Effect of Jordanian Oil Shale Fly Ash on Asphalt MixesIbrahim Asi1 and Abdullah Assa’ad2

Abstract: It is estimated that about 40 billion tons of oil shale is available in the southern part of Jordan. Several studies are being carriedout to utilize this source of energy efficiently. Upon direct combustion of this oil shale, more than 50% of its quantity will be left as flyash. Resulting fly ash is considered undesirable and environmentally hazardous. This investigation was conducted to make use of the flyash in the modification of local asphalt mixes. The modification efficiency was evaluated by the improvement in the performance ofprepared asphalt concrete mixes. To carry out this study, enough quantity of oil shale was collected from Al-Lajjoun quarries �about100 km south of Amman, Jordan�. This material was then crushed, sieved, and burned to obtain the fly ash. Chemical and physicalanalyses of the fly ash were then performed. Asphalt concrete mixes having different percentages of fly ash �0, 10, 50, and 100%� as areplacement of the mineral filler, material passing the 0.075 mm sieve, were prepared. These samples were characterized using theMarshall Stability, indirect tensile strength, stripping resistance, resilient modulus, dynamic creep, fatigue, and rutting tests. Test resultswere statistically analyzed and indicated that, in general, the addition of fly ash improved both strength, and water sensitivity of theasphalt concrete mixes. Replacing 10% of the mineral filler by fly ash proved to be the most effective percentage in improving themechanical properties of all the prepared samples.

DOI: 10.1061/�ASCE�0899-1561�2005�17:5�553�

CE Database subject headings: Fly ash; Oil shale; Asphalt mixes; Creep; Stripping; Plastic deformation; Jordan.

Introduction

There are 24 known outcrops and near-surface oil shale depositsin Jordan. These reserves have been estimated to contain amountsexceeding 40 billion tons of oil shale, which is equivalent toabout 3–4 billion tons of crude oil �MEMR 1999�. At the presentannual rate of national primary-energy consumption, these re-serves alone would be capable of meeting Jordan’s energy de-mands for the next millennium. Several studies were carried outto utilize this source of energy efficiently �Mustafa et al. 1993;Hamdan et al. 1995; Hamdan and Azzam 1999; Jaber et al. 1999;Jaber and Probert 2000�.

Direct combustion of oil shale will produce fly ash. It is esti-mated that 50% of the 40 billion tons of oil shale present inJordan shall be left as fly ash �Hamdan and Azzam 1999�. Leftover fly ash is undesirable and is considered environmentallyhazardous.

Fly ash as a by-product of oil shale combustion is known topossess some cementing characteristics �Marcus et al. 1985;Turner 1994�. A study about using the produced fly ash in stabi-lizing swelling soils was performed by Assa’ad �2003�. The studyindicated that addition of fly ash to potentially expansive soils

1Associate Professor, Civil Engineering Dept., Hashemite Univ., P.O.Box 150459, Zarqa 13115, Jordan �corresponding author�. E-mail:asi@hu.edu.jo

2Professor, Civil Engineering Dept., Jordan Univ., Amman 11942,Jordan. E-mail: assaad@ju.edu.jo

Note. Associate Editor: Louay N. Mohammad. Discussion open untilMarch 1, 2006. Separate discussions must be submitted for individualpapers. To extend the closing date by one month, a written request mustbe filed with the ASCE Managing Editor. The manuscript for this paperwas submitted for review and possible publication on March 23, 2004;approved on December 28, 2004. This paper is part of the Journal ofMaterials in Civil Engineering, Vol. 17, No. 5, October 1, 2005.

©ASCE, ISSN 0899-1561/2005/5-553–559/$25.00.

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decreases soil plasticity by decreasing the liquid limit and increas-ing the plastic limit. Katamine �2000� and Suliman and Awwad�2000� used the oil shale as an extender to the asphalt cement.The shale oil binders displayed inconsistent physical properties,which could be attributed to the incompatibility of the oil shalewith the asphalt cement or due to improper blending of the oilshale with the asphalt cement.

