Marshall Mix Design Procedure

8/9/2019 Marshall Mix Design Procedure

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Revised 2008, WKS Datasheets No. 24, 25, 26 & 27

MOHAWK COLLEGE OF APPLIED ARTS AND TECHNOLOGY

BUILDING AND CONSTRUCTION SCIENCES DEPARTMENT

Marshall Method of Asphalt Concrete Mix Design

INTRODUCTION

This procedure was originally developed by a bituminous engineer with theMississippi State Highway Department, Bruce Marshall. The U. S. Army Corps. ofEngineers improved and added to the procedure as well as developing mix design

criteria. The method documented in ASTM D 1559 and AASHTO T245 isapplicable only to mixes with maximum particle sizes of 25 mm (1) or less. Themethod can be used for both laboratory design and field control.

An asphalt mix design consists of two basic issues:

a) based on the gradations of the constituent aggregates to be used in the mix,determine the proportions of each aggregate that will produce a blendedgradation that meets the required grading specification (we will use thegrading spec. given in the sieve analysis lab, which is for HL3 from the OPSS

Spec.).

b) determine the optimum asphalt cement content that will satisfy the AsphaltInstitutes mix design criteria (we will consider the bulk specific, theMarshall Stability and the percent air voids in the compacted paving mixturein determining the optimum asphalt content).

In addition to the gradation of the constituent aggregates, it is also necessary toknow the bulk ASTM specific gravities of the coarse and fine aggregates, the

apparent specific gravity of the mineral filler and the specific gravity of theasphalt cement in order to be able to determine the percent air voids, voids in themineral aggregate (VMA), voids filled with asphalt (VFA) and the effective asphaltcontent.

This lab is organized into five segments (a d in the lab):

a) sieving and blending of stock aggregates into twenty-two 1200 gram


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batches using the proportions determined to produce the requiredgrading,

b) manufacturing 18 compacted test specimens (3 trials at 6 differentasphalt contents) and two loose specimens,

c) measuring and calculating the bulk specific gravity of each compactedspecimen and the maximum specific gravity of the loose specimens,

d) measuring the Marshall Stability and Flow of each preheated, compactedspecimen and

e) performing all the necessary calculations, plotting the required graphs,determining the optimum asphalt content and evaluating the mix

properties according to the Asphalt Institutes and Ontario ProvincialStandards criteria.


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PART A: PREPARATION OF AGGREGATE BATCHES

EQUIPMENT

1.

balance sensitive to 0.1 gram

2. Gilson Shaker: #4 and #8 screens and pan (the #4 and #8 U.S. Standard sievesand pans may also be required)

3. scoops, spoons, spatulas

4. batch pans (with workstation numbers labelled on sides)

5. three plastic pails for sieved stock aggregate

6. one loaf tin for total mineral filler requirement

PROCEDURE

1. In the week prior to this lab session, use a trial and error approach on thecomputer to arrive at a blend (proportions) of the coarse and fine aggregates andmineral filler that produces a gradation curve that is as close to the midpointsbetween the upper and lower limits of the grading spec as possible. The gradations

evaluated in the sieve analysis lab will be used to arrive at these proportions. Theseblends should have been submitted to the instructor as an interim report prior tothis lab.

2. It is estimated that a total of 32 kg of aggregate would have to be sieved inorder to produce enough stock to produce twenty-two 1200 gram batches ofaggregate.

The mineral filler is NOT to be sieved but weighed out directly into the 22

batch tins.

The coarse and fine aggregate are sieved on the Gilson shaker in two halves: theblending chart produced by the computer spreadsheet gives the amounts of eachtype of aggregate to sieve to produce 32 kg of the blend. These weights should behalved (and the mineral filler excluded) so as not to blind either of the screens.


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For example, if the chart calls for 16.32 kg of coarse (CA) and 14.40 kg of fine (FA)aggregate, weigh out 8.16 kg of CA and 7.20 kg of FA, place in the Gilson and sieveon the #4 and #8 screens for 5 minutes. Then empty the material retained on thescreens and pan into the 3 stock pails. Then sieve another 8.16 kg of CA and 7.20

kg of FA as before, emptying the different sized material into their respectivestock pails.

3. Using the batch masses given in the last column of the blending chart producedby the computer spreadsheet, weigh out the required amounts of each stockmaterial and place in each of the 22 batch tins in the following order:

First: mineral fillerSecond: Gilson pan stockThird: Gilson #8 stock

Lastly: Gilson #4 stock

4. Since the tins will be nested for storage and preheating, this ensures that thematerial that would be most likely to be picked up by a nested tin is furthest awayfrom the top of the aggregate.

If one size of sieved stock runs out before all the batches are produced, the #4and #8 U.S. Standard sieves and pans can be used to sieve small amounts ratherthan waiting for the Gilson. If, for example, it is estimated that one more kilogram

of mixed aggregate would suffice, then, based on the previous exampleproportions,16.32/32 or 0.51 kg of CA and 14.40/32 or 0.45 kg of FA should be sieved on the#4 and #8 sieves and pan.

5. When all 22 batches have been weighed out they should be nested (stacked) infours or fives (based on the shelf space available) and then stored on the shelfdesignated for your group.

6. Using the bulk specific gravities posted by the instructor for the coarse and fineaggregates and the mineral filler, apply the proportions used to blend the aggregate

to calculate the bulk specific gravity of the blended aggregate, Gsbon Datasheet25. Also enter the specific gravity of the asphalt to be used in the subsequent mixcalculations.


