Construction and Building Materials 70 (2014) 201–209

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Construction and Building Materials

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Asphalt modification using acid treated waste oil fly ash

http://dx.doi.org/10.1016/j.conbuildmat.2014.07.0450950-0618/� 2014 Published by Elsevier Ltd.

⇑ Corresponding author. Address: KFUPM, P.O. Box 1399, Dhahran 31261, SaudiArabia. Tel.: +966 38602235; fax: +966 38604234.

E-mail addresses: maparvez@kfupm.edu.sa (M. Anwar Parvez), hawahab@k-fupm.edu.sa (H.I. Al-Abdul Wahhab), rshawabk@kfupm.edu.sa (R.A. Shawabkeh),ihussein@kfupm.edu.sa (I.A. Hussein).

M. Anwar Parvez a, Hamad I. Al-Abdul Wahhab b, Reyad A. Shawabkeh a, Ibnelwaleed A. Hussein a,⇑a Department of Chemical Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabiab Department of Civil Engineering, King Fahd University of Petroleum and Minerals, Dhahran 31261, Saudi Arabia

h i g h l i g h t s

�Waste oil fly ash (OFA) from powergeneration plants was used to modifyasphalt performance.� OFA was chemically treated with

H2SO4 and HNO3 acids were used tofunctionalize it with carboxylic group(ACOOH).� Functionalization has improved its

dispersion and chemical bondingwith asphalt.� Functionalization was confirmed with

different characterization techniques.� Asphalt modification with treated

OFA proved that acid treatment ofOFA has enhanced the properties ofasphalt mixes.

g r a p h i c a l a b s t r a c t

a r t i c l e i n f o

Article history:Received 10 March 2014Received in revised form 24 June 2014Accepted 16 July 2014

Keywords:Asphalt modificationOil fly ashRheologyPerformance grading

a b s t r a c t

Oil fly ash (OFA) is generated in large quantities from power generation plants through combustion offuel oil. Waste OFA contains more than 80% carbon and can be used to improve asphalt performance.H2SO4 and HNO3 acids were used to functionalize OFA with carboxylic group (ACOOH) to improve its dis-persion and chemical bonding with asphalt. Thermo gravimetric analysis (TGA), FTIR and combined SEM/EDS techniques were used to characterize as-received and treated OFA. Asphalt modification with treatedOFA showed better results than that of untreated OFA. The treated OFA were blended with base asphaltand tested for rheological properties of pure and modified asphalt binders. OFA were used at 2–8% byweight of asphalt binder. Melt state rheology was investigated in ARES rheometer using temperaturesweep, dynamic shear and steady shear rheological measurements. Incorporation of OFAACOOH in themodified asphalt binders showed improvement in binder properties as investigated through steadyand dynamic shear rheology. OFAACOOH modification reduced temperature susceptibility of modifiedasphalt binder and increased the upper grading (performance) temperature. The rutting parameter G*/sind increased linearly with OFAACOOH content of asphalt binder. Activation energy was found todecrease with OFAACOOH content which indicated better resistance to low temperature cracking ofthe modified binder. Asphalt modification with treated OFA proved that acid treatment of OFA hasenhanced the properties of asphalt mixes.

� 2014 Published by Elsevier Ltd.

1. Introduction

Oil fly ash (OFA) is typically a black powder type waste materialthat results from the use of crude and residual oil in powergeneration. OFA is collected in the electrostatic precipitators which

202 M. Anwar Parvez et al. / Construction and Building Materials 70 (2014) 201–209

are installed on boilers burning residual oil for air pollution con-trol. According to a survey of American Coal Ash Association, coalfly ash production by coal fired plants in 2011 was 69.30 milliontons in the United States and 38% of this quantity was recycledand reused in different applications [1]. In Saudi Arabia, there are70 power plants consuming 22 million metric tons of diesel fuel,crude oil and heavy fuel oil and total amount of disposed OFA in2008 was about 240,000 cubic meters. The amount is expected toincrease to 400,000 cubic meters by 2014. These quantities mustbe disposed in an environment friendly way. The main applicationof OFA includes: partial replacement of Portland cement; fillermaterial for polymer, additive to asphalt and cementitious materi-als; stabilizing agent and adsorbent for solutes recovery, solidifica-tion for waste and sludge [2–5].

Additive or filler materials were normally used with asphaltbinders to repair and design against pavement due to the followingproblems: surface defects (raveling and stripping), structuraldefects (rutting, shoving and distortion) and cracking (fatigueand thermal). The effects of mineral fillers, which are materialspassing a sieve size of 0.075 mm, on the behavior of asphalt mixwere studied by many authors [6–10]. Filler materials can changethe mechanical properties of asphalt concrete mixes.