The Hashemite Kingdom of Jordan has invested considerableamount of funding in road construction over the past 25 years.Roads, which have been built according to international stan-dards, have shown early signs of distresses due to the harsh en-vironmental conditions and traffic loading �Suliman et al. 2004�.Local asphalt pavement temperatures range between −10°C inthe winter to 55°C in the summer. This wide range of tempera-ture created a need to improve the performance of the asphaltconcrete mixes to minimize stress cracking that occurs at lowtemperatures, and permanent deformation that occurs at high tem-peratures. Daily and seasonal temperature variations in addition tothe growing truck traffic volume, tire pressure and traffic loadinghave increased stresses on asphalt pavements. This has increasedthe demand to modify asphalt mixes. Different methods havebeen utilized to upgrade the properties of asphalt mixes. One ofthe most commonly used procedures is modification by additives.

Many authors have studied the effects of mineral fillers, ma-terial passing sieve #200, on the behavior of asphalt mixes �Ri-chardson 1914; Tunnicliff 1962; Anani and Al-Abdul Wahhab1982; Kandhal et al. 1998�. Mineral fillers include dust from thecrushing and screening of aggregates, lime, Portland cement, andfly ash. Although fillers usually contribute small portion, 5–7%,of the total aggregate mix, they have great effect on the mixproperties. Typically, fillers are used to improve bond betweenasphalt cement and aggregate, lower the optimum asphalt content,increase the density, and increase the stability �Brown et al.1989�. The main reason for using these fillers and some other

types of modifiers is to improve the performance of paving mix-

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ture to meet requirements under prevailing conditions.Another early method of asphalt modification consisted of

mixing two or more asphalt binders of different paving grades orsources. This technique has continued through the years and oftendelivers a satisfactory end product. One major problem with thistechnique is that sometimes asphalt is not chemically compatible.Compatibility cannot be predicted effectively and leads to prema-ture pavement distresses �Anderton 1991�.

Anderton �1991� has listed the following factors, which haveled to increasing interest in asphalt modification:1. The growing amount of traffic related distresses resulting

from escalating traffic demands on all types of asphalt pave-ments. Higher volumes of traffic, heavier loads, and increas-ing tire pressures are characteristics of these traffic-relateddistresses.

2. The increase in the cost of asphalt binders and the trend inrefineries of producing lighter fuels on the account of asphaltproduction.

3. Growing economic pressures that lead to thinner pavementsand differed maintenance.

4. Excess supplies of industrial by-products and waste materi-als. This promotes the idea of converting them into asphaltmodifiers.

5. Continued low-temperature thermal cracking and high-temperature deformation distresses.

Although the original idea of using asphalt modifiers was toget rid of waste materials, the trend is to produce high-tech modi-fiers to obtain specific improvements in asphalt binders �Terreland Epps 1989�. Modifiers have been used in asphalt binders todesign against or to repair pavements from the following dis-tresses: surface defects �raveling and stripping�, structural defects�rutting, shoving, and distortion�, and cracking �fatigue andthermal�.

Terrel and Epps �1989� suggested that modified asphalt–aggregate mixture should achieve the following requirements:1. Higher stiffness at high temperature to resist rutting and

shoving.2. Lower stiffness at low temperature conditions to reduce ther-

mal cracking.3. Lower stiffness at very high temperatures �mixing and com-

paction temperatures� to expedite pumping of the asphaltbinder and mixing and compaction of the asphalt mixture.

4. Increase adhesion between the binder and the aggregate toresist stripping.

Objective

Since fly ash, which is considered undesirable and environmen-tally hazardous, will be produced as a by-product from the directcombustion of oil shale. This investigation was undertaken toevaluate the performance of fly ash modified asphalt mixesthrough laboratory evaluation, and to find the optimum replace-ment percentage of the mineral filler with the fly ash.

Experimental Program

A schematic representation of the experimental program con-ducted in this investigation is shown in Fig 1. The work wasdivided into four phases. Phase I included collection and charac-terization of aggregate, asphalt and oil shale. Asphalt samples

were collected from the asphalt cement-producing refinery in

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Jordan. Physical evaluation of the collected asphalt samples wasconducted and is shown in Table 1. The aggregate selected for thelaboratory work was crushed limestone which was obtained fromAmman vicinity, Jordan. The selected aggregate gradation was inaccordance with the Jordanian Ministry of Public Works andHousing �MPWH� recommended gradation for heavy trafficwearing course �Fig. 2�.

