Effect of Sodium Hypochlorite-Activated Crumb Rubber on Rheological Properties of Rubber-Modified Asphalt

Abstract

Crumb rubber modifier (CRM) has been applied widely in modified asphalt production in the pavement industry and demonstrates many performance advantages. Further, its use makes it possible to recycle scrap tires and reduce the consumption of raw materials. However, CRM asphalt mixtures demand higher construction temperatures than do conventional asphalt mixtures because the CRM asphalt binder has higher viscosity, which increases energy consumption, emission of greenhouse gases, and disintegration of the crumb rubber. In this study, sodium hypochlorite (NaClO) was introduced to functionalize the CRM particles’ surface to alleviate these associated problems. The CRM particles’ surface was activated using different amounts of NaClO, and the microscopic morphology of the activated CRM was measured using scanning electron microscopy (SEM). The size characteristics of the two types of CRM (activated and inactivated) were measured using the Brunauer, Emmett, and Teller (BET) test. The Brookfield viscosity at 180°C and rheological properties of CRM asphalt binders with different activated CRM were measured. In addition, the correlation between pore size characteristic and rheological properties was calculated statistically. Subsequently, a rougher surface microscopic morphology was observed for CRM activated with NaClO solution than without. The pore characteristics’ indices (cumulative pore volume, cumulative pore area, most probable pore size, and mean pore size) decreased generally with lower amounts of NaClO and then increased when the NaClO exceeded a certain amount. Using NaClO solution to produce activated CRM can improve both the workability and rutting resistance issues associated with the application of CRM asphalt binder. The test results and correlation analysis indicated that the pore characteristics are a key factor for activated CRM to reduce viscosity values and increase the rutting factor significantly.