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8 PCC - ACIMETHOD

The American Concrete Institute (ACI) mix design

method is but one of many basic concrete mix

design methods available today. This section

summarizes the ACI absolute volume method

because it is widely accepted in the .!. and

continually updated by the ACI. "eep in mind that

this summary and most methods designated as

#mix design# methods are really $ust mixture

proportioning methods. %ix design includes trial

mixture proportioning (covered here) plusperformance tests.

This section is a general outline of the ACI proportioning method with specific

emphasis on &CC for pavements. It emphasizes general concepts and rationale

over specific procedures. Typical procedures are available in the following

documents'

The American Concrete Institutes (ACI) !tandard &ractice for !electing

&roportions for ormal* +eavyweight* and %ass Concrete (ACI ,--.-/-)as found in theirACI Manual of Concrete Practice 2000, Part 1: Materials

and General Properties of Concrete.

The &ortland Cement Associations (&CA) Design and Control of Concrete

Mixtures* -0th edition (,11,) or any earlier edition.

The standard ACI mix design procedure can be divided up into 2 basic steps'

-. Choice of slump

,. Maximum aggregate size selection

3. Mixing water and air content selection

0. Water-cement ratio

4. Cement content

5. Coarse aggregate content

6. Fine aggregate content

Major Topics on this Page

2.

-

Slump

2.

,

Maximum Aggregate Size

2.

3

Mixing Water and Air Content

Estimation

2.0

Water-Cement Ratio

2.

4

Cement Content

2.

5

Coarse Aggregate Content

2.

6

Fine Aggregate Content

2.

2

Adjustments for Aggregate

Moisture

2.

/

Summar

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2. Adjustments for aggregate moisture

8.1 Slup

The choice of slump is actually a choice of mix wor!a"ilit. 7or8ability can be

described as a combination of several different* but related* &CC properties related

to its rheology'

9ase of mixing

9ase of placing

9ase of compaction

9ase of finishing

:enerally* mixes of the stiffest consistency that can still be placed ade;uately

should be used (ACI* ,111). Typically slump is specified* but Table 4.-0 shows

general slump ranges for specific applications. !lump specifications are different for

fixed form paving and slip form paving. Table 4.-4 shows typical and extreme state

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Speci&ications/i0e /or Slip /or

(mm) (inches) (mm) (inches)

Typical ,4 64 - 3 1 64 1 3

9xtremes

as low as

,4

as high as

-64

as low as -

as high as

6

as low as 1

as high as

-,4

as low as 1

as high as

4

8.) Ma0iu Aggregate Sie

Maximum aggregate sizewill affect such &CC parameters as amount of cement paste*

wor!a"ilitand strength. In general* ACI recommends that maximum aggregate size

be limited to -@3 of the slab depth and 3@0 of the minimum clear space between

reinforcing bars. Aggregate larger than these dimensions may be difficult to

consolidate and compact resulting in a honeycombed structure or large air poc8ets.

&avement &CC maximum aggregate sizes are on the order of ,4 mm (- inch) to

36.4 mm (-.4 inches) (AC&A* ,11-).

8.2 Mi0ing 3ater an Air ContentEstiation

!lump is dependent upon nominal maximum aggregate size* particle shape*

aggregate gradation* &CC temperature* the amount of entrained air and certain

chemical admixtures. It is not generally affected by the amount of cementitious

material. Therefore* ACI provides a table relating nominal maximum aggregate

size* air entrainment and desired slump to the desired mixing water ;uantity. Table

4.-5 is a partial reproduction of ACI Table 5.3.3 (8eep in mind that pavement &CC

is almost always airentrained so airentrained values are most appropriate).

Typically* state agencies specify between about 0 and 2 percent air by total volume

(based on data from AC&A* ,11-).

ote that the use of waterreducing and@or setcontrolling admixtures can

substantially reduce the amount of mixing water re;uired to achieve a given slump.

Ta!le ".14$ Appro0iate Mi0ing 3ater an Air Content %e5uireents

&or Di&&erent Slups an Ma0iu Aggregate Sies 'aapte &ro ACI(

)***+

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Mi0ing 3ater 6uantit, in g72'l!7,2+ &or the liste Nominal Maximum

Aggregate Size

Slump." '*.29"

in.+

1)."

'*." in.+

1 '*.9"in.+

)" '1 in.+

29."

'1." in.+

"* ') in.+

9" '2 in.+

1** '# in.+

:on-Air-Entraine PCC

,4 41(- ,)

,16(341)

-//(334)

-/1(3-4)

-6/(311)

-55(,64)

-40(,51)

-31(,,1)

--3(-/1)

64 -11(3 0)

,,2(324)

,-5(354)

,14(301)

-/3(3,4)

-2-(311)

-5/(,24)

-04(,04)

-,0(,-1)

-41 -64(5 6)

,03(0-1)

,,2(324)

,-5(351)

,1,(301)

-/1(3-4)

-62(311)

-51(,61)

Typical entrapped air

(percent)3 ,.4 , -.4 - 1.4 1.3 1.,

Air-Entraine PCC

,4 41(- ,)

-2-(314)

-64(,/4)

-52(,21)

-51(,61)

-02(,41)

-0,(,01)

-,,(,14)

-16(-21)

64 -11(3 0)

,1,(301)

-/3(3,4)

-20(314)

-64(,/4)

-54(,64)

-46(,54)

-33(,,4)

--/(,11)

-41 -64(5 6)

,-5(354)

,14(304)

-/6(3,4)

-20(3-1)

-60(,/1)

-55(,21)

-40(,51)

>ecommended Air Content (percent)

%ild 9xposure 0.4 0.1 3.4 3.1 ,.4 ,.1 -.4 -.1

%oderate 9xposure 5.1 4.4 4.1 0.4 0.4 0.1 3.4 3.1

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!evere 9xposure 6.4 6.1 5.1 5.1 4.4 4.1 0.4 0.1

8.# 3ater-Ceent %atio

The watercement ratio is a convenient measurement whose value is well correlated

with &CC strengthand dura"ilit. In general* lower watercement ratios produce

stronger* more durable &CC. If natural pozzolans are used in the mix (such as fly

ash) then the ratio becomes a watercementitious material ratio (cementitious

material portland cement B pozzolonic material). The ACI method bases the

watercement ratio selection on desired compressi#e strengthand then calculates the

re;uired cement content based on the selected watercement ratio. Table 4.-6 is a

general estimate of ,2day compressive strength vs. watercement ratio (or water

cementitious ratio). alues in this table tend to be conservative (ACI* ,111). %ost

state

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The specified minimum cement content* if applicable. %ost state nit =olue o& PCC

&or Di&&erent /ine aggregate /ineness Mouli for Pavement PCC'a&ter ACI(

)***+

:oinal Ma0iu

Aggregate Sie

/ine Aggregate /ineness

Moulus

).#* ).4* ).8* 2.**

/.4 mm (1.364

inches)1.41 1.02 1.05 1.00

-,.4 mm (1.4inches)

1.4/ 1.46 1.44 1.43

-/ mm (1.64 inches) 1.55 1.50 1.5, 1.51

,4 mm (- inches) 1.6- 1.5/ 1.56 1.54

36.4 mm (-.4

inches)1.64 1.63 1.6- 1.5/

41 mm (, inches) 1.62 1.65 1.60 1.6,

otes'

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-. These values can be increased by up to about -1

percent for pavement applications.

