3. Precast Concrete Pavement

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PRECAST CONCRETE PAVEMENT

CHAPTER-1

INTRODUCTION

1.1 PRECAST CONCRETE PAVEMENT

Precast concrete is a form of construction, where concrete is cast in a reusable mould

or "form" which is then cured in a controlled environment, transported to the construction site

and lifted into place. In contrast, standard concrete is poured into site specific forms and

cured on site. Precast stone is distinguished from precast concrete by using a fine aggregate

in the mixture so the final product approaches the appearance of naturally occurring rock or

stone.

Precast pavement technology comprises new and innovative construction methods

that can be used to meet the need for rapid pavement repair and construction. Precast

pavement components are fabricated or assembled off-site, transported to the project site, and

installed on a prepared foundation (existing pavement or re-graded foundation). The system

components require minimal field curing time to achieve strength before opening to traffic.

These systems are primarily used for rapid repair, rehabilitation, and reconstruction of bothasphalt and portland cement concrete (PCC) pavements in high-volume-traffic roadways. The

precast technology can be used for intermittent repairs or full-scale, continuous rehabilitation.

In intermittent repair of PCC pavement, isolated full-depth repairs at joints and cracks

or full-panel replacements are conducted using precast concrete panels. The repairs are

typically full-lane width. The process is similar for full-depth repairs and full-panel

replacement. Key features of this application are slab panel seating and load transfer at joints.

Use of precast concrete pavements for reconstruction and rehabilitation is a very

viable alternative to conventional cast-in-place concrete pavement construction, especially in

situations where high traffic volumes and consideration of the delay costs to users due to lane

closures favor reconstruction and rehabilitation solutions that allow expedited opening to

traffic. Precast concrete also offers the advantage of being factory made in a more

controlled environment than cast-in-place construction and thus is potentially more durable

and less susceptible to construction and material variability.

Dept of Highway Technology, DSCE Page 1
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1.2 PAVEMENT TYPES

Hard surfaced pavements are typically categorized into flexible and rigid pavements:

1.2.1 FLEXIBLE PAVEMENTS:

Those which are surfaced with bituminous (or asphalt) materials. These types of

pavements are called "flexible" since the total pavement structure "bends" or "deflects" due

to traffic loads. A flexible pavement structure is generally composed of several layers of

materials which can accommodate this "flexing".

1.2.2 RIGID PAVEMENTS:

Those which are surfaced with portland cement concrete (PCC). These types of

pavements are called "rigid" because they are substantially stiffer than flexible pavements

due to PCC's high stiffness.

Each of these pavement types distributes load over the subgrade in a different fashion.

Rigid pavement, because of PCC's high stiffness, tends to distribute the load over a relatively

wide area of subgrade. The concrete slab itself supplies most of a rigid pavement's structuralcapacity. Flexible pavement uses more flexible surface course and distributes loads over a

smaller area. It relies on a combination of layers for transmitting load to the subgrade .

This Guide focuses on flexible pavements. In general, both flexible and rigid

pavements can be designed for long life (e.g., in excess of 30 years) with only minimal

maintenance. Both types have been used for just about every classification of road. Certainly

there are many different reasons for choosing one type of pavement or the other, some

practical, some economical, and some political.

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1.3 BENEFITS OF PRECAST PRESTRESSED CONCRETE

PAVEMENT

1.3.1 FASTER CONSTRUCTION:

What do we mean by faster construction? We're not necessarily talking about how

fast the pavement can be constructed, but rather how fast it can be opened to traffic.

Conventional cast-in-place pavement requires several days of additional curing time after the

concrete is placed before it is strong enough to withstand traffic loading. While "fast-setting"

concrete mixtures have been developed for this purpose, these can be cost-prohibitive for

large-scale pavement construction.

1.3.2 REDUCED USER DELAY COSTS:

What are user delay costs? These are costs to the drivers of the roadway that are

directly attributable to congestion caused by construction activities. Increased fuel

consumption, lost work time, increased vehicle wear and tear, and increased air pollution are

just a few of these costs. The savings in user delay costs realized through limiting

construction to only off-peak travel times (at night or over a weekend) can be substantial.

