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2 Construction and Building Materials 25 (2011) Contents lists available at ScienceDirect Construction and Building Materials journal homepage: Properties of Portland cement-modified asphalt binder using Superpave tests Ghazi G. Al-Khateeb *, Nabil M. Al-Akhras Department of Civil Engineering, Jordan University of Science and Technology, P.O. Box 3030, Irbid 22110, Jordan article info abstract Article history: Received 21 January 2010 Received in revised form 26 April 2010 Accepted 19 June 2010 Available online 14 July 2010 Keywords: Asphalt binder Additives Cement Superpave Dynamic shear rheometer Rotational viscosity Stiffness G Complex shear modulus This study investigates the effect of cement additive on some properties of asphalt binder using Superpave testing methods. Six cement-to-asphalt (C/A) ratios were considered in the study: 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30 by volume of asphalt binder. The experimental tests that were conducted in the study included the Superpave rotational viscosity (RV) test and the dynamic shear rheometer (DSR) test. The RV test was conducted at the Superpave-specified high temperature of 135 C that represents the average mixing and laydown temperature, and at seven different rotational speeds of 5, 10, 20, 30, 50, 60, and 100 rpm. On the other hand, the DSR test was conducted at four test temperatures of 58, 64, 70, and 76 C; one lower and two higher than the Superpave high performance grade (PG) temperature of the asphalt binder used in the study (PG 64). The loading frequency used in the DSR test was 10 rad/s (1.59 Hz) as specified by the Superpave system. Results of the study showed that the addition of Portland cement to asphalt binders increased the rotational viscosity (RV) of asphalt binders at 135 C and different rotational speeds. The C/A ratio of 0.15 was found to be the optimum ratio that achieved a balanced increase in the rotational viscosity and the value of the DSR G /sin d rutting parameter of asphalt binders. The C/A ratio had insignificant effects on the Newtonian behavior, the phase angle (d), and the elastic behavior of asphalt binders. The increase in C/A ratio increased the stiffness of asphalt binders represented by the complex shear modulus (G ) value. The increase in the C/A ratio improved the rutting parameter, G /sin d value, at all temperatures. The increase in C/A ratio improved the Superpave high PG temperature (the high temperature at which the asphalt binder passed the Superpave criteria for G /sin d value). It was also shown that the best function that described the relationship between each of RV, G, and G /sin d and the C/A ratio was the exponential function with high coefficient of determination (R 2 ). Ó 2010 Elsevier Ltd. All rights reserved. 1. Background Portland cement and asphalt are adhesive binders usually used for Portland cement concrete and hot-mix asphalt mixtures. Portland cement may be used as a filler or additive to improve many properties of asphalt binders and hot-mix asphalt mixtures. Many additives such as polymer, lime, styrene, fibers, and rubber were used previously by many researchers to improve the properties of asphalt binder and hot-mix asphalt [23,15,13,7]. The inclusion of polymers (such as SBS, SBR and polyethylene) to asphalt showed to improve the performance of asphalt mixtures. Polymer modified pavement exhibited higher resistance to rutting and thermal cracking, and reduced fatigue damage, stripping, and temperature susceptibility. Polymer-modified asphalt binders showed high performance at critical locations such as intersections of busy streets, airports, vehicle weigh stations and race tracks [23]. * Corresponding author. Tel.: x22129, 22198; fax: address: ggalkhateeb@just.edu (G.G. Al-Khateeb). URL: (G.G. Al-Khateeb). Cement may be used as additive with emulsified asphalt mixtures. Superplasticizer is usually used in the mixing procedure to facilitate mixing the cement and the emulsified asphalt. The cement hydrated with the water present in the emulsified asphalt. Using cement with emulsified asphalt enhanced many properties such as strength and durability of asphalt concrete mixtures [16,12]. Yildirim [23] used a design method for determining the alteration level of asphalt binders using waste toner. The asphalt binder design parameters included blending time, performance grading, storage stability, mixing and compaction temperature calculations. The test results indicated that the stiffness of the modified binder increased with the increase of the toner content. Black carbon was utilized as filler by Rostter et al. [18]. They concluded that the black carbon became part of the asphalt binder and completely dispersed in the asphalt mastic. The modified asphalt was found to have higher viscosity compared to the reference asphalt. The addition of sulfur to the asphalt binder was studied by Garrigues and Vincent [8] and Al-Sofi and Sarsam [1]. Garrigues and Vincent [8] investigated the influence of sulfur addition on some properties of the modified asphalt. The viscosity of the /$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi: /j.conbuildmat

