from about5 to 9 in. on center.

2.5.2 -- Distribution reinforcement, generallyconsisting of No. 4 or No. 5 bars, is placed transverse tothe primary reinforcement to provide for the two-way be-havior of the deck. The amount of distribution reinforce-ment is determined as a percentage of the primary rein-forcement, with more being placed in the middle half ofthe slab span than over the beams.

2.5.3 -- Shrinkage and temperature reinforcement is

Fig. 2.6--Halves of a core taken through a vertical crack.Notice the imprint of the top reinforcing bar (which hasbeen removed) and the penetration of road deposits to thelevel of the top

placed transverse to the primary reinforcement near thetop of the slab to control cracking resulting from dryingshrinkage and temperature changes in the concrete. Cur-rent practice uses No. 4 or No. 5 bars spaced from 12 in.to 18 in. on center and placed underneath the top pri-mary slab reinforcement. Transverse cracks, the mostcommon kinds of cracks found in bridge decks, tend toform parallel to, and directly over, the top primaryreinforcing bars, exposing them to attack from chlorides,moisture, and air (see Fig. 2.6). Furthermore, the tensilestresses caused by drying shrinkage are not uniformthrough the depth of a concrete slab, but are largest nearthe drying faces. It would appear, then, that a moreeffective way to “control” (i.e., reduce the widths of) thistype of cracking is to place the shrinkage and temper-ature reinforcement above the primary slab steel (whileproviding minimum 2 in. cover), in a more strategiclocation.

2.5.4 -- Prestressed box beam bridges generallydisplay reduced tendencies toward transverse crackingbecause of their stiffness. However, adjacent box beamsuperstructures (no space between the beams) often havethin, nonreinforced decks that frequently display unde-sirable longitudinal reflection cracks over the jointsbetween adjacent beams. One solution is to post-tensionthe beams together transversely and use a reinforcedconcrete deck on top.

2.6 Positive protective systems2.6.1 Overlays -- The common forms of bridge deck

deterioration, such as scaling, some types of cracking andsurface spalling, generally occur within the top 2 in. of adeck. Improper concrete placing and finishing practicesoften result in a lower quality concrete in this area.Since it is subjected to the most severe exposure and ser-vice conditions, the top portion of the deck slab shouldhave the best possible concrete quality. Considerationshould be given to placing an overlay on the bridge deckwhen it is constructed. Many different types of overlays

345R-8 ACI COMMITTEE REPORT

have been used successfully. Chapter 13 discusses several
types of overlays in detail.
2.6.2 Other positive protective systems -- Because of thehigh cost of repairing corrosion-caused damage, severaldifferent positive protective systems are being used forbridge decks in severe deicing salt areas and for somemarine structures. In addition to overlays, some of theother successful systems include:

a.

b.

c .

d.

Epoxy (electrostatically-applied powder) coatedreinforcing steelSilica fume concrete which reduces chloridepermeability and improves sulfate and alkaliaggregate attack durabilityCathodic protectionCalcium nitrite admixture

A recent study for the FHWA5 reports on theabilities of several different protective systems.

2.7 Skid resistance and surface texture2.7.1-- The requirements for surface texture are dic-

tated by the levels of skid resistance necessary to providesafety under the anticipated traffic speeds and volumes.The skid resistance of pavements has received extensivetreatment in the technical literature.6,7 While bridgedecks specifically have not been studied in the samedetail as pavements, similar requirements would seemappropriate.

Although attempts have been made to set numericallimits for skid numbers, none generally applicable havebeen established because of problems associated withtesting variability, varied local conditions (class of road,geometric factors, etc.).

The general conclusion, however, is that a minimumacceptable skid number determined by a locked wheeltrailer, meeting the requirements of ASTM E 274 at40 mph, should be in excess of 30. Data developed todate suggest that obtaining a satisfactory skid resistancedepends on providing a deeper and more severe texturethan is conventionally obtained by texturing with burlapor belts.

2.7.2 -- Textures with ridges and valleys perpendicularto the direction of traffic will provide maximum drainage,but will also cause greatest tire noise unless care is takenregarding spacing. Success in maximizing skid resistanceand minimizing tire noise have been reported by usingseveral texture configurations.8

Textures with ridges and valleys parallel to thedirection of traffic minimize noise, but require that extracare be taken to provide transverse drainage. The readeris directed to ACI 325.6R for recommended texturingpractices.

2.8 Joint-forming materialsThe design, selection, installation, and maintenance

of joints and joint-forming materials may be found inACI 504R.

Chapter 3 -- Inspection

3.1 General3.1.1 -- The primary objective of the inspection and

testing should be to aid in obtaining a quality bridge deckby preventing mistakes and assuring adherence to thespecifications. The responsibility for inspection should bevested in the engineer as a continuation of his or herdesign responsibility. If the inspection is not done byemployees of the engineer, the responsibility may bedelegated to an independent inspection agency. In allinstances, the fee for inspection should be paid directlyby the owner to those performing the inspection services.

3.1.2 -- The scope and nature of the inspectionservices will depend primarily on the size and importanceof the work. The organization and conduct of inspectionservices are described in detail in ACI 311.4R. Eachinspector should be thoroughly familiar with the contentof that publication. This chapter is designed to supple-ment ACI 311.4R and to direct attention to details thatare of particular significance to the construction of bridgedecks.

3.13 -- The specifications must define the re-sponsibility of the inspection agency and contractor. Inno instance should the inspection agency attempt toassume or accept the contractor’s responsibility forsupervision of the job. Specifications should require thatthe contractor conduct certain specific quality controltests of materials to be used in the job. These qualitycontrol tests may be made by his forces, by the testingagency employed by him, or by his subcontractors ormaterials suppliers. The existence of quality control pro-grams by the contractor does not relieve the inspectionagency which represents the owner of surveillance oversuch testing programs.

3.2 Inspection personnel3.2.1 -- Personnel responsible for inspection must be

qualified by experience and training. Those performingacceptance testing should be certified ACI Grade 1 fieldtesting technicians. Inspection and quality controlagencies should meet the requirements of ASTM E 329.

3.3 Inspection functions3.3.1 -- The scope of inspection required and as-

signment of responsibility should be defined in the jobspecifications. The scope will depend on the size andcomplexity of the job, but should include: inspection andtesting of materials; concrete batching and mixing facil-ities; concrete handling, placing, consolidation, finishing,and curing; inspection of forms, reinforcing, and embed-ded items; and inspection of stripping and curing opera-tions. More complete lists of functions are given inACI 311.4R.

3.3.2 -- The items deserving particular attention forbridge decks are as follows:

a. The concrete production and delivery equipmentshould be reviewed at the preconstruction plan-

345R-9
CONCRETE HIGHWAY BRIDGE DECK CONSTRUCTION
TABLE 3.1--Batching

Verify the use of approvedmaterials

Monitor aggregate moisture

Check batch weights,admixture quantities, andcharging sequences

Prepare batch certificates

Monitor mixing time

Conduct tests on slump,and temperatures.Make test specimens

air,

inspectors~~~_~_Placing

Check clearance and spacingof reinforcement

Verify adequate vibration

Monitor finishingagainst drying

to guard

Verify suitabletexture

surface

Verify cure at proper time

ning conferences discussed in Chapter 4 of this

Chapter 4 -- Preconstruction planning

4.1 Construction schedulesIn those sections of the country where bridge deck

performance has been found to be unsatisfactory, newdecks should not be placed during periods of extremeweather. Schedules should be drawn to allow for bridge

b.

c.

standard to insure that they are adequate to pro-vide a steady uninterrupted flow of concrete ofuniform properties.Before the placing of the actual deck, full-sizedbatches of the proposed mix proportions shouldbe mixed and tested.Elevations and dimensions of the forms, rein-forcing and screeds must be carefully checked asthe work progresses. The amount of cover overthe top reinforcing steel must receive special at-tention, both before and during concreting oper-ations (see Chapter 6).

d.

e.

Inspection forces must be prepared to check theair content and slump of practically every batchof concrete, using the ASTM C 231 test method.Rapid checks can be made with the Chace AirMeter and Kelly Ball, but not for acceptance orrejection purposes. Concrete temperatures shouldbe measured on every load. These testing func-tions should not impede the progress of the work.Placing and finishing procedures must beinspected to avoid unnecessary reworking of thesurface, finishing while bleed water is on thesurface of the concrete, or sprinkling of water onthe surface to aid finishing. The specified gradeand crown must be maintained to insure properdrainage of the surface and to avoid irregularitiesin the surface which will later impound water onthe surface.

3.3.3 -- Most agencies now recognize that at leastthree inspectors are required during concreting oper-ations to insure good construction practice and to keepgood records of materials and procedures. There shouldbe one inspector at the point of batching, one inspectorat the point of discharging and one inspector at the pointof placing. Their more important duties are given inTable 3.1.

deck placement during daylight hours in the spring andfall, and during nighttime hours in the summer. Wheresuch ideal scheduling is impractical, sufficient flexibilityshould be built into the schedule to await suitableweather conditions.

In general, from the time all superstructure framinghas been completed, one month per work crew should beallowed for casting the first 10,000 ft2 of bridge deck, andone week for each additional 10,000 ft2 thereafter. Oneday should be added for each day below 40 F or above90 F and less than 50 percent relative humidity.

4.2 Coordination of construction and inspectionIt is vital that contracting and inspecting forces

coordinate their schedules prior to beginning work. Beamelevations must be taken prior to building haunches.Deck forms must be inspected prior to placing rein-forcing steel. Reinforcing steel must be inspected in placeprior to installation of screed rails. Screed rail elevationsand the critical clearance over the top reinforcing steelmust be thoroughly checked just prior to ordering con-crete to the site.

The following recommended inspection times shouldbe programmed for each 10,000 ft2 of bridge deck for thework described above:

a. Surveying deflection control points 1 dayb. Calculating haunch elevations 1 dayc. Inspecting deck forms l/2 dayd. Inspecting reinforcing placement l/2 daye. Checking screed elevations 1 day

4.3 Review of construction methodThe contractor’s proposed methods should be made

clear to the inspection force so that compatibilitybetween the proposed methods and the requirements ofthe contract can be ascertained and all differences inmethods and requirements be resolved. Thus, a precon-struction meeting to review deck construction methodsshould be held between 30 and 60 days prior to begin-ning deck forming to provide opportunity for resolutionof any differences that may exist.

4.4 Manpower requirements and qualifications4.4.1 -- Manpower requirements for deck placement

vary according to the experience of the workmen, thesurface area of the placement, the placing and strikeoff

345R-10 ACI COMMlTTEE REPORT

equipment to be used, weather conditions and the speedof concrete delivery, including delivery from the batchingarea to the jobsite and from the delivery equipment tothe deck forms. A typical deck placement crew consistsof a minimum of six people.

4.4.2 -- Minimum manpower requirements are oftenestablished by union rules, and maximum manpower is afundamental prerogative of contractors. Hence, it is notrecommended that manpower limits be set forth in thespecifications. The judgment of an experienced supervisoris valuable in establishing manpower requirements.

4.4.3 -- The individual on the contractor’s forceresponsible for deck concreting should have a minimumof 2 years experience for simple span bridges with lengthsless than 100 ft and skewed no more than 5 deg fromnormal, and 5 years experience for all other types ofbridges.

4.5 Equipment requirements4.5.1 -- The following equipment is normally assem-

bled prior to a bridge deck placement: generator (withextra gasoline), vibrator (plus standby), strikeoff machine,16-ft longitudinal plow handle wood float or equivalentfinishing machines, long handle bull float, 10-ft straightedge, two separate foot bridges, texturing equipment, and“fogging” and curing equipment.

4.5.2 -- Self-propelled screeding machines should berequired on all bridges of more than one span.

4.5.3 -- Special attention should be given to methodsof transferring the concrete from the delivery point tothe point of placement, since poorly planned operationsin this area can result in excessive delay times which pro-mote such practices as retempering and sprinkling to aidfinishing. More thorough discussions of bridge deck con-struction equipment will be found in Chapters 8, 9,and 10.

4.6 Specialty concretesThe use of specialty concretes as overlays for bridge

decks is another area where special attention is required.Examples of such materials include latex-modified con-crete, low-slump and low-water-cement-ratio concrete(commonly called the “Iowa” system), and low-water-cement-ratio, higher slump concrete made using high-range water-reducing admixtures. On-site mixing usingproperly calibrated mobile mixers is recommended for allof the above systems, since such a procedure will facil-itate better quality control and permit concrete pro-duction and placement at equal rates. Other methods ofon-site production may be approved if the quality controlis comparable. Bonding of the overall concrete to thebase deck is another potential problem area. Bondinggrout, if used, must be thoroughly brushed into the cleanbase concrete and covered with overlay concrete beforeit dries. Special attention to curing is necessary tominimize shrinkage cracking of the overlay concrete. Ingeneral, wet burlap should be applied as soon as the newconcrete will support it without deformation. Addition-

ally, each specialty material will undoubtedly exhibitspecific properties which require additional precautions.As examples: a specialized heavy finishing machine isrequired to insure that a low-slump concrete is properlyconsolidated; the curing normally used with styrene-buta-diene latex-modified concrete is to cover for 24 hr withwet burlap followed by air drying; and concrete con-taining high-range water reducing admixtures oftenexhibits a higher than normal rate of slump loss withtime. To preclude problems, the engineer should contactmanufacturers and study the available literature on anyspecialty concrete prior to use.

Chapter 5 -- Falsework and formwork

5.1 General considerations5.1.1-- General considerations for formwork are pre-

sented in Formwork for Concrete (SP-4). The section onbridge decks in that document is particularly applicablehere.

5.1.2 -- The formwork for bridge decks must bedesigned to support the loads which will be imposed onit during construction by workers, equipment, reinforcingsteel, and plastic concrete. The positioning of the formsaffects both the thickness of the deck and the finallocation of the reinforcing bars. The forms for the con-crete should be constructed in a manner to providesmooth lines and a pleasing appearance to the finishedstructure.

5.1.3 -- Both removable and stay-in-place forms areused in bridge deck construction. The former, used inmost construction, serves only the functions of formingthe concrete and supporting materials, personnel, andequipment during construction. They are removed whenthose functions are served. Stay-in-place forms serve thesame functions as removable forms, but some of themserve the additional function of a stressed member incarrying service loads.

5.1.4 -- Falsework may be required on certain typesof structures, such as slab bridges, and should be de-signed to support the same loads as the formwork.Indicators, sometimes called “tell tales,” should beinstalled to check for unexpected settlement.

5.2 Consideration for type of formThe forms, whether removed or remaining in place,

must not detract from the appearance and properfunctioning of the finished structure.