,. Coarse aggregate volumes are based on oven

dryrodded weights obtained in accordance with

A!T% C ,/.

8.9 /ine Aggregate Content

At this point* all other constituent volumes have been specified (water* portland

cement* air and coarse aggregate). Thus* the fine aggregate volume is $ust the

remaining volume'

nit volume (- m3or yd3)

olume of mixing water

olume of air

olume of portland cement

olume of coarse aggregate

olume of fine aggregate

8.8 Ajustents &or Aggregate Moisture

nli8e +%A* &CC batching does not re;uire dried aggregate. Therefore* aggregate

moisture contentmust be accounted for. Aggregate moisture affects the following

parameters'

-. Aggregate weights. Aggregate volumes are calculated based on oven

dry unit weights* but aggregate is typically batched based on actual

weight. Therefore* any moisture in the aggregate will increase its weight

and stoc8piled aggregates almost always contain some moisture.7ithout correcting for this* the batched aggregate volumes will be

incorrect.

,. Aount of ixing water. If the batched aggregate is anything but

saturated surface dry it will absorb water (if oven dry or air dry) or give

up water (if wet) to the cement paste. This causes a net change in the

amount of water available in the mix and must be compensated for by

ad$usting the amount of mixing water added.

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8. Suar,

The ACI mix design method is one of many available methods. It has been

presented here to give a general idea of the types of calculations and decisions that

are typical in &CC mix design.

9 PCC - Testing

7hen aggregate* water and portland cement paste

are combined to produce a homogenous substance*

that substance ta8es on new physical propertiesthat are related to but not identical to the physical

properties of its components. Thus* several

common mechanical laboratory tests are used to

characterize the basic mixture and predict mixture

properties. nli8e $MA* it is difficult to draw a

clean distinction between characterization tests

and performance tests. Typically* &CC is

characterized by slump* air content and strength.

+owever* these characteristics can also be used as

performance predictors for wor8ability* durability

and strength respectively. Therefore* this section

does not distinguish between mixture characterization tests and performance tests.

7hereas +%A tests are often scale simulations of actual field conditions (such as rut

tests)* &CC tests are directed more at the basic physical properties of &CC as a

material.

The challenge in &CC testing is to develop physical tests that can satisfactorily

characterize 8ey &CC performance parameters and the nature of their change

throughout the life of a pavement. These 8ey parameters are'

Workability. This parameter* typically measured by slump* is indicative

of fresh concrete rheology.

Strength. This parameter is related to a rigid pavements ability to

support loads. Flexural strengthis commonly used in design and thencorrelated to compressive strengthfor use in field tests.

Durability. !everal tests can be conducted to determine susceptibility to

freeze-thawor chemical attackdamage.

Early age behavior. +I&9>&A* a software program* can be used topredict earlyage &CC behavior.

Major Topics on this Page

/.

-

Workability

/.

,

trength

/.

3

!urability

/.

0

"arly #ge $ehavior

/.

4

ummary

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Although there are many different &CC tests* only those typically used on pavement

&CC are discussed in this Guide.

9%& Workability

7or8ability is a general term used to describe the basic rheological aspects of fresh

&CC (e.g.* &CC in a wet* plastic state). 7or8ability is instrumental in the proper

placement and compaction of fresh &CC. In general* excessively stiff (or harsh)

fresh &CC can be difficult to place and compact resulting in large void spaces and a

honeycombli8e structure that can ;uic8ly fracture and disintegrate. This is

especially true in and around reinforcing steel. &avement &CC* especially that used

for slip form paving* is usually ;uite stiff and must be vibrated into place.

9xcessively fluid fresh &CC is easy to place but may not be able to hold the coarse

aggregate in place resulting in segregation and bleeding.

Slup Test

The slump test (see Digure 4.01) is the most common test for wor8ability. The

slump test involves hand placing an amount of fresh concrete into a metal cone and

then measuring the distance the fresh &CC falls (or #slumps#) when the cone is

removed.

The slump test is meant to be a basic comparative test. ariation in slump

measurement on the same &CC can be as much as 41 mm (, inches). The

American Concrete &avement Association (,11-) says the following about slump'

#The bottom line is that the slump test is useful only as a comparative tool. If

changes in slump are greater than , inches on a given $ob* one can conclude that

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there was li8ely a change in the mix. ariation in slump less than , inches is more

than li8ely from a combination of the testing and typical concrete variability. o

conclusion can be drawn from slump tests to the ;uality of the material. !trength

measurements must be used to indicate ;uality.#

The standard slump test is'

AA!+T= T --/* A!T% C -03' !lump of +ydraulic Cement Concrete

9%' trength

!trength is probably the most well8nown &CC performance parameter.

Compressive and tensile strength are fundamental to any building material in order

to properly proportion and design structural items made from that material.

Although &CC is most often 8nown for its compressive strength* it is typically its

tensile strength (or more exactly* its flexural strength) that governs its use in rigid

pavements. +owever* given the popularity and relative ease of the compressive

test* both tests are typically used in pavement applications. !trength concepts

covered are'

Compressive strength

Tensile strength(including splitting tension tests and (exural strength

tests)

A :ote on Age ;s. Strength

!ince &CC continues to gain strength over time* it is important to specify a

particular age at which a certain strength is measured. %ost often* ,2day strength

is specified although other strengths such as -day* 6day and /1day strength can

be used as well. Dor pavement applications* strength at a particular age is ;uite

important because typically* rigid pavements cannot be opened to traffic until the

&CC reaches a certain strength. Curing methodscan play a ma$or role in &CC strength

gain. =ften* &CC maturitis used to estimate strength at a particular time.

9.2.1 Compressive Strength

&CC is most often 8nown by its compressive strength. This is because &CC is much

stronger in compression than it is in tension and thus* is often used in

compression. The ACI Concrete Code gives some rough rulesofthumb for

converting compressive strength to tensile and flexural strength'

StrengthTensileSplit = %&' StrengthFlexural = (&%

where' cf compressive

strength

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Compressive strength is most often measured by forming -41 mm diameter* 311

mm long (5 inch diameter* -, inches long) test cylinders and then brea8ing them at

a specified age (typically ,2 days) although it can also be performed on specimens

of different sizes and origins (such as field cores or the remnants of a flexural test).

