The use of waste materials in asphalt concrete mixtures

Waste Manage Res 2003: 21: 83–92Printed in UK – all rights reserved

Waste Management & Research 83

Copyright © ISWA 2003Waste Management & Research

ISSN 0734–242X

IntroductionDisposal of industrial wastes is a worldwide problem.Environmental awareness of the drawbacks of landfill sitesis forcing nations to look for better ways to recycle indus-trial wastes. The use of industrial wastes as additives inasphalt mixtures is not a new technique. Additives havebeen used in road construction for more than 80 years (Al-Abdul-Wahhab & Al-Amri 1991). They are incorporatedin asphalt mixtures to enhance the properties and perfor-mance of asphalt concrete pavements. Large scale use ofrubber from waste tyres in asphalt mixtures appears attrac-tive and promising from the engineering and environmen-tal point of view. Pavements made of rubber and plastic

modified asphalt concrete have better skid resistance, lesscracking and a longer pavement life in comparison to con-ventional asphalt pavements (Al-Abdul-Wahhab & Al-Amri 1991, Flynn 1993). Studies have been done toinvestigate the effects of rubber particles from tyres in thepreparation of asphalt concrete mixtures in the laboratory.In these investigations, scrap rubber was used to modifythe asphalt at 10%, 20% and 30% of aggregate weight(Haas et al. 1983). Khedaywi et al. (1994) reported thatwhile the softening point of the binder increased, penetra-tion and ductility of the binder decreased with increasingrubber content.

Mustafa TuncanAhmet TuncanAltan CetinDepartment of Civil Engineering, Anadolu University, Iki EylulKampusu, 26470, Eskisehir, Turkey.

Keywords: Waste tyre, crumb rubber, waste plastic, Marshall sta-bility, indirect tensile strength, moisture susceptibility, wmr 506–4.

Corresponding author: Mustafa Tuncan, Department of CivilEngineering, Anadolu University, Iki Eylul Kampusu, 26470,Eskisehir, Turkey.Fax: 90-222-323 95 01 E-mail: [email protected]

Received 23 January 2003, accepted in revised form 18 February2003.

The purpose of this study was to investigate (a) the effectsof rubber and plastic concentrations and rubber particlesizes on properties of asphalt cement, (b) on properties ofasphalt concrete specimens and (c) the effects of fly ash,marble powder, rubber powder and petroleum contami-nated soil as filler materials instead of stone powder in theasphalt concrete specimens. One type of limestone aggre-gate and one penetration-graded asphalt cement (75-100)were used. Three concentrations of rubber and plastic (i.e.5%, 10% and 20% of the total weight of asphalt cement),three rubber particle sizes (i.e. No. 4 [4.75mm] – 20 [0.85mm], No. 20 [0.85mm] – 200 [0.075mm] and No. 4[4.75mm] – 200 [0.075mm]) and one plastic particle size(i.e. No. 4 [4.75mm] – 10 [2.00mm]) were also used. Itwas found that while the addition of plastic significantlyincreased the strength of specimens, the addition of rub-ber decreased it. No. 4 [4.75mm] – 200 [0.075mm] rub-ber particles showed the best results with respect to theindirect tensile test. The Marshall stability and indirecttensile strength properties of plastic modified specimensincreased. Marble powder and fly ash could be used asfiller materials instead of stone powder in the asphalt con-crete pavement specimens.

The use of waste materials in asphalt concrete mixtures

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Mustafa Tuncan, Ahmet Tuncan, Altan Cetin

84 Waste Management & Research

Many studies have shown that the addition of rubber toasphalt concrete mixtures in amounts ranging from 10% to30% of the asphalt binder increases the viscosity and resis-tance to moisture damage and reduces the susceptibility totemperature and the tendency to flow (Haas et al. 1983,Lalwani et al. 1982, Oliver 1982). Addition of crumb rub-ber to hot-mix asphalt concrete was reported by severalauthors to improve rheological properties of the asphaltsuch as viscosity, softening point, penetration, temperaturesusceptibility, strength and durability (Khedaywi et al.1994).