5.2.1 -- Forms that are removed should be designedfor ease and economy in handling both during instal-lation and removal. They should be durable enough towithstand multiple use handling. Benefits in the use ofthis type of form include:

a. Economy of materials through multiple use formsb. A clear view of the bottom of the concrete to

facilitate inspection

GE DECK CONSTRUCTION 345R-11
CONCRETE HIGHWAY BRID
Fig. 5.1--Steel stay-in-place forms

5.2.2 -- Stay-in-place forms are either steel9 (Fig. 5.1),concrete” (Fig. 5.2), or wood. They should be designedto remain firmly anchored in the finished structure. Steelstay-in-place forms in bridge construction are used forconvenience in forming. They are not designed for liveload stresses, although they bond to the cast-in-placedeck. They offer the following advantages:

a. The nonremoval feature saves construction time,obviates interference with traffic below the deck,and eliminates safety problems associated withform removal

b. Reduced cracking resulting from compositeaction between the cast-in-place deck and thesteel form has been reported.11

Disadvantages might include:a. The bottom surface of the cast-in-place deck

cannot be seen for inspection purposesb. Water, and the salts that it might carry, are

retained at the interface of the form and theconcrete. Such a condition could promotedeterioration in that region

c. When minimum cover is maintained betweenreinforcing steel and the tops of the steel formcorrugations, the extra concrete required to fillthe corrugations results in extra dead weight.This either necessitates an increase in thecapacity of the supporting members or decreasesthe reserve capacity of these members (see Fig.2.5)

5.2.3 -- Prestressed concrete stay-in-place forms arealso available. Initially they serve as forms, and later theybecome an integral part of the load-bearing deck. Thecast-in-place deck bonds to the precast, prestressed ele-ments during placement of the deck. In some cases,mechanical interlock is provided through shear lugs

Precast Prestressed Slob

Precast Prestressed Girders

DECK DETAIL

Fig. 5.2--Concrete stay-in-place forms

which are cast in the precast elements during fabrication.Advantages offered by this type of form are:

a.

b.c.d.

A

The nonremoval feature saves construction time,obviates interference with traffic below the deck,and eliminates safety problems associated withform removalForms can be placed rapidlyProvides for economic use of materialThe double purpose prestressed elements giveadded advantages structurally. Both field and lab-oratory tests10,12 have shown that this type ofconstruction is structurally sound

disadvantage might include the fact that thebottom surface of the cast-in-place deck cannot be seenfor inspection purposes.

5.2.4 -- Wood stay-in-place forms are usually re-stricted to box girder structures. The constructionsequence of a box girder structure is to first construct thebottom slab and webs, strip the web forms, and thenform and place the deck. Inasmuch as the interior of thebox is not visible to the traveling public and the formsare in no way detrimental to the performance of thedeck, they are usually left in place. Also, their removalwould be costly.

5.3 MaterialsMaterials which have been used in bridge deck

formwork consist of wood, metal, concrete, plastic, andwood covered with a form protector. Steel forms whichremain in place should be galvanized or coated.

5.4 RemovalForms are usually of the removable type. Therefore,

they should be designed so that they can be removedwith ease and economy, without destruction or disfigure-ment to the concrete, and with minimum spoilage inform materials so that reuse is possible.

5.5 WorkmanshipForms should be mortar tight, and this can only be

accomplished with good workmanship. The underside ofthe bridge deck is not often viewed, but unless it has asmooth, unblemished appearance, the public develops thefeeling that the bridge is not as sound as it should be.


Chapter 6 -- Reinforcement

6.1 General considerationsReinforcing steel for bridge decks should meet the

requirements of AASHTO M 31 or ASTM A 615. Ofequal importance, every effort should be made to assurethat bars are of proper size and length, that they areplaced and spliced in accordance with the plans, and thatadequate concrete cover is maintained, especially overtop steel. Adequate cover over bottom steel may beequally important in marine environments and grade sep-aration bridges over high-speed trunk lines. Coatedreinforcement should comply with AASHTO M 284, orASTM A 775 and ASTM D 3963.

6.2 ArrangementBridge decks depend on accurate placement of steel

for designed performance, thus tolerances should besmall.

6.3 Reinforcement support and tiesReinforcement should be held securely by suitable

supports and ties to prevent displacement during con-crete placement. Precast concrete blocks are sometimesused for support of the steel; more generally, metallicreinforcement chairs, with or without plastic protectedends, are used. Plastic chairs are also available. Coatedtie wire and reinforcement supports should be used withepoxy-coated reinforcement. For some deep deck sec-tions, welded support assemblies are sometimes used, orthe primary reinforcement may be in the form of resist-

Fig. 6.1--Improperly supported reinforcement deflectingunder weight of workmen

To end up with a bridge deck that will be durableand smooth riding is a very important part of the work-manship that must take into consideration the deflec-tions, precision of joints and final grades that are directfunctions of the craftsmen involved in the formwork. Thefinal grades are a function of the screeds that may be apart of the forms. The problems of accurately establish-ing the form lines are discussed in Chapter 10.

Fig. 6.2--Permanent deflection6.1 during concrete placement

of reinforcement frommFig.

ance welded trusses which simplify accurate placement.Whatever the system used, there must be assurance thatthe supports will be adequate to carry construction loadsbefore and during placement, will not stain concretesurfaces, displace excessive quantities of concrete, norallow reinforcing bars to move from their proper posi-tions. The consequences of inadequate use of rein-forcement supports are illustrated in Fig. 6.1 and Fig. 6.2.Several suggested systems for support of deck steel areshown in Chapter 3 of the CRSI “Manual of StandardPractice.”13

While deck strength is not affected by the number ofintersections tied, it is essential that sufficient ties andwire of adequate size are used to assure that steel will beheld in proper position during the concrete placing andconsolidation operations. A safe rule would require thatevery other reinforcing bar intersection be tied and thatwire not smaller than 16 gage be used.

6.4 Cover over steel6.4.11 -- It is essential that the specified depth of

concrete cover over the reinforcing steel be maintained.Concrete cover under the bottom mat is easily controlledby bar supports of the required height. Cover over thetop mat is, however, much more difficult to control dueto the inherent flexibility of the strikeoff screed systemand possible differential deflections of adjacent girders.

6.4.2 -- Several methods for checking expected topmat cover are:

a. Obtain and plot elevations of the top steel on agrid pattern and compare the results withelevations along the strikeoff screeds

b. Stretch a string line between the screeds andmeasure down to the steel

c. Run the strikeoff mechanism along the screedsand measure the space between the float boardand steel, or attach a block of wood to the floatboard which has a thickness equal to the requiredcover

In all checking methods, deflections and settlementsof the screeds and screed supports must be taken into

345R-13

consideration. This includes differential deflections ofexterior and interior steel girders and cantilevered formsdue to concrete and strikeoff equipment loading. Thethird checking method given above -- using the strikeoffequipment -- is preferred because it reduces the numberof corrections to be applied.

6.4.3 - To insure that proper allowances were madefor deflections and settlements, it is important to mea-sure periodically the actual cover over the steel duringdeck placement. Stabbing the concrete above the steelwith a putty knife is a good checking technique. Alsometal detection instruments, specifically designed andcalibrated for determining depth of cover of reinforcingsteel, are commercially available. They are suitable foruse on fresh or hardened concrete.

6.4.4 - Before final acceptance, the actual concretecover over the reinforcing steel should be ascertained. Inaddition, the entire deck should be sounded with a rodor other device to locate any subsurface voids or fractureplanes. Such areas should be chipped out and replacedwith bonded concrete patches.

6.5 CleanlinessBefore placing the concrete, reinforcement should be

free from mud, oil, or other coatings that may adverselyaffect bonding capacity. Most reinforcing steel is coatedwith either mill scale or rust to some degree. Steel withrust, mill scale, or a combination of both, is consideredsatisfactory, provided the minimum dimensions, includingheight of deformations and weight of a hand wire-brushed test specimen, are not less than the applicableASTM specification requirements.

6.6 Epoxy-coated reinforcing steelEpoxy-coated reinforcing steel, developed under the

Federal Highway Administration research program in1972-73,14 is now in widespread use as a technique foreliminating or minimizing detrimental corrosion of thereinforcing steel in deicing salt and coastal environments.Epoxy-coated bars have been used extensively in bridgedecks. Bridge decks consisting of high-quality concreteand epoxy-coated reinforcing steel will provide a long-term durability in deicing salt environments. The cost ofepoxy-coated reinforcing steel is relatively low in com-parison to other protective systems. Recent practiceprovides that both top and bottom steel must be coated.

Conventional reinforcing bars are heated, cleaned toa near white metal finish (normally by shot- or grit-blasting), conditioned by heating to a specific temp-erature, usually 400 to 450 F, and then coated with pow-dered epoxy resin to the required thickness in anelectrostatic spray chamber. On contact with thegrounded bar, the charged epoxy resin melts and flows.Curing of the epoxy occurs rapidly and the bar is cooledby air or water quenching. The coated bar is then testedwith a holiday detection device that electrically examinesthe reinforcing bar for minute cracks or pinholes in thecoating. Holidays are patched with a liquid epoxy which

is compatible with the powdered resin coating.Procedures for handling, fabrication, transportation,

and placement of epoxy-coated reinforcing bars are sim-ilar to the normal procedures used for uncoated bars,with the exception that special precautions such aspadded slings for lifting bundled bars, additional bundlesupports during transportation, and nonmetallic coatedtie wires and nonmetallic bar chairs are commonly used.The reader is directed to Section 5.7.9 of ACI 301 forfurther information. Research has shown that damagedepoxy-coated bars (which are not electrically connectedto uncoated steel) will not be subject to rapid rates ofcorrosion at the bare areas.4 As a result, most speci-fications do not require field repair of the coating,provided the total damaged area is less than 1 or 2 per-cent of the bar surface area, and individual damagedareas are small (1/4 in. square or smaller).

Chapter 7 -- Concrete materials and properties

7.1 GeneralRecent studies15 have shown that, while attention to

the properties of the component materials and the con-crete is of importance, other aspects such as designfeatures and construction practices are equally importantin determining the performance of a concrete bridgedeck. This section will be devoted primarily to a dis-cussion of those aspects of concrete properties andmaterials which have special significance to bridge deckperformance.

ACI 201.2R, Section 4.5, provides important recom-mendations in this area.

7.2 MaterialsAlthough the bridge deck exposure is recognized as

a severe one for concrete, both from an environmentaland structural point of view, the quality requirements forthe materials used in the concrete do not need to bemore restrictive than for materials normally used in pave-ment concrete. Thus, standard specifications used forconcreting materials for these purposes will generally beapplicable as indicated below.

7.2.1 Cement -- Hydraulic cement, meeting the fol-lowing specifications, is recommended for bridge deckconstruction:

a. ASTM C 150 -- Portland cementb. ASTM C 595 -- Blended hydraulic cementc. ASTM C 845 -- Shrinkage-compensating hydrau-

lic cement

Shrinkage-compensating cements have been used inselected bridge decks in a few states. ASTM C 845cement has been used in the United States, and an ex-pansive component is added to the concrete mixture inJapan.


Potential advantages are:1. Shrinkage cracking has been reduced by as much

as 25 percent,166although some authors havereported significantly better results in the UnitedStates16,17 and in Japan18

2. Significantly higher abrasion resistance thanportland cement concrete at equal strengths orwater-cement ratios (ACI 223)19,20

3. Increased concrete flexural tensile strengths inreinforced concrete sections (ACI 223)17

Special Considerations are:1. Higher cost of shrinkage compensating cements

(130 to 160 percent of the Type I cement,depending on location)

2. Shrinkage-compensating concrete requires ahigher water content (as much as 10 to 15percent more) than portland cement concrete.No decreases in durability or strength occur dueto the greater amount of chemically-boundwater20,21

3. A higher initial slump is required to compensatefor slump loss in shrinkage-compensating con-crete with elevated concrete temperatures(exceeding 85 F) (ACI 223)28

4. Stricter controls on delivery times andtemperatures are required, especially on long-haul projects in warm weather (AC1 223)

5. Curing procedures providing additional water tothe concrete are preferred (i.e., ponding, contin-uous sprinkling, or wet coverings). Plasticsheeting and other moistureproof covers can alsobe used. Cold-water curing on warm concretesurface should be avoided (ACI 223)

6. Long-term storage may lead to a loss in expan-sion level, with some materials rich in free lime,so cement should be tested prior to use perASTM C 845 for mortar bar expansion, as out-lined in ASTM C 806

Additional consideration should be given to thefollowing during construction or design to produce max-imum benefits:

1. The expansion level of the concrete, as tested byASTM C 878, must be adjusted to the degree ofthe maximum internal steel restraint and thevolume-to-surface ratio to provide full shrinkagecompensation20,22

2. Placement patterns are required that avoid “in-fill” sections which could prevent the deck fromexpanding in two adjacent directions23

3. Casting decks to precast or prestressed girdersand beams is to be avoided as this will presentexcessive external restraint against potentiallongitudinal expansion that will prevent theneeded internal resilient steel strain required forthe shrinkage-compensating action.24-26 Castingdecks to steel beams and girders has been more

successful with appropriate potential concreteexpansion levels attained.16-18,25,27

When shrinkage-compensating concrete is used, it isrecommended that all aspects of good concrete design,mixing, placing, and curing practice be rigidly enforced asoutlined in ACI 223.

Regardless of the type of cement used for deck con-struction, a positive corrosion protection system, such asepoxy-coated reinforcing bars, is recommended for useon concrete bridge decks constructed in deicing salts orcoastal environments (see Section 6.6 and Chapter 13).

If the specifications for the structure do not indicatethe type of cement to be used, it is recommended thatType I or II portland cement be used.

7.2.2 Aggregate7.2.2.1-- Aggregate for bridge deck concrete may

be either normal weight aggregate conforming to ASTMC 33 or lightweight aggregate conforming to ASTMC 330. ASTM C 33 (also see ACI 221R) contains a re-quirement for soundness which is satisfactory for mostpurposes. The high unit cost of bridge decks, however,justifies giving additional attention to this aspect ofaggregate quality. Past performance is a reasonablyreliable basis on which to judge whether an aggregatewill be durable when exposed to freezing and thawing. Inthe absence of a service record, an evaluation should bemade by laboratory freezing and thawing tests of air-entrained concrete containing the aggregate, such as thefreeze-thaw procedures described in ASTM C 666, C 671,C 672, and C 682.

7.2.2.2 -- Since the bleeding characteristics of theconcrete are of importance in the potential performanceof the concrete deck, it is important that the grading ofthe fine aggregate, in particular, adheres to the limitsprescribed by ASTM C 33, with respect to the amount ofmaterial passing the No. 50 and 100 sieves. It is equallyimportant to have uniformity of grading batch to batch sothat bleeding and finishability will not be subject todisturbing variability.

7.2.3 Water -- Practically any water that is drinkableand has no pronounced taste or odor will be satisfactoryas mixing water for concrete. Sea water should not beused in concrete for bridge decks because of thepossibility that corrosion of the reinforcement may behastened.

Specifications for concrete mixing water are shown inAASHTO T-26.