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PART B: MANUFACTURING TEST SPECIMENS

EQUIPMENT

1. asphalt kettle and balance sensitive to 0.1 gram

2. mechanical mixer and metal mixing bowl

3. large mixing spoon and spatula

4. hot water bath and 2 sets of compaction mould assemblies (base, mould, collar)

6. compaction hammer and hot plate

7.

compaction pedestal and mould holder

8. vinyl gloves and padded oven gloves

9. paper filter disks and keel (coloured wax crayon)

10. cold water bath (pail with snow/ice in water)

11. arbour press

12.

large loose mix trays (2)

COMPACTED SPECIMEN PROCEDURE

1. Before arriving for this lab session, each group should have calculated the mass ofasphalt cement that should be added to each 1200 gram batch of aggregate toproduce a mix with the desired percent asphalt content. Three trial specimens(A, B and C) will be produced at each of the following asphalt contents: 4.5%,5.0%, 5.5%, 6.0%, 6.5%and 7.0%. Two loose mixtures will be produced at 5.0%

and 6.0%for determinations of the maximum specific gravity, Gmm. The asphaltcontent for this lab is based on the mass of the total mix.

If the mass of aggregates, Msbin each batch is 1200 grams, the mass of theasphalt, Mbwould be calculated as follows for the 4.5% case:


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b

b

M1200M

0.045+

=

bb M0.045M12000.045 =+

b0.955M54.0=

56.40.95554.0

Mb ==

2. The batches of aggregate mixed in the preceding session should have been heatedin the ovens to a temperature between 177 and 190 C prior to your arrival. Theasphalt in the kettle should be between 121 and 138C. The procedure describedhereafter is repeated for each specimen. Efficiency is of the essence as the mixmust be at or above a temperature of 107C when the mix is compacted. There isno time to stand around discussing the weekends exploits! Each member of thegroup should be assigned a task and be aware of the sequence of activities. Thismeans everyparticipant should be familiar with these procedures BEFOREenteringthe lab to perform them!

3. The mixing bowls must be kept in the oven when not in use. Similarly, the mouldassemblies should be kept in the water bath until required and returnedimmediately after use and the compaction hammers must also be kept on the hot

plate when not in use. Everything that comes into contact with the asphalt mixmust be kept above the compaction temperature of 107C. If the mix drops belowthis temperature before compaction, the mix must be discarded.

4.

The contents of an aggregate tin are placed in a mixing bowl and stirredthoroughly, placed on the balance or scale, a crater is formed in the centre of theaggregate and the balance (scale) is tared (set to 0).

5. The required weight of asphalt cement is added from the kettle. To avoid adding

too much, use a piece of heavy paper to intercept the asphalt cement stream whenthe required weight is displayed. Since the stream can be controlled by a valve,start to close the valve when the weight is within a couple of grams. If too much isadded, remove some by dipping the paper into the crater where the majority of theasphalt cement has collected being careful not to remove any aggregate.

6. Quickly mix on the mechanical mixer until the asphalt cement is uniformlydistributed (no light coloured material, i.e., uncoated aggregate).


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7.

When the mixing is almost complete, one member of the group wearing the vinylgloves should remove and assemble a mould assembly on the bench top. A filterpaper disk should be placed in the mould before spooning the mix into the mould.

Spade the mixture vigorously 15 times around the perimeter and 10 times over theinterior. This moves the coarser material to the inside and the fines to the outsideto ensure a better shaped specimen. Remove the collar and smooth the top to aslightly rounded shape.

Place another disk of filter paper on top, replace the collar and quickly insert themould assembly into the holding frame on the compaction pedestal.

8.

Apply 50 blows with the compaction hammer, keeping the face of the hammer

parallel to the base plate. This can only be done by holding the hammer vertically,so someone in the group should observe and ensure that this happens. The handthat lifts the weight on the hammer should have a protective mitt (not a vinyl glove)

just in case that hand reaches the bottom of the hammer before the weight does.This does happen, quite a lot actually.

9. Remove the collar, invert the mould on the base, replace the collar and applyanother 50 blows with the hammer. The hammer should be set on the hot platewhile the mould is being inverted.

10.

Remove the collar and base, remove the filter paper from the specimen and placethe mould and specimen in the cold water bath until it is firm enough to beextruded, without distortion, in the arbour press. This is usually when it feelswarm (not hot) while being held in your unprotected hands.

11.After extrusion in the arbour press, record the group number, asphalt contentand trial (e.g., 8-4.5B would be group eights second (B) trial at an asphalt contentof 4.5%) on the sideof each specimen. This is done using the piece of yellow or redkeel supplied. As the specimen will still be a bit warm, this identification will

probably fade as the specimen cools. This ID should be touched up again beforestoring.

The three trials for each asphalt content should be stacked and stored in thedesignated shelf for your group once completed and cooled. It is recommended tostart with 4.5% AC and complete all three trial specimens (A, B and C) before goingon to 5.0% and so on. One member of the group should be in charge of keeping


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track of the specimens to avoid unnecessary repetition (doing four trials for oneasphalt content instead of just three).

13. Dont even think of leaving until all the utensils, mixing bowls, mould assemblies,asphalt decanting areas and water baths have been cleaned (Varsol is used toremove asphalt from utensils). The cleanup should only take about half and hour ifeveryone pitches in and helps.

LOOSE MIXTURE PROCEDURE

1. After preparing the 3 compacted specimens at 5.0% asphalt, prepare one moremixture at 5.0%. Instead of following the compaction procedure, however, this mixshould be spooned directly out of the mixing bowl onto a special metal tray so as to

cover the entire surface in the thinnest layer possible.

