Construction and Building Materials 23 (2009) 2324–2331

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Construction and Building Materials

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Estimation of resistance to moisture destruction in asphalt mixtures

Saeed Ghaffarpour Jahromi *

Department of Civil Engineering, Shahid Rajaee Teacher Training University, Lavizan, Tehran, Iran

a r t i c l e i n f o

Article history:Received 1 September 2008Received in revised form 28 October 2008Accepted 4 November 2008Available online 16 December 2008

Keywords:Asphalt mixturesMoistures destructionSurface free energiesDynamic modulus

0950-0618/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.conbuildmat.2008.11.007

* Tel.: +98 9122878083; fax: +98 (21)22970021.E-mail address: Saeed_Ghf@srttu.edu

a b s t r a c t

Moisture damage in asphalt mixtures refers to loss in strength and durability due to the presence ofwater. The level and the extent of moisture damage, also called moisture susceptibility, depend on envi-ronmental, construction, and pavement design factors; internal structure distribution and the quality andtype of materials used in the asphalt mixture. In order to assess the moisture destruction, the currentstudy bears out an analytical approach based on surface energy. Two types of bitumen represent very dif-ferent chemical extremes (AC-10 and AC-20) and the three aggregates represent a considerable range inmineralogy (limestone, siliceous gravel, and granite) were evaluated during the course of this study.Repeated compressive test was conducted on samples in dry and wet conditions under controlled tem-perature and moisture destruction was monitored as a change in dynamic modulus with load cycles. Fur-ther, mixtures including the two types of bitumen with or without hydrated lime were evaluated todetermine quantity improvement of hydrated lime on moisture destruction. The result show that AC-20 have less moisture induced damages compared to AC-10 and dynamic modulus values for mixes withAC-20 were higher than the one with AC-10 for all the aggregate types. Hydrated lime increased thedynamic modulus values and wet/dry ratio stiffness. Addition of lime for river gravel samples showedsignificant difference between two types of bitumen but no major differences were found in crashedgranite.

� 2008 Elsevier Ltd. All rights reserved.

1. Introduction

Distress and corrosion of large number of pavements, largelydue to moisture destruction, is an indication of the significanceand the severity of the problem such as premature rutting, ravel-ing, and wear. Generally, the moisture destruction can be classifiedwith two mechanisms: (a) loss of adhesion due to water in be-tween the bitumen and the aggregate and stripping away the bitu-men film and (b) loss of cohesion due to softening of bitumenmixtures mastic [1]. Further, the moisture destruction is knownto be dealing some other factors like the changes in bitumen, de-crease of bitumen content to satisfy rutting associated withincreasing traffic, changes in aggregate quality, widespread use ofselected design features, and poor quality control [2].

So far, a number of test procedures have been developed toevaluate the moisture destruction potential of HMA. However,with pavement performance prediction, these tests do not confirmthe effects of moisture on material properties, hence, they need tobe developed to estimate the behavior of the mixtures in resistingrutting, fatigue, and thermal cracking when subjected to moistureunder different traffic levels [3]. Resistance of compacted bitumi-nous mixtures to moisture induced destruction or AASHTO T283

ll rights reserved.

is the standard method used to predict the effect of moisturedestruction in HMA. AASHTO T283 has also been recommendedby Strategic Highway Research Program (SHRP) to evaluate thewater sensitivity of HMA within the superpave volumetric mix-tures design system [3].

In order to reduce moisture destruction, particularly stripping,the treatment methods include the application of good aggregates,their pretreatment, and the use of additives such as hydrated lime.Based on the laboratory and field testing in recent years, it hasbeen proved that hydrated lime improves the composition of themastic and produces multifunctional benefits in the mixtures andconsequently it can improve the resistance of the HMA to perma-nent deformation damage at high temperatures [4,5]. Hydratedlime substantially improves low temperature fracture toughnesswithout reducing the ability of the mastic to dissipate energythrough relaxation. Acting as filler, the hydrated lime reacts withbitumen resulting in some of the beneficial mechanisms, in termsof strength. Further, it was also found beneficial for the reducedsusceptibility to age hardening and the improved moisture resis-tance [6].