!ome state agencies use compressive strength as a field ;uality assurancemeasurement of a flexural strength specification. Dlexural strength is first

correlated to compressive strength based on mix design test results. Then* using

this correlation* ;uality assurance field tests can use the easier and more widely

8nown compressive strength test* which can be converted bac8 to flexural strength

through the previously determined correlations.

%ost pavement &CC has a compressive strength between ,1.52 and 30.06 %&a

(3111 and 4111 psi) (AC&A* ,11-). +ighstrength &CC (usually defined as &CC with

a compressive strength of at least 0-.36 %&a (5111 psi)) has been designed forcompressive strengths of over -36./1 %&a (,1*111 psi) for use in building

applications.

The standard compression tests are'

AA!+T= T ,, and A!T% C 3/' Compressive !trength of Cylindrical

Concrete !pecimens

AA!+T= T -01 and A!T% C --5' Compressive !trength of Concrete

sing &ortions of ?eams ?ro8en in Dlexure

9.2.2 Tensile Strength

Although &CC is not nearly as strong in tension as it is in compression* &CC tensile

strength is important in pavement applications. Tensile strength is typically used as

a &CC performance measure for pavements because it best simulates tensile

stresses at the bottom of the )CC surface courseas it is sub$ected to loading. These

stresses are typically the controlling structural design stresses. Tensile strength isdifficult to directly measure because of secondary stresses induced by gripping a

specimen so that it may be pulled apart. Therefore* tensile stresses are typically

measured indirectly by one of two means' a splitting tension test or a flexural

strength test.

9%'%'%& plitting Tension Test

A splitting tension test uses a standard -41 mm diameter* 311 mm long (5inch

diameter* -,# long) test cylinder laid on its side. A diametral compressive load is

then applied along the length of the cylinder until it fails (see Digure 4.0-).

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?ecause &CC is much wea8er in tension than compression* the cylinder will typically

fail due to horizontal tension and not vertical compression.

/igure ".#1$ Split Tension Test 'Clic picture to aniate+

The standard split tension test is'

AA!+T= T -/2 and A!T% C 0/5' !plitting Tensile !trength of Cylindrical

Concrete !pecimens

9%'%'%' Flexural trength Tests

Dlexural strength (sometimes called the modulus of rupture) is typically used in &CC

mix design for pavements because it best simulates slab flexural stresses as they

are sub$ected to loading. ?ecause the flexural test involves bending a beam

specimen* there will be some compression involved* and thus flexural strength will

generally be slightly higher than tensile strength measured using a split tension

test. sually* mix designs are typically tested for both flexural and compressive

strengthE they must meet a minimum flexural strength* which is then correlated to

measured compressive strengths so that compressive strength (an easier test) can

be used in field acceptance tests.

There are two basic flexural tests' the thirdpoint loading (Digure 4.0,) and the

centerpoint loading (Digure 4.03). Dor maximum aggregate sizesless than 41 mm (,

inches)* each test is conducted on a -4, x -4, x 412 mm (5 x 5 x ,1 inch) &CC

beam (see Digures 4.00 and 4.04). The beam is supported on each end and loadedat its third points (for the thirdpoint loading test) or at the middle (for the center

point loading test) until failure. The modulus of rupture is then calculated and

reported as the flexural strength. The thirdpoint loading test is preferred because*

ideally* in the middle third of the span the sample is sub$ected to pure moment with

zero shear (%indess and Foung* -/2-). In the centerpoint test* the area of

eventual failure contains not only moment induced stresses but also shear stress

and un8nown areas of stress concentration. In general* the centerpoint loading

test gives results about -4 percent higher (AC&A* ,11-).

/igure ".##$ /le0ural Test

?ea

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/igure ".#"$ Casting /le0ural

?ea Test Speciens in the

/iel

The standard flexural strength test is'

AA!+T= T /6 and A!T% C 62' Dlexural !trength of Concrete (sing

!imple ?eam with Third&oint Goading)

AA!+T= T -66 and A!T% C ,/3' Dlexural !trength of Concrete (sing

!imple ?eam with Center&oint Goading)

9%) !urability

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as the water in &CC freezes and expands it exerts osmotic and hydraulic pressures

on capillaries and pores within the cement paste. If these pressures exceed the

tensile strength of the cement paste* the paste will dilate and rupture (&CA* -/22).

As this process repeats itself over a number of freezethaw cycles* the result can be

crac8ing* scaling and crumbling of the &CC mass.

In the late -/31s it was discovered that purposefully increasing &CC air content

(called #air entrainment#) mitigates the effects of freezethaw damage. This occurs

because the greater air content provides extra void space within the &CC into which

the freezing water can expand. Thus* hydraulic and osmotic pressures on the

cement paste are minimized* which effectively prevents dilation and rupture. The

total air content of the mortar (cement paste B fine aggregate) re;uired to give

optimum freezethaw protection is about / percent* which results in an air content

by volume of &CC of between 0 and 2 percent (%indess and Foung* -/2-). In

addition to the total volume* the distribution of air within the cement paste is also

important for freezethaw resistance. A properly airentrained &CC contains a

uniform dispersion of tiny bubbles throughout the cement paste. As these bubbles

get larger and farther apart* it becomes more difficult for the freezing water to

migrate through the cement paste into them. In general* the smaller the bubbles

and more uniform their distribution* the better. Actions such as excessive vibration

or pumping can adversely affect both total air volume and air distribution. Today*

most &CC for exterior use (this includes pavements) is entrained with air to mitigate

freezethaw effects.

9%)%&%& Freeze-Thaw TestGaboratory testing of &CC freezethaw

resistance involves sub$ecting a specimen

to a series of rapid freezethaw cycles* then

reporting a durability factor. Dirst*

specimens are created such that they are

between 64 -,4 mm (3 4 inches) in

width and depth or diameter and between

,21 011 mm (-- -5 inches) long (see

Digure 4.05). !pecimens are then

sub$ected to a number of freezethaw

cycles in the following manner (AA!+T=*

,111a)'

-. The temperature is alternately

lowered from 0.0*C (01*D) down to

-6.2*C (1*D) and then raised bac8 to0.0*C (01*D).

,. 9ach of these cycles should ta8e anywhere from , to 0 hours.

3. The specimen can be thawed in either water or air (the procedures areslightly different).

/igure ".#4$ ?ea Speciens &or

>se in /reee-Tha< Tests

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0. >emove the specimen from the freezethaw apparatus at intervals not to

exceed 35 cycles and determine its dynamic modulus of elasticity and

length.