2. As the mix cools, it must be split and separated frequently to minimize the size ofindividual clumps of the mix using a spatula. Ideally, no particles larger than a limabean should be left in the specimen by the time it has cooled to room temperature.

3. This procedure must also be repeated after the 6.0% specimens are compactedfor an asphalt content of 6.0%.

4. After all the compacted specimens have been produced, they are to be stacked

and placed in a cupboard as directed by the instructor. The two trays of loosemixes should be placed in the same cupboard on top on the compacted specimenstacks and properly labelled (group number and asphalt content).


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PART C: SPECIFIC GRAVITIES OF MIXES

BULK SPECIFIC GRAVITY EQUIPMENT

1. balance sensitive to 0.1 gram at a weigh-in-water station

2. absorbent towels/paper towels

BULK SPECIFIC GRAVITY PROCEDURE

1.

Weigh all 18 specimens in air to 0.1 gram. Record the mass as Mmbon the masterdatasheet and on datasheet 26.

2.

After all Mmbs have been recorded, each specimen will be weighed in water andthen immediately patted surface dry and reweighed in air according to thefollowing steps:

a) Suspend the basket from the hook under the scale ensuring that the meshis submerged in the water. When stable, set zero on the scale.

b) Hold the specimen in the water inside the basket and shake with flicks ofthe wrist to loosen all bubbles of air that might be attached.

c) Set the specimen onto the bottom of the basket ON ITS SIDE (not the flattop or bottom), wait until the reading stabilizes and record the mass as Mmbw onthe master datasheet and on datasheet 26. According to the MTO, thespecimen should be submerged for no less than 3 minutes and no more than 5minutes prior to obtaining the reading.

d) The specimen should immediately be removed from the water and the surfacepatted dry using absorbent towels or paper towels. The specimen should then beweighed in air again (reset scale to zero prior to weighing) and the readingrecorded as Mmssd on the masterdatasheet and on datasheet 26.

e) This procedure is repeated for all specimens, taring the scale to zero withthe empty suspended bucket submerged in the water as in a) EVERY TIME.

3. Calculate the bulk specific gravity, Gmbof each specimen and record on datasheet26.


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4.

Check the Gmb values for outliers within each asphalt content. Datasheet 25should be completed before arriving at this lab as the maximum possible Gmmvalues for each asphalt content are recorded thereon and these provide a checkas they should be significantly higher than the G

mb values determined. If any

individual Gmbwithin one asphalt content group differs from the group average bymore than 0.015, the Gmbs must be verified by recalculation and if correct, theneach specimen within the group must be reweighed. If the specimen Gmbremainsmore than 0.015 from the mean then the group mean Gmbmust exclude this value.If the specimens have been manufactured consistently and weighed correctly, theGmbvalues should agree reasonably well within each asphalt content.

5. At this point in the process it is possible (and recommended) to determine theVMA of each specimen using the average specific gravity of the aggregate, Gsb

calculated on datasheet 25.

MAXIMUM SPECIFIC GRAVITY EQUIPMENT

1. balance sensitive to 0.1 gram at a weigh-in-water station

2. pycnometer (Mason jar)

3. vacuum apparatus

4. spatula

MAXIMUM SPECIFIC GRAVITY PROCEDURE

Forward: The maximum specific gravity of the voidless volume (uncompacted) of an asphaltmix is required to determine the percent asphalt absorbed by the aggregate and the percent

air voids in the mix. This test is also known as Rices test, named after its developer, James

Rice.

1. Take the 5% AC loose mix on the tray stored in the cupboard in Part B andloosen any particles adhering to the tray and to each other. If there are anysignificant sized chunks of mix make one last attempt to reduce them to therequired size.

2. Tare the scale to zero with the hanging basket submerged in the water barrel.


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3. Place the clean and empty pycnometer in the basket and wipe the inside and

outside of the pycnometer while it is submerged to remove any air bubbles.

4.

After the reading stabilizes, determine the mass of the pycnometer in water to0.1 gram and record it on the master datasheet and on datasheet 26 as Mpw.

5.

Remove the pycnometer and dry it off, making sure it is clean and dry (insideand out).

6. Tare the pycnometer to zero at the weigh station, then, carefully pour the loosemix into the pycnometer until a mass of about 1000 grams is collected. Readthis mass to the nearest 0.1 gram and record it on the master datasheet and on

datasheet 26 as Mmm.

7.

Carefully insert the pycnometer into the water barrel and admit enough waterto cover the entire sample of loose mix (about full) and then remove and drythe outside of the pycnometer.

8.

Attach a lid with vacuum hose to the pycnometer and vacuum for 15 2 minutes.Agitate the pycnometer vigorously every 2 minutes.

9. After vacuuming out the air from the sample and removing the vacuum lid,tare the scale to zero again with the hanging basket submerged in the waterbarrel, carefully immerse the pycnometer in the water barrel as before andset it into the submerged basket, taking care to wipe any bubbles from the jarsurface without touching the sample.

10.

After the reading stabilizes, determine the mass of the pycnometer and samplein water to 0.1 gram and record it on the master datasheet and on datasheet 26as Mpws.

11.

The maximum specific gravity, Gmm should be determined IMMEDIATELY(before doing anythingelse). If the Gmmvalue obtained is less than any of theGmb values at that asphalt content or greater than the maximum possible Gmmvalue tabulated at that asphalt content on Datasheet 25, then something iswrong and another trial to determine Gmmwill have to be made in Part D. TheGmmshould decrease as asphalt content increases. This fact should also be usedto rationalize the validity of Gmmvalues determined.