In a recent patent, our research group used untreated OFA (3–10%) in asphalt binder and asphalt concrete mix [11]. Addition ofuntreated OFA improved rutting resistance, stability and modulus.However, the fatigue properties of the mix were poor due to poordispersion of ash which is likely due to the inert nature of the OFAsurface. Surface modification and grafting were widely used in thepolymer literature to improve the bonding between different poly-mers or between polymers and asphalt. Our group used function-alized polymers to improve the compatibility of polymers withasphalt [12,13]. The use of surface modified or functionalizedmaterials is not new to the pavement industry. OFA contains morethan 80% carbon, 7% oxygen, 9% sulfur and the rest are trace metal.

Recently, surface modification of carbon nanotubes (CNT),which resembles OFA in composition, has succeeded in improvingthe dispersion in polymers and improved the interfacial bondingbetween the polymer and CNT [14]. Such success suggests thepotential of improving the dispersion of OFA in asphalt throughsurface modification of OFA. Therefore, it is suggested to use thesame previous CNT surface modification techniques to treat thesurface of OFA. The focus of the present study is on the surfacemodification of OFA through acid treatment to attach a carboxylicgroup (ACOOH) and produce treated OFA (OFAACOOH). Then theinfluence of OFAACOOH on asphalt binder thermo-rheologicalproperties is studied. The authors are not aware of any previousresearch that attempted to use acid treated waste OFA in asphaltmodification.

2. Experimental

2.1. Materials

OFA was collected from Shuaibah power plant of Saudi Electricity Company. Theconcentrated sulfuric acid (H2SO4, 98%) and nitric acid (HNO3, 68%) were suppliedby Sigma Aldrich Company and they were used as-received. Asphalt cement of60/70 penetration grade was obtained from Saudi Aramco Riyadh Refinery.

2.2. OFA functionalization

As-received OFA was washed with water to separate trace oil and some sandparticles. Washed OFA was then dried in the oven at 105 �C to evaporate theremaining water. The OFA was then treated with H2SO4 and HNO3 at a volumetricratio of 3:1. This ratio of acid mixture was determined, in a previous study by ourgroup, to be the optimum composition that produced the highest surface area ofmodified OFA [15]. Our preliminary results (not shown here) also indicated thattreated OFA produced through this formulation showed better viscoelastic proper-ties for OFA–asphalt mixes. A weight of 200 g ash sample was taken into a 3 l glassbeaker and the acid solution was slowly poured into the ash. After 10 min, the ash/

acid mixture turned to a liquid solution. The beaker with OFA/acid solution was putin a hot plate magnetic stirrer assembly. The temperature and speed of rotation ofthe hot plate were set at 165 �C and 100 rpm, respectively. The reaction wasallowed to continue for 12 h to create the carboxylic acid group on the OFA surface.The reactant mixture was then cooled down to room temperature. The mixture wasdiluted with deionized water and filtered using vacuum-filter through a 3 lmporosity filter paper to remove unreacted acid. The filtered OFA was then dried inhot chamber at temperature �90 �C. The chemically treated OFA produced throughthis method is referred to in this manuscript as OFAACOOH.

2.3. FTIR characterization

The chemical structure characterization of as-received OFA and modified OFA(OFAACOOH) were carried by means of FTIR measurement using a Nicolet 6700spectrometer from Thermo Electron™. A sample of 1–2 mg of the OFA and 1.0 gof KBr powder were mixed thoroughly. The resulting mixture was then pressedhydraulically in a Carver press to obtain a thin circular transparent disc. The circulardisc sample was dried in an oven at 100 �C for 2 h to remove any water vapor. FTIRspectra were taken in the range 600–4000 cm�1 at room temperature. The spectralresolution was fixed to 4 cm�1.

2.4. TGA–DSC analysis

The thermo-gravimetric analysis was performed in a Netzsch model STA 449 F3Jupiter� where changes in mass and exothermic/endothermic transitions weremeasured. The instrument was equipped with a PtRh furnace which operates inthe range 25–1500 �C. TGA–DSC experiment was conducted on a small sample ofabout 7–10 mg by using platinum crucibles with Al2O3 liners and pierced lids.Nitrogen gas with a flow rate of 50 ml/min was used to maintain inert environmentinside the chamber. The sample was heated from room temperature to 800 �C at arate of 10 �C/min. The digital resolution of the balance was 1 lg.

2.5. SEM and EDX

The combined SEM and EDX technique was used to assess the qualitative char-acteristics and morphology of as-received and treated oil fly ash sample. SEMmachine from JEOL, model JSM 6400 was used. Fly ash sample was coated with goldto produce a conductive surface. The sample was then viewed on FE-SEM at variousmagnifications to see the surface distribution of the sample. The elemental compo-sition of the ash sample was determined by using Energy dispersive X-ray analysis.