Deterioration of asphalt pavements leading to perma-nent deformation or rutting is one of the major problems inTurkey. It has considerably reduced the service lives ofpavements and increased maintenance costs. In hotweather, the dynamic stiffness of the asphalt pavementdecreases and thus higher stresses are transmitted to thelayers below, resulting in greater deformation (Brown1978).

Using industrial wastes in the asphalt concrete pave-ment can not only decrease environmental problems butalso improves some properties of the pavement. Severalauthors investigated the effects of fly ash on properties ofasphalt mixtures (Ali et al. 1996). Results of these studiesindicated that fly ash could be used as a mineral filler toimprove the resilient modulus characteristics and strippingresistance. The New Jersey Environmental EngineeringProtection department conducted a study to evaluate thefeasibility of using petroleum contaminated soil in the pro-duction of hot-mix asphalt (Meegoda et al. 1996). Testresults showed that this asphalt produced a much betterpaving material with higher stability values than standardhot-mix asphalt. The durability of the asphalt against freez-ing and thawing was the same as that of the control mix-tures.

In this study, the effects of waste materials as additivesand filler materials on the properties of asphalt concretepavement mixtures were investigated.

Materials

Aggregate One type of limestone aggregate was used in this study.This aggregate is the most commonly used for asphalt con-crete pavement construction in Turkey. The gradation andsome other properties of the aggregate determined in thelaboratory are given in Fig. 1 and Table 1 respectively.

Asphalt cement One penetration-grade asphalt cement 75-100 is widely

used in Turkey. This asphalt was obtained from the AsphaltWork Site of the Municipality of Eskisehir, Turkey. Thistype of asphalt was chosen because it is widely used inpavement construction in the city of Eskisehir. Table 2gives a summary of the test results obtained from theasphalt cement in the laboratory. Amounts of saturates,aromatics, resins and asphaltenes in the asphalt cement are5.1%, 63.8%, 18.6% and 12.5%, respectively.

Crumb rubberCrumb rubber used in this study was obtained by choppingscrap automobile and truck tyres. The specific gravity ofthe rubber is 1.11. Crumb rubber from three size ranges,No. 4-20, No. 20-200 and No. 4-200 was used as a modifi-er at 5%, 10% and 20% by total weight of asphalt cement.Grain size distributions of crumb rubber are given in Fig. 2.The scanning electron microscopy picture of a crumb rub-ber particle between the No. 40 and No. 60 sieves is shownin Fig. 3a.

PlasticDiscarded plastic grocery bags, dry cleaning bags andhousehold plastics were used. The use of polymers to mod-ify the characteristics of the asphalt pavement in asphaltcement mixtures is acceptable in the highway constructionindustry (Flynn 1993). Some of the concerns about the useof recycled plastic as an asphalt cement modifier are per-formance and durability, cost effectiveness, availability,recyclability, health and environmental impacts. The plas-tic generally comes from grocery bags and household plas-tics. In this study, plastic from a single size range betweenthe No. 4 and No. 10 sieves was used as a modifier at 5%,10% and 20% by total weight of asphalt cement. The scan-ning electron microscopy picture of a plastic particle isshown in Fig. 3b.

Filler materialsIndustrial wastes such as fly ash, marble powder and petro-leum contaminated soil (PCS) were used as filler materialsto prepare asphalt concrete mixtures. Some properties andhydrometer analyses of fly ash, marble powder and PCS aregiven in Table 3 and Fig. 4 respectively.

Fly ashFly ash is an industrial residue of the coal burning process.It was obtained from a coal fired power plant near the cityof Ankara, Turkey. This fly ash is a fine silt size materialconsisting of spherical glassy particles and is composed of45.68% silicon oxide, 9.04% aluminum oxide, 7.04% ironoxide and 15.20% calcium oxide. The total amount of sili-con, aluminum and iron oxides is 61.76%. The minimum




85Waste Management & Research

acceptable requirement is 50% to be a type C fly ash(Conner 1990). Type C fly ash, used in this study, has ahigher lime content than type F fly ash and therefore it canbe self-cementing.