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PART D: MARSHALL TEST AND MAXIMUM SPECIFIC

GRAVITY

MARSHALL TEST EQUIPMENT

1. Compression testing machine

2. Marshall Stability heads

3. two to four brownie tins

4. hot water bath and vinyl gloves

5. flow strain gauge

MARSHALL TEST PROCEDURE

1. With two compression machines for 4 groups it is more practical to have eachgroup test all its specimens on a machine rather than alternate use. The criticalfactor is that the specimens must be immersed in the hot water bath at 60C for30 to 40 minutes before they are tested for stability and flow. A schedule fortesting will be developed and posted prior to the lab session.

2.

Before starting and as required, clean the inside faces of the testing head andlubricate the guide rods with a thin film of oil to allow the upper head to slidefreely without binding. The Flow strain gauge should be zeroed by inserting the 102mm cylinder into the testing head.

3. Remove a specimen from the hot water bath, quickly dry the surface with a rag orpaper towel, place it (centred) in the lower testing head, fit the upper head in placeand centre the heads in the testing machine.

4.

The loading rate is 51 mm (2) per minute. Start the machine and load until failureoccurs. It is necessary to anticipate the point at which the dial load starts todecrease in order to stop the machine and obtain an accurate reading of the strain(flow) dial. Record both the load dial and strain dial readings. No more than 30secondsshould elapse from the time the specimen is removed from the water bathuntil failure occurs.


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5. The Marshall Stability is the load in Newtons at which the specimen failed,adjusted, if necessary, for the volume of the specimen. The load ring constant onthe Marshall tester is multiplied by the recorded load dial reading to produce theMarshall Stability in Newtons. The load at failure in Newtons on the Versatester

can be read directly from the machine dial.

6. The Marshall flow is the deformation (change in diameter) of the specimen at thetime of failure. To obtain this reading, someone in the group must be watching thestrain dial and noting the reading when failure occurs. The person following theload dial should say Now when the maximum load (failure) is reached. TheMarshall Flow is recorded in hundredths of an inch.

If the strain dial reading, for example, is noted as 22 units on a strain gauge with100 divisions, each representing 0.01 of deformation, the Marshall Flow number is

22, whereas if each division represents 0.001 of deformation, the Flow number is2.2.

If one full revolution of the strain dial divided into 100 divisions represents 1 mmof deformation (i.e., each division represents 0.01 mm) and the reading at failurewas 559 units (five full revolutions and a final reading of 59), then the MarshallFlow is 559/25.4 = 22.

On the face of each strain gauge the value of each division (1 div. = 0.01 or 0.01

mm) is printed. This should be noted before starting the testingso that theproper units can be recorded for flow.

7. Each trial specimen (A, B and C) for the first two sets of asphalt content (5.0%and 6.0%) should be saved in brownie tins (the three 5.0% AC specimens in oneand the three 6.0% AC specimens in the other). The member(s) designated toperform the Maximum Specific Gravity, Gmmdeterminations (if necessary) shouldbegin their tasks as soon as the first specimens (5.0% AC ) become available. Sincethe Gmmtests are not always successful, it might be wise to also save the 5.5% andmaybe even the 6.5 % specimens as well (just in case). These should be labelledwith the asphalt content on a piece of paper for identification because thespecimens look pretty much the same after testing. If Gmmvalues weresuccessfully obtained in Part C for 5% and 6% AC then this step can be

ignored along with the procedure described below.


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MAXIMUM SPECIFIC GRAVITY EQUIPMENT

1. pycnometer (Mason jar)

2. mixing tray, trowels

3. balance sensitive to 0.1 gram at weigh-in-water station

4. vacuum apparatus

MAXIMUM SPECIFIC GRAVITY PROCEDURE

Forward: This procedure is performed at this time only in the event of failure to

produce reasonable results for either or both asphalt contents in Part C.

1. As soon as the specimens for the required %AC have been tested in the MarshallStability test, they should be broken apart in a mixing tray using trowels and byhand. The specimens should be broken into particles no larger that a lima bean.

By quartering in the mixing tray, obtain a sample of between 900-1000 grams (3 x(1200 + 63) /4 = 947).

2. Tare the scale to zero with the hanging basket submerged in the water barrel.

3.

Place the clean and empty pycnometer in the basket and wipe the inside andoutside of the pycnometer while it is submerged to remove any air bubbles.

4. After the reading stabilizes, determine the mass of the pycnometer in water to0.1 gram and record it on the master datasheet and on datasheet 26 as Mpw.

5.

Remove the pycnometer and dry it off, making sure it is clean and dry (inside andout).

6.

Tare the pycnometer to zero at the weigh station, then, carefully pour the loosemix into the pycnometer until a mass of about 900-1000 grams is collected. Readthis mass to the nearest 0.1 gram and record it on the master datasheet and ondatasheet 26 as Mmm.


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7. Carefully insert the pycnometer into the water barrel and admit enough water tocover the entire sample of loose mix (about full) and then remove and dry theoutside of the pycnometer.

8.

Attach a lid with vacuum hose to the pycnometer and vacuum for 15 2 minutes.Agitate the pycnometer vigorously every 2 minutes.

9.

After vacuuming out the air from the sample and removing the vacuum lid, tarethe scale to zero again with the hanging basket submerged in the water barrel,carefully immerse the pycnometer in the water barrel as before and set it intothe submerged basket, taking care to wipe any bubbles from the jar surfacewithout touching the sample.

10.

After the reading stabilizes, determine the mass of the pycnometer and sample inwater to 0.1 gram and record it on the master datasheet and on datasheet 26 asMpws.