7.2.4 Admixtures7.2.4.1-- A variety of admixtures, either chemical

or mineral, is used in bridge decks. For a detailed expo-sition regarding types and uses of admixtures, see ACI212.3R, ACI 226.1R, and ACI 226.3R. Of those dis-cussed, useful admixtures for concrete bridge deckconstruction include air-entraining admixtures meetingASTM C 260, and water-reducing, retarding, and accel-erating admixtures meeting ASTM C 494, Types A, Band C. Combination water-reducing and retarding and


water-reducing and accelerating admixtures are alsocovered under ASTM C 494 as Types D and E, respec-tively. High-range water reducing (HRWR) and high-range, water-reducing and retarding admixtures arecovered by ASTM C 494, Types F and G, respectively.Fly ash and raw or calcined natural pozzolans, ASTMC 618, Types N, F and C, are also discussed inACI 226.3 R.

7.2.4.2 -- The effectiveness of an admixture isinfluenced by numerous factors such as type and amountof cement, water content, aggregate gradation and shape,length of mixing period, time of addition to the mix,consistency, and temperature of the concrete. Admixturesshould be evaluated in trial mixtures, using the jobmaterials under the temperature and humidity conditionsanticipated for the job. Incompatibility between admix-tures and other components, particularly the cement, maythus be revealed, and steps taken to remedy the situation.The amount of the admixture used in such trials, or inthe actual job when there is no provision for such trials,should be based on recommendations of the manufact-urer.

7.2.4.3 -- Occasionally, the use of admixtures willproduce side effects in concrete, in addition to those par-ticular effects desired. For instance, although waterreducers increase the slump of concrete for a given watercontent, the loss of slump with time may be greater thanfor concrete without the water reducer. Attention shouldbe directed to this possibility, since some changes may berequired in the scheduling of mixing, placing, compacting,and finishing operations. Some water reducers may alsocause significant increases in drying shrinkage of theconcrete, even though their use may permit less totalwater to be used. This effect should be evaluated, sincean increase in shrinkage can influence the amount ofcracking and subsequent performance of the deck. Re-tarders are used to delay setting time of the concrete sothat more time is available for placing and finishing, par-ticularly when casting large deck areas in a continuousstructure where setting before completion of placing andfinishing operations could result in cracking due todeflections resulting from loads in adjacent spans. Re-tarders of the hydroxylated carboxylic acid types alsogenerally increase the rate and capacity of bleeding.Changes in bleeding characteristics will require compen-sating changes in the timing of finishing operations andthe provision of sun shades, windbreaks, or fogging toavoid crusting of the surface before bleeding iscompleted.

7.2.4.4 -- Calcium chloride, the most commonlyused accelerator for reducing setting time, generallyincreases drying shrinkage and may accelerate corrosionof the reinforcing steel. For this reason, calcium chlorideshould not be used for bridge decks.

7.3 Properties of concreteThose characteristics of the concrete which influence

its watertightness, resistance to freezing and thawing, and

abrasion are particularly important as compared withthose necessary for other applications of structuralconcrete. Even when the concrete is made with satis-factory materials, construction operations such as propor-tioning, transporting, placing, and finishing can detri-mentally influence the deck performance unless thedesired properties are obtained by diligent attention tothe details of good concreting practice.

7.3.1 Workability and consistency7.3.1.1 -- It is important that the workability of

the freshly mixed concrete, as it is being placed in thebridge deck form, should be such that the concrete canbe readily compacted, struck off, and finished. Consis-tency measurements arc helpful in control, but the actualoperations just mentioned will reveal the need for pos-sible changes in mix proportions, aggregate grading, orsome other aspect to enhance workability, Fig. 7.1

.“

*

Fig. 7.1--Inability of screeding operations to close the decksurface due to improper consistency of the concrete mixture

illustrates the difficulty that can be encountered infinishing operations with concrete of improper con-sistency.

7.3.1.2 -- Concrete slump should be kept to theminimum required for adequate compaction and finishingoperations. It is equally important that the slump beuniform batch to batch for efficient and effectiveoperations. If structural lightweight aggregate concrete isbeing used, the slump can be reduced somewhat withlittle or no sacrifice in workability.

7.3.2 Bleeding7.3.2.1 -- The bleeding of concrete is a matter of

importance in bridge deck construction, particularlyduring hot weather. Bleeding is controlled by the pro-vision of adequate fines in the concrete; i.e., a relativelyhigh cement content, fine aggregates containing therequired amount of materials passing the No. 50 sieve,intentionally entrained air, and the minimum amount ofwater per unit volume which will provide the desired con-sistency. Care should be exercised in the use of certainadmixtures which may, as a side effect, increase the rateand capacity of bleeding (see Section 7.2.4.3).

7.3.2.2 -- As water is removed from concrete by


bleeding, subsidence of the solid material takes place.Under certain conditions early cracking at the surface ofthe concrete deck can result from the interaction of thesubsidence of the plastic concrete and the restraint pro-vided by the top reinforcing steel or other rigidly fixeditems such as void forms.

7.3.2.3 -- It is important to avoid rapid drying atthe surface during the bleeding period, particularly whenrate and capacity for bleeding are minimized. Exposureto sun and wind can result in the development of a sur-face crust beneath which bleeding water can collect andproduce a zone of weakness, and which is more prone tocrack over the top steel under the influence of restraintto settlement forces. Plastic shrinkage cracking may alsooccur (see Fig. 7.2).2 Shading from the direct rays of the

Fig. 7.2--Plastic shrinkage cracking

sun and the use of fine water spray by means of fognozzles may be required to avoid or minimize suchdevelopments (ACI 305R).

7.3.3 Shrinkage7.3.3.1-- Hardened concrete responds to changes

in moisture content by expanding as moisture content in-creases and by shrinking as it dries. If kept continuouslywet after casting, the amount of expansion is small,usually less than 0.015 percent, and can be accom-modated with no problem. Shrinkage on drying, usuallyevaluated in plain concrete specimens with no rein-forcement, generally ranges from about 400 to 800millionths (0.04 to 0.08 percent) when exposed to dryingat 50 percent relative humidity. Reinforced concretes infield exposure generally show movements of about half

those noted above for laboratory specimens. Althoughthese are also small movements, all structures have built-in restraints to such shortening, restraints which canresult in cracking of the concrete. These restraints consistof reinforcing steel, stringers, beams, shear connectors,section size, etc. Such cracking may make the reinforcingsteel more vulnerable to corrosion and increase thechange of surface spalling. Accordingly, steps should betaken to minimize the amount of shrinkage on drying.

7.3.3.2 -- The most important controllable factoraffecting shrinkage is the amount of water used per unitvolume of concrete. Shrinkage can be minimized bykeeping the water content of the paste as low as possibleand the total aggregate content of the concrete as highas possible. Use of low slumps and placing methods thatminimize water requirements of the concrete are majorfactors in reducing shrinkage. High slumps and highinitial concrete temperatures will increase water re-quirements and should be avoided. Total aggregate con-tent is maximized by using the largest size coarseaggregate consistent with steel reinforcing spacing.

7.3.4 Durability7.3.4.1-- The primary potentially deteriorating

influences on concrete bridge decks are freezing andthawing, particularly in the presence of deicing chemicalsand corrosion of the reinforcing steel.

The resistance of concrete to freezing and thawing,even when various deicers are used, is significantlyimproved by the use of intentionally entrained air. Air-entraining admixtures meeting the requirements ofASTM C 260, when used to produce the recommendedvolume of entrained air, provide the proper size anddistribution of air voids for effective protection. Air voidcharacteristics representative of an adequate system, asmeasured in hardened concrete by the linear traversemeasurement technique (ASTM C 457), are: (1) cal-culated spacing factor less than about 0.008 in., (2) asurface area of the air voids greater than about 600in.2/in.3 of air void volume, and (3) a number of air voidsper linear inch of traverse significantly greater (aboutdouble) than the numerical value of the percentage of airin the concrete. These characteristics are usually obtainedwhen the air content of the fresh concrete meets therequirements in Table 7.1, Section 7.3.6.

When ASTM C 494, Types F and G high-range,water-reducing admixtures are used in concrete, theabove air void parameters still apply. The fact thatHRWR’s do not affect the durability of the concrete wasreported by Whiting and Schmitt in NCHRP-29628 (alsosee Reference 29). Hence, the total air content should
still be held within the prescribed limits of Table 7.1.
7.3.4.2 -- The permeability of the concrete is alsoof importance. Low water-cement ratio and rich mixeswith a minimum cement center of 564 lb/yd3 are recom-mended, since they will provide concrete less permeableto water and deicer solution. For such concretes, thespecified compressive strength f

,c, as defined in ACI 214,

should be at least 4500 psi at a test age of 28 days. The


Chapter 8 -- Measuring and mixing

8.1 GeneralThe preconstruction planning step discussed in

Chapter 3 is of particular importance since the concreteis often furnished by a subcontractor or third party andsince whole decks or large segments of decks are placedon a single day with little opportunity for rehearsal. The

TABLE 7.1--Recomended air contents for bridge deck con-crete subject to freezing

Nominal maximum Air Content,*+aggregate size, in. percent by volume

1 l/2 5 l /23/4 6l/2 73/8 7 1/2

*A reasonable tolerance for air content in field construction is +1 1/2 percent.+Where deicers are not used, but freezing occasionally occurs, thetarget air contents may be reduced 1 to 1 1/2 percent.

7.3.6 Air content7.3.6.1 -- Field experience and laboratory studies

have shown that the amount of entrained air required isa function of the maximum size of coarse aggregate used,as shown in Table 7.1.

7.3.4.3 -- If a mixture incorporating eitherchemical admixtures (Types A, B, C, D, F, or G ofASTM C 494) or pozzolans (Types F, N, or C of ASTMC 618, Fly Ash and Raw or Calcined Natural Pozzolans)or a combination of chemical admixtures and pozzolansis contemplated, less than 564 lb/yd3 may be used, pro-vided the following criteria are met:

a.

b.C.

Air content recommended in Table 7.1 isobtainedProper slump is usedThe absolute volume of cement plus pozzolan isequal to or greater than that of 564 lbs/yd3 ofcement

d.

e.

The average compressive strength is sufficient toensure thatf,c is equal to or greater than 4500 psiThe water-cementitious material (total weight ofcement plus fly ash or natural pozzolan) ratiodoes not exceed 0.45 by weight7.3.4.4 -- A low ratio of water to cementitious

maximum ratio of water to cementing materials forbridge deck concrete should not exceed 0.45 by weight.

materials is helpful not only with respect to scaling, butalso with respect to corrosion of the reinforcing steel.Most deicers are chlorides and their penetration to thesteel can result in rapid corrosion. A low water-cementratio paste provides a more effective barrier to the pen-etration of chlorides. Rich mixes help by enhancing theprobability for reduced water-cement ratios and by in-creasing the capability for maintaining a high pH in theconcrete, an environment which reduces the potential forsteel corrosion.

Recent work for the FHWA5 has shown that depthof cover is very important to control galvanic corrosion.With only 1 in. of cover, early corrosion was detected, re-gardless of water-cement ratio. The only exception waswhen a silica fume admixture was present in the con-crete. It is recommended that 2 in. of concrete be theminimum cover.

7.3.5 Strength -- Concrete strength is primarily afunction of the water-cement ratio and the extent ofmoist curing. Concrete proportions are selected on thebasis of strength and durability requirements. For moredetailed information, see ACI 211.1 and ACI 211.2 onproportioning, and ACI 201.1R on durability.

In most instances, the requirements for durability

previously discussed will govern the selection of water-cement ratio, and the actual strength developed will bemore than required from structural design considerations(i.e., the limiting maximum water-cement ratio must beused).

7.3.6.2 -- Air-entraining admixtures which meetthe requirements of ASTM C 260 will provide the propersize and distribution of air voids. Current field controlpractice, however, involves only the measurement of thevolume of air in the freshly mixed concrete. The volumeof air entrained is primarily a function of the amount ofair-entraining admixture used. However, significantchanges in air content can result from changes in ag-gregate gradation and fine aggregate content, slump,concrete temperature, other admixtures, and mixing time.These factors should be controlled within the limitsestablished.

7.3.7 Skid resistance7.3.7.1-- The skid resistance of a concrete bridge

deck is influenced by the properties of the concrete, theproperties of the component materials, and by the tex-ture of the surface.

The most important factor in skid resistance of con-crete surfaces, especially at normal highway speeds, issurface texture. Satisfactory textures can be produced bybrooming, wire drags, and flexible wire brushes. To pro-mote retention of skid-resistant properties related totexture, deep texturing and practices that minimize wearare desirable. The latter includes low water-cement ratioconcrete mixtures, durable fine aggregates, avoidance ofplacing and finishing practices that tend to bring finesand water to the surface, and proper curing of the con-crete surface.

7.3.7.2 -- With increasing pavement wear orslower speeds, the characteristics of the fine aggregatebecome increasingly important in skid resistance of con-crete surfaces. The silica content of the fine aggregate isthe primary determinant in this instance, and acid-insoluble (6N HCL) residue contents of 25 percent orgreater provide good skid resistance.30

Coarse aggregate is relatively unimportant unlessconditions have resulted in excessive wear and the coarseaggregate has become exposed at the surface.


need for a steady flow of concrete of uniform propertiescannot be over-emphasized.

8.2 Reference documentsThe basic specifications and practices required are

outlined in the following documents:

a. ASTM C 94b. ACI 304Rc. ACI 305Rd. ACI 306Re. ASTM C 685

8.3 Measuring materials8.3.1-- Cement and cementitious materials should be

weighed on a separate scale and in a separate weighhopper from the aggregates. Typical specifications re-quire that they be weighed to & 1 percent of the amountbeing weighed. These tolerances need to be broadenedsomewhat when cement and a pozzolan are weighedcumulatively on conventional batching equipment. In allcases, the cement should be weighed in first. Specialprecautions are required in handling certain fly ashmaterials, since they flow through small cracks andcrevices much more readily than cement. Compartmentsbetween cement and fly ash bins must be sealed, andbatching valves and devices require close tolerances toassure positive cutoff.

8.3.2 -- Aggregates must be uniform in grading andmoisture content if excessive variations in consistency andwater content are to be avoided. ACI 304R outlines cer-tain precautions to be observed. Typical specificationsrequire that aggregates be weighed to about 2 2 percentof the required weight. For small batches and batchescontaining lightweight aggregate, ASTM C 94 permitssomewhat more liberal tolerances.