Petroleum contaminated soil (PCS)

Petroleum drilling waste was used as petroleum contami-nated soil. Wastes contain drilling mud and cuttings.Drilling mud is normally classified as oil-based or water-based (Rogers 1963). Drilling cuttings are the solid cut-tings which are brought to the surface from a well duringboring. PCS consists of chloride, barite, bentonite clay,caustic soda, carboxyl methyl cellulose and crude oil.

Laboratory studyExperiments were conducted at the laboratories of theDepartment of Civil Engineering at Anadolu University inEskisehir, Turkey. In this study, the optimum asphaltcement content in the regular asphalt concrete withoutany waste was found to be 4.5%, using the Marshall stabil-ity test. Therefore, an asphalt cement content of 4.5% byweight of aggregate was used for all specimens regardless ofthe amount of rubber or plastic added to the asphaltcement. The Marshall stability test procedure was used toprepare test specimens. A total of 160 rubber and plasticmodified specimens were prepared. Five specimens of eachindustrial waste modified mixtures were tested. A total of220 industrial waste modified specimens were prepared.The Marshall stability and flow test (ASTM D1559), theindirect tensile test (AASHTO T283) and the compres-sive strength test (ASTM D1074) were performed todetermine the mechanical properties of industrial wastemodified asphalt concrete specimens. The moisture sus-ceptibility test (AASHTO T283) was also performed byusing both the Marshall stability and the indirect tensiletests for conditioned and control specimens. Softeningpoint, penetration and ductility of rubber and plastic mod-ified asphalt cement were determined using ASTM D36,ASTM D5 and ASTM D113, respectively.

Table 1: Properties of Aggregate.

Properties Values

Los Angeles Abrasion Test [%] 24(ASTM C131)Soundness [% loss of Na2SO4 ] 1.0

(ASTM C88)Flakiness Index [%] 11(BS 812)Stripping Resistance [%](ASTM D1664)

AC (60-70)* 55-60AC (150-200)# 50-55

*AC (60-70): Asphalt cement penetration of 60-70 #AC (150-200): Asphalt cement penetration of 150-200

Fig. 1: Grain Size Distributions of Aggregate and Upper and Lower Limit Specifications of Turkish General Directorate for Highways 1994.



Preparation of rubber and plastic modified asphaltcement mixturesFirst, asphalt cement was heated in an oven at a tempera-ture of at least 160˚C. Second, the required amount ofasphalt was weighed into the beaker, then the amount ofrubber and plastic required to yield the desired rubber-to-asphalt ratio or plastic-to-asphalt ratio was added. Thebeaker was placed on a hot plate to maintain a mixing tem-perature of at least 160˚C. Third, the laboratory mixer was

placed so that the propeller was about 15 mm above thebottom of the beaker. The mixer was then started, and theprepared amount of rubber or plastic was added graduallyto the beaker while stirring. The speed of the mixer wasincreased up to 500 rpm. The mixing was continued for atleast 30 minutes until a homogeneous rubber or plasticmodified binder was obtained. Finally, the rubber or theplastic modified asphalt cement was mixed with the heat-ed aggregate to prepare rubber or plastic modified asphaltconcrete mixtures.

Preparation of industrial waste modified asphalt concretemixturesFive percent of stone powder was replaced by an equalweight of industrial waste finer than the No. 200 sieve.These wastes were oven dried at 105˚C before using asfillers. Specimens were prepared according to the Marshalltest procedure (ASTM D1559).



Table 2: Properties of Asphalt Cement.

Properties Values

Penetration [0.1 mm] at 25˚C, 100 g, 5 s 83(ASTM D5)Softening Point [0C], ring and ball 45(ASTM D36)Ductility [10 mm] at 25˚C 100+(ASTM D113)Specific Gravity 1.024(ASTM D70)

Table 3: Properties of Filler Materials.