2. Chemistry of the bitumen aggregate bond

Bitumen and aggregates are the two main components of HMAand their interaction with each other plays a major role in the

S.G. Jahromi / Construction and Building Materials 23 (2009) 2324–2331 2325

performance of a pavement. Both the components possess separatechemical and physical properties and interact with each otherwhen they are in close contact. Aggregates vary widely in termsof composition, surface chemistry, and morphology, includingsurface area, pore size distribution, and friability. During the prep-aration of aggregate, dust composed of clays or other mineralsfrequently coats the surface and is not completely removed.Having different surface chemistries from the same aggregate, thisis resulted in different parts of the surface. Also, aggregates possessvarious active and inactive sites on its surface, which play asignificant role in the interaction of bitumen molecules withit [7].

So far as variation in surface texture is concerned, there arecertain aggregates with larger surface area as well as a favorablepore size for adequate bitumen penetration. At times, it is foundthat air is entrapped in these fine pores and makes it difficult forbitumen to penetrate on entire aggregate surface. Consideringthis, there are various active and inactive sites on aggregate sur-face. On the other hand, bitumen is composed of mixtures ofhydrocarbons that contain some polar functionalities, as well asorganometallic constituents that contain metals like nickel, vana-dium, and iron [7]. During their study, Fritschy and Papirer foundthat with the interaction of bitumen and aggregates, oxygen con-taining groups from bituminizes were preferentially adsorbed onthe aggregate surface [8]. It is thus believed that the chemistry ofthe interface between the bitumen and aggregate not only leadsto bonding interactions but influences the ultimate adhesivestrength as well. The aggregate provides a surface that is hetero-geneous with variety of sites of different composition and levelsof activity. These active sites frequently contain partial chargesleading to attract and orient the polar constituents of bitumen.Radiographic experiments by Ross have confirmed the presenceof active sites on the aggregate surface [9]. The polar functional-ities present at the contact point between the bitumen film andthe aggregate surface stick to the surface due to electrostaticforce, hydrogen bonding, or Vander Waals interactions. If the po-lar surface character of the aggregate is covered completely witha non-polar surface coating, the adsorption characteristics of theaggregate change radically.

Chemical reactions between bitumen and aggregates occur atthe time of mixing. When hot bitumen coats the aggregate particle,it tends to enter any available crevice or pore. A charged aggregatesurface attracts an oppositely or partially charged functional groupcontained in the bitumen. A quasi equilibrium state may remainfor some time at the bitumen aggregate bond. The disruptioncaused by attiring forces changes the equilibrium state either intoa new quasi equilibrium or into a state of steady, though perhapsslow, decay of the bitumen aggregate bond [7].

The failure of bitumen aggregate bond can fail at the interface,either as a cohesive failure in bitumen, or as a structural failurewithin the aggregate. Aging is one of the reasons for the declin-ing state of HMA. Hardening of the bitumen may be expected toinfluence the bitumen aggregate bond because of changes in thechemical composition that occur during the aging. The changescaused by oxidative aging could change the nature of the chem-istry of acids, and ketones [7], both of them having high affinityfor the aggregate surface. Studies show that carboxylic acids, ke-tones, and sulfoxides increase with oxidative aging, both at theinterface and in bitumen, at a distance of 25–100 lm from theaggregate surface [10]. The adhesion of the bitumen to the sur-face is dependant upon the types of functional groups at theinterface and their ability to bond strongly to the surface. Theresistance of that bond to environmental factors, particularlythe intrusion of water, is essential for maintaining a long life ofmixes.

3. Chemistry involved in stripping mechanism

Stripping is one of the major distresses caused by penetratingwater within the interface of bitumen aggregate matrix. Watermay be present in aggregate pores used for making a mix, or itmay invade by seeping through cracks in the bitumen. Conse-quently, water can destroy bitumen aggregate bond by diffusingthrough the bitumen film and then reaching the surface and com-peting for the active sites present on the aggregate surface. Basedon the literature, there are about seven different mechanisms ofstripping; detachment, displacement, spontaneous emulsification,pore pressure, hydraulic scour, pH instability, and the effects ofthe environment on bitumen aggregate material systems [11–13].