4. Cycles are continued until either of the following occur'

o The specimen has been sub$ected to 311 freezethaw cycles.

o The specimen dynamic modulus of elasticity reaches 51

percent of its initial value.

o (=ptional) the specimen has experienced a 1.-1 percent

increase in length.

The durability factor is then calculated as'

M

NPDF

=

where' esistance of Concrete to >apid

Dreezing and Thawing

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AA!+T= T -,-' %ass &er Cubic %eter (Cubic Doot)* Field* and Air

Content (:ravimetric) of Concrete

A!T% C 56-' Critical

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using grinding or sandblasting in order to simulate vehicular wear. !mall dams are

then built around all but one slab (designated the control slab) and sub$ected to

continuous ponding of a 3 percent sodium chloride (aCl) solution to a depth of -3

mm (1.4 inches) for /1 days. After /1 days the aCl solution is removed and the

slabs are wire brushed to remove any salt buildup. !lab samples are then ta8en

and measured for chloride ion content at two depths'

-.5 mm (1.15,4 inches) -3 mm (1.4 inches)

-3 mm (1.4 inches) to ,4 mm (-.1 inches)

These chloride ion concentrations are compared to the average chloride ion

concentration of the control slab to determine the amount and extent of chloride ion

penetration. Critical chloride ion concentrations for reinforcing steel corrosion are

on the order of 1.5 -., 8g Cl@m3(-.1 ,.1 lb Cl@yd3) of &CC.

Although sulfate attac8 is a &CC concern* it is generally not an issue in &CC

pavement.

!ome standard tests for chemical attac8 are'

AA!+T= T ,4/' >esistance of Concrete to Chloride Ion &enetration

AA!+T= T ,66 and A!T% C -,1,' 9lectrical Indication of Concretes

Ability to >esist Chloride Ion &enetration

AA!+T= T 313 and A!T% C ,,6' Accelerated

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spallingand excessive plastic shrin8age. +I&9>&A addresses these issues and

others by modeling earlyage &CC pavement performance (see Digure 4.41).

/igure ".#8$ PCC Earl, Age Crac in

Palale( CA

/igure ".#$ Close->p o& Earl, Age

Crac

/igure "."*$ One Output o& HIPE%PA= Sho

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9%0 ummary

All pavements can be described by their fundamental characteristics and

performance. Thus* &CC tests are an integral part of mix design because they can

describe &CC characteristics and provide the means to relate mix design to intended

performance. Typically* &CC performance tests concentrate on basic physicalproperties such as strength and durability. 9arly age behavior modeling can also be

beneficial in predicting early strength gain* excessive plastic shrin8age* crac8ing

and spalling. &CC performance modeling provides the crucial lin8 between

laboratory mix proportioning and field

performance.

1 PCC - Fun2amentals

&CC consists of three basic ingredients' aggregate*

water and portland cement. According to the &ortland

Cement Association (&CA* -/22)'

#The ob$ective in designing concrete mixtures is to

determine the most economical and practical

combination of readily available materials to

produce a concrete that will satisfy the

performance re;uirements under particular

conditions of use.#

&CC mix design has evolved chiefly through experience and welldocumented

empirical relationships. ormally* the mix design procedure involves two basic

steps'

-. Mix proportioning. This step uses the desired &CC properties as inputs

then determines the re;uired materials and proportions based on a

combination of empirical relationships and local experience. There are

many different &CC proportioning methods of varying complexity thatwor8 reasonably well.

,. Mix testing. Trial mixes are then evaluated and characterized by

sub$ecting them to several laboratory tests. Although these

characterizations are not comprehensive* they can give the mix designer

a good understanding of how a particular mix will perform in the field

during construction and under subse;uent traffic loading.

This section covers mix design fundamentals common to all &CC mix design

methods. Dirst* two basic concepts (mix design as a simulation and weightvolume

terms and relationships) are discussed to set a framewor8 for subse;uentdiscussion. !econd* the variables that mix design may manipulate are presented.

Major Topics on this Page

6.

-

Concepts

6.

,

3ariables

6.

3

4b5ectives

6.

0

$asic Proce2ure

6.

4

ummary

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Third* the fundamental ob$ectives of mix design are presented. Dinally* a generic

mix design procedure is presented.

1%& Concepts

?efore discussing any mix design specifics* it is important to understand a couple of

basic mix design concepts'

6ix 2esign is a simulation

Weight-volume terms an2 relationships

7.1.1 i! "esign is a Sim#lationDirst* and foremost* mix design is a laboratory simulation. %ix design is meant to

simulate actual &CC manufacturing* construction and performance. Then* from this

simulation we can predict (with reasonable certainty) what type of mix design is

best for the particular application in ;uestion and how it will perform.

?eing a simulation* mix design has its limitations. !pecifically* there are substantial

differences between laboratory and field conditions. Dor instance* mix testing is

generally done on small samples that are cured in carefully controlled conditions.

These values are then used to draw conclusions about how a mix will behave under

field conditions.

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-. Aggregate. Items such as type (source)* amount* gra2ation an2 size*toughness an2 abrasion resistance* 2urability an2 soun2ness* shape an2textureas well as cleanlinesscan be measured* $udged and altered to

some degree.

,. Portland ceent. Items such as type* amount* 7neness* soun2ness*hy2ration rateand additives can be measured* $udged and altered to

some degree.

3. !ater. Typically the volume and cleanliness of water are of concern.

!pecifically* the volume of water in relation to the volume of portland

cement* called the watercement ratio* is of primary concern. sually

expressed as a decimal (e.g.* 1.34)* the watercement ratio has a ma$or

effect on &CC strength and durability.

0. Admixtures. Items added to &CC other than portland cement* water and

aggregate. Admixtures can be added before* during or after mixing and

are used to alter basic &CC properties such as air content* watercement

ratio* wor8ability* set time* bonding ability* coloring and strength.

1%) 4b5ectives

?y manipulating the mixture variables of aggregate* portland cement* water and

admixtures* mix design see8s to achieve the following ;ualities in the final &CC

product (%indess and Foung* -/2-)'

-. Strength. &CC should be strong enough to support expected traffic

loading. In pavement applications* flexural strength is typically more

important than compressive strength (although both are important) since

the controlling &CC slab stresses are caused by bending and not

compression. In its most basic sense* strength is related to the degree

to which the portland cement has hy2rate2. This degree of hydration is*

in turn* related to one or more of the following'

o Water-cement ratio. The strength of &CC is most directly

related to its capillary porosity. The capillary porosity of a

properly compacted &CC is determined by its watercement

ratio (%indess and Foung* -/2-). Thus* the watercement

ratio is an easily measurable &CC property that gives a good

estimate of capillary porosity and thus* strength. The lower

the watercement ratio* the fewer capillary pores and thus*

the higher the strength. !pecifications typically include a

maximum watercement ratio as a strength control measure.

o Entrained air (air voids). At a constant watercement ratio* as

the amount of entrained air (by volume of the total mixture)

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increases* the voidscement ratio (voids air B water)

decreases. This generally results in a strength reduction.