Type of Filler Specific pH Electrical Conductivity Organic Matter Gravity [mS/cm] Content [%]

(ASTM D854) (EPA Method 9045) (Wilcox 1946) (ASTM D2974)

Fly ash 2.33 12.34 10.38 1.1Petroleum Contaminated Soil 2.66 8.74 35.8 6.51Marble Powder 2.72 9.69 0.24 1.5

Fig. 2: Grain Size Distributions of Crumb Rubber.



Experimental results

The effect of rubber and plastic concentration and rubberparticle size on properties of asphalt cement Fig. 5a shows that the softening points of the asphaltcement increases with an increase in the amount of rubberand plastic added. In the case of plastic, there is a chemi-cal reaction between the asphalt and plastic. Therefore,plastic modified asphalt cement has a very high softeningpoint. Addition of rubber and plastic reduces susceptibilityto temperature of asphalt cement according to softeningpoints. Fig. 5b shows that the penetration decreases withan increase in the amount of rubber and plastic in theasphalt cement. Asphalt cement with No. 4-20 rubber par-ticle sizes shows higher penetration, whereas asphaltcement with No. 4-200 and No. 20-200 rubber particlesizes shows the lowest penetration. Addition of rubber gen-erally improves the viscosity of asphalt cement. Fig. 5cshows that the ductility of asphalt cement decreases with



Fig. 3: Scanning Electron Microscopy Pictures of : (a) Crumb RubberSample (between No. 40 and No. 60); (b) Plastic Sample.

Table 4: Marshal Stability Test Results of Control Specimens.

Properties Values

Asphalt Content [%] 4.5Bulk Specific Gravity 2.470Void Total Mix [%] 2.33Flow [mm] 2.44Stability [kN] 15.53

Fig. 4: Hydrometer Analyses of Industrial Wastes.



increasing rubber and plastic content. Asphalt cementwith finer than No. 100 rubber particle size shows slightlyhigher ductility, whereas asphalt cement with No. 4-20rubber particle sizes shows the lowest ductility. Asphaltcement with finer than No. 100 and No. 20-200 rubberparticle sizes are more homogeneous than that of No. 4-200 and No. 4-20 rubber particle sizes. Addition of coarserubber particles reduces the penetration and ductility ofasphalt cement. Addition of plastic in the asphalt cementalso decreases the penetration and ductility to around zeroand makes the asphalt cement very hard, stiff and brittle.

The effect of rubber and plastic on asphalt concrete mixtures

Marshall stability and flow test

The Marshall stability test results of control specimens pre-pared with an optimum asphalt cement content of 4.5%are given in Table 4. The variation of Marshall stability andflow values are given in Fig. 6. It was found that while theaddition of rubber decreased the Marshall stability, theaddition of plastic increased it. This is because plastic meltsin the asphalt cement and therefore binds the aggregates.Marshall stability of rubber modified asphalt concrete spec-imens are above the limit value of 8.83 kN (“Standard”1994), except with the addition of 20% rubber betweenNo. 4 and No. 20 sieves. Marshall stability significantlydecreased after adding 10% rubber. Addition of rubberincreased the flow properties of asphalt concrete mixtures.However, the addition of plastic decreased it. When theMarshall stability and flow test standard is applied, the flowvalues of modified mixtures are within the limits of 2 mmand 4 mm (“Standard” 1994). While the flow values ofcrumb rubber particle sizes between No. 20 and No. 200sieves and between No. 4 and No. 200 sieves were withinthe limits, those of No.4-20 rubber particle sizes wereabove the limits. Therefore, this mixture was not suitablefor the asphalt concrete pavement. The addition of rubberabove 10% did not show good results according to theMarshall stability test (Al-Abdul Wahhab & Al-Amri1991).