2.6. Sample preparation for rheological testing

High shear blender was used to blend OFAACOOH and pure asphalt. Oil bathwas equipped with blender chamber to maintain constant temperature. Mixingwas done according to the following steps: asphalt was heated in electric oven at145 �C; asphalt sample of about 250–260 g was taken into a steel can and put ina thermoelectric heater; and the temperature of the bath was set to 145 �C. A ther-mocouple was used to monitor the sample temperature. A high speed shear mixturewas dipped into the sample when the temperature reached to 145 �C. The bath tem-perature was adjusted to 145 ± 1 �C and the speed was set to about 1000 rpm. Aknown amount of treated OFA was added gradually to base asphalt. OFA andasphalt were blended for 10 min at high shear to obtain a uniform mixture. After10 min of blending asphalt sample was poured into silicone molds to prepare spec-imens for rheological tests. Sample specimens were kept in a refrigerator at 5 �C.

2.7. Rheological measurements

The effect of OFAACOOH on the modified asphalt binder rheology was investi-gated using dynamic and steady shear rheological tests. Advanced rheometricexpansion system (ARES) rheometer was used to conduct dynamic temperaturestep tests. ARES is a constant strain rheometer which has a motor to apply a con-trolled strain and a heavy transducer (range 2–2000 g for normal force; 2–2000 g cm for torque) is equipped to get the response of the sample. The dynamictemperature step measurements were performed in the range 64–100 �C using par-allel plate geometry of 25 mm diameter. Asphalt sample was put in the lower plateand heated for 5 min at 64 �C. The geometry gap between the platens was set to1.52 mm. The final gap between the platens was auto adjusted to 1.5 mm. Asphaltsample that extruded beyond the platen rim was cleaned using a metal spatula. Thefinal gap (test gap) of 1.50 mm was set when the test chamber temperature hadreached 64 �C. A strain sweep test was performed (not shown here) at a frequencyof 10 rad/s to determine the linear viscoelastic range. All the experiments were per-formed using nitrogen to avoid oxidation during testing. The Orchestrator softwarewas used to calculate the viscoelastic properties of all samples.

Dynamic frequency sweep tests were performed at 60 �C in the frequency range100–0.1 rad/s and a constant strain of 10%. Steady shear rheological tests were con-ducted at 50 �C and a shear rate of 0.01–10 s�1.

M. Anwar Parvez et al. / Construction and Building Materials 70 (2014) 201–209 203

3. Results and discussion

3.1. OFA surface modification

Surface modification of OFA was done according to the proce-dure described in Section 2.2 to introduce carboxylic group. Thecarboxylic group (ACOOH) was successfully attached to the surfaceof OFA and it was detected through different characterization tech-niques such as: FTIR spectra, SEM/EDS analysis and TGA–DSCanalysis.

3.1.1. SEM/EDX analysisThe elemental composition of the ash samples were obtained

through Energy Dispersive X-ray analysis (EDX) as shown inTable 1. The surface morphology of as-received and treated OFAsamples are shown in Fig. 1(a and b). Most of the ash particles werespherical in shape with high porosity. Approximate particle sizedistribution was in the range 10–100 lm. The results of SEM/EDX analysis of OFA particles were used to compute the ratio ofcarbon, oxygen and sulfur in these OFA samples. Oxygen to carbonratio is an indicator of the degree of oxidation before and aftertreatment.

Oxygen to carbon ratio has changed according to the acid treat-ment method. The ratio of oxygen/carbon in ash before treatmentwas 0.087 whereas in the treated ash, it was 0.283. This increase inthe ratio could be attributed to the addition of ACOOH group toOFA surface. Another finding is that, the acid treatment completelyremoves the trace metals such as vanadium, iron, and nickel fromOFA. Acid treatment also increased the ratio of sulfur/carbon. Thiscould be due to the formation of CO2 and CO gases as it was visibleduring the first 30 min of reaction. These gases escaped from ashsample, which decreased the amount of carbon and thus increasedthe relative amount of sulfur.

3.1.2. FTIR analysisThe presence of new functional group in the chemically modi-

fied OFA sample was determined by FTIR technique. Fig. 2(a andb) shows the FTIR test results of as-received and treated OFA sam-ple over the range 4000–600 cm�1. The intensity of the peaks foras-received OFA is very small compared to that of treated OFA.An inset of the main portion of as-received sample spectra showsthat it has three peaks at 2022, 2162.3 and 2183 cm�1. The peakat 2022 cm�1 is assigned to transition metals (Fe and Ni) carbonylcompound whereas the peaks at 2162.3 and 2183 cm�1 are due tothe C„C stress of medial alkyne [16].

