Natural rubber latex-modified asphalts for pavement application: effects of phosphoric acid and sulphur addition

This research aims to investigate physical, storage stability, morphology and rheological properties of asphalt modified by natural rubber (NR), polyphosphoric acid and sulphur. NR is used in a latex form to avoid a severe mixing condition. A small quantity of PPA and sulphur are proved to be effective modifiers in addition to NR. It is found that when asphalt is modified with 0.6–4.5 wt% of NR, 1–2 wt% of PPA and 0.3–1.0 wt% sulphur (based on 100 parts of NR), penetration of the modified asphalt systematically decreases while its softening points and Brookfield viscosity increase with increasing NR and PPA contents. An addition of sulphur in the asphalt system shows complementary improvement in its toughness and tenacity. Our results suggest the modified asphalt with 3.2 wt% of NR, 2 wt% of PPA and 0.3 wt% of sulphur is a suitable formula for the road condition in Thailand.