11.If the Gmmvalue obtained is less than any of the Gmbvalues at that asphaltcontent or greater than the maximum possible Gmmvalue tabulated at that asphaltcontent on Datasheet 25, then something is wrong.

At this point, since nothing has been discarded, the Gmmtest could be repeated,repeated with a different quarter of the sample or that asphalt content could be

abandoned in favour of another asphalt content (e.g., 5.5% or 6.5 %).

The Gmmshould decrease as asphalt content increases. This fact should also beused to rationalize the validity of Gmmvalues determined.


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PART E: CALCULATIONS AND MIX EVALUATION

I. DATASHEET 24

This datasheet summarizes the sieving results from lab 1 and the blendedgradations, including the evaluation of grading using U.S.C. criteria and the NominalMaximum Particle Size as defined by the Asphalt Institute and by O.P.S.

II. DATASHEET 25

The purpose of this datasheet is to determine the bulk specific gravity andabsorption capacity of the blended aggregate, Gsband to document the specific

gravity of the asphalt cement, Gb. THREE DECIMAL PLACES are required for allspecific gravity values. Rounding to lower precision will result in errors in the mixcalculations.

Average Bulk Specific Gravity of Blended Aggregate

It is important to bear in mind that specific gravity, G, is the density of thematerial divided by the density of water and as such there are no units. Since the

density of water is 1 g/cm3

, then the specific gravities are essentially the mass ingrams divided by the volume in cm3. If the percentages of each mineral stock aredesignated PCA, PFAand PMF, then these would also be the masses of each type ofmineral stock for 100 grams of blended aggregate.

The bulk volume of coarse aggregate, VBAbwould then be:

CAb

CACAb G

PV =

The bulk volume of fine aggregate, VFAbwould be:

FAb

FAFAb G

PV =


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Assuming that mineral filler has an absorption capacity of approximately 0%,the bulk specific gravity would equal the apparent specific gravity and the bulkvolume of mineral filler, VMFbwould be:

MFbMFMFb G

PV =

The total bulk volume of blended aggregate, Vsbwould then be:

MFb

MF

FAb

FA

CAb

CAsb G

P

GP

GP

V ++=

Given that PCA+ PFA+ PMF= 100 grams, the bulk specific gravity of the blendedaggregate, Gsbwould then be:

MFb

MF

FAb

FA

CAb

CA

MFFACAsb

GP

GP

GP

PPPG

++

++=

whereGCAb= bulk specific gravity of the coarse aggregateGFAb= bulk specific gravity of the fine aggregateGMFb= bulk specific gravity of the mineral filler

Whether the percentages of aggregates are given in terms of total aggregateor total mix, this equation is valid in both cases.

Average Absorption Capacity of Blended Aggregate

In estimating the absorption capacity of the blended aggregate, it is assumedthat the mineral filler, being such a fine material, will not absorb a significant amountof water or asphalt cement. Therefore, only the absorption capacities of the coarseand fine aggregates are required. The average absorption capacity of the blended

aggregate is estimated using the following formulation:

CAFA

CACAFAFAsb PP

ABSPABSPABS

+

+=

whereABSsb= percent absorption capacity of blended aggregateABSFA= percent absorption capacity of fine aggregate


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ABSCA= percent absorption capacity of coarse aggregatePFA= percent of total aggregate mass composed of fine aggregatePCA= percent of total aggregate mass composed of coarse aggregate

Apparent Specific Gravity of Aggregate Blend, Gsa

Although not used directly in the calculations, the estimated apparent specificgravity of the blended aggregate provides and upper limit for the effective specificgravity of the blended aggregate. The bulk specific gravity of the blendedaggregate, Gsawould then be:

where

GCAa= apparent specific gravity of the coarse aggregateGFAa= apparent specific gravity of the fine aggregateGMFa= apparent specific gravity of the mineral filler

Maximum Possible Asphalt Absorbed by Blended Aggregate, Pbamax

If the apparent specific gravity is used as an upper limit for the effectivespecific gravity of the blended aggregate, the an upper limit can also be set on the

rate at which the blended aggregate can absorb asphalt, Pbamax,which is estimated

using the following formulation:

whereGb= apparent specific gravity of asphalt cement

Max. Possible Gmmfor Aggregate Blend, Pbamax

The most critical test performed in this lab is the determination of the

maximum specific gravity (Rices Test) at two different asphalt contents. Fromthese values the percent asphalt absorption and air voids are determined for allasphalt contents. If either or both of these values measured are in error, all theremaining calculations for the lab are compromised. These can be calculated for eachasphalt content being used prior to and as a check on Rices Test using the followingequation:

MFa

MF

FAa

FA

CAa

CA

MFFACAsa

GP

GP

GP

PPPG

++

++=

=

sasbbbamax G

1G1

GP

( )

sa

b

b

bmaxmm

GP1

GP

1G

+

=


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III. DATASHEET 26

Bulk Specific Gravity of Compacted Mix, Gmb

1. The volume of the compacted mix, Vmbis determined using Archimedes Principle(an objects volume is the equal to the volume of water that it displaces):

mbwmssdmb MMV =

whereVmb= bulk volume of the specimen (cm

3)Mmssd= SSD mass of the specimen in air (grams)

Mmbw= mass of the specimen in water (grams)

2. The bulk specific gravity of the compacted mix, Gmbis calculated as follows:

wmb

mbmb

VM

G

=

whereGmb= bulk specific gravity of compacted mixM

mb= mass of the specimen in air (grams)