This is where the primary economic benefit of precast pavement will be realized.

1.3.3 IMPROVED DURABILITY AND PERFORMANCE:

Precast concrete has a proven track record as a durable high-performance product for

bridge and commercial building construction. This is the result of a high degree of quality

control that can be achieved at a precast fabrication plant. High strength, low permeability

concrete mixtures with a low water-cement ratio and uniform aggregate gradation are used

routinely by precast fabrication plants. At most plants concrete batching and quality control

is done on-site and the concrete is transported only a short distance from the batch plant to

the forms, minimizing changes in concrete properties between the mixing and placing

operations. What's more, precast fabrication plants offer tremendous flexibility over the

curing operation. Precast concrete elements can be fabricated indoors, they can be wet-mat

cured, steam cured, and curing can be maintained as long as necessary after casting.

Problems that can plague cast-in-place pavement construction such as surface strength loss,

"built-in" curling, and inadequate air entrainment, can all be eliminated with precast concrete



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1.3.4 WHY PRESTRESSED PRECAST PAVEMENT?

Prestressing has a proven track record for enhancing the performance and durability

of concrete structures. And though it has seen very limited use in pavements, there are

clearly benefits of prestressed concrete pavement, such as...

1.3.5 REDUCED CRACKING:

While conventional pavements are "designed" to crack at specific locations or at

regular intervals, in general cracking is not desirable. Cracks can spall, they can permit water

to penetrate the underlying base, they can fault, and they can eventually lead to severe

pavement failures such as punch outs. Prestressing helps to minimize or even eliminate

cracking. By putting a pavement in compression there is less likelihood of cracking due to

tensile stresses. What's more, the so-called "elasto-plastic" behavior of prestressed concrete

will help keep any cracks that do form tightly closed.

1.3.6 REDUCED SLAB THICKNESS:

While the underlying pavement structure is also a factor, the primary controlling

factor in pavement thickness design is the magnitude and number of wheel load repetitions on

the pavement over its expected design life. For a given pavement support structure and a

given wheel load, tensile stresses in a thinner pavement will be higher than those in a thicker

pavement. These higher stresses wear out or fatigue a concrete pavement faster. Prestressing

can be used to reduce the tensile stresses in a thinner pavement slab to those of a much

thicker pavement slab, increasing the design life of the pavement.

1.3.7 BRIDGING CAPABILITY:

Prestressing gives the pavement a certain "bridging" capability that permits the

pavement slab to span small voids and "soft" base materials beneath the pavement. This is

critical for pavement removal and replacement operations that are limited to short

(overnight) construction windows when it is often not possible to recondition or replace the

underlying base material.



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CHAPTER-2

PRECAST PAVEMENT CONCEPT

The basic precast prestressed pavement concept consists of a series of individual

precast panels that are post-tensioned together in the longitudinal direction after installation

on site. Each panel can be pretensioned in the transverse direction (long axis of the panel)

during fabrication, and ducts for longitudinal post-tensioning are cast into each of the panels.

The basic features (typical) of the PPCP system are as follows:

1. Panel size: up to 38 ft (11.6 m) wide, typically 10 ft (3 m) long, and 7 to 8 in. (178

to 203 mm) thick (or as per design).

2. Panel types: a. Base, joint, and central stressing panels (as originally developed).

b. Base and joint stressing panels (as installed at a demonstration project in Missouri).

3. Tongue-and-groove transverse epoxied joints.

4. Post-tensioning details:

a. 0.6-in. (15 mm) diameter 7-wire monostrand tendons typically spaced at 24 in.

(600 mm).

b. Tendon load: 75 percent of ultimate tendon load, typically.

c. Prestress force: sufficient to ensure about 150 to 200 lbf/in2 (1.0 to 1.4 MPa)

residual prestress at the mid-point of each series of prestressed panels.

d. Grouted post-tensioning ducts.

5. Expansion joint spacing: ~ 250 ft (76 m), typically.

6. Base type:

a. Hot-mix asphalt concrete base with polyethylene sheet over base or asphaltconcrete interlayer in the case of an overlay application.

b. Permeable base (as used in the Missouri demonstration project).

c. Lean concrete base (as used in the California demonstration project).

d. Aggregate base (as used in the Iowa demonstration project).