Indirect tensile strength test

The indirect tensile strength test is very useful in predict-ing long-term flexible pavement performance (Foxworthyet al. 1996). The variations of indirect tensile strength withrubber and plastic content are given in Fig. 7. Indirect ten-sile strength of mixtures decreased as the amount of rubberincreased. Addition of 20% rubber between No. 4 and No.200 sieves decreased indirect tensile strength values by 7%.However, the largest decrease (36%) occurred by mixingrubber particle sizes between No. 20 and No. 200 sieves.This was because of the fine rubber particles in the mix-ture. When the rubber consisted of coarse rubber particles,indirect tensile strength increased. This occurred when therubber particle sizes were used between No. 4 and No. 200sieves. Tensile strength of plastic modified asphalt cementwas increased, with an increase in the amount of plastic.Asphalt cement with 20% plastic increased the indirecttensile strength value by 69%. A chemical reactionoccurred between the plastic and asphalt cement and alsobetween the crumb rubber and asphalt cement, therefore,the strength of specimens increased.



Fig. 5: Effect of Rubber or Plastic Content on : (a) Softening Point; (b) Penetration; (c) Ductility of Asphalt Cement.



Compressive strength test

The compressive strength test results are given in Fig. 8.While additions of 5% and 10% rubber increased thestrength values by 10% and 5% respectively, compared tothe control specimens, addition of 20% rubber decreasedits value by 12%. Addition of rubber increased the straincapacity of specimens. Therefore, addition of rubberincreased the flexibility and toughness. These resultsshowed that the addition of rubber improved the strengthof the pavement, as long as the amount added in the trialdid not exceed about 12%.

Moisture susceptibility test

Damage to asphalt concrete pavements caused by moistureis an important problem. The moisture damage in asphaltconcrete is due to the loss of adhesion or the loss of cohe-sion, but both mechanisms are interrelated (Hicks 1991).It can be seen from Fig. 9a that Marshall stability of rubberand plastic modified and conditioned specimens wereslightly increased and decreased, respectively, compared tothe control specimens. Indirect tensile strength of rubber

and plastic modified and conditioned specimens wereslightly decreased compared to the control specimens (seeFig. 9b). Moisture susceptibility of the plastic modified andconditioned specimens was stronger than that of the rub-ber modified and conditioned specimens. While indirecttensile strength of rubber modified and conditioned speci-mens decreased compared to the control specimens, theMarshall stability of rubber modified and conditioned spec-imens increased. In fact, the Marshall stability of rubbermodified and conditioned specimens should decrease com-pared to the control specimens. Therefore, Marshall stabil-ity did not show a good indication of the strengthvariations of rubber modified asphalt concrete mixtures.However, the indirect tensile strength test showed morereliable results than the Marshall stability test.

The effect of industrial wastes as filler material on asphaltconcrete mixturesStone powder was replaced by fly ash, marble powder, rub-ber powder and petroleum contaminated soil (PCS) as afiller material. These wastes were sieved to pass the No.



Fig. 6: (a) Marshall Stability; (b) Flow Values of Rubber or Plastic Modified Specimens.

Fig. 7: Indirect Tensile Strength of Rubber or Plastic ModifiedSpecimens.

Fig. 8: Compressive Strength of Rubber Modified Specimens.



200 sieve. The Marshall stability and flow test, the indirectstrength test, the compressive strength test and the mois-ture susceptibility test were performed on these industrialwaste modified asphalt concrete mixtures.

Marshall stability and flow test

Marshall stability and flow test results are given in Fig. 10.While addition of rubber significantly reduced theMarshall stability value by 73%, addition of marble powderincreased its value by 10% compared to the control speci-mens. Addition of PCS and fly ash decreased the Marshallstability values by 1% and 6%, respectively. When theMarshall stability and flow test standard is applied, the flowvalues of mixtures were within the limits of 2 mm and4 mm (“Standard” 1994), except for rubber powder modi-fied specimens. The addition of marble powder showed thebest results according to the Marshall stability test.

Indirect tensile strength test

The indirect tensile test results are given in Fig. 11. Whileaddition of fly ash increased the indirect tensile strengthvalue by 1.9%, additions of marble powder and PCSdecreased its values by 0.7% and 25%, respectively, com-

pared to the control specimens. It can be concluded thatPCS negatively affects the asphalt concrete pavement.This is because it consists of bentonite clay and organicmatter. The addition of fly ash showed the best resultaccording to this test.