Fig. 2(a) shows five major peaks for OFAACOOH at 1216.9,1365.4, 1742.4, 2849.3 and 2917.3 cm�1, respectively. The peakat 1216.9 cm�1 is due to the skeletal vibration of CAC bondwhereas the peak at 1742.37 cm�1 is attributed to the C@O stretch-ing mode of carboxylic acid group [17] indicating the presence ofACOOH group on the surface of treated OFA. The peaks around2849.3 and 2917.3 correspond to the HAC stretch modes of

Table 1Elemental analysis of OFA before and after treatment.

SN Elements Before treatment After treatment

Weight% Atomic% Weight% Atomic%

1 C 79.99 89.40 67.58 77.752 O 7.02 5.89 19.15 16.543 S 8.74 3.66 13.16 5.724 V 1.83 0.48 0 05 Fe 1.07 0.26 0 06 Ni 1.36 0.31 0 0

Total 100 100 100 100

HAC@O in the carboxyl group. The peak at 1365.4 correspondsto the presence of OAH functional group. Therefore, the FTIR studyconfirmed that carboxylic acid functional group was incorporatedon the surface of OFA through acid treatment.

3.1.3. TGA–DSC analysisFig. 3(a and b) presents TGA–DSC results of as-received OFA and

OFAACOOH. Mass changes below 100 �C are due to release ofmoisture from OFA sample. Mass changes around 200–450 �C areattributed to the decomposition of associated organic groups. Theexothermic peak at 234 �C for OFAACOOH sample is due to thedecomposition of ACOOH group. A similar result was also reportedin the literature for the decomposition of ACOOH group [18]. Theendothermic peak at 569 �C corresponds to the oxidation of carbondue to the decomposition of the carboxylic group releasing oxygeninto the chamber of the TGA–DSC system. This confirmed the pres-ence of carboxylic group in the acid treated OFA sample which sup-ports the earlier findings from FTIR analysis.

3.2. Rheology of OFAACOOH/asphalt binders

3.2.1. Temperature sweep measurementsTemperature step tests were performed for all binders in the

range 64–88 �C. Viscoelastic properties such as complex modulus,G* and phase angle, d, were obtained as function of temperature.Rutting resistance of pure and modified asphalt binders are gener-ally estimate by using the parameter G*/sind according to theguidelines of the strategic highway research program (SHRP)[19]. The value of G*/sind for the original sample should beP1 kPa at the possible maximum pavement design temperature.Asphalt binders with higher values of G*/sind are better for hot cli-mate since they will have higher resistance to permanentdeformation.

Fig. 4 shows G*/sind versus temperature for pure asphalt, 4% as-received OFA modified asphalt and 4% OFAACOOH modifiedasphalt binder. The increase in G*/sind for as-received OFA is verysmall compared to that of treated OFA/asphalt binder. Theimprovement of OFAACOOH modified asphalt binder comparedto that of as-received OFA modified binders is due to the fact thattreated OFA has more surface area, better reactivity and compati-bility as it has functional groups (ACOOH, AOH, etc.) on to itssurface.

Fig. 5 shows G*/sind versus OFAACOOH content of asphalt bin-der for different temperatures. It shows that the modification ofasphalt binder with OFAACOOH has increased the rutting resistantsignificantly. A linear relation between OFAACOOH content and G*/sind is observed. Table 2 lists the maximum temperature attainedat G*/sind P 1 kPa. It is mentioned that the maximum local pave-ment temperature for Saudi Arabia is 76 �C for hot summer season[20]. Base asphalt cannot fulfill SHRP criteria as the maximum tem-perature at G*/sind P 1 is 70 �C. So, there is a need for modificationof pure asphalt binder to increase G*/sind to improve rutting resis-tance. It is noticed that addition of 2% OFAACOOH is needed toupgrade the binder performance from 70 �C to 76 �C. As the per-centage of OFAACOOH increases in the binder, the stiffness ofbinders goes up. Therefore, the asphalt modification with treatedOFA is expected to improve the rutting resistance of permanentdeformation and increase the temperature range of its application.

The complex modulus, G* has two components, elastic modulus(G0) and loss modulus (G00). So, G*/sind does not represent the elas-tic behavior of the binder only. Rheological data of temperaturesweep measurement can be quantitatively appreciated by intro-ducing a modification index, IM. Similar analysis was also usedfor SBS modified bitumen [21]. To assess the elastic modificationof the modified binders an elastic modification index was definedas the ratio of two elastic moduli as:

(a) As-received OFA

(b) Acid treated OFA sample

Fig. 1. SEM/EDS analysis of OFA samples.

Fig. 2. FTIR spectrum (a) OFA before treatment and (b) OFA after chemicaltreatment.