3 G.G. Al-Khateeb, N.M. Al-Akhras / Construction and Building Materials 25 (2011) sulfur-modified asphalt was found lower compared to the reference asphalt. Al-Sofi and Sarsam [1] concluded that the amount of sulfur added had a substantial effect on the properties of modified asphalt. The penetration and ductility decreased and the softening point increased of the sulfur-modified asphalt with the increase of sulfur content. Takamura and Heckmann [19] found that using 3% SBR latexmodified asphalt improved remarkably the rutting resistance of asphalt concrete pavements. Styrene ethylene butadiene styrene (SEBS)-modified asphalt with kaolinite clay (KC) was investigated by Ouyang et al. [17]. They concluded that the SEBS/KC ratio had a large effect on the high temperature storage behavior. The effect of using Portland cement and lime as additives on the properties of cold in-place recycled mixtures with asphalt emulsion was investigated by Niazi and Jalili [15]. The Portland cement was utilized in powder form and lime was used as hydrated lime in powder form as well. The results of the study demonstrated that the Marshall stability, resilient modulus, tensile strength, resistance to moisture damage, and resistance to permanent deformation increased with the increase of lime and Portland cement. A study on the inclusion of chromium-tanned leather waste to the cold asphalt layer was investigated using the dry mix by Krummenauer and Andrade [11]. The results of the study showed that inclusion of 0.3% of leather sawdust increased the engineering properties of asphalt mixes and minimized the cracking of pavement surface layer. The utilization of various plastic wastes containing high density polyethylene (HDPE) as bitumen modifier in asphalt concrete mix was investigated by Hinislioglu and Agar [9]. The effect of mixing time, mixing temperature and different contents of HDPE were investigated on the Marshall stability, flow and Marshall quotient (stability to flow ratio). It was concluded that waste HDPE-modified asphalt binder provided improved performance against permanent deformations due to the high stability and Marshall quotient. Vural Kok and Yilmaz [21] studied the effect of using lime and SBS on moisture sensitivity resistance of hot-mix asphalt. The asphalt binder was modified with 2%, 4% and 6% SBS. The lime was used as 2% by weight of total aggregate as filler. The properties investigated included dynamic shear rheometer (DSR) properties, rotational viscosity (RV), Marshall stability, stiffness modulus, indirect tensile strength, and moisture susceptibility. The test results showed that the SBS modified binder with lime improved the stability, stiffness, and strength characteristics of hot-mix asphalt. Specimens incorporating 2% lime and 6% SBS showed the highest stiffness modulus (2.3 times higher than reference specimens). The effect of oil shale ash, rubber ash, husk ash, and polyethylene on the properties of asphalt binder was investigated by Khedaywi and Abu-Orabi [10]. Asphalt binder was prepared by adding 5%, 10%, 15% and 20% oil shale ash, rubber ash, husk ash, and polyethylene to the asphalt binder. Penetration, ductility, softening point, and specific gravity for the modified binder were investigated. The results of the study showed that the penetration and ductility for the modified binder decreased with the increase of these additives in the modified binder. The specific gravity increased with the increase of the added amount of ashes and decreased with the added amount of polyethylene in the modified binder. Additionally, the softening point of the modified binder increased with the increase of the additives in the modified binder. The incorporation of waste rubber in hot-mix asphalt was investigated by many researchers [14,22,6,20]. The studies showed that the rubber content has a significant effect on the performance of asphalt mixtures. Additionally, inclusion of waste tire rubber in asphalt mixtures improved the rutting resistance, reduced the resilient modulus values, and improved the fatigue life of the modified mixtures. Based on the literature survey conducted in this study, no previous studies were conducted on the properties of Portland cement-modified asphalt binder using selected Superpave tests. This study investigates the effect of cement additive on the properties of asphalt binder using Superpave testing methods under many experimental parameters including cement-to-asphalt ratios of 0.00, 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30, different test temperatures, several loading frequencies, and two Superpave tests (RV and DSR). 