7. Injection of bedding grout to firmly seat panels (after post-tensioning).



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Figure 2.1. Cross section of the precast panels

Figure 2.2. PPCP design details and panel types.

Figure 2.2 illustrates the design concept underlying this precast pavement technology.

The base panels make up the majority of the post-tensioned pavement section and are placed

between the joint panels and central stressing panels, if used. All of the panels havecontinuous tongue-and-groove keyways along the transverse face of the panels (see figure

2.3). The joint panels are located at the ends of each post-tensioned section of pavement. The

joint panels contain dowelled expansion joints that allow the expansion and contraction

movements of the post-tensioned section. The joint panels also contain the post-tensioning

anchorage for the longitudinal post-tensioning tendons. The anchors are cast into the joint

panels on either side of the expansion joint. Block outs or pockets cast into the joint panels

provide access to the post-tensioning anchors. Figure 2.4 shows the placement of a panel on

a prepared base.



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Figure 2.3. Tongue-and-groove keyway. Figure 2.4. PPCP panel being placed over

polyethylene sheet placed over a base.

When the central stressing panels are used, the post-tensioning strands are fed into the

ducts at the large block outs cast into the central stressing panels. Strands are fed in either

direction from each block out down to the anchors in the joint panels. The strands from

either side of the block out are then coupled together and tensioned. The post-tensioning canalso be applied at the joint panels without use of the central stressing panels.

2.1 PANEL ASSEMBLY:

The basic precast prestressed pavement concept consists of a series of individual

precast panels that are post-tensioned together in the longitudinal direction after installationon site. Each of the panels are pretensioned in the transverse direction (long axis of the

panel) during fabrication, and ducts for longitudinal post-tensioning are cast into each of the

panels. The basic panel layout consists of three types of panels.



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2.2 BASE PANELS:

Base panels make up the majority of the post-tensioned pavement section and are

placed between the joint panels and central stressing panels. All of the panels have

continuous tongue and groove keyways along the edges of the panels. The pretensioning

strands extend along the length (long axis) of the panels, and the post-tensioning ducts are

oriented across the width (short axis) of the panels.

Figure 2.5. Base Panel

2.3 JOINT PANELS:

The joint panels are located at the ends of each post-tensioned section of pavement.

The joint panels contain dowelled expansion joints which "absorb" the expansion and

contraction movements of the post-tensioned section. Each half of the joint panel is tied to

the panels on either side of the actual expansion joint. The joint panels also contain the post-

tensioning anchorage for the longitudinal post-tensioning tendons. The anchors are cast into

the joint panels on either side of the expansion joint. Block outs or pockets cast into the joint

panels provide access to the post-tensioning anchors.



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2.4 CENTRAL STRESSING PANELS:

Post-tensioning is completed at the central stressing panels. The post-tensioning

strands are fed into the ducts at the large block outs cast into the central stressing panels.Strands are fed in either direction from each block out down to the anchors in the joint

panels. The strands from either side of the block out are then coupled together and tensioned.

Figure 2.6. Joint Panels

2.5 PANEL JOINTS:

As described above, tongue and groove keyways are cast into the edges of the precast

panels. These keyways help ensure vertical alignment between panels as the panels are

installed. The keyways also provide temporary load transfer between panels prior to post-

tensioning. It should be noted that the panels are not match-cast. The tolerances of the

keyway dimensions are such that the panels can be fabricated on a long-line casting bed

without the need to match-cast. What's more, match-casting requires the panels to be

installed in a very specific sequence, whereas "standard" panels can be utilized for long-line

fabrication.



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A highly viscous epoxy is normally applied to the keyways prior to assembling the

panels. The epoxy acts as a lubricant during panel installation and also seals the joints

between panels to prevent the intrusion of water and incompressibles. The epoxy also bonds

the panels together so that they act as a continuous slab after post-tensioning.

Figure 2.7 Panel Joints

2.6 EXPANSION JOINTS:

As described above, the joint panels contain the expansion joints at the end of each

post-tensioned section of pavement. Up to four inches of movement can be expected at the

expansion joints, so they must be robust and able to withstand repeated heavy wheel loading.