204 M. Anwar Parvez et al. / Construction and Building Materials 70 (2014) 201–209

IM ¼Elastic modulus of modified binder

Elastic modulus of pure asphaltð1Þ

The calculated modification index from Eq. (1) has been plottedagainst temperature in Fig. 6 in a semi log plot.

It shows that the viscoelastic properties of treated OFA modifiedasphalt binder increase with respect to temperature. If the value ofIM is higher than 1 then the modified binder has more resistance totemperature deformation. IM increased with both temperature and

OFAACOOH content. IM versus temperature data are well fitted byexponential equation of the following form:

IM ¼ aebT ð2Þ

where a and b are fitted parameter which are listed in Table 3. Thevalues of the parameters increase with the increase in OFAACOOHcontent of the modified binders. It should be noticed that thechange in the modification index within a certain temperaturerange is controlled by the material sensitivity to temperature. So,the slope of the IM values (b) is an indirect indicator of the thermalsensitivity which can be used to describe the influence of tempera-ture on the rheological properties. However, higher IM values alsoindicate that the corresponding sample will be stiff and can crackeasily at low pavement temperature. Hence, the amount ofOFAACOOH content should be optimized to suit both high andlow temperature applications. The above results have shown thattreated OFA contains carboxylic groups on its surface. At the blend-ing condition, high temperature and shear force could cause thedecomposition of the carboxylic group and generate crosslinks withunsaturated molecules that are part of the asphalt binder. Theimprovement of the elastic properties with temperature could bedue to the cross-linking of OFAACOO� with asphalt.

The effect of temperature on the viscosity of asphalt was ana-lyzed using the temperature step data. The well-known Arrheniusequation was used to calculate the activation energy of pure and

(a) As received OFA sample

(b) OFA-COOH samples

Fig. 3. TGA–DSC analysis of OFA sample.

Fig. 4. G*/sind versus temperature for treated and as-received OFA–asphalt binder.

Fig. 5. G*/sind versus OFAACOOH content of asphalt binder for differenttemperature.

Table 2Maximum temperature at G*/sind = 1 kPa for all binders.

Binder # OFA content, % Max. temperature attained, �C @ G*/sind = 1 kPa

OFA as-received OFAACOOH

1 0 69.62 69.622 2 70.90 76.153 4 71.20 81.254 6 74.18 85.255 8 75.09 88.50

Fig. 6. Elastic modification index (IM) as function of temperature for differentamount of OFAACOOH content.

Table 3Model parameters for Eq. (2) for all binders.

OFAACOOH content, % Model parameters

a b R2

2 0.23 0.0371 0.9994 0.57 0.0422 0.9886 0.65 0.0565 0.9948 0.86 0.0696 0.996

M. Anwar Parvez et al. / Construction and Building Materials 70 (2014) 201–209 205

modified asphalt binders. The equation was written in the follow-ing format:

G�

x¼ g� ¼ Ae Ea=RTð Þ ð3Þ

where Ea is the flow activation energy, A is the pre-exponentialterm, and R is the universal gas constant. Asphalt viscosity isstrongly influenced by the activation energy, Ea. Complex viscosityversus 1000/T are shown in Fig. 7 for pure and modified asphaltbinders. The data showed good fit to Arrhenius model. Calculatedvalues of Ea are plotted in Fig. 8. Activation energy for pure asphaltis 113 kJ/mol.

It is observed that addition of OFAACOOH to asphalt reducesthe activation energy of the modified asphalt binder as comparedto pure asphalt. This reduction of activation follows a linear rela-tionship with OFAACOOH content of the binders which is shownin Fig. 8. Activation energy reduction ranges from 4.6% to 27.95%for 2% to 8% OFAACOOH. The maximum percentage of activationenergy reduction is 27.95% for 8% OFAACOOH. Activation energy,Ea was related to the binder thermal susceptibility [22]. Lower acti-vation energies were expected to reduce the thermal susceptibility.

η

, η

Fig. 7. Effect of temperature on complex viscosity for all binders.

Fig. 8. Activation energy as function of OFAACOOH content of the asphalt binders.

206 M. Anwar Parvez et al. / Construction and Building Materials 70 (2014) 201–209

So, from Fig. 8 it was concluded that all modified asphalt binderswould have lower temperature susceptibility than pure asphalt.