2. Superpave overview Superpave stands for SUperior PERforming asphalt PAVEments. Superpave is the outcome of the asphalt research portion of a 5- year, $150 million applied research program between 1987 and 1992 to improve the performance, durability, safety, and efficiency of the United States (US) highway system. The program was called the Strategic Highway Research Program (SHRP). One of the major developments in the resulting Superpave system was performance grading (PG) system of asphalt binders, and new asphalt binder tests and specifications. The Superpave asphalt binder performance grading system provides more accurate and precise classification for asphalt binders with minimum overlap between the different grades. In the Superpave system, prevailing climatic and environmental conditions as well as the temperature range at a particular site are considered. Short-term aging and long-term aging that normally take place during mixing and laydown, and during the service life of asphalt pavements, respectively, are simulated as well. Tests and specifica- Fig. 1. Rotational viscosity test containers and asphalt sample.

4 928 G.G. Al-Khateeb, N.M. Al-Akhras / Construction and Building Materials 25 (2011) tions of asphalt binders have aimed at including both unmodified as well as modified asphalt binders, and the evaluation process is based on pavement performance. 3. Test materials and preparation of samples The original (fresh) asphalt binder that was used in this study is a 60/70-penetration grade asphalt binder (PG refers to the Superpave performance grade) obtained from Jordan Petroleum Refinery (JPR). The Portland cement material was also obtained from a local source. The asphalt-cement mastics were prepared according to the cement-to-asphalt (C/A) ratios: 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30 by volume of asphalt binder. Each mastic was prepared using mechanical mixer at the mixing temperature range of the asphalt binder ( C) that was determined based on the American Society for Testing and Materials (ASTM) temperature viscosity relationship. Two rotational viscosities at 135 C and 160 C are needed to obtain the mixing temperature range of asphalt binder from this chart. Rotational viscosity (RV) test samples were prepared following the procedures described in Refs. [3,4]. Enough material from the original asphalt binder and from each of the asphalt cement mastics was heated until it became sufficiently fluid to pour. The rotational viscosity test container was then filled with the asphalt material to about 1 2 cm below the top of the container (Fig. 1) to avoid asphalt overflow when the RV spindle is lowered into the container. Dynamic shear rheometer (DSR) test samples were prepared according to the procedures described in Refs. [2,5]. Silicon molds having a diameter of 25.0 mm as shown in Fig. 2 were used to fabricate the DSR test samples. The asphalt binder (or asphalt-cement mastic) was heated until it became sufficiently fluid to pour. Then it was poured into the silicone mold to get the required DSR test sample (Fig. 2). The next two sections of this paper present the methodology used in this study and the specifics about the rotational viscosity test and the DSR test, respectively. The rotational viscosity (RV) test was conducted for the original asphalt binder (cement-to-asphalt ratio = 0.0) and the six different asphalt cement mastics having cement-to-asphalt (C/A) ratios of 0.05, 0.10, 0.15, 0.20, 0.25, and 0.30 by volume of asphalt binder. In the rotational viscosity (RV) test (Fig. 3), a cylindrical spindle with a specified diameter and effective length rotates inside a container filled to an appropriate height with the asphalt material at a specified speed (Fig. 4). The torque required to maintain this constant rotational speed (20 rpm as specified in Superpave) is measured. The shear strain rate and the torque are converted into dynamic (rotational) viscosity as described in the following equations: s ¼ T 2pR 2 s L c ¼ x 2 ðr 2 c R2 s Þ g ¼ s c 2-R2 c R2 s where s is the shear stress (N/cm 2 ); T the torque (N m); L the effective spindle length (m); R s the spindle radius (m); c the shear strain rate (s 1 ); x the rotational speed (rad/s); R c the container radius ð1þ ð2þ ð3þ 4. Rotational viscosity (RV) test Fig. 3. Superpave rotational viscosity (RV) test device. Applied Torque Spindle Asphalt Sample Sample Chamber Fig. 2. DSR silicon molds with test samples. Fig. 4. Concept of rotational viscosity (RV) test.