8.3.3 -- Admixtures are generally batched by volume,but may be batched by weight. A typical tolerance is *3 percent, but a somewhat larger tolerance of perhaps& 5 percent (ACI 304R) is considered acceptable. Liquidadmixtures should be batched in mechanical dispensingequipment equipped with a visual sight gage or otherpositive means of determining that the proper quantityhas been batched. In general, different admixtures shouldnot be batched in the same dispenser or lines unless pro-vision is made to flush out the system between each use.Similarly, different admixtures should not be intermingledbefore the start of mixing unless they are known to becompatible. The manufacturer’s recommendations shouldbe followed. When several admixtures are to be used ina batch, they should be batched with different ingredientssuch as the water or sand, or in separate parts of thewater or sand. They should not be batched directly incontact with the cement before mixing. The time of ad-dition of the admixture to the concrete and the presenceof other admixtures often affect the amount of each re-quired to produce the desired effect -- air content, retar-dation, etc. (ACI 212.3R). Often each of a number of

different admixture batching procedures can be used suc-cessfully. However, once a procedure is selected, itshould be carefully followed.

8.3.4 -- The current ASTM C 94 and ASTM C 685require that added water be measured to within + 1percent of the required total mixing water. Additionally,the total mixing water, which includes free moisture onthe aggregates, is required to be measured to within f 3percent. This amounts to about + 1 gal/yd3 (8 lb/yd3).Because of the difficulty of determining aggregatemoisture contents, it is extremely rare that this accuracycan be obtained by direct measurement. The control ofwater content is discussed in Section 8.5 of this doc-
ument. In truck mixers, any wash water retained in themixer from the preceding batch should be accuratelymeasured, and if this is not practical, the wash watershould be discharged.
8.4 Charging and mixing8.4.1 -- All batches of concrete, whether mixed in

central or truck mixers, must be uniformly mixed anduniform in composition throughout the discharge. ASTMC 94 and ASTM C 685 contain a recommended testingprocedure for determining uniformity and establishedpermissible limits for variation of (1) weight per cubicfoot (air free), (2) air content, (3) slump, (4) coarseaggregate content, (5) unit weight of mortar (air free),and (6) compressive strength. Although each of the sixlimits given is important, those on air content are ofparticular significance in bridge deck construction, andoccasional checks of concrete from different parts of thebatch during discharge are recommended. If tests showthat the ASTM limits on uniformity are not being met,corrective measures must be taken. In both stationaryand truck mixers, the method of charging the ingredientscan have an important effect on uniformity of mixing.Good mixing is enhanced by blending of all ingredientsas they enter the mixer. When cement is charged sepa-rately, mixing is likely to be much more difficult andsensitive to minor variations in charging speed, methodof addition of water, brand of mixer, and other factors.In these circumstances, different drum and blade designsmay require somewhat different procedures. In truckmixers, charging and mixing at drum speeds up to 18 or20 rpm -- well above typical specification maxima of 10-12 rpm -- may greatly improve uniformity obtained in agiven number of drum revolutions.31

8.4.2 -- When properly charged, typical large centralmixers are capable of producing uniformly mixed con-crete in 90 seconds or less. When reduced mixing timesare permitted, based on uniformity tests, mixers shouldbe equipped with suitable timers to prevent dischargebefore completion of the required minimum mixing.When such mixers are operated at short mixing times, adelay in discharge and the resulting additional mixingtime may lead to greatly increased air content. For thisreason, the mixers must be capable of being stopped andrestarted under full load to avoid maximum mixing times


8.5 Control of mixing water and delivery8.5.1 -- The ultimate quality of the concrete depends

on the water-cement ratio or the quantity of water at agiven cement content. As mentioned in Chapter 6, in-creased water content or water-cement ratio decreasesstrength, increases drying shrinkage, and in general,adversely affects concrete quality. Mixed concrete losesslump with time or requires additions of water to main-tain slump at a constant level. The rate at which thechemical reaction between cement and water proceeds,or the rate at which slump decreases depends on manyfactors, including the temperature and properties of thecement, admixtures, and aggregate.

Direct control of mixing water is achieved by:a. Limits on maximum water-cement ratio or water

contentb. Control of retempering water within water-

cement ratio design limitc. Maximum and minimum slumps

more than about 60 seconds greater than the reducedmixing time being employed.

The mixing time can be very short when a centralmixer is used only to shrink mix or intermingle theingredients. Here mixing is completed in a truck mixer.The amount of mixing in the truck should only be thatsufficient to produce the required uniformity. Olderversions of ASTM C 94 required 50 to 100 revolutions ofmixing in the truck mixer. These limits are good guidesfor shrink mixing, but may be unnecessarily restrictive inindividual instances.

8.4.3 -- When concrete is mixed completely in a truckmixer, specifications generally require 70 to 100 rev-olutions at mixing speed after all ingredients are in thedrum. The number of mixing revolutions required to pro-duce uniformly mixed concrete may be either more orless than this range. The number required will dependimportantly on the load procedure, condition of themixer and other factors. In general, the total number ofdrum revolutions at both agitating and mixing speedshould not exceed 300. This limit is designed to avoidexcessive grinding of soft aggregates and cement, thegeneration of excessive heat and the loss of entrained air.After completion of mixing, the concrete does not needto be agitated continuously and the drum can be stoppedif an additional 40 to 50 revolutions at mixing speed areemployed immediately prior to discharge. This final add-itional mixing is needed with all concretes to eliminatesegregation and bleeding that can occur in transit.

The interior of all mixers should be periodicallyexamined for accumulations of hardened concrete andexcessive blade wear which will reduce mixing efficiencyand rate of discharge of low slump concrete. Truckmixers of relatively recent manufacture in good mech-anical condition should be able to discharge 2 to 21/2 in.slump concrete without difficulty; however, if 1 to 11/2 in.slump is required, units designed for this purpose may berequired.

d. Limits on the maximum temperature of the con-crete, generally about 90 F, but occasionallylower

Indirect controls such as time limits and total rev-olutions are quite common. However, these factors arenot detrimental if the addition of water is within thelimits of the maximum water-cement ratio and the con-crete is in satisfactory condition for proper placementand consolidation.

8.5.2 -- The establishment of a maximum water-cement ratio or water content should solve the problemof retempering and insure quality concrete. However, inmost situations, aggregate moisture contents are notknown with the required accuracy to insure absolute con-fidence. Additionally, relatively small variations inaggregate grading, and properties of aggregates andcements will affect the level of slump obtained at a giventotal mixing water content or at a given water-cementratio and cement content. At the present state of the art,it is very difficult to compute the quantity of additionalwater required and be certain of obtaining the requiredslump. Certain adjustments will have to be made, gen-erally by the person responsible for mixing the concrete.

When maximum total water contents are establishedthrough the use of trial batches made in the laboratory,care and judgment must be exercised in translating theserequirements to the field. Full-sized batches of the pro-posed mix should be made and used in less critical workareas before it is used in the actual bridge deck. Gen-erally, the maximum water content is specified withouttolerances. To provide for unusual circumstances, atolerance of 25 to 30 lb/yd3 of concrete is required abovethat needed to produce the desired slump under usualcircumstances. Existing specifications generally do notcontain such tolerance. This and the concomitant dif-ficulties of accurately establishing the actual watercontent constitute a major problem in control of themixing process. Even with this tolerance, aggregates willhave to be uniform in grading and moisture content. Toobtain uniform moisture contents, coarse aggregates needto be stockpiled 6 to 12 hr, and fine aggregates 24 hr orlonger, before they are placed in storage bins forbatching. Electrical moisture meters can be useful tools,but they require frequent recalibration and maintenance.Electrical meters are seldom used successfully on coarseaggregates and may be insensitive if sand moisture con-tents exceed 9 to 12 percent. Electric meters do not workwhen the sand contains even small amounts of solublesalts. The selection of the location and arrangement ofprobes are very important. In cold weather when aggre-gates must be heated, the control of moisture content iseven more difficult.

8.5.3 -- Procedures designed to control water-cementratio or total water content of truck-mixed concrete mustpermit some tolerance in the total water content batchedto compensate for the fact that aggregate moisture con-tents are seldom known with sufficient accuracy, and thatnormal variations in delivery times due to traffic and job


Chapter 9 -- Placing and consolidating

9.1 General considerationsThe procedures outlined in ACI 304R are applicable

to the general problem of placing concrete. Only suchadditional points will be made here as are consideredpeculiar to or especially pertinent in the case of bridgedecks. Concrete bridge decks differ from most concreteplacements in their relatively thin sections, high per-centage and close spacing of reinforcing steel, numerouspoints of stress reversal and exposure to the abrasion,impact and vibration of traffic.

The construction conditions associated with trans-porting, placing, and finishing of concrete bridge decksare far from ideal, and all contribute to the difficultiesencountered in control of the finished deck. Chemicalsused to melt ice and snow are known to be aggressive toconcrete and steel. Decks are also subjected to morefreeze and thaw cycles in the winter and wider temp-erature variations in the summer than slabs on grade.

delays will affect the quantity of water or water-cementratio required to produce the desired slump. ASTM C 94controls the situation by specifying maximum time limitsand by limiting the addition of water to the initial mixingand on arrival at the job when the slump is less thanspecified. When water is added on arrival at the job, anadditional 30 revolutions of the drum are required toobtain proper distribution and no later retempering ispermitted.

8.5.4 -- Actual mixing of truck-mixed concrete isgenerally done either at the plant or after arrival at thejobsite. Mixing is rarely done during transit because ofthe danger of turning over a truck. A system involvingmixing to a designated slump in the yard and temperingonly on arrival at the jobsite contributes to centralizedcontrol, but may limit permissible delivery time ordistance. As suggested earlier, after completion of mixingthe drum, speed should be reduced to agitating speed, orpreferably stopped, on the way to the job.

8.5.5 -- When damp aggregates, cement and part ofthe water are intermingled during charging, and themixing is delayed until arrival on the job, a substantialproportion of the cement will be wetted and the slumploss for a given time delay will be only slightly less thanif the concrete had been thoroughly mixed at the plant orin a central mixer.32,33

8.6 CommunicationRegardless of the method used to produce the

concrete, a reliable method of communication is neededbetween the jobsite and the batch plant to insure asteady continuous flow of concrete and to avoid thedelays that occur if mixers accumulate on the job waitingto discharge. In remove locations involving long hauls,extra trucks may be needed in case of a breakdown orrejection of a load.

9.2 TransportationACI 304R is again referred to with additional stip-

ulations due to the necessity of placing relatively smallquantities of concrete over a large area. The transportingequipment should be geared to the consistencies of con-crete proportioned for the job. Admixtures may be usedto improve the workability of the concrete, provided theselected water-cement ratio is not exceeded. Some typesof truck mixers, bucket gates, or pumps are slow orunworkable when harsh or very stiff mixes are used. Ap-proval of every piece of transporting equipment proposedfor use on the project should depend on its ability tohandle bridge deck concrete without segregation.

The rejection of concrete for a bridge deck oftengives rise to further complications, since the high per-centage of reinforcement steel makes bulkheads difficultto install and cold joints are always undesirable. Conse-quently, the time spent in checking equipment in advanceand in checking concrete at the batch plants is wellinvested.

9.3 Rate of deliveryIt is essential that concrete for bridge decks be

delivered to the site at a uniform rate adapted to themanpower and equipment to be used in placing andfinishing. On one major project on which specific recordswere kept, bridge deck concrete delivery was found toaverage 27.2 yd3/hr, with a standard deviation of 5.5 yd3.Sufficient hauling units with at least one spare unitshould be determined and established between the con-tract producer and officials in charge of placing andfinishing.

The difficulties of obtaining a satisfactory deliveryrate can be overcome by mixing on the job. However,other methods of mixing concrete can serve equally aswell when radio or other methods of communication aremaintained between batch plant and job site.

9.4 Placing equipmentWhen mechanical strikeoff equipment is used and the

delivery of concrete to the job site is adequate, themovement of the concrete from the delivery point to thedeck is often the delaying operation and it should receiveparticular attention. A variety of types of placing equip-

Fig. 9.1--Concrete delivery by conveyor


ment is available.9.4.1 Belt conveyors -- Inclined and horizontal

conveyors designed specifically for moving concrete havebeen used successfully in placing bridge deck slabs.Combined with a radial swing conveyor, concrete hasbeen placed at rates up to 120 yd3/hr. An example isshown in Fig. 9.1. (Another example can be seen inFig. 10.2.) At such high rates, attention must be given to
the equipment and manpower required to stroke off andfinish the concrete.
All transfer points in the conveyor system should beequipped with discharge hoods (see Fig. 9.1) to preventsegregation at points of transfer. Length should becontrolled so that the transport time, from chargingconveyor to point of placement, does not exceed 15 min.Belts should be kept clean by means of one or morescrapers to avoid paste loss that could affect workability.

9.4.2 Concrete pumpss -- The capacities of pumps usedfor placing of concrete on bridge decks can vary from 20to 80 yd3/hr, dependent on height of lift, length of hori-zontal run, and number of pipe elbows used, plus typeand size of concrete pump and pipe. The pumps requireattention, guidelines for which are covered in ACI 305R.Delivery of concrete by pumpline is shown in Fig. 9.2.

Fig. 9.2--Concrete delivery by pumpline

Inspection of steel pipe should be required prior touse. Hardline pipe must be clean and not severelydented. Couplings should be properly designed andcapable of withstanding line pressures and surges.

Flexible pipe, when used, should be of such materialthat no bending or kinking will occur during use, and soconstructed that excessive mortar leakage will not occurat pipe connections. The use of aluminum alloy pipeshould be prohibited.

9.4.3 Concrete buckets -- Buckets have been in use formany years for placing bridge deck concrete. The bucketshould be self-cleaning on discharge, and concrete flowshould start on opening of the discharge gate. Openingof the gate to its wide-open position so as to dischargeconcrete in one solid mass directly below the bucketshould be prohibited. Control of bucket and opening

Fig. 9.3--Concrete placemen t from bucket

should be done in such a manner as to insure a steadystream of concrete discharge against concrete previouslyplaced. Free-fall of concrete from bucket discharge gateto bridge deck should not exceed 30 in. (see Fig. 9.3).The use of two buckets per crane, as shown in Fig. 9.4,
is recommended. Depending on the size of bucket, lift,and boom travel, concrete can be placed using twobuckets on large deck jobs at 20 to 40 yd3/hr. One bucketof the same size with equal lift and travel can place 15 to25 yd3/hr. These capacities are based on using a skilledcrew.
9.4.4 Manual or motor-propelled buggies -- Buggiesshould work on smooth rigid runways set well above thedeck reinforcing steel. Concrete being transferred bybuggies tends to segregate during motion. Plankingshould be butted rather than lapped to maintain asmooth surface. In placing deck concrete from eithermanual or power-driven buggies, the concrete should bedumped against concrete previously placed. Recom-mended maximum distance to transfer concrete bymanual buggies is 200 ft and for power buggies, 1000 ft.One type of power buggy is shown in Fig. 9.5.

Hand buggies vary in capacity from 6 to 8 ft3. Placingcapacity will average between 3 to 5 yd3/hr. Powerbuggies are available in sizes from 9 to 12 ft3 with placing


Fig. 9.4--Use of two buckets for deck placement. One isbeing loaded while the other (at the upper right) is beingdelivered to the deck

Fig. 9.5--Power buggy used for bridge deck placement

capacity range from 15 to 20 yd3/hr.