Adhesive failure in the aggregates and the bitumen occurs at aninterface, while cohesive failure occurs directly within bitumen oraggregate surface. Under harsh water treatment, the outer surfaceof the aggregate breaks away from the main body, carrying bitu-men with it [14]. It is also evident that the components with thehighest affinity to the aggregates are the most sensitive to thewater [7]. Adsorption of bitumen from solution and its subsequentdesorption by water are dependent upon the bitumen composition,the aggregate chemistry as well as morphology [15].

Aggregates can be mainly divided into siliceous and calcareoustypes where the first type is generally slick and smooth at the sur-face, and the second type little bit rough hence, it might promotebonding between aggregate and bitumen. Once the bitumendamps the aggregate surface, some of its organic chemical func-tionalities enter into bond formation with the aggregate constitu-ents. The functional groups frequently combine with alkalimetals present on the aggregate surface to form water soluble salts[7]. Being ionic in nature, these bitumen aggregate bonds weakenor solubilize with exposure to moisture over time.

There are various methods of preventing stripping, one of whichis by adding antistripping agent such as hydrated lime withinHMA. It is noteworthy that some of the lime treated aggregatestend to form stronger, more robust and durable bonds with bitu-men, especially due to the insensitivity of these bonds to the actionof water. The bonds formed in this case are stronger and insoluble.Also, the effect of fines within HMA plays a critical role. The pres-ence and amount of fines determine the extent of stiffening of thebitumen near the aggregate surface by having a bridging effect be-tween the bulk bitumen and aggregate surface [16].

4. Predicting moisture destruction using surface energy concept

The performance of bitumen pavement is much dependentupon cohesive and adhesive bonding within the bitumen aggregatesystem hence, this bonding is related to the surface free energycharacteristics of the system [17]. Stripping, as an adhesion failure,is most likely to occur either at the pavement surface or internallywithin the mixtures. Stripping starts occurring at the weak pointssuch as pavement joints and the areas of high air void content dueto improper compaction. When such patches of pavements passthrough various loading conditions due to heavy traffic, the masticbond with the surface of the coarse aggregates weakens in pres-ence of water and temperature.

Theory of adhesion uses surface free energy to reflect the phys-ical and chemical interaction of the surface. As a matter of fact, theenergies on the surface of aggregates and binder are main compo-nents of HMA that play an important role in predicting the pave-ment behavior after load application. The surface energies ofdifferent aggregates and their binder types can be measured usingdifferent methods, one of this being universal sorption device(USD). Also, the surface free energies of bitumen can be measuredthrough Wilhelmy plate method [17].

Table 2Cohesive bond energy values for bitumen.

Bitumen types Cohesive bond energy DGtotal (ergs/cm2)

AC-10 55.3AC-20 98.4

2326 S.G. Jahromi / Construction and Building Materials 23 (2009) 2324–2331

The surface free energies of bitumen and aggregates are mainlycomprised of non-polar and acid–base components. During hisstudy, Ding Xin Cheng applied the equations developed by Goodand Van Oss [18] to find combined surface free energy of aggre-gates and bitumen in the presence and absence of water. Here,the total surface free energy of both aggregate and bitumen canbe individually described as [19]

C ¼ CLW þ CAB ð1Þ

where C is the surface free energy of bitumen or aggregate, CLW isLifshitz van der Waals component, and CAB is acid–base componentof the surface free energy. From the thermodynamic point of view,the free energy of cohesion, DGc

i , is the energy needed to create a‘‘cohesive” unit area of a crack within a material under vacuum.For an individual component it can be shown as

DGci ¼ 2Ci ð2Þ

Hence; Eq. (1) can be written as

DGch ¼ ðDGc

hÞLW þ ðDGchÞAB ð3Þ

The free energy of adhesion corresponds to the creation of an‘‘adhesive” unit fracture of two unlike bodies in a vacuum. Theequation showing combined surface energy of two componentsi.e., bitumen and aggregate is as follows:

DGaij ¼ ðDGa

ijÞLW þ ðDGaijÞAB ð4Þ

This can be written as

DGaij ¼ 2

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðCiÞLWðCjÞLW

qþ 2

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðCiÞþðCjÞ�

qþ 2

ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiðCiÞ�ðCjÞþ

qð5Þ

If the value of the free energy of cohesion or adhesion is posi-tive, the two phases of the material tend to bind together andthe higher magnitude of free energy of cohesion or adhesion givesthe higher bonding strength. In contact with a third medium likewater, the free energy of adhesion of two different materials is gi-ven as

DGa1 3 2 ¼ C1 3 þ C2 3 � C1 2 ð6Þ

where 1 = bitumen; 2 = aggregate; 3 = water.Above equation can be used to calculate the adhesive bond

strength of HMA in the presence of water. Hence, using aboveequations, it is also possible to calculate the surface free energyof individual components of mixtures i.e., aggregates and bitumenas well as combined surface energy values for entire mix. Surfaceenergy values for individual component are defined as cohesivebond energy values while for combined components these are de-fined as adhesive bond energy values. Based on this concept, somelaboratory tests were performed where the individual surface en-ergy values for aggregates and bitumen were measured and shownin Tables 1 and 2 [8]. It was observed that the bond strength calcu-lated in presence of water turned out to be lesser than the bondstrength in the absence of water. Briefly, based on these values,the quality of the mixtures in terms of bond strength can be char-acterized and the best possible combinations of aggregate andbitumen can be used in the preparation of mixtures for pavements.To know the validity of the above tests and calculations, a perfor-

Table 1Adhesive bond energy values for mixes with and without moisture.

Aggregate mixtures DG1 2 (ergs/cm2) DG1 3 2 (ergs/cm2)

Limestone + AC-10 143.5 65.6Limestone + AC-20 209.2 32.5Crushed granite + AC-10 156.7 45.2Crushed granite + AC-20 190.5 31.1

mance test was conducted, which will be shown in the subsequentchapter.

5. Effect of hydrated lime as mineral filler

The previous laboratory and field testing have proved that hy-drated lime not only improves the composition of the mastic ratherproduces multifunctional benefits in the mixtures. It substantiallyimproves low temperature fracture toughness without reducingthe ability of the mastic to dissipate energy through relaxation.Further, hydrated lime acts as filler and reacts with bitumen result-ing in some of the beneficial mechanisms, in terms of strength. Ithas been widely observed that there are also benefits of the re-duced susceptibility to age hardening and the improved moistureresistance [19].

During his investigation, Tarrer concluded that water has a highpH at the aggregate surface and that is why most liquid anti stripagents remain at the surface as they are water soluble at high pHlevels. Hydrated lime creates a very strong bond between the bitu-men and the aggregate; preventing stripping at all pH levels [20].Some of the creep tests performed at Texas by Little et al also showthat hydrated lime promotes high temperature stability, therebyincreasing resistance to permanent deformation [21]. Little et alevaluated the changes in rheology, aging kinetics and oxidativehardening created by adding hydrated lime to HMA. It finallyshowed improvements in resistance to permanent deformation, fa-tigue cracking and low temperature fracture [22,23].

Various methods have been adopted to add hydrated lime in theproduction of HMA [20], some of these are: adding lime in propor-tion to the drum or batch mixer, adding dry lime to dry and wetaggregate, adding lime slurry to dry aggregate prior to making amix, marinating or stockpiling lime treated aggregates prior tomixing.

Meanwhile, all the above methods have their own advantagesand disadvantages. In the case of lime slurry, it improves resistanceof the treated HMA to stripping; reduces dusting associated withthe addition of dry lime and improves distribution of the lime onthe aggregate. However, this method has number of disadvantagesas it adds more water than typically used for conventional limeapplications and can substantially increase the water content ofthe aggregate prior to entering the drying and mixing portions ofthe HMA facility. The advantage of marinating and stockpiling isreduction in moisture content and improvement in the resistanceto moisture. Its disadvantages being carbonation of lime in stock-piles and washing of lime from the aggregate. The other methodwhich applied prior to marinating is adding dry lime to dry andwet aggregate. Moisture on the aggregate surface ionizes the limeand helps distribute it on the aggregate surface. Here, instead ofmarinating these aggregates, a faster rate of drying can be achievedby heating them for few hours prior to the production of HMA.

