Ordering and Steric-Hardening in SBS-Modified Bitumen

Abstract

Styrene−butadiene−styrene (SBS)-modified bitumen shows good cracking resistance at low temperatures. With the knowledge of the microstructure of SBS-modified bitumen being incomplete, the reasons for the low-temperature performance remain partly unclear. In this work, modulated differential scanning calorimetry (MDSC) was used to study the ordering of crystallizable alkanes and that of alkyl aromatics in SBS-modified bitumen. These compounds are responsible, respectively, for the cold-crystallization (CC) and the steric-hardening (SH) visible on the nonreversing heat-flow (NRHF) curves obtained from MDSC. In blends of bitumen with 3, 6, and 10 wt % SBS, CC and SH enthalpies were measured. SBS was found to reduce both the CC and the SH in bitumen, the reduction being disproportionately higher than expected on the basis of polymer concentration. The loss of CC and SH enthalpies demonstrate the reduced capacity of alkanes and alkyl aromatics to order in the presence of SBS.