9.5 Vibration and consolidationACI 304R and ACI 309R should be consulted for

general requirements relating to vibration. Deck re-quirements differ in some respects in that concrete sub-sidence is restrained by closely-spaced and chair-supported reinforcing steel, and the head of concrete islow. In hot, windy weather, surface crusting is a problemwhich tends to promote early finishing. This, in turn,forces vibration operations to be completed before thesubsidence of the concrete due to bleeding is complete.Sometimes there is concern that concrete will be “over

vibrated” or “over finished.” This more than likely impliesthat the concrete was of a consistency so wet that itshould not have been vibrated at all, or that the finisherswere working on the drying surface crust an hour ormore before bleeding, and subsidence was completed.

It is essential that bridge deck concrete be thoroughlyvibrated at a time late enough to assure close contactwith the reinforcing steel after the concrete has ceased tosubside. This may require revibration if bleeding is pro-longed, and it generally occurs for a much longer timethan is obvious. It may be necessary to use an evapor-ation inhibitor to delay the time the finishers start andstill vibrate at a late enough time to get proper con-solidation. Retarding admixture may delay initial set timeand permit later vibration, but may not prevent surfacecrusting due to drying. For interim curing, fog sprays, ifthey provide a true “fog,” and monomolecular films arehelpful.

9.6 Sequence of placingConcrete should be placed in a uniform heading in

a line roughly parallel to the screed machine. Crackingsometimes can be reduced in continuous bridge decks byplacing the concrete in a sequence designed to minimizethe effect of form and falsework deflections. While thisprocedure is not as widely practiced as it was a few yearsago, it is worth consideration, though it may add severaldays to the time necessary to complete a deck. By placingthe center portions of the spans first, cracking producedby negative bending over the piers is reduced. Sometimesconstruction joints are placed at the piers.

9.7 Manpower requirements and qualificationsAs discussed in Chapter 4, every effort should be

made to assure that sufficient competent manpower is onhand to proceed properly with a concrete deckplacement.

9.8 Reinforcement --Special care during placingAssuming that reinforcing steel is properly positioned

and securely tied, the freedom from spalling of a bridgedeck may largely depend on the degree to which the steelis tightly encased in concrete, without cracks over bars

Fig. 9.6--Horizontal crack above top reinforcing steel

GE DECK CONSTRUCTION 345R-23

Chapter 10 -- Finishing

10.1 GeneralFinishing operations constitute the most difficult, and

yet one of the most important phases of bridge deck con-struction, with respect to durability and riding quality.The difficulty in handling, placing, and finishing concretebridge decks, due to the suspended nature of bridges,necessitates the employment of special construction tech-niques and controls (See ACI 304R, 305R, 306R,AASHTO Specifications, and References 15, 34, and 35).

CONCRETE HIGHWAY BRID

Fig. 9.7--Voids under reinforcing bar due to poor consol-idation of concrete

(see Fig. 2.6) or horizontal cracks starting at the bars(Fig. 9.6), or without voids or water channels along thebars. Since decks usually have closely-spaced bars, andparticularly where there are splices, it is difficult toassure that voids (Fig. 9.7) along bars, or cracks do notdevelop during bleeding and subsidence of the concrete.Best results are obtained with mixes having low water-cement ratios, ample and repeated vibration, and wherefinishing is delayed as long as possible.

9.9 Reference documentsReferences have been made throughout this chapter

to recommendations made by other ACI committees.Helpful information related to concrete placement can beobtained from the work of ACI Committees 211, 304,305, 309, and 311.

After the concrete has been struck off by machineand consolidated by vibration, it should be furthersmoothed and consolidated with a longitudinal float of asuitable design approved by the engineer.

Following the floating operation but while the con-crete is still plastic, the contractor should test the slabsurface for trueness with a straightedge (10 ft to 16 ftlong). The straightedge should be used to check the sur-face for bumps or depressions and should be advancedalong the deck in successive stages of not more than one-half the length of the straightedge. Any depressionsshould be filled immediately with freshly mixed concrete,

struck off, consolidated and refinished. High areas shouldbe cut down and refinished.

10.2 Timing of operationsThe entire plan of operation, placing and finishing

times, and the equipment of the contractor must be eval-uated to insure that the operation can be performedsmoothly and efficiently. This phase should be carriedout during the preconstruction meeting discussed inSection 4.3.

Final floating should be delayed as long as possibleto allow for completion of bleeding of the concrete. Thisis necessary to prevent “crusting,” the formation of aweakened plane immediately below the finished surfacewhich results in rapid scaling when the deck surface isexposed to deicers and freeze-thaw action.

10.3 Manual methodsManual methods of strikeoff should not be used

except where the use of a finishing machine is impracticalor impossible such as on variable width sections or tofinish, to a temporary bulkhead, the concrete alreadydeposited in the event of breakdown of the mechanicalfinisher. When allowed, a manual strikeoff should beaccomplished with a steel or steel-shod wood screed.

Floating may be done manually as well as by mech-anical means (see discussion of mechanical floatingequipment in Section 10.5). Manual methods are com-
monly employed, using plow-handled floats and long-handled “bull” floats from work platforms spanning thedeck transversely as shown in Fig. 10.1. Proper finishing,using manual methods, requires the skills of anexperienced pavement finisher.
10.4 Finishing aidsThe practice of sprinkling the struck surface of the

deck to facilitate floating should be strictly prohibited.This practice may produce a surface that has an exces-sively high water-cement ratio and low entrained aircontent. These conditions will contribute to rapid surface

Fig. l0.1--Longitudinal floating of a bridge deck with “bull’float


Fig. 10.2--Longitudinal travel, longitudinal finish screed.Note also the use of conveyor in foreground and workbridge behind the screed for curing and other minor acti-vities

10.5 Mechanical equipment10.5.1 -- Machinery used in the finishing of concrete

placed on bridge decks consists of several types. Nomen-clature varies because it is possible to describe thisequipment in terms of either its direction of travel or theorientation of the striations imparted to the surface.Since the direction of motion and the orientation of thestriations may be perpendicular to each other, the po-tential for conflicting nomenclature is apparent. For thepurposes of this standard practice, the direction ofstriations will be used to designate the machine as“longitudinal” or “transverse.” The direction of travel ofthe entire machine will be used for secondary identi-fication. It is this latter feature which dictates thegeometry of placement and thus influences progressivedeflections. Depending on the specific design of theequipment, the motion of the strikeoff plate may notcoincide with the direction of the entire machine.

deterioration under the actions of traffic, freezing andthawing, and deicing chemicals.

To aid the finishing operations (floating), especiallyunder hot, dry conditions, a monomolecular filming agentmay be applied to the struck surface.36 The purpose ofthe filming agent is to prevent rapid evaporation of bleedwater and “crusting,” thereby extending the period oftime during which floating operations can be carried out.

10.5.1.1 Longitudinal finish, longitudinal travel --Most commonly used is the combination strikeoff andfinishing machine shown in Fig. 10.2, which is supportedin a structural frame, is self-propelled on rails and travelsin a longitudinal direction (i.e., parallel with traffic flow).Strikeoff and finishing machinery is suspended from thisframe. It is power driven to perform the task of strikeoffand finishing to the established tolerances. The finishingis accomplished in a longitudinal direction as the power-

Fig. 10.3--Close up of longitudinal travel, longitudinal finishscreed. The equipment is moving toward the camera

Fig. 10.4--Longitudinal travel, transverse finish screed

Fig, 10-5--Traverse travel, longitudinal finish screed


driven vibrating and/or oscillating screed (float) travelstransversely across the deck. A closer view is shown inFig. 10.3.

10.5.1.2 Transverse finish, longitudinal travel -- Inanother type of machine supported on longitudinal railsand traveling in the direction of the traffic flow, finishingis accomplished by the transverse action of the power-driven vibrating and/or oscillating screed. Strikeoff offresh concrete is obtained through a strikeoff plateattached ahead of the finishing screed, moving placedconcrete longitudinally. An example is shown in Fig. 10.4.

10.5.1.3 Longitudinal finish, transverse travel -- Theframe supporting the strikeoff and finishing machinery ismounted on rails placed transversely (i.e., 90 deg to traf-fic flow or on adjacent decks). The strikeoff travelslongitudinally; i.e., same as traffic flow; power-drivenfinishing is performed by a longitudinal oscillating screedwhile the machine travels transversely across the deck.An example is shown in Fig. 10.5.

10.5.1.4 -- Regardless of the type of equipmentused, freshly placed concrete should be distributeduniformly ahead of the strikeoff and finishing machine,and as close to its final position as practicable. Concreteshould not be moved horizontally with vibrators or byother methods which cause segregations.

10.5.2 Rails and guides10.5.2.1 Equipment traveling longitudinally -- The

adjustable screed supports provide the initial surfacingcontrol and set the final longitudinal profile. Therefore,they should be set to proper elevation with allowance foranticipated settlement, camber and deflection of false-work, as required to form a bridge roadway deck true tothe required grade and cross sections. The screedsupports should be vertically adjustable and set byinstrument. Temporary supports should be removablewith minimum disturbance of the concrete. The railsshould be set above finished grade and should extendbeyond both ends of the scheduled length for concreteplacement, a distance sufficient to permit the float of thefinishing machine to fully clear the concrete to be placed.

Fig. 10.6 shows an idealized arrangement for a bridge

Fig. 10.6--Idealized arrangement of longitudinal travel,transverse finish equipment

deck strikeoff machine designed to travel longitudinallyand incorporating several important features. Theseinclude:

a. Screed rail supports that are placed in anunfinished area requiring later concrete cover

b. Adjustable supports to allow for progressivedeflections

c. Screed rails located above the finished surface toavoid disturbing significantly the concrete whenthe rail is removed10.5.2.22-- The question of beam deflections

during concreting poses a difficult problem for goodbridge deck finishing. All beam deflections should becarefully calculated and compared at the deflectioncontrol points. Progressive longitudinal deflections mustbe carefully considered as concreting proceeds down thelength of the span.

Fig. 10.7--Typical deflection characteristics of a beam atvarious stages of loading by a screed traveling longitudinally

The problem of progressive deflections on a typicalbeam is illustrated in Fig. 10.7 for various conditions ofloading. (The figure is grossly exaggerated for clarity.)Screed rails should initially be set coincident with Line 1.If the rails become disturbed or otherwise require ad-justment as the work progresses, variations similar tothose shown in Lines 2, 3, or 4 must be considered. Notethat, except for Lines 1 and 5, one-quarter and three-quarter point deflections are not equal.

The problem of transverse differential deflections isfar more difficult to correct and, in fact, cannot beprecisely resolved in contemporary practice. Most fasciabeams deflect less than interior beams. Yet it is on thefascia beams that screed rails are usually supported. Con-sequently, cross-slopes are altered as the beams areloaded. These differentials are usually greatest at mid-span and nonexistent at span ends. Therefore, if com-plete deflection calculations are not available, it is best touse the cross-sloped configuration of the span ends toinsure adequate deck thickness and, most important, toinsure sufficient cover over the reinforcement steel.

On sharply skewed bridges, the problem becomesconsiderably more complex, and consultation with the


designer is advised before concreting begins. Thefinishing machine, when possible, should be set parallelin the skew of the bridge to avoid differential deflectionon multigirder bridges.

On short spans or any relatively rigid spans withminor deflections, the problem may be ignored.

10.5.2.3 Equipment traveling transversely -- Thistype of machine is most often used on simple spans of100 ft or less, though it has been used on spans ofgreater length. The transverse screed rails supporting themachine are normally set to the finished grade at eachend of the span. The finished elevation of intermediatepoints on the deck are set on the longitudinal strikeoffedge of the screeding machine. Assuming structuralstability of the machine, these elevations remain fixedand are independent of the girder deflections occurringduring concrete placement. Consequently, the thicknessof the concrete deck is dependent on two major factorswhich should be recognized during construction. Theseare:

a. The differential temperatures existing betweenthe top and bottom flanges of the girders duringconcrete placement, as opposed to those thatmay have existed when the forming elevationswere established

b. The transverse position of the concrete deadloading at the time a final screeding pass is madeover a given point on the span

The possible influence of the first factor is illustratedin Fig. 10.8. If no temperature differential exists betweenthe upper and lower flanges of a simply supported bridgegirder, it would be in a thermally neutral position (Fig.10.8A). Due to solar radiation, differential temperatureswill generate expansive forces in the upper flange whichare resisted by opposing forces in the lower flange. Theresulting effect is an upward deflection of the girder (Fig.10.8B). If the deck forms were established to grades com-plying with the neutral position of the girder, but theconcrete deck screeded to grade under differential ther-mal conditions, the thickness of the deck will bedecreased by an amount (Fig. 10.8C).

BRIDGE GIRDER

A: NEUTRAL POSITION

B: TOP FLANGE HOT

C: TOP FLANGE HOT, DECKING

Fig. 10.8--Effectt of differential temperatures on a deckscreeded with a screed traveling transversely

The influence of the second factor is illustrated inFig. 10.9. Conventional design procedures for calculatingdead-load deflections normally assume that each girderis free to deflect independently of other girders in abridge span. Under partial transverse loading conditionssuch as the example shown; however, the conventionalcalculation method yields a midspan transverse deflectionpattern markedly different from the actual field de-flection pattern. Thus, if the concrete were struck off tograde over the first girder, the midspan deck thickness atthis point would be decreased by the difference betweenthe two deflection curves. In addition, the finished gradeat this point will be low by an identical amount when allthe deck concrete is placed.

Neither of the two factors discussed above can be exactly compensated for during construction, but their effects can be minimized by observing the following

practices:a. Establish forming elevations when the thermal

conditions on the girders approximates those ant-

y -0.6P5

-0.8

GIRDER NUMBER

Fig. 10.9--Comparison of conventionally calculated deflec-tions with that measured in the field on a bridge being fin-ished with a screed traveling transversely


icipated at the time of concrete placement, adjustthe deck forms vertically at a time when the ther-mal condition of the girders approximates thecondition expected to prevail at the time of con-crete placement, or both. The precaution for ver-tical adjustment is most important since the in-place forming will shield the lower portion of thegirders from solar radiation. Differential thermaleffects can be virtually negated, of course, byconcreting very early or very late in the day.

b. Delay the final strikeoff pass of the screedingmachine over any given area at least three girderspaces behind concrete placement -- preferablymore. For exceptionally wide roadway widths(more than the equivalent of three 12 ft trafficlanes), the bridge designer should be consulted.

10.53 -- Work platforms that span the deck in the di-rection parallel to the finishing machine, and whichemploy the same rails to facilitate movement, are com-monly employed to aid in finishing operations (see Fig.10.2). They should be required when manual finishingmethods are used.

10.6 Texturing10.6.1 -- Decks with deep surface textures will retain

skid resistance longer than those with shallower textures.Satisfactory textures can be produced by wire brooming,wire drags, and flexible wire brushes (ACI 325.6R).