Both armored joints (similar to those used for bridge decks) and plain dowelled joints have

been utilized on projects to date. The type of joint will depend on the expected traffic loading

and movement of the pavement slab. Regardless of the type of joint used, dowels across the

joint are essential for providing load transfer.

CHAPTER-3



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PANEL FABRICATION

3.1 PROCEDURE

The precast panels are fabricated at an established precast plant, preferably as close as

possible to the installation site. For larger jobs, particularly in remote locations, it may be

possible to set up a temporary precast bed near the jobsite. The concrete mixtures used are

similar to those utilized for other precast prestressed elements and are not be restricted to

"paving" mixtures. Steam curing, wet mat curing, or membrane curing are all options for

precast pavement panels.

The panels were fabricated on a wide flat steel casting table which was long enough

to produce up to two panels end to end. Steel sideforms and bulkheads were custom made

for the panels. The pretensioning strands extended through both panels, anchored at

bulkheads at either end of the self-stressing casting bed. Bulkheads between the precast

panels, bolted down to the casting bed, were used to hold the pretensioning strands at the

proper elevation at the ends of the precast panels. Steel chairs were used to harp the strands

within the precast panels to match the strand profile provided in the panel detail drawings.

Figure.8 shows the forms as the pretensioning strands are threaded through the forms.

In general, two base panels were cast each day. Panels were normally stripped from

the forms in the morning and the bed was cleaned and set up for an afternoon pour. Joint

panels required additional form set-up time due to the anchor blockouts and additional

reinforcement and post- tensioning anchors. Joint panels were each cast in two halves on

separate days.

A separate sideform was used to hold the dowel bars in place and form the recess

for the header material at the expansion joint. The first half of the joint panel was cast and

steam cured, but the pretensioning strands were not released until after the second half had

been subsequently cast and cured.

3.2 PANEL TREATMENT



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3.2.1 REINFORCMENT

Minimal mild-steel (non-prestressed) reinforcement was provided in the base

panels. As the panel detail drawings in the Appendix show, only perimeter steel at the

top and bottom of the panel was provided for the base panels. Joint panels also had

perimeter steel, but were heavily reinforced with stirrups around the stressing pockets

and post-tensioning anchors. Epoxy-coated grade 60 No. 4 deformed bars were specified

for all non-prestressed reinforcement. For the joint panels abutting the existing cast-in-

place pavement, the half of the panel not post-tensioned was reinforced with mild steel in

the longitudinal direction. No. 6 epoxy-coated reinforcing bars spaced at 200 mm (8inches) on center provided approximately 0.65 percent steel for this portion of the

precast panel. Figure 3.1 shows the reinforcement for the non-post-tensioned half of a

joint panel prior to concrete placement.

Figure 3.1. Reinforcement for the non-post-tensioned joint panel.

3.2.2 PRETENSIONING



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All pretensioning steel was 13 mm (0.5 inch) diameter, Grade 270 low relaxation 7-

wire strand. For the base panels, eight strands were required. The strands were spaced

evenly across the width of the base panels and alternated above and below the post-

tensioning ducts to minimize any prestress eccentricity. For the joint panels, the

pretensioning strands were concentrated in the outer edges and along the expansion joint to

avoid crossing through the post-tensioning blockouts. Twelve strands were specified for the

joint panels for to provide additional flexural strength for handling panels with post-

tensioning blockouts. For both the base panels and joint panels, the strands were

maintained at a constant depth over the portion of the panel which was 200 mm (8 inches)

or thicker (traffic lanes). However, in the shoulder regions of the panels, it was necessary to

harp the strands slightly to follow the top surface of the panels.

