A rheological study of behavior of polymer-bitumen blends

Abstract

The influence of the elastomer such as SBS and SBR and their mixtures on the structure and rheological properties of blown bitumen B 65 blends, was studied. The crude oil denoted as SEB (Soviet Export Blend) was used to obtain the B 65 sample. Ten PMB samples were produced by modifying the bitumen with the so called polyfunetional additives (PA) which were produced by mixing SBR- and SBS-elastomer and 25/75, 50/50 and 75/25 SBR/SBS mixtures with a fatty acid distillation residue. PA contents in PMB amounted to either 3 or 5 wt %. The PMB samples were obtained by a simple stirring operation (a usual stirrer with 300 r.p.m) and represented the stable homogeneous mixtures. Some standardized examinations and the determination of the dynamic mechanical properties were used for the characterization of the PMB samples. SBR-elastomer lowered the Fraass breaking point slightly more than SBS-elastomer. In PMB samples which contained more SBS- than SBR-elastomer, the softening point increase was the main cause for the broader interval of plasticity. If SBR-elastomer prevailed, Fraass point decrease contributed more to the greater broadness of the interval of plasticity. SBS-elastomer caused a higher increase of the softening point than SBR-elastomer. The elastic recovery measurements showed that even 5 wt % of SBR-elastomer in PMB was not enough to reach the 50% value. This important demand could be satisfied only if the elastomer part of PA contained 50% or more of SBS-elastomer. The master curves of the dynamic viscosity or the storage shear modulus versus reduced frequency were used to examine the influence of the SBR/SBS ratio in PMB samples on their viscoelastic parameters. The Zero shear storage modulus G′ 0 , value of G′ at 20 and 60 °C. the glass transition temperature as a loss modulus peak temperature (G″ peak) and the inflection point of turndown of the modulus G′ at the glass transition region, as well as the flow activation energies and viscosities were determined. Compared to SBR-elastomer, SBS-elastomer caused a greater increase of viscosity and flow activation energies. The presented results showed that a balanced improvement in both the low-and high-temperature thermomechanical properties of PMB was attainable by addition of mixtures of SBS- and SBR-elastomer.