5 G.G. Al-Khateeb, N.M. Al-Akhras / Construction and Building Materials 25 (2011) Table 1 RV testing matrix. C/A a ratio , 0.05, 0.10, 0.15, 0.20, 0.25, 0.30 Temperature ( C) Rotational speed 7 5, 10, 20, 30, 50, 60, 100 (rpm) Readings 5 Total = 245 a Rotational Viscosity, RV (mpa.s) C/A = cement-to-asphalt ratio by volume of asphalt binder. 2,000 1,600 1, Shear Rate, γ (rad/sec) (m); x the radial location where shear rate is being calculated (m); in this case it is equal to the radius of the spindle (R s ) because the viscosity is being determined at the surface of the spindle. g is the dynamic (rotational) viscosity (Pa s). The RV test was conducted at 135 C according to the Superpave specifications. This temperature represents the average mixing and laydown temperature for hot-mix asphalt (HMA). Different rotational speeds in the range of rpm were used to investigate the Newtonian behavior of the asphalt binder with the existence of the Portland cement material. Rotational speeds of 5, 10, 20, 30, 50, 60, and 100 rpm were used in the RV test. The testing matrix for the RV test is shown in Table 1 below: The rotational viscosity (RV) values for the different asphaltcement mastics were plotted versus the shear strain rate (c) as shown in Fig. 5. The effect of rotational speed or shear rate on the rotational viscosity was insignificant particularly at higher shear rates and low C/A ratios, i.e., the rotational viscosity was approximately steady with the shear rate for the same C/A ratio. However, there was a slight decrease in the rotational viscosity with the shear rate at values lower than 30 rad/s and for C/A ratios higher than For instance, the values of percentage decrease in the RV as the shear rate increased from about 3 to 30 rad/s were 3%, 4%, and 4% for C/A ratios of 0.20, 0.25, and 0.30, respectively. This increase was statistically insignificant at the 5% significance level (95% confidence interval). In general, it can be concluded that the asphalt binder behaved like a Newtonian fluid (the viscosity is constant at different shear rates, i.e., the relationship between the shear stress and the shear rate was linear) even with the addition of the Portland cement material up to a C/A ratio of On the other hand, there was a significant increase in the rotational viscosity with the increase in the C/A ratio from 0.00 to 0.30 at a rotational speed of 20 rpm (shear rate = 12.2 rad/s). This increase was 270% and it was statistically significant at the 5% significance level. In the Superpave system, a higher viscosity value is required for the asphalt binder used in HMA to minimize the rutting or permanent deformation that occurs in asphalt pavements; Fig. 5. Rotational viscosity versus shear rate at 135 C for different C/A ratios. Rotational Viscosity (mpa.s) 2,000 1,600 1, y = e x R 2 = however, in Superpave, there is a maximum limit for the rotational viscosity value at 135 C, that is 3 Pa s = 3000 mpa s = 3000 cp (centi-poise) to avoid cracking in asphalt pavements. Consequently, the RV results obtained in this study can be optimized to provide the best outcome desired in HMA construction. Fig. 6 shows the relationship between the rotational viscosity and the C/A ratio at a rotational speed of 20 rpm (shear rate = 12.2 rad/s). The best-fit function (model) that described this relationship was the exponential function with a high coefficient of determination (R 2 ) of A 0.15 C/A ratio provided a significant increase of 75.4% in the rotational viscosity at a rotational speed of 20 rpm and at the same time achieved the Superpave specifications (a maximum of 3000 cp or mpa s). Although the rotational viscosity increased at higher C/A ratio, the optimum value of C/A ratio that is considered economical and improves the rotational viscosity is Dynamic shear rheometer (DSR) test The dynamic shear rheometer (DSR) (Fig. 7) applies a shearing force to a thin asphalt disc (Fig. 8) sandwiched between two plates; the lower plate is fixed, and the upper plate oscillates back and forth across the asphalt sample at a frequency of 10 rad/s (1.59 Hz) to create the shearing action. In the DSR test, the value of the complex shear modulus (G ) and the phase angle (d) of the tested asphalt material are measured. By measuring the complex shear modulus of the asphalt material, the total complex shear modulus value as well as its elastic and viscous 855 1,100 1,550 1, C/A Ratio Fig. 6. Rotational viscosity at 135 C and 20 rpm versus C/A ratio. Fig. 7. Superpave dynamic shear rheometer (DSR).