It should be noted that the pretensioning strands were only tensioned to 75 percent of

theirultimate strength, rather than 80 percent assumed during the design process. While this

will reduce the effective prestress in the panels, the lump-sum prestress loss assumed in the

design calculations is likely very conservative anyway. Based on actual lifting and handling

of the precast panels, the pretensioning level was clearly adequate to prevent cracking

3.2.3 POST-TENSIONING

Monostrand post-tensioning ducts with an inside diameter of 23 mm (0.9 inches)

were used for the longitudinal post-tensioning tendons. The ducts were developed

specifically for monostrand post-tensioning and are made of corrosion-proof polyethylene

material. The ducts are ideal for monostrand bonded tendons, with ribs to facilitate bond

with the concrete and two continuous channels along the length of the duct to facilitate the

flow of grout. The ducts are flexible and required adequate chairing and the use of bar

stiffeners inserted in the ducts during concrete placement to prevent sagging and bowing of

the duct under the mass of fresh concrete.

Encapsulated monostrand anchors were used for the post-tensioning anchors. The

anchors were cast into the joint panels and bolted to the post-tensioning blockout formers.



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Grout ports were located just in front of the anchors and in every 5th base panel along the

length of each post- tensioned section of pavement. Trumpeted openings and recesses for the

foam gaskets were formed at the ends of the post-tensioning ducts in each panel using

machined steel recess formers. Figure 3.2 shows the post-tensioning duct, anchor, and

blockout former used in the joint panels.

Figure 3.2. Post-tensioning duct, anchor, and blockout former in a joint panel.

3.2.4 CONCRETE PLACEMENT, FINISHING, AND CURING



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The concrete mixture was transported from the batch plant to the forms. Concrete

was placed in the forms in two lifts; the first filling the forms to the level of the post-

tensioning ducts, and the second, immediately following the first, filling the forms to the top

surface. The flowable nature of the mixture required only minimal vibration to consolidate

the concrete around the reinforcement, ducts, and blockouts.

A hand screed was used to initially strike off the concrete surface, flowed by a

vibratory screed to achieve a uniform, smooth surface. An intermediate curing compound

was sprayed over the surface between the hand screed and vibratory screed to minimize

moisture loss from the large surface area of the fresh concrete. Immediately following the

vibratory screed, a light broom texture was applied along the length of the panels (transverse

to the direction of traffic flow). A carpet drag texture was specified in the original Job

Special Provisions, but was changed to a broom finish after problems were experienced with

the carpet drag. Figure 3.3 show the screeding and texturing operations.

.

Figure 3.3. Application of the light texture to the panel surface.

After application of the surface textures,the panels were covered with tarps and

steam cured overnight. The steam was generally turned off by 5 am at which time strength



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was checked. If the strength was adequate for release, the tarps were removed and the

pretensioning strands de-tensioned. If strength was not adequate, the steam was turned

back on for 1-2 hours until adequate strength had been achieved. While steam curing was

used to achieve the necessary release strength overnight, some additional form of curing

on the top surface and sides of the panels was required for a minimum of 72 hours after

concrete placement or until the 28-day strength had been achieved. This requirement was

satisfied by covering the panels with wet burlap and plastic sheeting for an additional 24

hours after they were moved from the forms to the storage area, as shown in Figure 3.4.

Figure 3.4. Curing and Storage.

CHAPTER-4

PAVEMENT CONSTRUCTION



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4.1 BASE PREPARATION

The reconstructed base beneath the PPCP section consisted of 100 mm (4 inches) ofpermeable asphalt treated base over 100 mm (4 inches) of dense graded granular base. To

better ensure that the precast panels would be properly supported and the polyethylene

sheeting used as friction-reducing material beneath the precast panels was rolled out just

prior to placement of each panel. Figure show the construction of the permeable base and

the final surface.

Figure 4.1. Construction of the permeable asphalt treated base.

4.2PANEL INSTALLATION

4.2.3 TRANSPORTATION AND STAGING



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Delivery of the precast panels to the site is a critical aspect of the installation process.

Enough delivery trucks must be available to meet the required installation rate. Care must be

taken during the delivery process to ensure that the panels are not damaged in any way during

shipment

The panels were transported to the job site on flat bed tractor trailers truck. The

crawler crane used for panel installation was positioned on the base in front of the panel

installation. Panel delivery trucks lined up on the existing pavement south of the project, then

pulled onto the shoulder next to the PPCP section where the crane picked the panels off the

truck and lowered them into place, as shown in Figure 4.2.

Figure 4.2. Staging of delivery trucks and the installation crane.