Many tests performed to evaluate such additives are based so-lely on short term retained strengths and do not represent longterm performance of bitumen. It is therefore needed to come upwith a simple and repeatable test that could easily evaluate themultifunctional aspects of pavement performance. Such type oftests and methods has been evolved recently to assess the perma-nent deformation in HMA due to addition of fillers. Developingmore advanced methods to predict the performance of HMA

Fig. 2. Permanent strain test and initiation of tertiary creep [24].

Table 3Properties of bitumen’s.

Properties AC-10(PG58-28) AC-20(PG64-16)

Penetration, 0.1 mm (25 �C, 100 g, 5 s) 96 64Ductility, cm (4 �C, 1 cm/mm) 66.8 5.2Softening point, (�C) (R&B) 45 118

Viscosity, poise60 �C 1231 1986135 �C 342 561

S.G. Jahromi / Construction and Building Materials 23 (2009) 2324–2331 2327

however needed to go through the available knowledge regardingeffects of additives in HMA. The present study has tried to developone such method, which shows the effect of hydrated lime on theHMA in terms of permanent deformation.

6. Behavior of asphalt mixtures under cyclic loading

When bitumen mixtures subjected to repetitive loading, thecomponents used in HMA exhibit different types of behaviorincluding viscoelastic behavior. There are two kinds of viscoelasticmaterials: linear and nonlinear. Linear viscoelastic materials aredependent on the time history of the loading or deformation whilenonlinear viscoelastic materials are dependent on the stress orstrain history [6].

Fig. 1 shows the stress and strain behavior of viscoelastic mate-rial for one cycle of load. The area of loop displays the amount ofdissipated energy, which increases with the increasing damage. Acertain amount of energy is lost during load cycle when the mate-rial deforms and returns back to certain position. This energy isknown as dissipated strain energy.

Bitumen mixes exhibit microcracking during repeated loading.During the initiation process, the cracks begin from microscopicsize and grow to macrocracking size, where crack propagation be-gins. Recent studies indicate that the development of microcracksaccelerates permanent deformation in the bitumen layer under re-peated loading applications [6]. Work hardening occurs in well de-signed HMA, while it may lack in rut susceptible mixtures. If HMAwork hardens under repeated loading with accumulating plasticdeformation, but neither contains microcrack arresters nor healsrapidly, it may reach a point where it is stiff enough for micro-cracks to initiate and grow [24]. On initiation of these microcracks,with more permanent deformation is accumulated in HMA com-monly called ‘‘tertiary creep” (Fig. 2).

Fig. 3. Gradation aggregates.

7. Materials

Two types of bitumen represent very different chemical extremes used for test-ing are AC-20 (PG64-22) and AC-10 (PG58-28) and their properties are shown inTable 3. Aggregates used in this testing include river gravel, limestone, and crushedgranite, which are widely used in the construction of asphalt pavements and repre-sent a considerable range in mineralogy. River gravel is siliceous, sub rounded,smooth surface texture. Limestone is characterized as a very hard, with low poros-ity, and low absorption, and somewhat dolomite limestone. It has much more angu-larity and rough texture compared to the river gravel. Crushed granite is rougher interms of surface texture, which is also more angular and hard. The gradation of allaggregates and their properties are shown in Fig. 3 and Table 4, respectively.

Two types of fillers used were material retained in #200 sieves and hydratedlime as an additive. Fillers were tested with binders AC-10 and AC-20 and the ac-quired results of both fillers were compared. Hydrated lime is an interactive addi-tive and has been used as an antistripping agent for a longtime. According tovarious postulates, lime interacts with acids in the bitumen that are readily ab-sorbed on the aggregate surface; lime provides calcium ions which can replace

Fig. 1. Stress–strain behavior of ma

hydrogen, sodium, potassium, and other cations on the aggregate surface; and limereacts with most silicate aggregates to form a calcium silicate crust which has astrong bond to the aggregate and has sufficient porosity to allow penetration ofthe bitumen cement to form another strong bond. Testing was carried out in orderto verify how well this characteristic of lime works with different type of HMA.

terial at low temperatures [6].