10.6.2 -- After the concrete has been brought to therequired grade, contour, and smoothness, the textureshould be applied. It is difficult to obtain a satisfactorytexture with a burlap drag unless it consists of multiplelayers and several passes are made. At the current stateof technology, a broom finish is the most practicalmethod for obtaining a satisfactory texture. Wire broomsare preferable, and the bristles should be spaced so as togive a coarse texture. Due to the importance of securingproper drainage, transverse ridges are preferable unlessminimization of noise is of importance.

The broom strokes should be square across the slabfrom edge to edge, with adjacent strokes slightly over-lapped. Brooming may be obtained either manually, i.e.,pulling of broom across the surface from a work platformby skilled workmen, or mechanically by self-poweredmachinery traveling longitudinally with power-drivenbroom moving transversely.

10.6.3 -- Texturing should not be carried out on decksurfaces that are to be sealed with a waterproofingmembrane (see Section 13.6.1).

10.7 Correction of defectsAfter the first pass of the finishing machine, add-

itional concrete should be added to honeycombed andlow spots, and the concrete struck off again. These areasmust not be eliminated by tamping or grouting. Thesurface of finished concrete after floating should bechecked with a 10 ft straightedge placed parallel to theroadway centerline and at several positions from one

edge of the deck to the other before moving to the nextlocation. Successive locations should not exceed one-halfthe length of the straightedge. Any depressions foundshould immediately be filled with fresh concrete, re-vibrated, struck off and refinished. Any areas notcorrected in the manner described above may have to becorrected by grinding at a considerably greater cost later,and with attendant loss of surface texture.

Chapter 11 -- Curing

11.1 General considerationsThe first few days in the life of a concrete deck are

critical insofar as its strength and durability charact-eristics are concerned. A rapid increase in quality duringthis initial period (which is commonly referred to as the“curing” period) requires favorable temperature and littleor no loss of mixing water.

To insure continued hydration at the optimum ratefor a given temperature, the cement paste must be keptas nearly saturated as possible. Water must be availableto compensate for evaporation from the surface, and toreplenish water removed from the pores by the chemicalprocess called self-desiccation. For a typical mixture, theamount of water needed during the first week to re-plenish depletion due to self-desiccation is about onepart water to 24 parts cement by weight.

Particular attention should be given to the equipmentwhich will be used to accomplish the cure. All equipmentand facilities must be ready so that the curing may beginwithout delay as soon as the concrete is ready for it.

11.2 Curing methodsAn ideal curing medium or agent will prevent any

substantial loss of moisture. Unfortunately, there is noideal curing agent; however, there are a number of meth-ods by which concrete decks can be kept in a moist con-dition and at a favorable temperature. The most popularmethods either supply additional moisture to the surface(continuous application of water), minimize moisture lossby sealing the surface (membrane curing compound), orby covering the surface (moisture barrier material).

11.2.1 Continuous water cure -- A continuous watercure may be maintained by a continuous spray, pondedwater on the surface, or by a surface covering of absor-bent material such as sand, cotton mats, old rugs, orstraw, which are kept saturated.

When the continuous water method is used to cureconcrete, the most important point to keep in mind isthat the surface of the concrete must not be allowed todry out once the curing period begins. Continuity isimportant because volume changes, due to alternate wetand dry periods, promote the development of patterncracking. The need for continuous curing is greatestduring the first few hours after placement.

Prewetting moisture-retaining material before it isplaced is an ideal but impractical system due to the


excessive weight. Hence, it is usually placed dry. Whenplaced dry, there is danger that absorption of water fromthe deck will cause surface damage. To minimize thechange for damage, the deck surface should be thor-oughly wet down prior to placing the material, and thematerial should be thoroughly wet down as soon as it isplaced.

11.2.2 Membrane curing -- There are three advantagesof membrane cure over continuous water cure: (1) It isgenerally applied earlier; (2) it is not cut off sharply; and(3) it is extended over a much longer period. A dis-advantage is that a membrane cure does not offer thecooling effect afforded by a continuous water cure.

For hot weather concreting, white pigmented curingcompounds are preferred over clear or lightly tintedcompounds because they allow less heat to build up fromsolar radiation, and offer better visual evidence ofuniform application.

Only curing compounds meeting the requirements ofASTM C 309 should be used on bridge deck concrete.Because of the lower allowable water loss, compoundsmeeting the requirements of federal specifications arepreferable (CRD-C-300).37

11.2.3 Sheet materials -- Curing by materials such asplastic sheets or waterproof paper is effective only if thedeck surface is thoroughly wet down just prior to layingthe barrier material and air is not permitted to circulateunder the material. Moisture barrier curing is difficult tocontrol in windy areas, in that the edges of the lightmaterial usually used are vulnerable to lifting by thewind.

11.3 Time of application11.3.1 -- In placing deck concrete in hot weather, it

is necessary to keep the operation confined to a smallarea and to proceed on a front having the minimum ex-posure surface against which concrete is to be added. Afog nozzle should be used generously to cool the air, tocool the forms and steel immediately ahead, and tolessen rapid evaporation from the concrete surface beforeand after each finishing operation. Excessive fog spraying(that which would wash the fresh concrete surface orcause water to stand on the surface during floating ortroweling) must be avoided.

Without such fog spray between the finishing oper-ations in hot weather, particularly if it is windy andhumidity is low, water may be evaporated from the sur-face faster than it will rise naturally to the surfacethrough bleeding. This will create growing tension in thesurface which often causes irregular, plastic shrinkagecracking (Fig. 7.2).

11.3.2 -- Membrane curing should begin as soon asthe bleed water sheen leaves the concrete surface, butbefore the surface dries. If the sheen is not uniform overthe area or if for some reason application of the mem-brane curing is delayed, the surface should be kept wetby fogging. It is important that the surface be damp whenthe membrane material is placed.

11.3.3 -- When the temperature will be near freezing,the use of plastic coverings, wet burlap, waterproof papercovering, or similar curing methods should be employed.See ACI 306R for further information.

11.4 DurationThe period of positive or controlled curing which

follows the setting of concrete is intended to insure theobtainment of reasonable strength at an early age, and toprevent the formation of surface cracks due to rapid lossof water while the concrete is low in strength. For bridgedecks, the minimum curing period should be no less than7 days.

In cold weather concreting, the curing period shouldbe extended if heat is not applied to the concrete. Anextended cure period or heat is especially important forincreasing the strength of a deck over the supports ofcontinuous structures, and thereby minimizing stresscracking when the span falsework is struck.

11.5 Related informationFurther information on curing will be found in ACI

308, ACI 305R, and ACI 306R.

Chapter 12 -- Postconstruction care

12.1 GeneralIn many cases, completion of the deck represents the

end of any concern for its care. This is unfortunatebecause even if all of the constraints and variablesdescribed in prior chapters have been successfullyaccommodated, relaxation of attention to details sub-sequent to the completion of concreting can impair thelong-term durability of the deck. Without question, theproblems resulting from improper care subsequent toconstruction are normally less serious than those derivedfrom poor practices during design or construction. Never-theless, they deserve attention if the deck is to be giventhe best possible change to survive in the very severeenvironment to which it is exposed. Not all of the pre-cautions listed in this chapter are of equal seriousness,and some are more important in some geographical areasthan in others.

12.2 During continuing construction12.2.1-- Perhaps the most common postconstruction

defects result from improper loading of the structureduring continuing construction operations. Much con-struction equipment imposes loads in excess of theservice loads for which the slab was designed. The effectsof these loads is especially severe because the concrete isrequired to carry such equipment at an early age beforeits load-carrying properties are fully developed. Greatcare should be exercised when loading comparatively newdecks with cranes, pavers, ready-mixed concrete trucks,and other heavy equipment to insure that the concrete isnot overstressed. Early cracking in negative moment


Chapter 13 -- Overlays

13.1 ScopeThis chapter deals with overlays placed on a cured

bridge deck as a protective shield against water, chem-icals, abrasion, or slipperiness. It does not includeconsiderations of penetrating sealers, such as silanes,used to inhibit chloride penetration.

Throughout this chapter, no distinction will be madeas to the age of the bridge at the time of overlay place-ment. Also, no attempt will be made here to discuss the

areas of continuous spans is often caused by suchpremature loadings.

12.2.2 -- Associated with premature loading butworthy of separate emphasis is the need to protect ex-pansion joints from infiltration of foreign material duringthe interim between their construction and sealing withexpansion joint materials. Moving heavy equipment overimproperly sealed or protected joints will result in jointspalls or incipient fractures which will dislodge under ser-vice traffic. When non-rubber-tired equipment must bemoved over unsealed joints, timber or other protectivedevices should be employed for protection.

Sealing and/or protection of the joints is also nec-essary to restrict infiltration of incompressible foreignmaterials which cause subsequent spalling when the deckundergoes thermal length changes.

12.2.3 -- Too rapid exposure of the surface of theslab to the hot sun at the end of a water cure may causeexcessive drying shrinkage in the surface when it is stillrelatively weak. Also, concrete cured in warm enclosures,as in winter concreting of bridge decks, should not besuddenly exposed to cold ambient temperatures, other-wise thermal shrinkage cracking or restraint cracking mayoccur.

Whatever the curing medium may be, it should beremoved at a time and in a manner that will allow theconcrete temperature to change slowly.

12.2.4 -- Storage of stain-producing materials, such asreinforcing steel or oil containers, can sometimes causeobjectionable discolorations. Such stains may be of con-cern from the standpoint of esthetics but are of nodetriment to the durability of the slab.

12.3 Construction associated preventive maintenance12.3.1 -- In areas of freezing, drains should be kept

open to prevent ponding of water during constructionand should be left open upon completion of the job. Asnoted earlier, areas of high saturation are especiallyvulnerable to subsequent deterioration.

12.3.2 -- Although deicing chemicals are not normallyapplied during construction, it is advisable to rememberthat such materials should not be applied until theconcrete has gained a certain degree of maturity. Afterthe concrete has acquired its design strength, a period ofdrying should elapse before the application of deicingsalts. This drying period should be at least 1 month.Longer periods may be desirable, depending on climaticconditions. It it is likely that deicers will be appliedsooner than 30 days after completion of the curing per-iod, a surface treatment such as linseed oil or neutralpetroleum oil should be used to give additional pro-tection.

12.3.3 -- The use of protective coatings to reducescaling associated with the use of deicing chemicals hasbeen the focus of research and testing for many years.Many materials have been promoted and studied. Theseinclude a wide variety of resins; petroleum products; oilsof various kinds including linseed, tung, and tall; and

other organic materials. Snyder;38 Furr, Ingram, andWinegar;39 and Stewart and Shaffer40 reported the resultsfrom tests of 110, 19, and 32 different materials, re-spectively. In some cases, several classes of materialshave imparted some additional durability to poorly air-entrained surfaces by delaying the onset of scaling. Ofthe numerous materials studied, linseed oil has repeat-edly been shown to be the most efficient when both pro-tection and economics are considered. Thus, it is by farthe most widely used. The beneficial influence of linseedoil for non- or poorly air-entrained concrete is thor-oughly documented.38-422 There is no documented evidencethat linseed oil treatments are necessary to adequatelyprotect air-entrained concretes. The difficulties of pre-cisely controlling entrained air in the field have beenpreviously discussed.

A report by Rye11 and Chojnacki43 recommendedagainst the use of linseed oil, since it delayed rather thanprevented scaling, and led to a “false sense of security.”They emphasized the importance of air entrainment. Adetailed comparison of their results with those reportedby others discloses no real conflicts, but rather adoptionof a different strategy for insuring desired performance.

In considering all of the information available to it,Committee 345 believes that the use of linseed oil orneutral petroleum oil surface treatments is a goodinvestment as added insurance, but that major emphasisshould be placed on the control of entrained air andother ingredients of the concrete, along with finishingand curing practices.

Oil treatments normally consist of two applications ofequal parts of (1) commercial boiled linseed oil and asolvent such as turpentine, naphtha, or mineral spirits, or(2) neutral petroleum oil and Stoddard solvent. Recom-mended linseed oil coverages are about 40 to 50 yd2/gal.for the first application and about 70 yd2/gal. for thesecond application. Petroleum oil is usually applied inequal applications, totaling about 17 yd2/gal. If possible,concrete temperatures should be about 50 F or higher atthe time of application to assure proper penetration andto hasten drying. Since oil treatments will produce aslippery surface until absorbed, it may be necessary tokeep traffic off the deck until sufficient drying has takenplace, or to apply sand for traction during the dryingperiod.


relative merits of various overlays to prevent deterior-ation of concrete bridge decks. It is assumed thatoverlays will only be placed on structurally soundsurfaces, regardless of age.

13.2 Need for overlays13.2.1 Waterproof barrier -- The primary reason for

the use of overlays is the prevention and repair ofspalling on concrete bridge decks. Such spalling is theresult of expansive forces built up within the deck con-crete by the products of corrosion of reinforcement steel.Such corrosion is advanced by the presence of moistureand chlorides. Cracks over the reinforcement or porousconcrete can accelerate the rate of deterioration. Thus,where cracks or porous concrete are evident and deicersare used, some type of waterproof barrier should beprovided or spalling may be anticipated.

It should be reemphasized that careful attention togood design and construction practices, as set forth else-where in this standard practice, should significantlyreduce the propagation of cracks and prevent the accept-ance of poor quality concrete. However, where repaircosts have become excessive or where good practice isknown to have been compromised, an overlay may be acost effective means of extending service life.

13.2.2 Slipperiness -- Bridge decks, like all roadwaysurfaces, must be adequately skid resistant. Occasionally,rapid surface wear, due to construction deficiencies andinadequate skid-resistant aggregates, induces slipperiness.Overlays provide a means for correcting this deficiency.

13.2.3 Wearing course -- The use of studded tires hasmarkedly increased the abrasive wear on some bridges.Consequently, overlays may be considered as a sacrificialwearing course since the loss through abrasion of anoverlay would not reduce the section modulus or the crit-ical clear cover over reinforcing steel in the structuralslab. Overlays can be replaced with relative ease andcost.

13.2.4 Reduction of wheel load effect -- Asphalticconcrete (AC) overlays are commonly used to providewheel load distribution and a smooth riding surfacewhich helps reduce impact. They are also used as a ridingsurface over waterproofing membranes.

13.3 Required properties of overlaysThe required properties of overlays depend on their

intended purpose, as discussed above.13.3.1 Properties required of all overlays -- Several

properties are generally required of all overlays, regard-less of the reasons leading to their use.

13.3.1.1 -- Adhesion to concrete or bond is afundamental requirement for most overlays. Withoutadhesion, overlays soon delaminate which, at best,presents an unsightly appearance and, at worst, requiredextensive repair.

13.3.1.2 -- Cohesion or resistance to shear withinthe overlay itself is necessary to resist the stresses in-duced by the turning and braking of the heaviest trucks.

This resistance may be relevant when considering the useof unreinforced thermoplastic materials, such as asphalt.

