Feasibility Study for Using Waste Tire Rubber in Bituminous Concrete

An experimental programme was undertaken to investigate the performance of rubber modified bituminous mixes by using rubber as an aggregate, bitumen modifier and filler. The research was carried out in three stages. In the first stage, bitumen was modified by blending it with 5, 10, 15 and 20% (by weight of bitumen) crumb rubber (75–150 µ). In the second stage, fine aggregates in bituminous mixes were replaced with 2.5, 5, 7.5 and 10% rubber aggregates (<4.75 mm) whereas coarse aggregates were replaced with 2, 4 and 6% rubber (by weight of aggregates) of similar size (4.75–13.2 mm) by dry process. In the third stage, the mineral filler was replaced with 2, 5 and 8% crumb rubber (by weight of aggregates) passing 75 µ sieve. Marshall mix design was performed for bituminous concrete at different bitumen contents to evaluate the performance of the bituminous mixes having rubber in different proportions. It was observed that penetration and ductility of modified bitumen decreased whereas the softening point, elastic recovery and viscosity increased with the increase in rubber content. When rubber was introduced into the bituminous concrete mix as a fine aggregate mix performance was comparatively better than the mix having coarse rubber aggregates. However, in both cases, stability values showed a declining trend with the increase in rubber content. The optimum bitumen content increased as the percentage of the rubber increased in the bitumen modified and coarse aggregate mixes. Performance of bitumen modified mixes was found to be better as compared to the mixtures where it was used as an aggregate or as a filler.