Table 4Aggregates properties.

Bulk specificgravity

Bulk specificgravity (SSD)

Apparent specificgravity

Absorption(%)

Rivergravel

2.606 2.632 2.676 1.01

Limestone 2.649 2.669 2.717 1.11Crushed

granite2.698 2.715 2.744 –

Table 7Tests performed on mixtures.

Without hydrated lime With hydrated lime

Aggregate type Bitumen type Test type Test typeRiver gravel AC-10 Dry and wet Dry and wet

AC-20 Dry and wet Dry and wetLimestone AC-10 Dry and wet –

AC-20 Dry and wet –Crushed granite AC-10 Dry and wet Dry and wet

AC-20 Dry and wet Dry and wet

2328 S.G. Jahromi / Construction and Building Materials 23 (2009) 2324–2331

8. Mix design

Table 5 shows the basic criteria applied for proper asphalt mixwhereas Table 6 shows mix design properties for all aggregates.These criteria satisfy for both the type of materials with theirrespective mix design.

9. Testing procedure

Aggregates are preheated to dry them to maximum extent (175)and the binder is heated at an appropriate mixing temperature(149 �C). Mixing is done according to field conditions. Here, a rota-tor was used for at least 4 min in the laboratory in order to achieveproper missing. Compaction temperature for mix is about 140 �C.Compaction of mix is done using gyratory compactor in order toget the samples with 100 mm diameter and about 150 mm heightconsidering required density and maintaining 4% air void. Samplesare preconditioned before testing them on loading machine. Drysamples are kept in an oven at 40 �C for 3 h and wet samples aresoaked in water at 40 �C and vacuumed for 4 h, till they are fullysaturated.

10. Permanent deformation test

After preconditioning, the samples are loaded on UTM-25 ma-chine. The test continued with 1 Hz haversine wave loading andrest period for 50,000 cycles. A preset program is used to recordthe selected data at 1, 10, 100, 1000, 10,000, 20,000, 30,000,40,000, and 50,000 cycles, respectively. In a sample, the permanentdeformation is obtained by measuring the micro strain obtainedthrough two LVDT on the sample’s periphery. Dry samples aretested in dry condition while wet samples are tested in wet condi-tions by keeping the sample in water at the time of loading.

Table 5Criteria of asphalt mixtures design.

Mixture property Criteria

Air voids 4.0%VMA min 13.0%VFA 65–75%Filler proportion 0.6–1.2Gmm at Nin Less than 89%Gmm at Nmax Less than 98%

Table 6Mix design of asphalt mixtures.

Optimumbitumen (%)

Rice specific gravity (Gmm)without hydrated lime

Bulk specificgravity (Gmb)

Rivergravel

3.6 2.484 2.385

Limestone 4.3 2.512 2.412Crushed

granite4.5 2.451 2.358

Three samples were compacted out of one batch of bitumenmixtures and were subjected to dynamic loading and data check.An average result was considered out of three obtained test results.The testing is performed considering with hydrated lime as min-eral filler and without hydrated lime as shown in Table 7.

11. Result analysis

Output of repeated dynamic compressive loading is in terms ofpermanent microstrain due to deformation occurring in the sampleat intermediate loading cycles. The stress level is kept constant andstrain values are measured up to 20,000 loading cycles. A graphicaldisplay of increasing strain values with each loading cycle is doneafter obtaining data for each sample. Using the data obtained fromUTM and known stress level applied during each test, dynamicmodulus values are calculated with the help of peak stress andpeak strain at each load cycle. These dynamic modulus values areplotted against number of loading cycles for each sample. Thenthe dynamic modulus values for each dry and wet sample of amix are compared. It is observed that the dynamic modulus valuesof wet mixes are low compared to the one for dry mixes. After thatthe dynamic modulus values for the same aggregate with two dif-ferent bitumen types have been compared, where it is observedthat the dynamic modulus of mix with AC-20 bitumen is higherthan AC-10. Thereafter, the ratios of dynamic modulus values ofwet and dry tests are calculated and subsequently compared forboth the bitumen types with same aggregate. Similar kind of ana-lytical approach has been used to show the effect of adding hy-drated lime as mineral filler in the bitumen mixtures. Here, thedynamic modulus values of mixes with hydrated lime are higherthan the one without lime in it. Also, the ratios of dynamic modu-lus values for wet/dry tests with and without lime are comparedgraphically for each mix. Dynamic modulus value (E*) for anymix at a particular loading cycle is given as