6 930 G.G. Al-Khateeb, N.M. Al-Akhras / Construction and Building Materials 25 (2011) components are determined. The phase angle is the time lag between the applied shear stress and the resulting shear strain converted into degrees according to Eq. (7) below: s max ¼ 2T pr 3 c max ¼ hr h jg j¼ s max c max d ¼ 360ðtÞðf Þ Fig. 8. Asphalt sample discs being prepared in rubber molds. where s max is the maximum applied shear stress; T the maximum applied torque; r the radius of binder specimen (either 12.5 or 4 mm); c max the maximum resulting shear strain; h the deflection (rotation) angle; h the specimen height (either 1 or 2 mm); G the complex shear modulus; d the phase angle ( ); t the time lag (s); and f is the loading frequency (1.59 Hz). Fig. 9 explains the two components of the total complex shear modulus value of the asphalt material. G cos d is the elastic portion of the material and G sin d is the viscous portion of the material. For purely elastic materials, the phase angle (d) is 0, and hence G cos d = G, and for purely viscous materials, the phase angle (d) is equal to 90, and therefore G sin d = G. The DSR test was conducted at a frequency of 10 rad/s (1.59 Hz) and four test temperatures: 58, 64, 70, and 76 C at 6 C increment similar to the increment used in the Superpave grading system for ð4þ ð5þ ð6þ ð7þ asphalt binders. High temperature properties of the asphaltcement mastics were obtained. However, low-temperature properties of the asphalt-cement mastics were not included due to the fact that in Jordan distresses related to high temperatures are the most common distresses that typically occur in asphalt pavements and low-temperature cracking is not a common distress for asphalt pavements in Jordan. The complex shear modulus (G ) value and the phase angle (d) value were obtained for all the C/A ratios at the four test temperatures. The testing matrix for the DSR test is shown in Table 2 below. The DSR G values obtained for the asphalt-cement mastics at the different temperatures were plotted with the C/A ratio as shown in Fig. 10. In this figure it is clear that the G value increases exponentially with the increase in the C/A ratio. The function that best fitted the data was the exponential function. Table 3 shows the exponential function (model) obtained for the relationship between G value and C/A ratio at each test temperature. The effect of the C/A ratio on the phase angle (d) of the asphalt mastic was illustrated in Fig. 11. It is obvious that the phase angle (d) is not affected significantly by the increase in the C/A ratio. In other words, the elastic behavior of the asphalt material remains the same with the addition of the Portland cement material. In the Superpave system, the parameter that is believed to correlate highly with rutting (permanent deformation) of asphalt pavements is the G /sin d value. The Superpave specifications specify a minimum value of 1.0 kpa for the G /sin d of original asphalt Table 2 DSR testing matrix. C/A ratio , 0.05, 0.10, 0.15, 0.20, 0.25, 0.30 Temperature ( C) 4 58, 64, 70, and 76 Frequency, rad/s 1 10 (1.59) (Hz) Replicates 3 Total =84 G* Value (Pa) C 64C 70C 76C Viscous Portion = G * sinδ C/A Ratio Total Complex Shear Modulus = G * Fig. 10. G value versus C/A ratio at different temperatures. Phase Angle = δ Elastic Portion = G * cosδ Fig. 9. Complex shear modulus and its two components. Table 3 Relationship between G * value and C/A ratio. Temperature ( C) Model R 2 Value 58 G value = e 3.86 (C/A) G value = e 3.64 (C/A) G value = e 3.60 (C/A) G value = e 3.68 (C/A) 0.98