3.2.2. Dynamic frequency sweepsDynamic frequency sweep test was conducted at 60 �C and the

frequency was varied from 100 to 0.1 rad/s. A strain (10%) in thelinear viscoelastic range was used. Storage modulus and dynamic

ω

Fig. 9. Dynamic storage moduli G0 function of frequency at 60 �C.

viscosity as function of frequency are shown in Figs. 9–11. G0 asfunction of frequency is shown in Fig. 9 for pure and modifiedbinders at 60 �C. The results are given for 0%, 2%, 4%, 6% and 8%OFAACOOH. The data showed good fit of the five elements Max-well model. The modified asphalt binder has improved storagemodulus, G0, as compared to base asphalt for the whole frequencyrange. The increase in G0 is higher at higher concentrations ofOFAACOOH. G0 is highly sensitive to the morphological state ofa heterogeneous system [23]. The value of G0 of the modifiedasphalt binders is an indication of how much elasticity can beboosted by asphalt modification. The advantage of high G0 is inhigh temperature climates. Higher G0 values at low frequencysuggest better flexibility. The slopes of logG0 versus logx forlow x were calculated and their values are in the range0.49–1.43 for modified binder. Hence, the melt rheology ofOFAACOOH modified asphalt binder suggests that modifiedasphalt binders are expected to show better rutting resistanceat high temperature.

The dynamic viscosity as function frequency at 60 �C is shownin Fig. 10. Data showed good fit to Carreau model. The profile ofg0(x) for pure asphalt showed typical Newtonian behavior overalmost the entire frequency range. However, OFAACOOH modifiedasphalt binder displayed non-Newtonian behavior, which wasmore pronounced at high OFAACOOH concentrations. Similarbehavior was observed for asphalt modification with polymers[11,12,24].

Phase angle versus G* profile is shown in Fig. 11 for all binders at60 �C. This representation is well-known as Black diagram. It ismentioned in literature [25,26] that the reduction of phase angleis an indication of elastic networks or entanglements in the modi-fied binder. It is observed that blending of OFAACOOH with asphaltbinders reduces the phase angle. This behavior is a measure ofimprovement in elastic properties of the binders. This improve-ment in elastic properties can be due to increase in the degree ofcrosslinking and/or interfacial bonding between entanglementsproduced by OFAACOOH and asphalt matrix. The simultaneouseffect of heat shear in the blender could results in several changesin the modified asphalt binder some of which are: (1) decomposi-tion of OFAACOOH group into OFAACOO- and its reaction withasphaltenes and maltenes (2) increase in compatibility ofOFAACOOH and asphalt which could increase the dispersion ofOFA in asphalt matrix (3) change in compositions of asphalt bythermal and mechanical degradation. The combination of thesephenomena can lead to cross-linking or improvement in dispersionthat will eventually enhance the viscoelastic properties of themodified asphalt binders.

ω

η

η

Fig. 10. Dynamic shear viscosity as function of frequency at 60 �C.

δ

δ

Fig. 11. Black diagram representation of asphalt binders at 60oC.

η

η

Fig. 12. Steady shear viscosity function at 60 �C.

Fig. 13. Creep test results for pure modified binder at 60 �C and 100 Pa.

M. Anwar Parvez et al. / Construction and Building Materials 70 (2014) 201–209 207

3.2.3. Steady shear rheologySteady shear rheology was studied to examine the effect of

shear on the viscosity of pure and modified asphalt binders. Thetest was conducted at 60 �C and the shear rate was varied from0.01 to 4 s�1. Fig. 12 presents the shear viscosity for pure andOFAACOOH modified binders. Pure asphalt samples displayed longNewtonian plateau up to the shear rate �2 s�1. A very small widthof Newtonian plateau was observed for OFAACOOH modified bind-ers which were diminishing with the increase in OFAACOOH in themodified binders. Polymer modification of asphalt binders isreported to show similar trends [27]. Carreau model fits this typeof behavior very well. The model equation is given by the followingform:

Table 4Carreau model parameters for steady shear data.

OFAACOOH content Carreau model parameters

Zero-shear viscosity, go, (Pa s)

0 5132 74914 17,7876 108,8008 262,000

g ¼ g0

1þ _c_cc

� �2� �a ð4Þ

where g0 is the zero shear viscosity, _cc is the critical shear rate. Thecritical shear rate is the onset of shear thinning region. This isparameter that related to the slope of shear tinning region. Steadyshear viscosity data were well fitted to the model as shown inFig. 12. The incorporation of OFAACOOH has increased the viscosityof the binder. As the amount of OFAACOOH is increased in the bin-der the Newtonian plateau decreases and the shear thinning regionincreases. This shear thinning behavior can be attributed to thebroad molecular weight distribution which results from the sizeheterogeneity due to the addition of OFA and the possible cross-linking of OFAACOOH and asphalt.

