The Effects of Waste Tire Rubber on Penetration, Softening Point, Viscosity, Ductility, Flash Point, Specific Gravity, Solubility and Aging of Bitumen Used In Kenya

This study was carried out to assess the effect of rubber on conventional bitumen used in road construction in Kenya. This study aimed at characterizing the effects of modifying bitumen with waste-crumbed rubber. The properties of penetration, softening point, viscosity, ductility, solubility, flash point,specific gravity and aging characteristics of bitumen were analysed. The samples of tire rubber were obtained from the dump sites location in Donholm and bitumen samples for penetration grade 80/100, were purchased from Colas East Africa in Nairobi County. The results obtained in this study showed that penetration of bituminous binders reduced from 88 to 41 tenths of a mm at 20 % rubber content. This implied that modified binders became more harder with addition of rubber as a modifier and can withstand fluctuating temperatures of asphalt pavements. Softening point, a candidate also crucial for pavement temperature susceptibility, increased from 48.8oC to 63.9oC at 20 % waste rubber content. This showed that the modified binders can withstand the elevated temperatures of asphalt pavement surfaces. The flashpoint and specific gravity of the neat and rubber-modified binders did not significantly because tire rubber is not very flammable and is of almost same specific gravity as bitumen of 1.1g/cc. Viscosity at 135oC increased from 304.3cSt to 330.7cSt at a waste rubber content of 12% and became unworkable at rubber content beyond 12% when determined using the standard reverse flow viscometers method. Ductility at 25oC reduced from 135.5cm to 48.3cm as 3% to 20% waste tire rubber was added, implying that the rubber makes bituminous binders stiffer. Solubility decreased from 99.6% to 98.3% when 20% of rubber was added implying that addition of more rubber increased impurities in the bitumen. The loss on heating due to aging increased from 0.2% to 0.4% at 12% rubber content and further increased to 1.2% at 20% waste tire rubber content. This showed that the quantity of volatiles increased with addition of more waste tire rubber.