13.3.1.3 -- Skid resistance is a fundamentalrequirement of an overlay, whether or not that is thepurpose for which it was intended, because the overlaybecomes the road surface. This property requires theaddition of an abrasion-resistant aggregate to most of thepolymer-type materials currently marketed as overlays.Grooving (diamond blade saw cut of hardened concrete)or texturing (of plastic concrete) is usually required whenplacing concrete overlays.

13.3.1.4 -- Durability, used here as resistance toabrasion, deformation and decay, is another importantproperty. Many materials, such as bitumens, soften underhigh temperatures and become subject to rutting. Suchrutting may be imperceptible in the roadway, but createsan undesirable bump at bridge joints. Other productsmay become brittle with age or when oxidized, and thusmay not retain the properties for which they wereintended. Extended service histories should be invest-igated for any proposed overlay.

13.3.2 Properties required of waterproof barriers -- Inaddition to the properties listed above, waterproof bar-riers should be designed, considering the conditionswhich could lead to the intrusion of moisture andchloride ions.

13.3.2.1 -- Impermeability is an important prop-erty of waterproof barriers. Materials may be imperm-eable in lab test conditions, but may be affected byultraviolet or by the heat from asphalt paving. Intro-ducing aggregates for skid resistance or as bulk fillersmay also create interconnected voids that admit water.Some construction techniques induce foaming and por-osity which may increase water intrusion.

13.3.2.2 -- Crack resistance is another importantrequirement of a waterproof barrier. Development ofcracks in concrete is one of the conditions leading to theuse of a waterproof barrier. Hence, barrier materialsmust be capable of bridging such cracks in the underlyingdeck and remaining waterproof. Reflective cracking inbridge decks is a much greater problem on long-span,cast-in-place decks.

13.3.2.3 -- Bridge decks expand and contract withtemperature change, and overlays placed on them mustdo likewise without loss of bond. Where thermal incom-patibilities exist between the concrete and the membrane,shear stresses will be created by temperature change.These stresses are proportional to the membrane thick-ness. Such stresses may exceed the bond strength of themembrane or the shear strength of the concrete, and theresulting failure will destroy the membrane’s effective-ness. Thus, the coefficient of expansion of any membranematerial is a significant property where substantialtemperature changes occur.

13.4 Types of overlaysOverlays can be grouped into three categories (see

Fig. 13.1):


13.6 Construction considerations13.6.1 Deck construction to accommodate overlays --

Where the use of overlays is anticipated, texturing of the

Type I -- Thin overlapType II -- Concrete-based overlapType III -- Combined-system overlap

13.4.1 Thin overlays -- Thin overlays have thicknessesof 1/2 in. or less and therefore add minimal dead load tostructures. Their primary function may be to increaseskid resistance on slippery decks or to act as surfacemembranes to minimize penetration of water and chlor-ide ions. They must generally be applied to dry concretesurfaces. They usually involve durable, abrasion-resistantaggregates glued together by various binders includingasphaltic emulsions, polymer resins, and polymer-modified cements. Thin overlays are generally not recom-mended for badly spalled or deteriorated decks. Special-ized expertise may be needed to properly apply thesesystems. A detailed discussion of these systems is beyondthe scope of this document, but additional informationmay be found in ACI 548.1R.

13.4.2 Concrete overlays -- This type of overlay variesfrom 1 in. to about 21/2 in. deep. They include latex-mod-ified concrete, polyester-modified concrete, low-slumpdense concrete, fast-setting concrete, and some variationsinvolving steel fiber or silica fume, or high-range water-reducing mixtures or cathodic protection. The primaryfunction of these systems is to replace deteriorated con-crete or asphalt wearing surfaces with an economical,durable, crack-resistant, low-permeability material with-out significantly increasing the dead load on thestructure. The relative advantages and disadvantages ofthe systems may vary from one region to another, de-pending on local economic, climatic and design factors.Choice of a system should involve consideration of theactual problems. Shrinkage and surface cracking of con-crete overlays are likely to be significant factors in coldclimates where deicing salts are used, as compared withmilder climates with little use of deicing salts. Shrinkagecracking is also a significant factor in dry and windyclimates. High-slump mixes (higher than 4-in. slump) arenot recommended for decks with longitudinal gradesexceeding 2 percent. Cathodic protection systems shouldbe routinely monitored to insure continued performance.The use of steel fibers, or admixtures such as silica fumeor super-plasticizers, is generally intended to improvecrack resistance and impermeability. Prior to use, thefield experience of any particular system should beinvestigated.

13.4.3 Membrane and AC overlays -- This type ofoverlay involves a waterproofing membrane covered withone or two courses of asphaltic concretes. The totaldepths usually range from 2 to 4 in. The economics ofasphalt when available may make this a good option forusing the good riding quality and shock-absorbingqualities of the material. Membranes are not recom-mended for repairing badly delaminated decks with cor-roded reinforcing bars close to the surface.

There are many types of membranes, including hot-applied, rubberized membranes; sheet membranes; and

liquid-applied, polymer membranes. The membranesshould be capable of bonding to concrete, bridgingcracks, waterproofing, and bonding to AC overlays with-out being affected by 300 F asphalt. Some membranes re-quire protection boards and two passes of asphaltic con-crete in order to minimize damage during compaction,and these systems may not be suitable for repair ofexisting bridges that were not designed for the extra deadload. Some sheet membranes may not bond well to con-crete, or may debond at later dates if exposed to heatand sunlight, which creates vapor pressure and weakenedbond due to temperature. Liquid-applied membranesmay require special expertise. Some jurisdictions requirewarranties on membrane installation.

13.4.3.1 -- Wearing courses are generally asphalticconcretes. The design of such courses is beyond thescope of this standard practice.

An AC overlay should not be used directly on a port-land cement concrete deck without a waterproofingmembrane. All AC mixtures are inherently porous andreadily conduct water and chlorides to the portlandcement concrete deck where they cannot be flushed off.Such impounded brine greatly accelerates bridge deck de-terioration which is then difficult to observe or measurebelow the asphalt. The permeability of AC greatly in-creases with age.

13.5 Design considerationsFor Type I, and most Type II overlays, no special

design considerations are usually necessary for the con-crete bridge deck. On the other hand, for some Type IIand all Type III overlays, the designer must carefullyconsider several details.

Thick concrete overlays, and membrane and ACsystems may increase the dead load on an existing deck.If so, structural design calculations should be reviewed,particularly on long-span structures.

In addition, a thick concrete or an asphalt overlaymay require raising the bridge deck joints and surfacedrainage facilities to meet the new grade. The raised endjoints, together with the effect of the bridge curbs, maycreate a void into which the overlay is placed. Whilewater which permeates this wearing course should notaffect a properly constructed interlayer membrane, itcould, on freezing, disrupt the wearing course itself. Forthis reason, some designers prefer to install smalldiameter subsurface drains to conduct the water thatponds below the asphalt through the deck slab. To pre-vent the leakage from causing deterioration of the deckunderside, the drains should extend slightly below thedeck or be surrounded by a drip groove. They shouldalso be located so as to miss dripping on the supportinggirders, or they may be extended to drip below the levelof the girders.


TYPES OF BRIDGE DECK OVERLAYS

TYPE I TYPE II TYPE III

\Mortar Overlay

CONCRETE

DECK

Wearing Courselnterlayer Membrane

COATINGS MORTARS COMBINED SYSTEMS

Fig. 13.1--Several types of overlays showing wearing courses and / or interlayer membranes

portland cement concrete surface may be unnecessary.Sheet membranes generally bond better to smooth con-crete, while thin overlays may bond better to the rough-ness created by light brooming.

Manufacturer’s recommendations should beconsulted. For Type II and Type III overlays, deck sur-face tolerances for screeding and flatness need be lessstringent than where Type I or no overlays are antici-pated. Minor irregularities in profile and cross-slope canbe corrected by the subsequent concrete or AC overlay.

Some curing compounds may inhibit the bondstrength between Type I and Type II overlays and thedeck surface. Where such materials are used, sand-blasting or shotblasting should be required beforeapplying the overlay.

13.6.2 Constructing the overlay -- Nearly all Type Iand Type II overlays require scrupulous cleaning of thedeck surface prior to application. Sandblasting, shot-blasting, or waterblasting are generally preferred, al-though waterblasting is not recommended prior toapplying most polymer materials. Manufacturer’s recom-mendations should be checked. Shotblasting involves lessrisk or human error than sandblasting and is often pre-ferred. Surface preparation for Type III overlays is alsodependent on the kind of membrane selected. Resinousmembranes for Type III overlays may require the samedegree of surface preparation as Type I and Type IIoverlays. Bitumen membranes may require only carefulsweeping.

The degree of surface dryness required for Type Iand Type II overlays is dependent on the type of mem-brane material. Most epoxies will not bond well to amoist surface. Asphalt also will not bond well to a wetsurface. In contrast, the emulsions often used with re-inforced membrane systems may bond better to a moistsurface than to a dry one. Manufacturer’s instructionsshould be consulted.

Type II overlays generally bond best to surfaces thatare saturated-surface-dry. For low slump, dense concrete

overlays, a bonding slurry of cement and water isbroomed on just ahead of the concrete placement.

The ambient temperature is significant for nearly alloverlays. Virtually all common materials require temp-eratures above freezing, and most above 40 F, to effectproper cure. One exception is the prefabricated sheets.

In the absence of specific information, a good rule ofthumb is that all overlays bond best to a clean, dry(except emulsions), and warm deck.

13.6.2.1 -- Type I overlays may be applied byspraying or pouring the liquid binder, followed byspreading and back-rolling. Aggregates are then cast overthe surface. Another method is to premix the aggregatesand binder, and screed the overlay, sometimes in narrowlongitudinal strips. Sometimes the premix system is pre-ceded by a primer coat.

13.6.2.2 -- Type II overlays are usually applied byscreeding in place. Low-slump overlays require mobileconcrete mixers and special screeds. Other overlaysplaced at 2- to 4-in. slump involve conventional screeds.High-amplitude air screeds or the use of air screeds withmix slumps higher than 4 in. are not recommended dueto their effect on the concrete air void system andresulting freeze-thaw durability of the overlay. Super-plasticized concrete overlays should not be overvibratedor overfinished, to avoid durability problems.

13.6.2.3 -- Type III overlays are constructedaccording to the kind of membrane used. Membranessimilar to Type I overlays are applied as in Section13.6.2.1. Bitumen membranes are similarly applied exceptthat mesh, usually of fiberglass, may be embedded ratherthan aggregate. Some types of prefabricated sheets arerolled in place after applying a suitable tack coat.Emulsion-based tack coats are preferred, since volatilesfrom asphalts may cause blistering in the sheets. Watervapor freed from emulsions may also cause blistering ifadequate time is not permitted for the emulsion to cureproperly. Some types of sheet membranes are applied byusing torches to melt the bottom layer as the sheet is


rolled in place.Wearing courses are placed, using conventional

rubber-tired equipment and care so as not to damage themembrane. Many bitumens used in built-up, mesh-rein-forced layers are vulnerable to damage and may requirehand application of a binder course, followed by thesurface wearing course.

13.7 Other considerationsNot all bridges have the same design and exposure

conditions, so the resulting bridge deck problems are notalways similar, and neither are the solutions. Severalfactors should be considered when choosing an overlay.

13.7.1 Geographic and climatic factors -- Annual rain-fall, maximum and minimum expected temperatures, an-nual ranges of humidity, and annual number of freeze-thaw cycles are all significant factors relating to expectedservice life that vary from region to region. Dry climatesgenerally result in greater shrinkage and cracking ofType II overlays. Warm, wet climates are conducive torapid rates of steel corrosion. Cold climates create tensilestresses from temperature change and cause many mater-ials to become brittle and fail when subjected to live loadstresses. Salt may be present in the aggregates of someregions, or may come from bodies of saltwater or fromdeicing chemicals used in Northern regions. Abrasive sur-face wear may be greatly increased by the presence ofstudded tires or tire chains. Some regions are beginningto experience acid rain. Rates of carbonation also varyregionally. Both acid rain and carbonation lower the pHlevel of the concrete, which may result in increasedreinforcing steel corrosion.

Chapter 14 -- References

14.1 Recommended referencesThe documents of the various standards-producing

organizations referred to in this document are listedbelow with their serial designation:

American Association of State Highway and TransportationOfficials (AASHTO)

Standard Specifications for Highway Bridges

M31 Deformed and Plain Billet-Steel for ConcreteReinforcement

M284 Epoxy Coated Reinforcing BarsT-26 Quality of Water to be used in Concrete

American Concrete Institute (ACI)

117 Standard Specification for Tolerances forConcrete Construction and Materials

201.1R Guide for making a Condition Survey ofConcrete in Service

201.2R Guide to Durable Concrete211.1 Standard Practice for Selecting Proportions for

Normal, Heavyweight, and Mass Concrete211.2 Standard Practice for Selecting Proportions for

Structural Lightweight Concrete212.3R Chemical Admixtures for Concrete214 Recommended Practice for Evaluation of

Strength Test Results of Concrete221R Guide for Use of Normal Weight Aggregates

in Concrete222R Corrosion of Metals in Concrete223 Standard Practice for the Use of Shrinkage-

Compensating Concrete226.1R Ground Granulated Blast-Furnace Slag as a

Cementitious Constituent in Concrete226.3R Use of Fly Ash in Concrete304R Guide for Measuring, Mixing, Transporting and

Placing Concrete305R Hot Weather Concreting306R Cold Weather Concreting308 Standard Practice for Curing Concrete309R Guide for Consolidation of Concrete311.4R Guide for Concrete Inspection318 Building Code Requirements for Reinforced

Concrete325.6R Texturing Concrete Pavements503.3 Standard Specification for Producing a Skid

Resistant Surface on Concrete by the Use of aMulti-Component Epoxy System

504R Guide to Joint Sealants in Concrete Structures515.1R Guide to the Use of Waterproofing, Damp-

proofing, Protective, and Decorative BarrierSystems for Concrete

548.1R Guide for the Use of Polymers in ConcreteSP-2SP-4

ASTM

A 615

A 775

C 33C 94C 150C 191

C 231

C 260

C 309

C 330

ACI Manual of Concrete InspectionFormwork for Concrete

Steel Bars Specification for Deformed and PlainBillet Steel Bars for Concrete ReinforcementSpecification for Epoxy-Coated ReinforcingSteel BarsSpecifications for Concrete AggregateSpecifications for Ready Mixed ConcreteSpecifications for Portland CementTest Method for Tiie of Setting of HydraulicCement by Vicat NeedleTest Method for Air Content of Freshly MixedConcrete by the Pressure MethodSpecifications for Air-Entraining Admixturesfor ConcreteSpecifications for Liquid Membrane FormingCompounds for Curing ConcreteSpecification for Lightweight Aggregates forStructural Concrete

345R-34

15. “Durability of Concrete Bridge Decks, ACooperative Study,” Portland Cement Association,Skokie, Reports No. 1, 1965, 130 pp.; NO. 2, 1965, 107pp.; NO. 3, 1967, 142 pp.; No. 4, 1968, 119 pp.; and No.5, 1969, 49 pp.