Recently, some researchers reported that he SHRP ruttingparameter G*/sind is not very effective in predicting the ruttingperformance of modified binders [28,29]. Zero shear viscosity(go) has been suggested by many researchers as a possible measurefor the rutting resistance of modified asphalt binders in such situ-ation [30,31]. go was calculated for all binders using Eq. (4) and thevalues are shown in Table 4. The steady shear viscosity increaseswith the increase in OFAACOOH which is in agreement with theprevious dynamic shear data. The increment in go is more pro-nounce at high OFAACOOH content. Also, power law index, n,was obtained and displayed in Table 4. The results show enhance-ment in shear thinning due to the addition of OFAACOOH.

3.2.4. Creep test resultsCreep test was conducted for all binders at 60 �C to assess the

rutting behavior of pure and modified asphalt binder. The appliedpressure was held constant at 100 Pa and the corresponding strainwas measured as function of time. Fig. 13 shows the strain responseas function of time. The results show that addition of OFAACOOH to

Power law index, n Regression coefficient, R2

0.68 0.9790.32 0.999�0.60 0.984�0.75 0.991�0.83 0.995

Fig. 14. Strain at 10 min versus OFAACOOH content.

208 M. Anwar Parvez et al. / Construction and Building Materials 70 (2014) 201–209

asphalt increases the rutting resistance. Fig. 14 represents strain at10 min versus OFAACOOH concentration in the binders. It showsthat strain decreases exponentially with the increase in OFAACOOHwhich supports our previous analysis in Section 3.2.1.

4. Conclusions

OFA was treated successfully by acid solution to incorporatecarboxylic (ACOOH) group to the surface of OFA. The presence ofthe functional group was detected through different techniquessuch as: TGA–DSC, FTIR and SEM/EDS. Dynamic, steady and tem-perature sweep rheological measurements of OFAACOOH/asphaltbinders were carried out to assess the impact of functionalizedOFA on the binder’s rheology. The following conclusions are drawnon the basis of this investigation:

(1) The addition of OFAACOOH significantly increased the visco-elastic properties of the modified asphalt binders. SHRP rut-ting parameter G⁄/sind increases with OFAACOOH contentand it showed linear relationship with OFAACOOH content.The high temperature performance grading was increasedfrom 70 �C to 88 �C with the addition of 8% OFAACOOH to pureasphalt.

(2) Elastic modification index (IM) was developed and the mod-ified binders showed less temperature susceptibility. Anexponential model was developed to fit the modificationindex as function of temperature.

(3) Addition of OFAACOOH to pure asphalt reduced the activa-tion energy. A linear relationship of Ea and OFAACOOH con-tent showed OFAACOOH modification improved lowtemperature behavior of the modified asphalt binders.

(4) Addition of OFAACOOH increased both G0 and g0 as sug-gested by dynamic shear rheology. Black diagram represen-tation of dynamic data proved that an OFAACOOHmodification of the asphalt binder leads to enhancement inthe viscoelastic properties through chemical bonding.

(5) OFAACOOH modification of asphalt binders increased thesteady shear viscosity. Addition OFAACOOH to asphaltdecreases the Newtonian plateau and increases the shearthinning behavior which indicates ease of processing as sug-gested by the results of power law index.

Finally, the chemically treated waste OFA can be utilized in themodification of asphalt binder. It will solve the waste disposalproblem of OFA as well as reduce the amount of asphalt pavementto be used in.

Acknowledgement

The authors thank King Abdul Aziz City of Science and Technol-ogy (KACST) for its support for this research through project #AR-29-101. The authors are thankful KFUPM for supporting thisresearch.

References

[1] American Coal Ash Association. Coal Combustion Product (CCP) Production &Use Survey Report; 2011.

[2] Sinha A, Singh M, Singh S. Study of use of beneficiated pulverized coal fly-ashas filler and rice straw fibers in manufacturing of paper. In: Conference andTrade Show; 2010.

[3] Shawabkeh R, Harahsheh A. H2S removal from sour liquefied petroleum gasusing Jordanian oil shale ash. Oil shale 2007;24:109–16.

[4] Shawabkeh R, Harahsheh A, Al-Otoom A. Copper and zinc sorption by treatedoil shale ash. Sep Purif Technol 2004;40:251–7.

[5] Yeh T, Wu Y, Lee Y. Graphitization of unburned carbon from oil-fired fly ashapplied for anode materials of high power lithium ion batteries. Mater ChemPhys 2011;130:309–15.

[6] Anani B, Al-Abdul Wahhab HI. Effects of baghouse fines and mineral fillers onproperties of asphalt mixes. Transp Res Board 1982;843:57–64.

[7] Asi I, Assa’ad A. Effect of Jordanian oil shale fly ash on asphalt mixes. J MaterCiv Eng 2005;17:553–9.

[8] Kandhal P, Lynn C, Parker F. Characterization tests for mineral fillers related toperformance of asphalt paving mixtures. Auburn: National Center for AsphaltTechnology; 1998.