The oil shale used in this research was from Al-Lajjoun quar-ries �about 100 km south of Amman, Jordan�. The oil shale wascrushed, sieved on sieve No. 140 and directly burned at an aver-age temperature of 900°C. The analysis of the oil shale is pre-sented in Table 2 and the chemical analysis of the obtained fly ashis presented in Table 3.

Table 1. Physical Properties of the Used Asphalt Cement

Property Value

AASHTO specificationsfor 60/70 penetration

asphalt

Minimum Maximum

Penetration �0.1 mm� 66 60 70

Flash point �°C� 320 232 —

Ductility at 25°C �cm� 134 100 —

Specific gravity at 25°C 1.032 1.01 1.06

Softening point �°C� 53 48 56

Penetration of residue�% of original�

66 54 —

Weight loss on heating �%� 0.58 0.8

Fig. 1. Flow chart of the experimental program

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In Phase II, Marshall Mix design procedure �ASTM D1559�,currently followed procedure in Jordan for asphalt concrete mixdesign using 4 in. samples, was used to determine the optimumasphalt content. Optimum asphalt content �OAC� was selected toproduce 4% air voids. Obtained OAC was 5.25% AC of total mixweight. At obtained OAC, Marshall Stability, flow, voids filledwith asphalt, and voids in mineral aggregate values were checkedto verify that they are within the specification limits of MPWHfor heavy traffic loads wearing course. Using the obtained OAC,5.25%, 30 asphalt concrete samples from each of the followingmixes were prepared: a mix having 0% fly ash, as the control mix,and mixes having 10, 50, and 100% fly ash as a replacement ofthe mineral filler.

In Phase III, effectiveness of modification was judged by theimprovement in Marshall Stability, indirect tensile strength, resil-ient modulus, rutting, fatigue, creep, and stripping resistance ofprepared samples.

Phase IV focused on selecting the optimum replacement of themineral filler by fly ash.

Table 2. Ingredients Analysis of Al-Lajjoun/Jordanian Oil Shale

PropertyValue�%�

Average oil content 8.9

Ash content 46.6

Organic matter 23.7

Carbon dioxide 16.1

Sulfur 2.5

Moisture content 2.2

Fig. 2. Jordanian Ministry of Public Works and Housing specifiedgradation limits and used gradation

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Results and Discussion

Classification tests were performed on the asphalt cement thatwas used in the study. Results of the performed tests, as indicatedin Table 1, show that the used asphalt can be graded as 60/70penetration asphalt according to AASHTO M 20 specifications.Tests on the oil shale, shown in Table 2, indicate that about half ofthe burned oil shale will be left as fly ash which is consideredundesirable and environmentally hazardous. Table 3 clearlyshows that two thirds of the fly ash is soluble in water, this shallenhance the expected pozzolanic reaction with the aggregateminerals.

Marshall Stability Test Results „ASTM D1559…

From each fly ash percentage, six samples were placed in thewater bath at 60°C. After 30 min immersion in the water bath,three samples from each set were tested for Marshall Stability.The other three samples, from each group, were tested for Mar-shall Stability after 24 h immersion in the water bath. Table 4shows results for the tested samples. From this table, it can beseen that the samples with 10% fly ash, after 30 min immersion inwater bath, have the highest Marshall Stability values, followedby the 0, 100, and 50% fly ash, respectively. Although, there isinconsistency in these results with the fly ash content, the differ-ence between the Marshall Stability values was not notably high.In general, Marshall Stability may not be a good discriminatortest. Table 4 also indicates that increasing the percentage of flyash resulted in decreasing the loss in the Marshall Stability. Thismight be attributed to the pozzolanic cementing nature of the flyash.

Water Sensitivity Test„Lottman Test AASHTO T-283-89…

The improvement in stripping resistance �water susceptibility� ofthe asphalt concrete mixes due to the addition of the fly ash wasevaluated by the decrease in the loss of the indirect tensilestrength �ITS� after immersion in water for 24 h at 60°C, accord-ing to AASHTO T-283 test procedure. The obtained results�Table 5� indicate that the average loss in strength due to waterdamage is reduced by the increase in the quantity of the fly ash.The highest improvement in the ITS loss value was 18% whichwas for the mixes with 100% replacement of the mineral fillerwith fly ash. This value is within the 20% allowable loss limit

Table 3. Chemical and Physical Analysis of the Ash Generated fromBurned Jordanian Oil Shale

Element Fe Mg Na K Al

weight % 1.44 0.53 0.23 0.23 1.52

Insoluble matter �% by weight� 32.39

Loss on ignition �% by weight� 3.81

Unit weight �kg/m3� 698

Specific gravity 2.072

Particle shape Extremely spherical

Color Grey

Particle size range ��m� 10–75

specified in SUPERPAVE specifications �Cominsky et al. 1994�.