Vmb= bulk volume of the specimen (cm3)

w= the density of water (g/cm3)

Percent Voids in the Mineral Aggregate, VMA

1. The mass of asphalt in each specimen, Mbis calculated as follows:

mbbb MPM =

whereMb= mass of asphalt cement in the specimen (grams)Pb= percent asphalt content (grams of asphalt cement per gram of total mix)Mmb= mass of the specimen in air (grams)

2. The mass of aggregate in each specimen, Msbis calculated as follows:


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bbmsb MMM =

whereMsb= mass of aggregate in the specimen (grams)Mmb= mass of the specimen in air (grams)

Mb= mass of asphalt cement in the specimen (grams)

3. The volume of asphalt cement in each specimen, Vbis calculated as follows:

wb

bb

GM

V

=

whereVb= volume of asphalt cement in each specimen (cm

3)Mb= mass of asphalt cement in the specimen (grams)Gb= specific gravity of the asphalt cement used in the mixw= the density of water = 1.0 g/cm3

4. The volume of mineral aggregate in each specimen, Vsbis calculated as follows:

wsb

sbsb

GM

V

=

whereVsb= volume of mineral aggregate in each specimen (cm

3)Msb= mass of mineral aggregate in the specimen (grams)

Gsb= bulk specific gravity of the blended mineral aggregate in the mixw= the density of water = 1.0 g/cm

3

5. The volume of voids in the mineral aggregate, Vvmais calculated as follows:

sbmbvma VVV =

whereVvma= volume of voids in the mineral aggregate (cm

3)Vmb= bulk volume of the specimen (cm

3)Vsb= volume of mineral aggregate in each specimen (cm

3)

6. The percent voids in the mineral aggregate, VMAis based on the bulk volume, Vmb:

100%V

VVMA

mb

vma =

whereVMA = voids in the mineral aggregate in each specimen (% of bulk volume)


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Vvma= volume of voids in the mineral aggregate (cm3)


Marshall Stability and Flow

1.

The flow, which is the vertical deformation of the specimen when failure occurs,is measured in the standard units of hundredths on an inch. If a specimen fails at adeformation of 0.25 inches (a quarter of an inch), the flow value reported would be25.0.

2. If the deformation were measured in millimetres and found to be 6.35 mm atfailure, the flow would be reported as 6.35/0.254 or 25.0.

3. The standard dimensions of the Marshall specimens are 4 inches (101.6 mm) in

diameter and 2 inches (63.5 mm) in thickness. This would produce a standard bulkvolume of 31.416 cubic inches or 514.815 cm3.

Since the strength of the specimen is affected by its thickness and hence itsvolume, a correction must be made to the load at failure in Newtons to account fordeviations from the standard specimen dimensions. By carefully comparing thestrength of many test specimens to their dimensions, the Asphalt Institute produceda table of Correlation Ratios used to correct the measured load at failure orMarshall Stability into an Adjusted Marshall Stability.

By comparing the bulk volume, Vmbof each specimen in cm3to the ranges in Table

3.01 in subsection 2.3.2a of the course notes on the instructors website, theappropriate correlation ratio can be determined for each specimen. Since Vmbisdetermined to 0.1 cm3, there should be no ambiguity as to the tabulated range to use.

If, for example, the Vmbfor a specimen were measured as 543.6 cm3, this falls in

the range of 536 to 546 cm3for which a correlation ratio, CRof 0.93 is tabulated.If the Marshall Stability for this specimen was measured at 5600 N then theadjusted Marshall Stability would be determined as follows:

5208N0.935600Stability' ==

If the Vmbfor a specimen is greater than 625 cm3(the highest of Table 3.01), the

instructor should be consulted to extrapolate a CRvalue using an equation based onthe data in Table 3.01.


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22

Maximum Specific Gravity, Gmm

1. For two of the six asphalt contents, (5.0% and 6.0% is desired) a maximum

specific gravity, Gmmmeasurement is made on the uncompacted, loose or voidless mix.The maximum specific gravity, Gmmat any asphalt content should always be higherthan any of the bulk specific gravities, Gmbfor that asphalt content since the bulkspecimens had air voids in them which would make the bulk specimens less dense thanthe uncompacted mix. The maximum specific gravity is calculated as shown:

pwspwmm

mmmm MMM

MG

+=

whereGmm= maximum specific gravity of the voidless mixMmm= mass of loose mix sample (grams)Mpw= mass of the pycnometer and basket in water (grams)Mpws= mass of pycnometer + sample + basket in water (grams)


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23

Percent Air Voids, Pa

A. For Asphalt Contents where Gmmhas been Determined

For two asphalt contents (5.0% and 6.0% are desirable but not essential) Gmmwill have been determined. For these cases the determination of Percent air voids, Pais relatively simple. To save testing time for the remaining asphalt contents thepercent air voids, Pacan be determined based on the average effective specificgravity, Gseof the aggregate.