7 G.G. Al-Khateeb, N.M. Al-Akhras / Construction and Building Materials 25 (2011) δ (Degrees) C/A Ratio Fig. 11. Phase angle (d) versus C/A ratio at different temperatures. binders at the high performance grade temperature. The G /sin d values were plotted against the C/A ratios at the different temperatures as shown in Fig. 12. A similar relationship to the G value-c/ A ratio relationship was obtained in this case. The exponential function was found the best function to describe this relationship with a high coefficient of determination (R 2 ). The exponential functions (models) obtained at the four test temperatures are summarized in Table 4. The Superpave criterion of the G /sin d value of 1.0 kpa minimum was displayed by the dashed horizontal line in Fig. 12. The 58 C and 64 C curves passed the Superpave minimum requirement of the G /sin d value at all C/A ratios including the 0.00 ratio. On the other hand, the 76 C curve failed to meet the minimum requirement of the G /sin d value at all C/A ratios. However, the 70 C curve passed the criterion of the G /sin d value at C/A ratios of 0.15 and higher. The cost of the mastic of the asphalt binder with Portland cement increases with the increase of the C/A ratio. Even though at higher C/A ratios, the 70 C curve passes the Superpave criterion of the G /sin d value, the cost of the mastic increases. Therefore, the C/A ratio of 0.15 represents the optimum value that meets the Superpave criterion and at the same time is considered economical. In general, the addition of the Portland cement to the asphalt material improves the G /sin d value at all temperatures. In G*/sinδ Value (kpa) C 64C 70C 76C 58C 64C 70C 76C C/A Ratio Fig. 12. G /sin d versus C/A ratio at different temperatures. Table 4 Relationship between G /sin d value and C/A ratio. Temperature ( C) Model R 2 Value 58 G /sin d = e 3.87 (C/A) G /sin d = e 3.65 (C/A) G /sin d = e 3.60 (C/A) G /sin d = e 3.68 (C/A) 0.98 Superpave Criterion addition to this, the Portland cement improves the high performance grade temperature of asphalt binders; i.e., asphalt binders mixed with Portland cement can pass the Superpave specifications for G /sin d value at higher temperatures. Consequently, hot-mix asphalts with high rutting resistance are produced as a result of the addition of Portland cement at relatively high pavement service temperatures such as 70 C. 6. Conclusions and recommendations Based on the analysis and results of the study, the following conclusions and recommendations are drawn: 1. The addition of Portland cement to asphalt binders increased the rotational viscosity (RV) of asphalt binders at 135 C and different rotational speeds. 2. The C/A ratio had insignificant effect on the Newtonian behavior of asphalt binders. 3. The increase in C/A ratio increased the stiffness of asphalt binders represented by the complex shear modulus (G ) value. 4. The effect of the C/A ratio on the phase angle (d) and the elastic behavior of asphalt binders was insignificant. 5. The increase in the C/A ratio improved the Superpave rutting parameter, G /sin d value, at all temperatures. 6. The increase in C/A ratio improved the Superpave high performance grade temperature (the high temperature at which the asphalt binder passed the Superpave criteria for G /sin d value). 7. The cement-to-asphalt (C/A) ratio of 0.15 was found to be the optimum ratio that achieved a balanced increase in the rotational viscosity and in the value of the DSR G /sin d rutting parameter of asphalt binders. 8. The best function (model) that best described the relationship between each of RV, G, and G /sin d and the C/A ratio was the exponential function with high coefficient of determination (R 2 ). 9. 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