4.3 INSTALLATION PROCEDURE

Prior to lifting each panel from the delivery truck, epoxy (segmental bridge adhesive)

was applied to the mating faces of the panels, and the compressible foam gaskets were



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installed in the recess around each post-tensioning duct on the recessed keyway side of the

panel. After the polyethylene sheeting was rolled out each panel was installed. In general,

two precast panels were installed before moving the crane.

A laser was used to align the precast panels to the centerline of the pavement. The

laser was set on the panels already in place and aligned to nail heads marking the

pavement centerline, pre- surveyed into the base. An alignment guide was installed in the

post-tensioning duct at the centerline of each precast panel, and aligned the laser. Figure

36 shows the alignment laser and the alignment guide installed in a panel.

After two consecutive panels were installed, two temporary post-tensioning strands,

located approximately at the quarter points, were fed through the panels. Post-tensioning

rams were then used to temporarily post-tension the panels together from the face of the

newly installed panels.

Figure 4.3. Laser and alignment guide used to align the precast panels.

4.4 POST- TENSIONING

4.4.1 STRAND INSTALLATION



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Both armored joints (similar to those used for bridge decks) and plain dowelled joints have

been utilized on projects to date. The type of joint will depend on the expected traffic loading

and movement of the pavement slab. Regardless of the type of joint used, dowels across the

joint are essential for providing load transfer.

4.4.4 FILLING POCKETS

After completion of final longitudinal post-tensioning, the stressing pockets and mid-

slab anchor sleeves were filled and finished flush with the pavement surface using a pea

gravel concrete mixture. Subsequent diamond grinding of the pavement surface removed

any roughness associated with the stressing pockets.

4.5 TENDON GROUTING

Grouting of the post-tensioning tendons was essentially the final step in the

construction process, and was completed following post-tensioning and filling of the

stressing pockets. The post-tensioning system used for precast prestressed pavement is a

bonded post-tensioning system. Grouting not only provides an additional layer of corrosion

protection for the post-tensioning strands, but also bonds the tendons to the pavement so that

if it is necessary to remove a precast panel at a later time, the post-tensioning system will

remain intact.

In addition to tendon grouting, underslab grouting may also be required to fill any

voids beneath the pavement. Grout ports can either be cast into the panels or drilled on site.

Underslab grouting is essentially a "gravity" fed process as applying pressure can actually lift

the pavement.

Similarly to post-tensioning, grouting can be completed during a subsequent

construction operation if time constraints do not permit grouting immediately following panel

placement. Grouting should not be completed, however, until all post-tensioning tendons are

stressed and the pockets in the joint panels are filled.



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4.6 DIAMOND GRINDING

Diamond grinding to meet Interstate Highway smoothness requirements was

expected. While the finished pavement surface was smooth enough to open to traffic ifnecessary, it did not meet smoothness specifications for concrete pavement. Diamond

grinding was used to bring the pavement surface back into specification.

No major surface repairs were required for the finished pavement. While a number of

minor spalls were observed at the joints between panels, diamond grinding removed many of

these spalls. Deeper spalls will be monitored over time so that repairs can be made if needed.

Figure 4.5. Final pavement surface after diamond grinding.

4.7 OPEN TO TRAFFIC:

Precast pavement can be opened to traffic as soon as the panels are installed. Post-

tensioning and grouting operations can be completed during a subsequent operation if

necessary. The surface will be smooth enough to open to traffic and can be diamond ground

during a subsequent operation if necessary.



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4.8 RECOMMENDATIONS FOR FUTURE CONSTRUCTION

This demonstration project showed once again the adaption of PPCP technology to

specific project needs. Future projects should focus on applying PPCP technology under

circumstances where lane closures for construction are severely limited, such as busy urban

corridors. This type of project will require very careful planning and preparation to ensure

that none of the issues encountered on this initial demonstration project will occur during

short construction window projects.

Figure 4.6. Finished precast pavement after opening to traffic.

CHAPTER-5

CASE STUDIES

CASE STUDY-1



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5.1 THE TEXAS PILOT PROJECT

Figure 5.1 Georgetown PPCP project layout.