E� ¼ rmax

emaxð7Þ

where rmax is peak stress at a particular load cycle, and emax is peakstrain at a particular load cycle. The ratio of dynamic modulus forwet and dry tests is shown as

K ¼ E�wet

E�dryð8Þ

Higher the value of K is better the mix in terms of resistance tomoisture destruction. Similarly, in the case of hydrated lime, it isshown that the K value is higher for the mix with lime as mineralfiller in it. Further, the moisture destruction of the mixtures can bebetter understood by calculating the percentage of surface area ofthe aggregate that is replaced by water in the mixtures [19]. Thewet to dry compression stiffness ratio (ratio of stiffness underwet conditions to stiffness under dry conditions) can be approxi-mated by the work of adhesion ratio between bitumen and aggre-gate in wet and dry conditions shown as

Fig. 5. Wet/dry ratio of dynamic modulus (river gravel with AC-10 and AC-20).

Fig. 6. Test results of limestone with AC-10 and AC-20.

Fig. 7. Wet/dry ratio of dynamic modulus (limestone with AC-10 and AC-20).

S.G. Jahromi / Construction and Building Materials 23 (2009) 2324–2331 2329

E�wet

E�dry¼ DG1 2ð1� PÞ þ DG1 3 2P

DG1 2ð9Þ

For permanent deformation testing and cyclic loaded controlstress can be shown as

E�wet

E�dry¼ ðr=eÞwet

ðr=eÞdry¼ edry

ewet¼ DG1 2ð1� PÞ þ DG1 3 2P

DG1 2ð10Þ

where edry and ewet represent the strain induced in the mixtures inthe dry and wet testing condition, respectively. All of the variablesin Eq. (10) are obtainable from permanent deformation testing ex-cept P. This parameter is the percent of the aggregate surface areathat has been exposed to water due to each cycle. Thus, P can be cal-culated using Eq. (10). The results have shown that the ratio ofE�wet=E�dry is always less than one, so by applying the adhesive bondenergy values (Table 1) in Eq. (10), the P value will be higher forAC-10-aggregate mixtures, compare to AC-20-aggregate mixtures.Comparison of surface energy values with pseudo strain energy val-ues is another way of developing a correlation of surface energymeasurements with laboratory testing. Since, pseudo strain energycan be obtained by calculation; therefore, pseudo strain can be cal-culated from the relaxation modulus function and input strain func-tion using linear viscoelastic constitutive convolution integral [24].Relaxation modulus of a mix can be obtained through applying alow stress level to a sample in its initial testing condition, howeverit must be taken care that sample is not damaged. Using the relax-ation modulus with the input haversine strain wave function, a lin-ear viscoelastic stress under uniaxial loading can be calculatedusing the following equation:

rðtÞ ¼Z t

0Eðt � sÞd eðsÞ

d sd s ð11Þ

where r(t) is time dependent linear viscoelastic stress, t indicatespresent time, s is the time history at which strains were measured,E(t � s) is relaxation modulus of the material at loading time, t � s,under the undamaged condition and e(s) is measured strain at theprevious time, s.

Once the linear viscoelastic stress is calculated, the uniaxialpseudo strain can then be deliberated dividing the calculated linearviscoelastic stress by a reference modulus (ER)

eR ¼rðtÞER¼ 1

ER

Z t

0Eðt � sÞd eðsÞ

d sd s ð12Þ

eR is pseudo strain and obtained through the above equation. Thedata develop a hysteresis loop when these pseudo strain valuesare plotted against stress and the area within this loop exhibitspseudo strain energy. With the increase in load cycles the area ofthe loop changes. It is the real dissipated strain energy which showsthe real damage during the fatigue or permanent deformation tests,because both the time dependent viscoelastic behavior and the non-

Fig. 4. Test results of river gravel with AC-10 and AC-20.