C 403

C 457

C 494

C 595C 618

C 635C 666

C 671

C 672

C 682

C 685

C 806

C 845C 878

D 3963E 274

E 329

Test Method for Time of Setting of ConcreteMixtures by Penetration ResistancePractice for Microscopical Determination of AirVoid Content and Parameters of the Air-VoidSystem in Hardened ConcreteSpecification for Chemical Admixtures forConcreteSpecification for Blended Hydraulic CementsSpecification for Fly Ash and Raw or CalcinedNatural Pozzolana for use as a MineralAdmixture in Portland Cement ConcreteConcrete made by Column Continuous MixingTest Method for Resistance of Concrete to RapidFreezing and ThawingTest Method for Critical Dilation of ConcreteSpecimens Subjected to FreezingTest Method for Scaling Resistance ofConcrete Surfaces Exposed to De-IcingChemicalsPractice for Evaluation of Frost Resistance ofCoarse Aggregate in Air Entrained Concrete byCritical Dilation ProceduresSpecification for Concrete Made by VolumetricBatching and Continuous MixingMethod of Test for the Restrained Expansion ofExpansive Cement MortarSpecification for Expansive Hydraulic CementTest Method for the Restrained Expansion ofShrinkage Compensating ConcreteSpecification for Epoxy-Coated Reinforcing SteelTest Method for Skid Resistance of PavedSurfaces using a Full Scale TireRecommended Practice for Inspection andTesting Agencies for Concrete, Steel andBituminous Materials as Used in Construction

The above publications may be obtained from thefollowing organizations:

American Association of State Highwayand Transportation Officials

444 N. Capitol Street, N.W. - Suite 225Washington, D.C. 20001

American Concrete InstituteP.O. Box 19150Detroit, Michigan 48219

ASTM1916 Race StreetPhiladelphia, Pennsylvania 19103

14.2 Cited references

1. “Durability of Concrete Bridge Decks--A

Cooperative Study,” Final Report EBN067E, PortlandCement Association, Skokie, 1970, 36 pp.

2. Lerch, William, “Plastic Shrinkage,” ACIJOURNAL, Proceedings, Vol. 53, No. 8, Feb. 1957, pp.797-802.

3. Woods, Hubert, Durabil i ty of ConcreteConstruction, ACI Monograph No. 4, American ConcreteInstitute/Iowa State University Press, Detroit, 1968, 190pp.

4. Bergren, Jerry V., and Brown, Bernard C., “AnEvaluation of Concrete Bridge Deck Surfacing in Iowa,”Iowa Department of Transportation, Ames, Apr. 1975.

5. Pfeifer, D.W.; Landgren, R.J.; and Zoob A.,“Protective Systems for New Prestressed and SubstructureConcrete,” FHWA/RD-86/193, April 1987.

6. Kummer, H.W., and Meyer, W.E., “TentativeSkid Resistance Requirements for Main RuralHighways,” NCHRP Report No. 37, TransportationResearch Board, 1967, 96 pp.

7. Meyer, W.E.; Hegmon, R.R.; and Gillespie, T.D.,“Locked-Wheel Pavement Skid Tester Correlation andCalibration Techniques,” NCHRP Report No. 151,Transportation Research Board, 1976, 100 pp.

8. Mahone, D.C.; McGhee, K.H.; McGee, J.G.G.;and Galloway, J.E., “Texturing New ConcretePavements,” Transportation Research Record No. 652,Transportation Research Board, 1977, pp. l-10.

9. Deuterman, M.; Jones, T.J.; Lee, R.E.; Lessard,F.H.; and Spangler, R.W., “Metal Bridge Deck FormSpecifications Developed Cooperatively by Industry andGovernment,” Highway Research Record No. 302,Transportation Research Board, 1970, pp. 97-107.

10. Jones, H.L., and Furr, H.L., “Study of In-ServiceBridges Constructed with Prestressed Panel Sub-Decks,”Research Report No. 145-1. Texas TransportationInstitute, Texas A & M University, College Station, July1970.

11. Barnoff, R.J.; Larson, T.D.; and Love, J.S., Jr.,“Composite Action from Corrugated Bridge DeckForms,” Materials and Structural Research Report,Pennsylvania State University, University Park, Mar.1967, 43 pp.

12. Jones, H.L., and Furr, H.L., “DevelopmentLength of Strands in Prestressed Panel Sub-Deck,”Research Report No.145-2, Texas Transportation Institute,Texas A & M University, College Station, Dec. 1970.

13. Manual of Standard Practice, 24th Edition,Concrete Reinforcing Steel Institute, Shaumberg, Illinois,1986.

14. Clifton, J.R.; Beeghly, H.F.; and Mathey, R.G.,“Nonmetallic Coatings for Concrete Reinforcing Bars,”Final Report No. FHWA-RD-74-18, Federal HighwayAdministration, Washington, D.C., Feb. 1974, 87 pp.


34. Meininger, R.C., “Effects of a Delay BetweenBatching and Mixing on Concrete Strength,” TechnicalInformation Letter No. 226, National Ready MixedConcrete Association, Silver Spring, 1965, 7 pp.

35. Larson, Thomas D.; Cady, Philip D.; and Price,John T., “Review of a Three-Year Bridge Deck Study inPennsylvania,” Highway Research Record No. 226,Transportation Research Board, 1968, pp. 11-25.

Council, Washington, D.C., September 1987.29. Whiting, D. “Effects of High-Range Water

Reducers on Some Properties of Fresh and HardenedConcretes”; PCA, Research & Development BulletinRD061.01T.

16. Lower, D.O., “Summary Report on Type KShrinkage-Compensating Concrete Bridge DeckInstallation in the State of Ohio,” SP-64-10, WillsonSymposium on Expansion Cement, American ConcreteInstitute, Detroit, Mich., 1980, pp. 181-192.

17. Kesler, C.E., and Cusick, R.W., “Interim Report -Phase 3: Behavior of Shrinkage-Compensating Concrete

Suitable for Use in Bridge Decks,” T & AM Report 409,University of Illinois, Urbana, July 1976.

18. Kato, T., and Goto, Y., “Effect of WaterInfiltration of Penetrating Cracks on Deterioration ofBridge Decks,” Transportation Research Record, Vol. 950,pp. 202-209.

19. Report of Committee 223, “Expansive Cements -Present State of Knowledge,” Proceedings, Vol. 67, No.

8, American Concrete Institute, Detroit, Mich., August,1970, pp. 583-610.

20. Klieger, P., and Greening, N.R., “Utility ofExpansive Cement,” Proceedings, 5th InternationalSymposium on the Chemistry of Cement, (Tokyo: 1968),Cement Association of Japan, Tokyo, 1969, Paper No.IV-132.

21. Polivka, M.; Mehta, P.K.; and Baker, J.A., Jr.,“Freeze-Thaw Durability of Shrinkage-CompensatingCement Concretes,” Durability of Concrete, SP-47, ACI,Detroit, 1975, pp. 79-87.

22. Gulyas, R.J., and Garrett, M.F., “The Action andApplication of Two New ASTM Specifications forShrinkage-Compensating Cement in Concretes: ASTM C845 and C 878,” Cement, Concrete and Aggregates, Vol. 3,No. 1, ASTM, Philadelphia, Pa., Summer 1981, pp. 3-12.

23. Beckmann, P.A., Jr., and Gulyas, R.J., “Designand Construction with Shrinkage-Compensating ConcreteUsing ACI 223-83,” Proceedings, ASCE, Spring, 1986.(See Construction Materials for Civil Engineering Projects,William T. Johnson, Jr., Editor, ASCE, SBNO-87262-534-6, 1986.)

24. Kesler, C.E.; Seeber, K.E.; and Barlett, D.L.,“Interim Report - Phase 2: Behavior of Shrinkage-Compensating Concrete Suitable for Use in BridgeDecks,” T & AM Report 372, University of Illinois,Urbana, July 1973.

25. Borrowman, P.E.; Seeber, K.E.; and Kesler, C.E.,“Interim Report - Phase 2: Behavior of Shrinkage-Compensating Concrete Suitable for Use in BridgeDecks,” T & AM Report 392, University of Illinois,Urbana, July 1974.

26. Cusick, R.W., and Kesler, C.E., “Final SummaryReport - Behavior of Shrinkage-Compensating ConcreteSuitable for Use in Bridge Decks,” T & AM Report 416,University of Illinois, Urbana, April 1977.

27. Popovic, P.L., et al, “Deck Cracking Investigationof the Hope Memorial Bridge,” Wiss, Janney, Elstner(WJE No. 841247); Northbrook, IL 60062, January 1988(prepared for Ohio Department of Transportation).

28. Whiting, D., and Schmitt, J., “Durability of In-Place Concrete Containing High-Range Water-ReducingAdmixtures,” NCHRP Report No. 296, National Research

30. Colley, B.E.; Christensen, A.P.; and Nowlen,W.J., “Factors Affecting Skid Resistance and Safety ofConcrete Pavements,” Special Report No. 1 0 1 ,Transportation Research Board, 1969, pp. 80-89.

31. Bloem, Delmar L., and Gaynor, Richard D.,“Factors Affecting the Homogeneity of Ready-MixedConcrete,” Report No. 1, Phase I, 1969, National ReadyMixed Concrete Association, Silver Spring, 1970, 25 pp.Also Summary, ACI JOURNAL, Proceedings, Vol. 68,No. 7, July 1971, pp. 521-525.

32. Price, W.H., and Robinson, J.W., “Effect ofDelayed Mixing of Prebatched Moist Aggregates andCement on the Strength and Durability of Concrete,”Proceedings, ASTM, Vol. 48, 1948, pp. 962-967.

33. Meininger, R.C., “Study of ASTM Limits onDelivery Time,” NRMCA Publication No. 131, NationalReady Mixed Concrete Association, Silver Spring, Feb.1969, 17 pp.

36. Cordon, William A., and Thorpe, J. Derle,“Control of Rapid Drying of Fresh Concrete byEvaporation Control,” ACI JOURNAL, Proceedings, Vol.62, No. 8, Aug. 1965, pp. 977-986.

37. Handbook for Concrete and Cement, U.S. ArmyCorps of Engineers, CRD-C-300, “Membrane-FormingCompounds for Curing Concrete,” 1977 edition.

38. Snyder, M. Jack, “Protective Coatings to PreventDeterioration of Concrete by Deicing Chemicals,”NCHRP Report No. 16, Transportation Research Board,1965, 21 pp.

39. Furr, H.; Ingram, L.; and Winegar, G., “Freeze-Thaw and Skid Resistance Performance of SurfaceCoatings on Concrete,” Report No. 130-3, TexasTransportation Institute, Texas A & M University,College Station, 1969.

40. Stewart, P.D., and Shaffer, R.K., “Investigation ofConcrete Protective Sealants and Curing Compounds,”Highway Research Record No. 268, TransportationResearch Board, 1969, pp. 1-16.

41. Brink, Russell; Grieb, William E.; and Woolf,Donald O., “Resistance of Concrete Slabs Exposed asBridge Decks to Scaling Caused by Deicing Agents,”Highway Research Record No. 196, TransportationResearch Board, 1967, pp. 57-74.

42. Newlon, H.H., “Evaluation of Several Types ofCuring and Protective Materials for Concrete --


Laboratory and Outdoor Exposure Studies Preliminary toField Trials,” Virginia Highway Research Council,Charlottesville, 1970.

43. Ryell, J., and Chojnacki, B., “Laboratory andField Tests on Concrete Sealing Compounds,” D.H.O.Report No. RR150, Ontario Department of Highways,Downsview, Dec. 1969.


APPENDIX A

CONVERSION FACTORS---- INCH-POUND TO SI (METRIC)*

To convert from to multiply by

Length

inch .................................millimeter (mm) ........................... 25.4E+foot . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . meter (m) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.3048Eyard . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . meter (m) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.9144Emile (statute) .......................... kilometer (km) ............................1.609

square inch ........................ square centimeter (cm2) .........................6.451square foot .......................... square meter (m2) ...........................0.0929square yard .......................... square meter (m2) ...........................0.8361

Volume (capacity)

ounce ............................. cubic centimeter (cm3) ........................ 29.57gallon .............................. cubic meter (m3)t ...........................0.003785cubic inch ......................... cubic centimeter (cm3) ........................ 16.4cubic foot .............................cubic meter (m3) ...........................0.02832cubic yard ........................... cubic meter (m’)+ ...........................0.7646

Force

kilogram-force .......................... newton (N) .............................9.807kip-force . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . newton(N) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4448pound-force . . . . . . . . . . . . . . . . . . . . . . . . . . . . newton(N) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.448

Pressure or stress (force per area)

kilogram-force/square meter ................. pascal (Pa) ..............................9.807kip-force/square inch (ksi) ............... megapascal (MPa) ...........................6.895newton/square meter (N/m2) ................. pascal (Pa) ..............................1.000Epound-force/square foot .................... pascal (Pa) ............................. 47.88pound-force/square inch (psi) .............. kilopascal (kPa) ............................6.895


to convert from multiply by

Bending moment or torque

inch-pound-force ..................... newton-meter (Nm) ..........................0.1130foot-pound-force ..................... newton-meter (Nm) ..........................1.356meter-kilogram-force .................. newton-meter (Nm) . . . . . . . . . . . . . . . . . . . . . . . . . . 9.807

ounce-mass (avoirdupois) ....................... gram (g) .............................28.34 pound-mass (avoirdupois) .................. kilogram (kg) .............................0.4536

ton (metric) ...........................megagram (mg) ........................... 1.000E ton (short, 2000 lbm) .................... megagram (Mg) ............................0.9072

Mass per volume

pound-mass/cubic foot .............. kilogram/cubic meter (kg/m3) ...................... 16.02pound-mass/cubic yard .............. kilogram/cubic meter (kg/m3) .......................0.5933pound-mass/gallon ................. kilogram/cubic meter (kg/m3) ..................... 119.8

Temperature

degrees Fahrenheitdegrees Celsius (C)

. . degree Celsius (C) degree Fahrenheit (F)

tc = (tF - 32)/1.8. tF = 1.8t c + 32

*This selected list gives practical conversion factors of units found in concrete technology. The reference source forinformation on SI units and more exact conversion factors is “Standard for Metric Practice” ASTM E 380. Symbols ofmetric units are given in parenthesis.

+E Indicates that the factor given is exact.-C One liter (cubic decimeter) equals 0.001 m 3 or 1000 cm 3.$ These equations convert one temperature reading to another and include the necessary scale corrections. To

convert a difference in temperature from Fahrenheit degrees to Celsius degrees, divide by 1.8 only, i.e., a change from70 to 88 F represents a change of 18 F or 18/1.8 = 10 C deg.

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