Compressive strength test

It can be seen from Fig. 12 that addition of marble powderand PCS decreased the compressive strength values by11% and 27% respectively. However, there was no changewith the addition of fly ash. There was a similarity betweenthe results of the unconfined compressive test and theindirect tensile test. Addition of fly ash showed the bestresult for this test.

Moisture susceptibility test

While the addition of fly ash increased the Marshall stabil-ity of conditioned specimens compared to control speci-mens, the addition of other wastes decreased it (Fig. 13a).The addition of wastes decreased the indirect tensilestrength of conditioned specimens (Fig. 13b). The additionof fly ash showed the best results according to the Marshallstability test. However, none of the wastes showed a good



Fig. 9: (a) Marshall Stability; (b) Indirect Tensile Strength of Rubber orPlastic Modified Conditioned Test Specimens and Control Specimens.

Fig. 10: (a) Marshall Stability; (b) Flow Values of Industrial WasteModified Specimens.



result according to the indirect tensile test.

Conclusions

Addition of crumb rubber (1)Addition of rubber increased the softening point and

decreased the penetration and ductility of asphaltcement. Addition of coarse rubber particles disturbedthe homogeneity and also reduced penetration, soften-ing point and ductility of asphalt cement. Viscosity andsusceptibility to temperature of asphalt cement werealso improved.

(2)Addition of rubber decreased the Marshall stability butincreased the flow properties. All Marshall stability andflow values of rubber modified asphalt concrete speci-mens were within the limits of 8.3 kN and 2-4 mm(“Standard 1994”), respectively, except for addition of20% rubber particle sizes used between No. 4 and No.20 sieves according to the Marshall stability and flowtest method. Marshall stability were reduced when theamount of rubber was more than 10%.

(3)Addition of 10% rubber particle sizes between No. 4and No. 20 sieves in modified specimens showed thebest results according to the indirect tensile strengthtest. Indirect tensile strength values of 5% and 10% rub-ber modified mixtures were the same as those of thecontrol specimens.

(4)Addition of rubber increased strain capacity. Therefore,flexibility and toughness were improved. Compressivestrength were reduced when the amount of rubber wasmore than 12%.

(5)While the Marshall stability of conditioned specimenswere slightly increased, indirect tensile strength of con-ditioned specimens decreased by 25% compared to thecontrol specimens. Therefore, indirect tensile testapparently showed more reliable results than theMarshall stability test. Marshall stability test does notshow the decrease in the stability of conditioned speci-mens.

Addition of plastic(1)Addition of plastic significantly increased the softening

point and decreased the penetration and ductility ofasphalt cement. Therefore, susceptibility to temperatureand viscosity of asphalt cement were significantlyincreased.

(2)While the addition of plastic to asphalt cement signifi-cantly increased Marshall stability and indirect tensilestrength, it decreased the flow properties. This isbecause plastic melts when it is mixed with asphalt



Fig. 11: Indirect Tensile Strength of Industrial Waste ModifiedSpecimens.

Fig. 12: Compressive Strength of Industrial Waste Modified Specimens.

Fig. 13: (a) Marshall Stability; (b) Indirect Tensile Strength of IndustrialWaste Modified Conditioned Test Specimens and Control Specimens.





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cement, therefore, stronger mixtures are obtained. Thisis due to the chemical reaction between the plastic andthe asphalt cement. It also makes the asphalt cementvery hard, stiff and brittle.

(3)Addition of plastic significantly increased the indirecttensile strength of specimens.

Using industrial wastes as filler materialAdditions of fly ash and marble powder showed the bestresults among the industrial wastes used in this study.However, addition of rubber powder showed the worst

result among them because of its very low specific gravitycompared to the others. Fly ash and marble powder can besafely used instead of stone powder as a filler material inthe asphalt concrete pavement. While the addition ofpetroleum contaminated soil (PCS) significantly decreasedthe indirect tensile and compressive strength, it did notdecrease Marshall stability. This is because PCS containsbentonite clay and organic matter. It can be concludedthat the indirect tensile test showed more reliable resultsthan the Marshall stability test.

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