Natural rubber latex – modified asphalts for pavement application

Abstract

Elastomers are the most utilized modifiers for asphalt products worldwide. In Thailand, natural rubber is currently being used to modify asphalt for pavement throughout the country in order to promote the utilization of this major agricultural product. However, due to limited service life from poor stability of the obtained asphalt mixture, investigation to prolong the stability of the natural rubber-modified asphalt is necessary. This research aims to investigate physical, storage stability, morphology and rheological properties of asphalt using natural rubber (NR), polyphosphoric acid and sulfur as its modifiers. NR is a renewable and ecology friendly elastomer which can use in latex form to avoid severe mixing condition. In this work, small quantity of both PPA and sulfur are proved to be highly effective modifiers working in complementary with the elastomeric system to further enhance stability of the resulting asphalt. The experimental results reveal that when AC 60/70 penetration grade asphalt is modified with 0.6 to 4.5wt% of NR, 1 to 2wt% of PPA and sulfur (based on 100 parts NR) 0.3 to 1.0 wt% using a shear mixer, the penetration of the modified asphalt systematically decreases while its softening points and Brookfield viscosity increase with increasing NR and PPA contents. An addition of sulfur in the asphalt system shows improvement in toughness and tenacity property, as well as storage stability and also promotes compatibility between asphalt and natural rubber. Our results suggest the modified asphalt with 3.2 wt% of NR, 2 wt% of PPA and 0.3 wt% of sulfur (based on 100 parts NR) is a suitable formula to produce asphalt mixture with high stability for pavement application.