[9] Karasahin M, Terzi S. Evaluation of marble waste dust in the mixture ofasphaltic concrete. Constr Build Mater 2007;21:616–20.

[10] Zhang H, Yu J, Wang H, Xue L. Investigation of microstructures and ultravioletaging properties of organo-montmorillonite/SBS modified bitumen. MaterChem Phys 2011;129:769–76.

[11] Al-Methel M, Al-Abdul Wahhab HI, Hussein IA. Utilization of heavy oil fly ashto improve asphalt binder and asphalt concrete performance. Patent US8062413 B1; 2011.

[12] Iqbal MH, Hussein IA, Wahhab HI, Amin MB. Rheological investigation of theinfluence of acrylate polymers on the modification of asphalt. J Appl Polym Sci2006;102:3446–56.

[13] Hussein IA, Iqbal MH, Al Abdul Wahhab HI. Influence of Mw of LDPE and vinylacetate content of EVA on the rheology of polymer modified asphalt. RheolActa 2005;45:92–105.

[14] Abbasi SH, Adesina A, Atieh M, Ul-Hamid A, Hussein IA. Rheology, mechanicaland thermal properties of (C18-CNT/LDPE) nanocomposites. Int Polym Proc2013;28:3–13.

[15] Shawabkeh R, Khan MJ, Al-Juhani AA, Al Abdul Wahhab HI, Hussein IA.Enhancement of surface properties of oil fly ash by chemical treatment. ApplSurf Sci 2011;258:1643–50.

[16] Coates J. Interpretation of infrared spectra, a practical approach, inencyclopedia of analytical chemistry. Chichester: John Wiley & Sons Ltd.;2000.

[17] Bikiaris D, Vassiliou A, Paraskevopoulos K, Jannakoudakis A, DocoslisA. Effect of acid treatment multi-walled carbon nanotubes on themechanical, permeability, thermal properties and thermo-oxidativestability of isotactic polypropylene. Polym Degrad Stab 2008;93:952–67.

[18] Abuilaiwi FA, Laoui T, Al-Harthi M, Atieh M. Modification and functionalizationof multiwalled carbon nanotube (MWCNT) via Fischer esterification. Arab J SciEng 2011;35:37–48.

[19] The Asphalt Institute. Performance graded asphalt binder specification andtesting, SP-1. Lexington (KY): The Asphalt Institute; 2003.

[20] Al-Abdul Wahhab HI, Asi I, Ali M. Development of performance-basedbitumen specifications for the Gulf countries. Constr Build Mater1997;11:15–22.

[21] Airy G. Factors affecting the rheology of polymer modified bitumen, polymermodified bitumen-properties and characterization. In: McNally T, editor.Woodhead Publishing in Materials; 2011.

[22] García-Morales M, Partal P, Navarro F, Martinez-Boza F, Gallegos C, GonzálezN. Viscous properties and microstructure of recycled EVA modified bitumen.Fuel 2004;83:31–8.

[23] Kumar SA, Veeraragavan A. Dynamic mechanical characterization of asphaltconcrete mixes with modified asphalt binders. Mater Sci Eng A2011;528:6445–54.

[24] Cho Y, Jeong H, Kim B. Reactive hot melt polyurethane adhesives modified byacrylic copolymer nanocomposites. Macromol Res 2009;17:879–85.

[25] Airey G. Rheological properties of styrene butadiene styrene polymer modifiedroad bitumens. Fuel 2003;82:1709–19.

[26] Cuadri A, García-Morales M, Navarro F, Partal P. Enhancing the viscoelasticproperties of bituminous binders via thiourea-modification. Fuel2012;83:862–8.

[27] Polacco G, Stastna J, Biondi D, Zanzotto L. Relation between polymerarchitecture and nonlinear viscoelastic behavior of modified asphalts. CurrOpin Colloid Interface Sci 2006;11:230–45.

M. Anwar Parvez et al. / Construction and Building Materials 70 (2014) 201–209 209

[28] Shenoy A. Model-fitting the master curves of the dynamic shear rheometerdata to extract a rut-controlling term for asphalt pavements. ASTM J Test Eval2002;30:95–102.

[29] Bahia H, Zeng M, Zhai H, Khatr. Superpave protocols for modified asphaltbinders. In: 15th Quarterly progress report for NCHRP project 9–10, NationalCooperative Highway Research Program, Washington: DC; 1999.

[30] Binard C, Anderson D, Lapalu L, Planche J. Zero shear viscosity of modified andunmodified binders. In: Proceedings of the 3rd Eurasphalt & EurobitumeCongress, Vienna; 2004.

[31] Phillips M, Robertus C. Binder rheology and asphalt pavement permanentdeformation; the zero shear viscosity. Strasbourg: Eurasphalt & EurobitumeCongress; 1996.