Issue 53

M. Ameri et alii, Frattura ed Integrità Strutturale, 53 (2020) 177-186; DOI: 10.3221/IGF-ESIS.53.15 180 The properties of SBR polymer and rPET, which is produced from shredding recycling bottles are presented in Tab. 3. Property Value Diffractive index 1.4 Density 1.05 Viscosity (@100 ℃ ) 50 gr/(cm.s) Tensile strength (@145 ℃ , 35min, 500mm/min) 20 MPa Conductivity 130.3 µs/cm a) SBR properties Property Value Average molecular weight 30,000-80,000 gr.mol-1 Density 1.4 gr.cm- 3 Melting temperature 255-265 ℃ Glass transition Temperature 70-115 ℃ Young’s modulus 1700 MPa Water absorption (24h) 0.5% b) rPET properties Table 3: Properties of SBR and rPET polymers in this study Sample preparation In order to find the optimum asphalt binder content, the asphalt mixtures were designed and fabricated by using the standard marshal mix design method in accordance with ASTM D1599. Aggregates were heated for 24 h at the temperature of 180 ℃ , then mixed with 140 ℃ binder with different contents. Marshal specimens were fabricated by applying 75 blows on each side of cylindrical samples to simulate heavy-traffic loading [23]. Three similar specimens were used for each binder percentage, to increase the precision of optimum binder content determination. The optimum binder content was determined to be 5.6% based on maximum stability, maximum bulk specific gravity and designed limits including 4 percent air voids, percent voids in mineral aggregates and median of other limits for satisfactory asphalt mixture. Based on previous research, the optimum mixing content of SBR and rPET are 5% and 10% of the weight content of the base bitumen, respectively [24, 25]. In this research study, both additives were replaced as part of the bitumen with portions of 0%, 25%, 50%, 75%, and 100% of their optimum weight values. The additives were blended with bitumen, using a high shear mixer at 175 ℃ for 30 minutes at speed of 5000 rpm [26]. The different modified binders prepared for this research are presented in Tab. 4. Sample Composition N1 base bitumen N2 base bitumen with 5% SBR N3 base bitumen with 3.75% SBR and 2.5% rPET N4 base bitumen with 2.5% SBR and 5% rPET N5 base bitumen with 1.25% SBR and 7.5% rPET N6 base bitumen with 10% rPET Table 4: different modified binder constituents used in this research study R ESULT AND DISCUSSION Penetration Grade Results enetration test is a method to measure hardness and consistency of bituminous materials in accordance with ASTM- D5 [27, 28]. The test is conducted at 25 ℃ .The results of penetration test of base bitumen (control sample) and modified binders are presented in Fig. 1. Based on the test results presented in Fig. 1, it can be seen that modified binders (at all combination levels of SBR and rPET) are stiffer and have lower penetration indicia than the base bitumen. As can be observed from the test results presented in Fig. 1 show that with quantitative increase in the percent weight of SBR and rPET in the additive admixtures the binder penetration value is decreased. P