1. First, find the volume of the voidless mix, Vmmas shown:

wmm

mbmm

G

MV

=

where

Vmm= volume of the voidless mix (cm3)

Mmb= mass of the specimen in air (grams)Gmm= maximum specific gravity of the voidless mixw= the density of water (g/cm

3)

2. The effective volume of the mineral aggregate, Vseis calculated as follows:

bmmse VVV =

where

Vse= effective volume of the mineral aggregate (cm3)


Vb= volume of asphalt cement in each specimen from step 3 in VMA calc. (cm3)

3. The volume of air in the compacted mix, Vais then found:

mmmba VVV = where

Va= volume of air in the compacted mix (cm3)




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4. The volume of asphalt absorbed by the aggregate, Vbais found as follows:

mmsbbba VVVV +=

where

Vba= volume of asphalt absorbed by aggregate in the compacted mix (cm3)


Vsb= volume of mineral aggregate in each specimen (cm3)


5. The mass of asphalt absorbed by the aggregate, Mbais found as follows:

wbbaba GVM =

whereMba= mass of asphalt absorbed by aggregate in the compacted mix (grams)Vba= volume of asphalt absorbed by aggregate in the compacted mix (cm

3)

Gb= specific gravity of the asphalt cement used in the mixw= the density of water = 1.0 g/cm

3

6. The percent asphalt absorbed by the aggregate, Pbais then determined:

100%M

MP

sb

baba =

wherePba= percent asphalt absorbed by the aggregate in the mixMba= mass of asphalt absorbed by aggregate in the compacted mix (grams)Msb= mass of mineral aggregate in the specimen (grams)

7. The effective specific gravity of the aggregate, Gseis then found as follows:

wse

sb

se V

MG

=

whereGse= effective specific gravity of the blended mineral aggregate in the mixMsb= mass of mineral aggregate in the specimen (grams)Vse= effective volume of the mineral aggregate (cm

3)w= the density of water = 1.0 g/cm

3


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8. The percent air voids, Pain the compacted mix is then calculated:

100%

V

VP

mb

aa =

where

Pa= percent air voids in the compacted mixVa= volume of air in the compacted mix (cm

3)Vmb= bulk volume of the specimen (cm

3)

B. For Asphalt Contents WithoutGmm

For the asphalt contents where Gmm was not determined, the average effective

specific gravity, Gseof the aggregate from Aabove is used to find the percent airvoids, Pa, the percent asphalt absorbed, Pbaand to estimate the maximum specificgravity, Gmm.

1. First, find the effective volume of the mineral aggregate, Vseusing the

average Gsedetermined from Aas follows:

wse

sbse

GM

V

=

where


Msb= mass of mineral aggregate in the specimen (grams)Gse= average effective specific gravity of the blended mineral aggregatew= the density of water (g/cm

3)

2. The volume of the voidless mix, Vmmis then calculated as follows:

bsemm VVV +=

whereVmm= volume of the voidless mix (cm

3)




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3. The volume of air in the compacted mix, Vais then found:

mmmba VVV =

whereVa= volume of air in the compacted mix (cm

3)



4. The volume of asphalt absorbed by the aggregate, Vbais found as follows:

mmsbbba VVVV +=

whereVba= volume of asphalt absorbed by aggregate in the compacted mix (cm

3)


Vsb= volume of mineral aggregate in each specimen (cm3)


5. The mass of asphalt absorbed by the aggregate, Mbais found as follows:

wbbaba GVM =

whereMba= mass of asphalt absorbed by aggregate in the compacted mix (grams)Vba= volume of asphalt absorbed by aggregate in the compacted mix (cm

3)

Gb= specific gravity of the asphalt cement used in the mixw= the density of water = 1.0 g/cm

3

6. The percent asphalt absorbed by the aggregate, Pbais then determined:

100%MMP

sb

baba =

wherePba= percent asphalt absorbed by the aggregate in the mixMba= mass of asphalt absorbed by aggregate in the compacted mix (grams)Msb= mass of mineral aggregate in the specimen (grams)


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27

7. The maximum specific gravity of the voidless mix, Gmmis then estimated as

follows:

wmm

mbmm

VM

G

=

whereGmm= maximum specific gravity of the voidless mixMmb= mass of the specimen in air (grams)Vmm= volume of the voidless mix (cm

3)

w= the density of water = 1.0 g/cm3

It should be noted that the Gmmshould decrease with asphalt content and begreater than the bulk specific gravity, Gmbcalculated for each specimen at theasphalt content under scrutiny. These considerations can be used to determinewhether or not the properties of each trial specimen are rational and consistent.

8. The percent air voids, Pain the compacted mix is then calculated:

100%VV

Pmb

aa =

where

Pa= percent air voids in the compacted mix

Va= volume of air in the compacted mix (cm3)Vmb= bulk volume of the specimen (cm

3)

Percent of Voids Filled with Asphalt, VFA

1. The percent of the volume of voids in the mineral aggregate occupied by asphalt ineach specimen, VFAis calculated as follows:

( )100%

V

VVVFA

vma

sbmm

=

whereVFA = percentage of the volume of voids in the mineral aggregate filled with

asphalt cement in each specimenVmm= volume of the voidless mix (cm

3)Vsb= volume of mineral aggregate in each specimen (cm

3)Vvma= volume of voids in the mineral aggregate (cm

3)


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IV. DATASHEET 27

Datasheet 27 is a summary of all the calculations on the 6 copies (one for each

asphalt content) of datasheet 26. The averages for each parameter will be used togenerate plots of each parameter versus percent asphalt content.

The values being averaged must be reasonably close to each other numerically butthey must also make sense in terms of relationships between parameters:

a) The maximum specific gravities, Gmmshould be higher than the bulk specificgravities, Gmbfor each asphalt content. The maximum specific gravity, Gmmshould decrease as asphalt content increases.

b)

The percent asphalt absorbed, Pbashould not exceed the maximum possibleasphalt absorption capacity of the blended aggregate, Pbamax.

c) The Gmband Adjusted Marshall Stabilityvalues usually result in a maximizingshaped curve.

d) The VMAvalues usually range between 10 and 20 percent and show aminimizing shaped curve.

e)

The Marshall Flowvalues usually increase with asphalt content.

f) The percent air voids, Pa, usually decreases with increasing asphalt content.

g) The VFAvalues should increase with asphalt content, but not past 100%!

