Prediction of Dynamic Modulus for Elastomer-Modified Asphalt Concrete Mixes at Desert Environment

Two types of elastomeric polymers commonly used in gulf area are selected to modify the asphalt concrete mixtures produced from local materials that can serve at high temperatures and very heavy traffic loads. These polymers are styrene/butadiene/styrene (SBS), crumb rubber (CR). Because of significant contribution of asphalt binder on the performance of the mix at high temperatures, the objective of the study is to predict the dynamic moduli of asphalt concrete mixtures having polymer-modified binders satisfying the latest performance grading (PG ⁺). Results showed that 5–10% of CR-modified binders and 2% of SBS-modified binders have elastomeric properties only at temperatures lower than 58∘C. While 6% SBS-modified binder have shown elastomeric behavior at any temperature between 58 and 76∘C. In the case of 4% of SBS-modified sample; the elastomeric properties are affected when testing temperature is above 67∘C. It is concluded that PG 70(V) grade can be obtained by adding at least 3.9% of SBS, while 5.2% of SBS is required to reach PG 76(V) grade. In case of CR-modified binders, adding a minimum amount of 12.1 and 12.9% of CR is required to achieve the PG ⁺ grade of PG 70(V) and PG 76(H), respectively. The measurement of dynamic modulus | E^∗| values of modified asphalt concrete samples was conducted utilizing the asphalt mixtures performance tester (AMPT) then the results were used to create master curves using symmetrical sigmoidal model at any given performance grade of the asphalt binder in terms of polymer type and content.