+owever* airentrained &CC can have a lower watercement

ratio than nonairentrained &CC and still provide ade;uate

wor8ability. Thus* the strength reduction associated with a

higher air content can be offset by using a lower watercement ratio. Dor moderatestrength concrete (as is used in

rigid pavements) each percentile of entrained air can reduce

the compressive strength by about , 5 percent (&CA* -/22).

o Cement properties. &roperties of the portland cement such as

7nenessand chemical compositioncan affect strength and the

rate of strength gain. Typically* the type of portland cement is

specified in order to control its properties.

,. Controlle& shrinkage cracking. !hrin8age crac8ing should occur in a

controlled manner. Although construction techni;ues such as $oints and

reinforcing steel help control shrin8age crac8ing* some mix design

elements influence the amount of &CC shrin8age. Chiefly* the amount of

moisture and the rate of its use@loss will affect shrin8age and shrin8age

crac8ing. Therefore* factors such as high watercement ratios and the

use of high early strength portland cement types and admixtures can

result in excessive and@or uncontrolled shrin8age crac8ing.

3. "#ra(ilit). &CC should not suffer excessive damage due to chemical or

physical attac8s during its service life. As opposed to +%A durability*

which is mainly concerned with aging effects* &CC durability is mainlyconcerned with specific chemical and environmental conditions that can

potentially degrade &CC performance.

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freezing and migrating water and thus* specifying a minimum

entrained air content can minimize freeze-thaw 2amage.

o Cheical en%ironent. Certain chemicals such as sulfates*

acids* bases and chloride salts are especially 2amagingto

&CC. %ix design can mitigate their damaging effects throughsuch things as choosing a more resistant cement type.

0. Ski& resistance. &CC placed as a surface course should provide

sufficient friction when in contact with a vehicles tire. In mix design* low

s8id resistance is generally related to aggregate characteristics such as

texture* shape* size and resistance to polish. !mooth* rounded or

polishsusceptible aggregates are less s8id resistant. Tests for particleshape an2 texturecan identify problem aggregate sources. These

sources can be avoided* or at a minimum* aggregate with good surface

and abrasion characteristics can be blended in to provide better overall

characteristics.

4. $orka(ilit). &CC must be capable of being placed* compacted and

finished with reasonable effort. The slump test* a relative measurement

of concrete consistency* is the most common method used to ;uantify

wor8ability. 7or8ability is generally related to one or more of the

following'

o Water content. 7ater wor8s as a lubricant between the

particles within &CC. Therefore* low water content reduces

this lubrication and ma8es for a less wor8able mix. ote thata higher water content is generally good for wor8ability but

generally bad for strength and durability* and may cause

segregation and bleeding. 7here necessary* wor8ability

should be improved by redesigning the mix to increase the

paste content (water B portland cement) rather than by

simply adding more water or fine material (%indess and

Foung* -/2-).

o Aggregate proportion. Garge amounts of aggregate in relation

to the cement paste will decrease wor8ability. 9ssentially* if

the aggregate portion is large then the corresponding water

and cement portions must be small. Thus* the same problems

and remedies for #water content# above apply.

o Aggregate texture, shape and si&e. Dlat* elongated or angular

particles tend to interloc8 rather than slip by one another

ma8ing placement and compaction more difficult. Tests for

particle shape an2 texturecan identify possible wor8ability

problems.

o Aggregate gradation. :radations deficient in fines ma8e for

less wor8able mixes. In general* fine aggregates act as

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lubricating #ball bearings# in the mix. :radation specifications

are used to ensure acceptable aggregate gradation.

o Aggregate porosit". +ighly porous aggregate will absorb a

high amount of water leaving less available for lubrication.

Thus* mix design usually corrects for the anticipated amountof absorbed water by the aggregate.

o Air content. Air also wor8s as a lubricant between aggregate

particles. Therefore* low air content reduces this lubrication

and ma8es for a less wor8able mix. A volume of airentrained

&CC re;uires less water than an e;ual volume of nonair

entrained &CC of the same slump and maximum aggregate

size (&CA* -/22).

o Cement properties. &ortland cements with higher amounts of

C3! and C3A will hydrate ;uic8er and lose wor8ability faster.

"nowing these ob$ectives* the challenge in mix design is then to develop a

relatively simple procedure with a minimal amount of tests and samples that will

produce a mix with all the ;ualities discussed above.

1%+ $asic Proce2ure

In order to meet the re;uirements established by the preceding desirable &CC

properties* all mix design processes involve four basic processes'

-. Aggregate selection. o matter the specific method* the overall mix

design procedure begins with evaluation and selection of aggregate and

asphalt binder sources.

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The selected &CC mixture should be the one that* based on test results* best

satisfies the mix design ob$ectives.

1%0 ummary

&CC mix design is a laboratory process used to determine appropriate proportions

and types of aggregate* portland cement* water and admixtures that will produce

desired &CC properties. Typical desired properties in &CC for pavement are

ade;uate strength* controlled shrin8age* durability* s8id resistance and wor8ability.

Although mix design has many limitations it had proven to be a costeffective

simulation that is able to provide crucial information that can be used to formulate

a highperformance &CC.

8 6# - Testing

7hen aggregateand asphalt "inderare combined to

produce a homogenous substance* that substance*

+%A* ta8es on new physical properties that are

related to but not identical to the physical

properties of its components. %echanical

laboratory tests can be used to characterize the

basic mixture or predict mixture properties.

8%& 6ixture Characterization Tests

%ixture characterization tests are used to describe fundamental mixture parameters

such as density and asphalt binder content. The three primary mixture

characterization tests discussed here are'

$ulk speci7c gravity

Theoretical maximum speci7c gravity

#sphalt content:gra2ation

*.1.1 +#lk Speci,c ravit)

.ul! specific gra#itis essentially the density of a compacted (laboratory or field) +%A

specimen. The bul8 specific gravity is a critical +%A characteristic because it isused to calculate most other +%A parameters including air voids* %A* and T%

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This reliance on bul8 specific gravity is because mix design is based on volume*

which is indirectly determined using mass and specific gravity. ?ul8 specific gravity

is calculated as'

Volume

MassGravitySpecific =

There are several different ways to measure bul8 specific gravity* all of which use

slightly different ways to determine specimen volume'

-. !ater displaceent ethods. These methods* based on Archimedes

&rinciple* calculate specimen volume by weighing the specimen (-) in a

water bath and (,) out of the water bath. The difference in weights can

then be used to calculate the weight of water displaced* which can be

converted to a volume using the specific gravity of water.

o (aturated (urface Dr" #((D$. The most common method*

calculates the specimen volume by subtracting the mass of

the specimen in water from the mass of a saturated surface

dry (!!