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Dynamic Creep Test

The dynamic creep test is a test that applies a repeated pulseduniaxial stress on an asphalt specimen and measures the resultingdeformations in the same direction using linear variable differen-tial transducers �LVDTs�.

The test was performed in accordance with the protocol devel-oped by NCHRP 9-19 SUPERPAVE Models, Draft Test MethodW2 �Witczak et al. 2001�. The applied stress on the specimen wasa feed back haversine pulse. The pulse width duration was100 ms, and the rest period before the application of the nextpulse was 900 ms. The deviator stress during each loading pulsewas 207 kPa, and the contact stress that was applied so that thevertical loading shaft does not lift off the test specimen during therest period was 9 kPa. The test was performed at 40°C. Thespecimen’s skin and core temperatures during the test were moni-tored by two thermocouples which were inserted in a dummyspecimen and located near the specimen under test.

The testing was continued until the maximum axial strain limitreached 10,000 microstrains, or until 10,000 cycles, whicheveroccurred first.

Table 4. Effect of Fly Ash Addition on the Marshall Stabilities

% fly ash

Marshall stability after 30 minimmersion �kN�

Samplenumber Stability Average

0 1 14.48 14.55

3 15.417

5 13.738

10 7 18.135 17.97

9 17.258

11 18.513

50 13 12.97 13.03

15 13.022

17 13.098

100 19 12.501 13.59

21 13.181

23 15.076

Table 5. Effect of Fly Ash Addition on the Loss of Indirect Tensile Stre

% fly ash

ITS—nonconditioned �kPa�

Samplenumber ITS value Average

0 1 947.16 954.97

3 903.60

5 1,014.14

10 7 988.46 989.80

9 931.06

11 1,049.90

50 13 878.02 902.31

15 908.96

17 919.93

100 19 873.45 898.16

21 919.53

23 901.51

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Three samples �100�63.5 mm at 4% air void� from each flyash percentage were tested and the values of the accumulated/permanent and resilient strains at failure, accumulated strain slopeat failure, resilient modulus, creep stiffness, permanent and resil-ient deformations were recorded �Table 6�.

Fig. 3 shows the relationship between the number of cyclesand the axial accumulated permanent deformation for the fourtested groups �0, 10, 50, and 100% fly ash�. It can be noticed that10% fly ash mixes showed the best performance over the othermixes, followed by the 50, 100, and 0% fly ash mixes, respec-tively. Therefore, fly ash, due to its pozzolonic cementing prop-erties, has improved the creep resistance of the asphalt concretemixes. In spite of that, full or 50% replacement of the mineralfiller with fly ash reduced the amount of improvement of thecreep resistance due to the loss of the cohesive and plastic prop-erties of the original mineral filler, which is limestone.

Statistical analysis was performed to study the significance ofthe modification in changing the creep stiffness values, i.e., tocheck if the difference in the obtained creep stiffness values isdue to experimental error or due to the addition of the fly ash. The

Marshall stability after 24 himmersion �kN�

Average lossin Marshallstability �%�

Samplenumber Stability Average

2 8.394 9.17 37

4 9.199

6 9.921

8 11.265 11.44 36

10 11.177

12 11.887

14 9.671 10.74 18

16 10.085

18 12.453

20 11.299 11.96 12

22 11.003

24 13.582

TS�

ITS—after conditioning �kPa�Average

loss in ITS�%�

Samplenumber ITS value Average

2 605.61 652.71 32

4 613.03

6 739.49

8 744.92 757.21 24

10 759.36

12 767.34

14 691.47 697.27 23

16 709.82

18 690.53

20 751.24 739.41 18

22 730.48

24 736.52

ngth �I

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analysis of variance �ANOVA� for the single factor model wasused for this analysis. In general, the purpose of the analysis ofvariance is to test for the significant difference between the meansof variables or treatments ���. The appropriate procedure for test-ing the equality of treatment means is to check the followinghypothesis �Montgomery 1991�:

H0: �1 = �2 = ¯ = �a �1�

Table 6. Effect of Fly Ash Addition on the Creep Properties of the Mixes

Property

Fly ash quantity

0% 10% 50% 100%

Core temperature�°C�

40 40 40 40

Contact stress�kPa�

9.0 9.0 9.2 9.1

Deviator stress�kPa�

207.8 207.8 207.5 207.4

Dynamic load�kN�

1.632 1.632 1.629 1.629

Permanentdeformation �mm�

0.2618 0.1638 0.1929 0.2306

Resilientdeformation �mm�

0.0317 0.0368 0.0336 0.0404

Accumulatedstrain �%�

0.4045 0.2505 0.2930 0.3470

Resilient strain�%�

0.0490 0.0560 0.0515 0.0610

Resilient modulus�MPa�

424.9 371.2 406.2 343.4

Creep stiffness�MPa�

51.4 83.1 73.2 67.6

Fig. 3. Comparison of creep behavior of the different mixes at 40°C

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H1: �i � � j �2�

where �i=variable means. If H0 is true, then there is no differencein treatment means, and if H0 is not true then there is a significantdifference between the treatment means and it is unlikely that thetreatment means are equal.

The ANOVA calculations were performed using theSTATSTICA software �StatSoft 1997�. Statistically the results aresignificant whenever the P level is less than the selected signifi-cance level �S.L.�, which is usually selected to be 5%. This meansthat for 95% S.L., the P level should be less than 0.05 in order toachieve significant effect of any factor. ANOVA analysis of theobtained creep stiffness values indicated that at 5% S.L., differ-ence in the means of the creep stiffness values was significant,i.e., difference is due to the fly ash content.

Resilient Modulus Test, MR „ASTM D4123…

Resilient modulus is the most important variable to mechanisticdesign of pavement structures. It is the measure of pavement re-sponse in terms of dynamic stresses and corresponding strains.Three samples from each fly ash content were tested under thediametral resilient modulus �MR� test at two test temperatures �25and 40°C�. Fig. 4 shows the obtained MR values for all the testedmixes at 25 and 40°C. It indicates that fly ash modification hasimproved the diametral resilient modulus of the modified mixesas compared to the control mix for both test temperatures. Theaverage resilient modulus of the control mix at 25°C was foundto be 3,790 MPa; this value increased to 4,679 MPa for 10% flyash mixes, i.e., 23% increase in the resilient modulus value. Theaverage resilient modulus at 40°C increased from 677 MPa forthe control mix to 984 MPa for 10% fly ash mixes. For the 50,

Fig. 4. Comparison of MR values at 25 and 40°C

and 100% fly ash mixes, there was an increase in the resilient

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modulus values but not as high as the 10% fly ash mixes. This canbe attributed to the same reasons mentioned for the dynamiccreep testing.

Statistical analysis was performed to study the significance ofthe modification in changing the MR values. ANOVA analysis, forboth test temperatures, indicated that at 5% S.L., difference in themeans of the MR values was significant, i.e., difference is due tothe fly ash content.

Fatigue Performance

Samples from all the mixes were tested diametrally under re-peated pulsed uniaxial loading to determine the number of load-ing cycles required to fail the sample. To have a wide range offailure cycles, test samples were tested at different initial tensilestrain levels. At least nine samples from each mix �three at eachinitial tensile strain level� were tested at 40°C. Fig. 5 shows theresults of these tests. In this figure, regression lines were drawnthrough the mean of samples at each strain level. The results showa normal linear relationship between the logarithm of applied ini-tial tensile strain and the logarithm of fatigue life �number ofapplied load repetitions until failure�. The fatigue data were ana-lyzed by running a regression analysis to determine the fatiguerelationship parameters in the following form:

�t = I�Nf�S �3�

where �t=initial tensile strain; Nf =number of load repetitions tofailure; I=antilog of the intercept of the logarithmic relationship;and S=slope of the logarithmic relationship. Regression param-eters for Eq. �3� are shown in Table 7.