The calculated values for each specimen should be scrutinized for logical andstatistical viability. Values that are logically non-viable (eg., negative) should bestroked out with a horizontal line in the summary table of Datasheet 27. Statisticaloutliers should be crossed out (X) as in lab 2. The average value of each parameter

for each asphalt content should then be based only on the viable values.

In some instances, the calculated parameters might seem reasonable, but theMarshall Stability and flow results (for example) may seem unreasonable for oneparticular asphalt content. This could be the result of leaving the specimens in thewater bath for too long or not long enough or inconsistent water bath temperature.Sometimes one of the specimens is not tested correctly (missed the maximum load


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dial reading or flow dial reading at maximum load). If specimens are rejected due toirregularities in Marshall testing, parameters such as Gmb, Gmm, VMAand Pamay stillbe valid and need not automatically be excluded from the analysis. Again, any valuesrejected must be documented in the report.

V. DETERMINATION OF OPTIMUM ASPHALT CONTENT

There are five parameters to consider when selecting the best or optimumasphalt content for a mix design: Gmb, Stability, Flow, VMA,Pa and VFA. Tables 3.02and 3.03 in subsection 2.3.2 (b and c) of the course notes section of the instructorswebsite, specify ranges of acceptable values (according to the Asphalt Institute) forStability, Flowand Paand minimum values for VMA andVFA.

The first step to identifying the optimum asphalt content is to plot the average

values of these five parameters versus percent asphalt content. This can be donemost easily by using Excel to produce Scatter Plots and then requesting a trendlinewith its equation in Excel for each plot. A linear trendline should be specified for thePaplot and second order polynomials for all the other parameters.

The optimum asphalt content is estimated by averaging the asphalt contents forthe median value in the Parange, the maximum Gmbvalue and the maximum Stabilityvalue. These can be derived from the trendline equations.

Then, by substituting the optimum asphalt content into the equations, the valuesfor each parameter that would be expected when using the optimum asphalt contentcan be estimated.

The mix should then be evaluated by comparing these expected values to theranges of acceptable parameter values in Tables 3.02 and 3.03 in the course notesand to those for hot mix asphalt in the Ontario Provincial Standards.


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VI. REPORT

1. Visit the website for the Ontario Provincial Standards:

http://www.ops.on.ca/home.asp

and select Online Standards or click on the OPS link on the instructors

homepage. Using the standards indicated on the Report Forms, fill in the required

information for the report.

2. Seven graphs are required, each with trendlines and their equations and showingthe graphic estimation of parameter values for the optimum asphalt content.These should be annotated with titles, be arranged 6 on one page, the seventh

on a separate page and shall include:

a) top left: bulk specific gravity, Gmbversus percent asphalt content,

b) top right: maximum specific gravity, Gmmversus percent asphaltcontent,

c) middle left: Adjusted Marshall Stability versus percent asphaltcontent,

d)

middle right: flow versus percent asphalt content,

e) bottom left: percent air voids, Paversus percent asphalt content,

f) bottom right: VMAversus percent asphalt content, and

g) on a separate page, VFAversus percent asphalt content.

3. Datasheets 24 (1), 25 (1), 26 (6) and 27 (1) should be properly completed. Anyrejected data on datasheet 27 should be clearly indicated as described inSection IV above.

a) The determination of the optimum asphalt content should bedocumented in the appropriate section of the report as should theevaluation and comparison to the Asphalt Institute and O.P.S. criteriafor hot mix asphalt design.


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VII. GLOSSARY OF SYMBOLS (masses in grams, volumes in cm3)ABSsb percent absorption capacity of blended

aggregateABSFA percent absorption capacity of fine

aggregateABSCA percent absorption capacity of coarse

aggregateGb apparent specific gravity of the asphalt cement

used in the mixGCAb bulk specific gravity of the coarse aggregateGFAb bulk specific gravity of the fine aggregateGMFb bulk specific gravity of the mineral fillerGCAa apparent specific gravity of the coarse

aggregateGFAa apparent specific gravity of the fine

aggregateGMFa apparent specific gravity of the mineral fillerGmb bulk specific gravity of compacted mixGmm maximum specific gravity of the voidless mixGsb bulk specific gravity of the blended mineral

aggregateGse effective specific gravity of blended mineral

aggregateMb mass of asphalt cement in the specimenMba mass of asphalt absorbed by aggregateMmb mass of the specimen in airM

mssdmass of the SSD specimen in air

Mmbw mass of the specimen in water

Mmm mass of loose mix sampleMpw mass of the pycnometer + basket in waterMpws mass of pycnometer + sample + basket in waterMsb mass of mineral aggregate in the specimenPa percent air voids in the compacted mixPb percent asphalt content (% of total mix mass)Pba percent asphalt absorbed by the aggregate in the

mixPCA percent of total aggregate mass composed of

coarse aggregatePFA percent of total aggregate mass composed of fine

aggregatePMF percent of total aggregate mass composed of

mineral filler

w density of water = 1.0 g/cm3

Va volume of air in the compacted mixVb volume of asphalt cement in each specimenVba volume of asphalt absorbed by aggregateVmb bulk volume of the specimenVMA percent voids in the mineral aggregate

Vmm volume of the voidless mix

Vsb volume of mineral aggregate in each specimenVse effective volume of the mineral aggregate

Vvma volume of voids in the mineral aggregateVFA percent of voids in the mineral aggregate filled with

asphalt cement

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Marshall Mix Design Procedure

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