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/igure ".1"$ Para&&in Coate Saple

o Parafil. This method wraps the specimen in a thin paraffin

film (see Digure 4.-5) and then weighs the specimen in and

out of water. !ince the specimen is completely wrapped when

it is submerged* no water can get into it and a more accurate

volume measurement is theoretically possible. +owever* in

practice the paraffin film application is ;uite difficult and test

results are inconsistent.

/igure ".14$ Para&il Application

o Core)o*. This method calculates specimen volume li8e the

parafilm method but uses a vacuum chamber (see Digure

4.-6) to shrin8wrap the specimen in a high;uality plastic bag

(see Digure 4.-2) rather than cover it in a paraffin film. This

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method has shown some promise in both accuracy and

precision.

/igure ".19$ Coreo =acuu

Cha!er/igure ".18$ Coreo Specien

,. Diensional. This method* the simplest* calculates the volume based on

height and diameter@width measurements. Although it avoids problems

associated with the !!< condition* it is often inaccurate because it

assumes a perfectly smooth surface thereby ignoring surface

irregularities (i.e.* the rough surface texture of a typical specimen).

3. Gaa ra". The gamma ray method is based on the scattering and

absorption properties of gamma rays with matter. 7hen a gamma ray source of

primary energy in the Compton range is placed near a material* and an energy

selective gamma ray detector is used for gamma ray counting* the scattered

and unscattered gamma rays with energies in the Compton range can be

/igure ".1$Baa %a, De;ice

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counted exclusively. 7ith proper calibration* the gamma ray count is directly

converted to the density or bul8 specific gravity of the material (Troxler* ,11-).

Digure 4.-/ shows the Troxler device.

The standard bul8 specific gravity test is'

AA!+T= T -55' ?ul8 !pecific :ravity of Compacted ?ituminous %ixtures

sing !aturated !urface

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/igure ".)*$ Containers >se to Agitate an Dra< a =acuu on Su!erge

TMD Saples

The standard T%< test is'

J AA!+T= T ,1/ and A!T% < ,10-' Theoretical %aximum !pecific :ravity

and

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/igure ".)1$ Open Centri&uge >se

inSol;ent E0traction

/igure ".))$ Seconar, Centri&uge

>se in Sol;ent E0traction

The standard solvent extraction test is'

AA!+T= T -50 and A!T% < ,-6,' Kuantitative 9xtraction of ?itumen

from ?ituminous &aving %ixtures

8%&%)%' ;uclear #sphalt Content

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/igure ".)2$ :uclear Asphalt Content Bauge

/igure ".)#$ Ignition /urnace

8%&%)%) =gnition Furnace

The ignition furnace test* developed by CAT to replace the solvent extraction

method* determines asphalt binder content by burning off the asphalt binder of a

loose +%A sample. ?asically* an +%A sample is weighed and then placed in a

432 C (-16, D) furnace (see Digure 4.,0) and ignited.* * =nce all the asphaltbinder has burned off (determined by a change in mass of less than 1.1- percent

over 3 consecutive minutes)* the remaining aggregate is weighed. The initial and

final weights are compared and the difference is assumed to be the asphalt binder

weight. sing this weight and the weight of the original sample* a percent asphalt

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binder by weight can be calculated. A gradation testcan then be run on the aggregate

to determine gradation.

A correction factor must be used with the ignition furnace because a certain amount

of aggregate fines may be burned off during the ignition process. The correction

factor is determined by placing a sample of 8nown asphalt binder content in thefurnace and comparing the test result with the 8nown asphalt binder content.

?ased on a limited ational Center for Asphalt Technology (CAT) study (&rowell*

,11,)* both traditional and infrared ignition furnaces* if properly calibrated* should

produce statistically similar asphalt contents and recovered aggregate gradations.

The standard ignition furnace test is'

AA!+T= T 312'

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binder physical tests. Therefore* there is generally less attention paid to

developing tensile strength performance tests.

(tiffness. +%As stressstrain relationship* as characterized by elastic or

resilient modulus* is an important characteristic. Although the elastic

modulus of various +%A mix types is rather welldefined* tests candetermine how elastic and resilient modulus varies with temperature.

Also* many deformation resistance tests can also determine elastic or

resilient modulus.

Moisture susceptiilit". Certain combinations of aggregate and asphalt

binder can be susceptible to moisture damage. !everal deformation

resistance and tensile strength tests can be used to evaluate the

moisture susceptibility of a +%A mixture.

*.2.1 ermanent "e/ormation 0'#tting

>esearch is ongoing into what type of test can most accurately predict +%A

pavement deformation (rutting) There methods currently in use can be broadly

categorized as follows'

Static creep tests. Apply a static load to a sample and measure how it

recovers when the load is removed. Although these tests measure a

specimens permanent deformation* test results generally do not

correlate will with actual inservice pavement rutting measurements.

epeated load tests. Apply a repeated load at a constant fre;uency to a

test specimen for many repetitions (often in excess of -*111) and

measure the specimens recoverable strain and permanent deformation.

Test results correlate with inservice pavement rutting measurements

better than static creep test results.

Dynamic modulus tests. Apply a repeated load at varying fre;uencies to

a test specimen over a relatively short period of time and measure the

specimens recoverable strain and permanent deformation. !ome

dynamic modulus tests are also able to measure the lag between the

pea8 applied stress and the pea8 resultant strain* which provides insight

into a materials viscous properties. Test results correlate reasonably

well with inservice pavement rutting measurements but the test is

somewhat involved and difficult to run.

Empirical tests. Traditional veemand 6arshallmix design tests. Test

results can correlate well with inservice pavement rutting

measurements but these tests do not measure any fundamental material

parameter.

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Simulative tests. Gaboratory wheeltrac8ing devices. Test results can

correlate well with inservice pavement rutting measurements but these

tests do not measure any fundamental material parameter.

9ach test has been used to successfully predict +%A permanent deformation

characteristics however each test has limitations related to e;uipment complexity*expense* time* variability and relation to fundamental material parameters.

8%'%&%& tatic Creep Tests

A static creep test (see Digure 4.,4) is conducted by applying a static load to an

+%A specimen and then measuring the specimens permanent deformation after

unloading (see Digure 4.,5). This observed permanent deformation is then

correlated with rutting potential. A large amount of permanent deformation would

correlate to higher rutting potential.