Fig. 8. Test results of crushed granite with AC-10 and AC-20.

linear behavior have been eliminated by using nonlinear pseudostrain concept. This dissipated pseudo strain energy can also beused to predict the microcrack fatigue life. Figs. 4–17 highlightthe graphical presentation for each mix. The presentation is dividedin two parts:

Fig. 10. Test results of river gravel (with and without hydrate lime and AC-10).

Fig. 11. Wet/dry ratio of dynamic modulus (river gravel and AC-10, with andwithout hydrate lime).

Fig. 12. Test results of river gravel (with and without hydrate lime and AC-20).

Fig. 13. Wet/dry ratio of dynamic modulus (river gravel and AC-20, with andwithout hydrate lime).

Fig. 14. Test results of crashed granite (with and without hydrate lime and AC-10).

Fig. 9. Wet/dry ratio of dynamic modulus (crushed granite with AC-10 and AC-20).

Fig. 15. Wet/dry ratio of dynamic modulus (crashed granite and AC-10, with andwithout hydrate lime).

Fig. 16. Test results of crashed granite (with and without hydrate lime and AC-20).

2330 S.G. Jahromi / Construction and Building Materials 23 (2009) 2324–2331

Fig. 17. Wet/dry ratio of dynamic modulus (crashed granite and AC-20, with andwithout hydrate lime).

S.G. Jahromi / Construction and Building Materials 23 (2009) 2324–2331 2331

(1) Comparison of dynamic modulus values of mixes withouthydrated lime with different bitumen contents within sameaggregate type (Figs. 4–9).

(2) Comparison of dynamic modulus values of mixes with andwithout hydrated lime with both bitumen for each aggregatetype (Figs. 10–17).

12. Conclusions

Permanent deformation and moisture destruction are the seri-ous problems encountering the pavement industry in recent time.Many studies have been conducted and so are the different theo-ries propounded to explain the behavior of HMA showing perma-nent deformation and moisture destruction. As mentioned before,the basic theory explaining the moisture destruction within HMAis primarily based on adhesion and cohesion of materials used toprepare such mixes. Using surface energy concept and actual labo-ratory testing, this study has tried to explain the theoretical andexperimental concepts of predicting moisture destruction inHMA. It also shows the effects and importance of hydrated lime,mineral filler used to prevent permanent deformation and mois-ture destruction within the mixes.

Based on the results of compressive dynamic repeated loading,the data was analyzed for three different aggregate types; rivergravel, limestone, and crashed granite, respectively. Also, two dif-ferent binder types; AC-10 and AC-20 were considered in thecourse of testing. Tests were performed by making two types ofsamples; one with adding hydrated lime as filler in it and otherwithout adding lime. Samples for each type of mixes were sub-jected to dry and wet testing under controlled temperature onUTM machine. Following observations were made out of the dataanalysis:

– Using AC-20 bitumen, HMA showed less moisture induceddamages compared to the one with AC-10 bitumen in caseof all the aggregate types. Similar result is obtained fromthe values obtained by calculating combined surface freeenergies of HMA.

– Dynamic modulus values for mixes with AC-20 bitumenwere higher than the one with AC-10.

– From the data analysis can be fined the percentage of aggre-gate surface exposed to water (P) is higher in case of wettests compared to dry ones.

– Mixes with crashed granite as aggregate and both types ofbitumen showed highest wet/dry ratio in terms of dynamic

modulus compared to other two aggregate mixes. Even sur-face energy values exhibited similar result.

– Addition of hydrated lime increases the dynamic modulusvalues and wet/dry ratio (K) was higher for such mixes com-pared to the one without hydrated lime. This result againshow the effect of hydrated lime to reduced the moisturesusceptibility of the mix and in a way reduced the moistureinduced damages within the mix.

– In case of river gravel, addition of lime showed a significantdifference between two types of bitumen. No major differ-ences were found in the results of crashed granite withtwo different bitumen types.

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