The first PPCP project was constructed in Georgetown, Texas, during 2001 (Merritt

2001). Texas DOT placed approximately 2,300 ft (700 m) of two-lane pavement (plus

shoulders) on the frontage road along I-35. The project layout and panel systems used are

shown in figure 6.1. The project details are as follows:

Constructed: Fall 2001

Project location: Northbound I-35 frontage road near Georgetown, Texas

Project length: 2,300 ft (701 m) (2 lanes plus shoulders)

Panel dimensions: 10 ft x 36 ft (3.1 m x 11.0 m), 10 ft x 20 ft (3.1 m x 6.1 m), and 10

ft x 16 ft (3 m x 4.9 m)

Panel thickness: 8 in. (200 mm)

Number of panels: 339



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Number of post-tensioned sections: 7 at 250 ft (76.2 m), 1 at 225 ft (68.6 m), 1 at

325 ft (99.1 m)

Panel installation rate: 25 panels/6 hours

Features: Both full-width and partial-width construction. Project was the first

application of precast prestressed concrete pavement on a large scale.

For this project, it was decided to use both full-width (36 ft [11 m]) and partial-width

(16 ft and 20 ft [5 m and 6 m]) panels for the frontage road to test the concept for partial-

width panel construction. The partial-width panels were tied together transversely through

post-tensioning with an additional post-tensioning duct cast into each of the partial-width

panels. The precast, pretensioned panels were placed over a well-finished hot-mix asphalt

leveling course overlain with polyethylene sheets and then post-tensioned together in the

longitudinal direction. The tongue-and-groove connection at the transverse joints ensured

satisfactory vertical alignment during installation.

As the contractor became more familiar with the construction process, approximately

25 panelsequaling 250 ft (76 m) of pavementwere installed

Figure 5.1 Georgetown PPCP project layout. in a 6-hour period. Texas DOT found

that post-tensioning, completed after the panels were installed, generally took just a few

hours for each section of pavement. Aside from demonstrating the efficacy of placing the

slabs on grade, the Georgetown project demonstrated the viability of post-tensioning the

panels together in place. The project also showed that match-casting, which is commonly

used for precast segmental bridge construction, was not required to ensure a tight fit

between panels and to align the post-tensioning ducts. Because match casting is not

necessary, the manufacturer can fabricate the panels faster, and shipment and installation

are simplified.

The Georgetown pilot project presented many challenges for precast pavement

implementation (Merritt 2001). The most difficult aspect of the project was considered to be

the meshing of precast concrete and concrete pavement specifications.

This required flexibility on the part of both the precast supplier and Texas DOT. This

pilot project also represented unknown territory for the contractor, precast supplier, and

Texas DOT. Flexibility and a willingness to develop new techniques on the part of all parties



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were essential for the success of this project. After almost 7 years (as of November 2008), the

project is performing well and no maintenance-related issues have been reported.

Figure 5.2. Installation of the precast prestressed concrete pavement system in

Georgetown, Texas.

CASE STUDY-2

6.2 THE CALIFORNIA DEMONSTRATION PROJECT



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The Caltrans demonstration project used the PPCP system as a part of the widening

project on I-10 to provide high-occupancy vehicle lanes and reduce traffic congestion. Most

of the construction work was completed at night. The construction added 27 ft (8 m) of traffic

lanes and 10 ft (3 m) of shoulder to the existing lanes on the eastbound direction. The project

details are as follows:

Constructed: April 2004

Project location: Eastbound I-10, El Monte, California

Project length: 248 ft (76 m) (2 lanes plus shoulder)

Panel dimensions: 8 ft x 37 ft (2.4 x 11.3 m)

Panel thickness: 10 to 13 in. (254 to 330 mm)


Number of post-tensioned sections: 2 at 124 ft (37.8 m)


Features: Nighttime construction. Change in cross slope cast into the panel surface.

Photographs of the installation are shown in Figure 6. The project was located on a

section of the Interstate that had no change in vertical curvature and very minimal horizontal

curvature. The longitudinal geometry of the pavement was simple, but the pavement cross

section was more complex, with a change in cross slope from 1.5 percent in the traffic lanes

to 5 percent in the shoulders, which required variable thickness in the panel.