Creep tests have been widely used in the past because of their relative simplicity

and availability of e;uipment. +owever* static creep test results do not correlate

well with actual inservice pavement rutting (?rown et al.* ,11-).

/igure ".)"$ >ncon&ine

Static Creep Test

/igure ".)4$ Static Creep Test Plot

>ncon&ine Static Creep Test

The most popular static creep test* the unconfined static creep test (also 8nown as

the simple creep test or uniaxial creep test)* is inexpensive and relatively easy. The

test consists of a static axial stress of -11 8&a (-0.4 psi) being applied to a

specimen for a period of - hour at a temperature of 01 C (-10 D).* * The appliedpressure is usually cannot exceed ,15./ 8&a (31 psi) and the test temperature

usually cannot exceed 01*C (-10*D) or the sample may fail prematurely (?rownet al.* ,11-). Actual pavements are typically exposed to tire pressures of up to 2,2

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8&a (-,1 psi) and temperatures in excess of 51*C (-01*D). Thus* the unconfined

test does not closely simulate field conditions (?rown et al.* ,11-).

Con&ine Static Creep Test

The confined static creep test (also 8nown as the triaxial creep test) is similar to the

unconfined static creep test in procedure but uses a confining pressure of about-32 8&a (,1 psi)* which allows test conditions to more closely match field

conditions. >esearch suggests that the static confined creep test does a better $ob

of predicting field performance than the static unconfined creep test (>oberts et al.*

-//5).

Diaetral Static Creep Test

A diametral static creep test uses a typical +%A test specimen but turning it on its

side so that it is loaded in its diametral plane.

!ome standard static creep tests are'

AA!+T= T& /' epeated load tests are similar in concept to the triaxial resilient

modulus testfor unconfined soils and aggregates.

>epeated load tests correlate better with actual inservice pavement rutting than

static creep tests (?rown et al.* ,11-).

/igure ".)9$ %epeate oa Test Scheatic

ote' this example is simplified and shows only 5 load repetitions* normally

there are conditioning repetitions followed by a series of load repetitions

during the test at a determined load level and possibly at different

temperatures.

%ost often* results from repeated load tests are reported using a cumulative axial

strain curve li8e the one shown in Digure 4.,2. The flow number (D) is the load

cycles number at which tertiary flow begins. Tertiary flow can be differentiated

from secondary flow by a mar8ed departure from the linear relationship between

cumulative strain and number of cycles in the secondary zone. It is assumed that

in tertiary flow* the specimens volume remains constant. The flow number (D)can be correlated with rutting potential.

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/igure ".)8$ %epeate oa Test %esults Plot

>ncon&ine %epeate oa Test

The unconfined repeated load test is comparatively more simple to run than the

unconfined test because it does not involve any confining pressure or associated

e;uipment. +owever* li8e the unconfined creep test* the allowable test loads aresignificantly less that those experience by inplace pavement.

Con&ine %epeate oa Test

The confined repeated load test is more complex than the unconfined test due to

the re;uired confining pressure but* li8e the confined creep test* the confining pressure

allows test loads to be applied that more accurately reflect loads experienced by in

place pavements.

Diaetral %epeate oa Test

A diametral repeated load test uses a typical +%A test specimen but turning it on

its side so that it is loaded in its diametral plane.

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A!T% < 0-,3' Indirect Tension Test for >esilient %odulus of ?ituminous

%ixtures

8%'%&%) !ynamic 6o2ulus Tests

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The absolute value of the complex modulus* M9LM* is defined as the dynamic

modulus and is calculated as follows (7itcza8 et al.* ,11,)'

where' M9LM dynamic modulus

o pea8 stress amplitude

(applied load @ sample cross sectional area)

o pea8 amplitude of recoverable axial strain G@G. 9ither measured directly with

strain gauges or calculated from

displacements measured with linear

variable displacement transducers (G

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/igure ".2*$ A Protot,pe

Superpa;e SiplePer&orance Test 'SPT+

/igure ".21$ The SPT is a Con&ine

D,naic Moulus Test

Shear D,naic Moulus Test

The shear dynamic modulus test is 8nown as the fre;uency sweep at constant

height (D!C+) test. !hear dynamic modulus e;uations are the same as those

discussed above although traditionally the term 9L is replace by :L to denote shear

dynamic modulus and o and oare replaced by 1and 1to denote shear stress

and axial strain respectively. The shear dynamic modulus can be accomplished by

two different testing apparatuses'

-. (uperpa%e shear tester #(('$. The !!T D!C+ test is a is a constant

strain test (as opposed to a constant stress test). Test specimens are

-41 mm (5 inches) in diameter and 41 mm (, inches) tall (see Digure

4.3,). To conduct the test the +%A sample is essentially glued to two

plates (see Digures 4.33 through 4.34) and then inserted into the !!T.

+orizontal strain is applied at a range of fre;uencies (from -1 to 1.- +z)

using a haversine loading pattern* while the specimen height is

maintained constant by compressing or pulling it vertically as re;uired.

The !!T produces a constant strain of about -11 microstrain (7itcza8 et

al.* ,11,). The !!T is ;uite expensive and re;uires a highly trained

operator to run thus ma8ing it impractical for field use and necessitating

further development.

,. +ield shear tester #+('$. The D!T D!C+ test is a is a constant stress test

(as opposed to a constant strain test). The D!T is a derivation of the

!!T and is meant to be less expensive and easier to use. Dor instance*

rather than compressing or pulling the sample to maintain a constant

height li8e the !!T* the D!T maintains constant specimen height using

rigid spacers attached to the specimen ends. Durther* the D!T shears the

specimen in the diametral plane.

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/igure ".2)$ Superpa;e Shear

Tester 'SST+/igure ".22$ oaing Cha!er

/igure ".2#$ Prepare Saple /igure ".2"$ Prepare Saple 'le&t+

an Saple A&ter Test 'ile an

right+.

!tandard complex modulus tests are'

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-nconfined d"naic odulus. A!T% < 30/6' esults obtained from the wheel trac8ing devices correlate reasonably

well to actual field performance when the inservice loading and

environmental conditions of that location are considered.

7heel trac8ing devices can reasonably differentiate between binder

performance grades.

7heel trac8ing devices* when properly correlated to a specific site s*

traffic and environmental conditions* have the potential to allow the user

agency the option of a pass@fail or go@no go criteria. The ability of* *the wheel trac8ing devices to ade;uately predict the magnitude of the

rutting for a particular pavement has not been determined at this time.

A device with the capability of conducting wheeltrac8ing tests in both air

and in a submerged state* will offer the user agency the most options of

evaluating their materials.