Analysis of the obtained fatigue results shows significant im-provement in fatigue life of the mixes with 10% replacement ofthe mineral filler by fly ash, followed by the 50, 0, and 100% flyash, respectively. Therefore, fly ash, due to its cementing proper-ties, has improved the fatigue properties of the asphalt concretemixes. In spite of that, 50% replacement of the mineral filler with

Fig. 5. Comparison of fatigue behavior of the different mixes at40°C

fly ash reduced the improvement of the creep properties. In addi-

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tion, 100% replacement of the mineral filler by fly ash gave fa-tigue life lower than the control mix. This can be attributed to theloss of the cohesive and plastic properties of the original mineralfiller.

Permanent Deformation

Using two vertical LVDTs, the vertical permanent deformationwas simultaneously recorded while running the fatigue tests. Re-sults of the tests performed at a repeated stress of 200 kPa arepresented in Fig. 6. The three stages that the asphalt concretepasses through in rutting testing �densification, steady state andfailure� clearly appear in Fig. 6. The equation of the steady statepart of the permanent deformation curve can be determined usingthe following form:

�p = I�N�S �4�

where �p=accumulated permanent strain; N=number of load rep-etitions; I=antilog of the intercept of the logarithmic relationship;and S=slope of straight line.

Parameters I and S in Eq. �4� were obtained by using thesteady state portion of the permanent deformation experimental

Table 7. Regression Factors for the Fatigue Test

Fly ashcontent�%�

Regression factor Coefficient ofdetermination,

R2I S

0 2,521.7 −0.265 0.764

10 9,434.9 −0.417 0.877

50 6,249.3 −0.374 0.998

100 2,995.3 −0.324 0.934

Fig. 6. Comparison of permanent deformation behavior of thedifferent mixes at 40°C and at 200 kPa dynamic loading

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data in a regression analysis and are shown in Table 8. In com-paring the performance of the different mixes �Fig. 6 andTable 8�, the trend is similar to that of fatigue, i.e., the best per-formance was for the mixes with 10% replacement of the mineralfiller by fly ash, followed by the 50, 0, and 100% fly ash, respec-tively. Therefore, the reasons behind this behavior are similar tothat for fatigue behavior.

This study concentrated on the fly ash smaller than 0.075 mm.Extra precautions have to be considered when processing the flyash to obtain this portion of material. Special collection systemshave to be designed next to the combustion chambers of the oilshale to ease collection and processing of the fly ash. Since fly ashis very fine, it could readily become airborne and cause air qualityproblems. Therefore, fly ash can be combined with a high boilingpoint maltene oil to form pellets which are easier to handle in hotmix asphalt facilities.

Concluding Remarks

This investigation was undertaken with the primary objective toadopt a method to make use of the fly ash, produced as a by-product from the direct combustion of oil shale, in certain civilworks such as modification of the local asphalt mixes. To fulfillthis objective, laboratory evaluation of asphalt concrete mixeswith different replacement percentages of the mineral filler wereconducted. Based on the findings of the experimental results, thefollowing main conclusions can be drawn.1. Direct combustion of the Jordanian oil shale will produce

large quantities of fly ash, which are considered environmen-tally hazardous material.

2. Due to its pozzolanic cementing properties, modifying theasphalt concrete mixes with fly ash improved the mixes re-sistance to water damages. This improvement was propor-tional to the fly ash content.

3. Comparing the strength properties of the tested asphalt con-crete mixes indicated that replacing 10% of the mineral fillerby fly ash was the optimal replacement percentage.

4. Replacement of the mineral filler by fly ash can reach up to50% without imparting the performance properties of the as-phalt concrete mixes.

5. If the main problem with the asphalt mix is stripping, re-placement by fly ash can reach up to 100%. In this case theother mechanical properties of these mixes should bechecked to ensure that they are within specifications.

Acknowledgments

The writers would like to acknowledge the support of the Collegeof Graduate Studies and Scientific Research at Hashemite Univer-

Table 8. Regression Factors for the Permanent Deformation Tests

Fly ashcontent�%�

Regression factor Coefficient ofdetermination,

R2I S

0 0.0329 +0.833 0.997

10 0.0139 +0.813 0.999

50 0.0125 +0.894 0.997

100 0.0089 +1.106 0.999

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sity for funding this research study. Thanks are extended to Eng.Mazen Al-Zou’bi, for his assistance during the experimentalwork.

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