CASE STUDY-3

6.3 THE MISSOURI DEMONSTRATION PROJECT:



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The Missouri DOT evaluated the feasibility of using the PPCP as an alternative

solution for rapid pavement construction and rehabilitation. The project details are as follows:

Completed: December 2005

Project location:Northbound I-57 near Sikeston, Missouri (~ 10 mi (16 km) north of

I-55/I-57 interchange)

Project length: 1,010 ft (307.9 m) (2 lanes plus shoulders)

Panel dimensions: 10 ft x 38 ft (3.0 m x 11.6 m)

Panel thickness: 5.7511 in. (146280 mm)


Number of post-tensioned sections: 4 at 250 ft (76.2 m)


Features: Pavement crown cast into the panel surface. Non continuous keyways

between panels

The existing pavement was a jointed reinforced concrete pavement with 61.5-ft (18.8

m) joint spacing. The cross section consisted of an 8-in. (203 mm) slab resting on a 4-in.

(102 mm) granular base. The new PCPP cross section consists of a concrete slab of variable

thickness ranging from 10.9 in. (275 mm) at the peak crown to 7 in. (178 mm) at the edge of

the inside shoulder and 5.6 in. (142 mm) at the edge of the outside shoulder. The variable

thickness was necessary to accommodate the 2 percent crown. The PCPP slab rests on a 4-

in. (102 mm) permeable asphalt base. The panels were fabricated in Memphis and

transported to the project site, a distance of over 200 miles (320 km). Two panels were

fabricated each day. Figure 7 illustrates the construction process of the precast panels.

A few panels exhibited full-depth hairline longitudinal cracking at the fabrication

plant. It is believed that the panels may have experienced thermal shock during removal of

the panels from the forms. The temperature and strain data collected during the fabrication

process did indicate high and rapid changes in concrete temperature during fabrication.



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CHAPTER-6

CONCLUSION



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1. As discussed above, precast concrete pavement technology is ready for

implementation, excellent concrete quality with respect to strength and durability and

with respect to continuous applications.

2. The short-term performance of the installed PPCP systems indicates that PPCP

systems can provide rapid reconstruction and rehabilitation that will be durable.

3. The quality of the concrete used for the precast panels appears to meet the

expectations for durable concrete and there is no evidence of early age concrete

failures.

4. Precast pavements may have a higher first cost, the rapid installation that minimizes

lane closures and the long-term durability can easily offset the higher initial costs.

5. It is expected that innovations in this technology will ensure a permanent place for the

application of the precast concretepavement technology for durable, rapid repair and

rehabilitation of existing pavements and will help reduce the cost of panel fabrication

and installation.

6. Rapid construction techniques can significantly minimize the impact on the driving

public, as lane closures and traffic congestion are kept to a minimum.

CHAPTER-7

REFERENCES

1. FHWA Concrete Pavement Technology Program Update:

Precast Prestressed Concrete Pavement - CPTP Project Update.

http://www.fhwa.dot.gov/pavement/concrete/cptu305.cfmhttp://www.fhwa.dot.gov/pavement/concrete/cptu305.cfmhttp://www.fhwa.dot.gov/pavement/concrete/cptu305.cfmhttp://www.fhwa.dot.gov/pavement/concrete/cptu305.cfm


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2.FHWA Concrete Pavement Technology Program.

3. MoDOT/FHWA Precast Prestressed Concrete Pavement Showcasing Workshop update.

4. Shiraz Tayabji, Dan Ye, and Neeraj Buch.,Precast concrete pavements Technology

overview and technical considerations Journal.

5. Tinu Mishra, Phil French, and Ziad Sakkal., Engineering a better road: Use of two-way

prestressed precast concrete pavement for rapid rehabilitation journal.

6. Shabbir Hossain and Celik Ozyildirim., Evaluation of Concrete Pavement Repair Using

Precast Technology Journal.

7. Shiraz Tayabji and Neeraj Buch., Precast Concrete Pavement Technology Journal.
http://www.fhwa.dot.gov/pavement/concrete/index.cfmhttp://www.fhwa.dot.gov/pavement/concrete/index.cfm

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3. Precast Concrete Pavement

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