In other words* wheel trac8ing devices have potential for rut and other

measurements but the individual user must be careful to establish laboratory

conditions (e.g.* load* number of wheel passes* temperature) that produceconsistent and accurate correlations with field performance.

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=ieo ".1$ Asphalt Pa;eent Anal,er - A 3heel Tracing De;ice

*.2.2 Fatig#e i/e

+%A fatigue properties are important because one of the principal modes of +%A

pavement failure is fatiguerelated crac8ing* called fatigue crac!ing. Therefore* an

accurate prediction of +%A fatigue properties would be useful in predicting overall

pavement life.

8%'%'%& Flexural Test

=ne of the typical ways of estimating inplace +%A fatigue properties is the flexural

test (see Digures 4.35 and 4.36). The flexural test determines the fatigue life of a

small +%A beam specimen (321 mm long x 41 mm thic8 x 53 mm wide) by

sub$ecting it to repeated flexural bending until failure (see Digure 4.32). The beam

specimen is sawed from either laboratory or field compacted +%A. >esults are

usually plottedto show cycles to failure vs. applied stress or strain.

/igure ".24 'le&t+$ /le0ural Testing

De;ice

/igure ".29 'right+$ /le0ural Testing

De;ice

/igure ".28$ /le0ural Test Scheatic 'clic picture to aniate+

The standard fatigue test is'

AA!+T= T& 2' epeated Dlexural ?ending

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*.2.3 Tensile Strength

+%A tensile strength is important because it is a good indicator of crac8ing

potential. A high tensile strain at failure indicates that a particular +%A can tolerate

higher strains before failing* which means it is more li8ely to resist crac8ing than an+%A with a low tensile strain at failure. Additionally* measuring tensile strength

before and after water conditioning can give some indication of moisture

susceptibility. If the waterconditioned tensile strength is relatively high compared

to the dry tensile strength then the +%A can be assumed reasonably moisture

resistant. There are two tests typically used to measure +%A tensile strength'

=n2irect tension test

Thermal cracking test

8%'%)%& =n2irect Tension Test

The indirect tensile test uses the same testing device as the diametral repeated load test

and applies a constant rate of vertical deformation until failure. It is ;uite similar to

the splitting tension testused for &CC.

!tandard indirect tension test is a part of the following test'

AA!+T= T& /' estrained !pecimen Tensile

!trength

*.2. Sti4ness Tests

!tiffness tests are used to determine a +%As elastic or resilient modulus. Although

these values are fairly welldefined for many different mix types* these tests are

still used to verify values* determine values in forensic testing or determine values

for new mixtures or at different temperatures. %any repeated load tests can beused to determine resilient modulus as well.

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=f particular note* temperature has a profound effect on +%A stiffness. Table 4.-3

shows some typical +%A resilient modulus values at various temperatures. Digure

4.3/ shows that +%A resilient modulus changes by a factor of about -11 for a 45

C (-11 D) temperature change for #typical# densegraded +%A mixtures.* * Thiscan affect +%A performance parameters such as ruttingand sho#ing. This is one

reason why the Superpa#e )+ "inder grading sstemaccounts for expected servicetemperatures when specifying an asphalt binder.

Ta!le ".12$ T,pical %esilient Moulus =alues &or HMA Pa;eent Materials

Material

Resilient Modulus

'M%+

MPa psi

+%A at 3, D (1*C)* -0*111

,*111*111

+%A at 61 D (,-*

C)* 3*411 411*111

+%A at -,1 D*(0/ C)*

-41 ,1*111

Compare to other materials

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/igure ".2$ Beneral Sti&&ness-Teperature %elationship &or Dense-Brae

Asphalt Concrete

*.2.5 oist#re S#scepti(ilit)

umerous tests have been used to evaluate moisture susceptibility of +%AE

however* no test to date has attained any wide acceptance (>oberts et al.* -//5).

In fact* $ust about any performance test that can be conducted on a wet or

submerged sample can be used to evaluate the effect of moisture on +%A by

comparing wet and dry sample test results. Superpa#erecommends the modified

Gottman Test as the current most appropriate test and therefore this test will be

described.

The modified Gottman test basically compares the indirect tensile strength test

results of a dry sample and a sample exposed to water@freezing@thawing. The

water sample is sub$ected to vacuum saturation* an optional freeze cycle* followed

by a freeze and a warmwater cycle before being tested for indirect tensile strength

(AA!+T=* ,111a). Test results are reported as a tensile strength ratio'

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where' T!> tensile strength ratio

!- average dry sample tensile strength

!, average conditioned sample tensile

strength

:enerally a minimum T!> of 1.61 is recommended for this method* which should

be applied to &iel-proucerather than laboratoryproduced samples (>oberts et

al.* -//5). Dor la!orator,samples produced in accordance with AA!+T= T& 0

(%ethod for &reparing and

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0 6# - uperpave 6etho2

=ne of the principal results from the Strategic

$ighwa Research )rogram 3S$R)4was the !uperpave

mix design method. The !uperpave mix design

method was designed to replace the $#eemand Marshallmethods. The volumetric

analysis common to the +veem and %arshall methods provides the basis for the

!uperpave mix design method. The Superpa#e sstemties asphalt binder andaggregate selection into the mix design process* and considers traffic and climate

as well. The compaction devices from the +veem and %arshall procedures have

been replaced by a grator compactorand the compaction effort in mix design is tied

to expected traffic.

This section consists of a brief history of the !uperpave mix design method followed

by a general outline of the actual method. This outline emphasizes general

concepts and rationale over specific procedures. Typical procedures are available in

the following documents'

>oberts* D.G.E "andhal* &.!.E ?rown* 9.>.E Gee*

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3. ew methods of mixture analysis.

7hen !+>& was completed in -//3 it introduced these three developments and

called them the !uperior &erforming Asphalt &avement !ystem (!uperpave).

Although the new methods of mixture performance testing have not yet been

established* the mix design method is wellestablished.

0%' Proce2ure

The !uperpave mix design method consists of 6 basic steps'

-. #ggregate selection.

,. #sphalt bin2er selection.

3. ample preparation ,inclu2ing compaction/.

0. Performance Tests.

4. !ensity an2 voi2s calculations.

5. 4ptimum asphalt bin2er content selection%

6. 6oisture susceptibility evaluation%

5.2.1 Aggregate Selection

!uperpave specifies aggregate in two ways. Dirst* it places restrictions on

aggregate gradation by means of broad control points. !econd* it places

#consensus re;uirements# on coarse and fine aggregate angularity* flat and

elongated particles* and clay content. =ther aggregate criteria* which the Asphalt

Institute (,11-) calls #source properties# (because they are considered to be source

specific) such as 5&A& a"rasion* soundnessand water a"sorptionare used in !uperpave butsince they w