Experimental investigation of effect of PP/SBR polymer blends on the moisture resistance and rutting performance of asphalt mixtures

Abstract

Prevention of surface failure in flexible pavements and application of durable asphalt mixtures leads to the design of a high-quality pavements and improvement in safety and confidence of drivers. Moisture susceptibility, or stripping, is a type of failure which results in the separation of binder and aggregate in asphalt mixtures, and consequently intensifies other kinds of failures including fatigue and rutting. Improvement in properties of asphalt mixtures’ components can minimize the failures of road pavements. In such a context, binder modification with polymers is known as an effective method which enhance mixtures’ strengths against common damages. In This study, a blend of two inexpensive polymers has been suggested as binder additive to modify the performance of the asphalt mixtures against moisture. For this purpose, styrene-butadiene-rubber (SBR) and polypropylene (PP) are combined by different ratios 70:30, 50:50 and 30:70, then each of polymer blends were added in 60–70 binder with 3, 4 and 5% of the weight of the binder. Since the styrene butadiene styrene (SBS) polymer is a well-known and effective additive in term of moisture susceptibility of flexible pavements, mixtures containing modified binders with blended polymer (SBR/PP) were compared to mixtures containing SBS modified bitumen with 4% and 5% polymer content. In all samples, 1.5% Nanoclay (by mass) was utilized to increase the stability of polymers in the binder. To evaluate the moisture susceptibility and permanent deformation, Texas boiling test, Marshall stability, Resilient modulus, Indirect tensile strength (ITS) and Dynamic creep tests were carried out on mixture samples modified by polymer blends, mixtures modified by SBS and also an unmodified sample (control mixture). As the experimental results show, by increasing SBR content in asphalt mixtures, the performance of the samples against moisture failure has been improved. Furthermore, among all tested samples, the asphalt mixture containing 5% polymer blends with 70% of SBR Shows the best performence which can be introduced as an economical alternative for mixture with high dosage of SBS.