Evaluation of Rubberized Limestone Filler in Asphalt Paving Mixtures

Abstract

Abstract The method of direct dispersion of small amounts of rubber particles in asphalt binder was associated with difficulties in controlling degradation, mix uniformity, oxidation, and noxious fumes generated by grinding rubber. This study showed that asphalt cements can be modified by adding carboxylated butadiene rubber chemically bound to calcium carbonate to give a wide range of products of different compositions and consistencies. These rubberized fillers can disperse more rapidly in the hot asphalt during the mixing operation and require no adjustments or changes in conventional mixing practices. The conclusions that can be drawn from the experiments conducted include the following: 1. The relatively high stiffening effect of rubberized filler on the F/A binder system is related to its high surface activity or interfacial energy. Limiting values of viscosity increase in F/A binder systems were developed from the effective volume concentration values of rubberized filler to keep resistance to compaction of asphalt paving mixtures within desirable limits. 2. The surface of limestone filler chemically reacted with rubber is rendered more hydrophobic. This results in a pronounced reduction in the stripping of asphalt aggregate surfaces. For uncoated limestone filler, however, the stripping potential increased with the increase of immersion time in water. 3. Temperature susceptibility is decreased by adding rubberized limestone filler to asphalt. 4. Initially, the increase in the RL/L ratio of filler used in the sand-asphalt mixture causes an increase in Marshall stability. After a critical limit (corresponding to the critical effective volume concentration of the fillers in the F/A system), however, the stiffening offers significant resistance to compaction, causing the Marshall stability to decrease. 5. The addition of rubberized filler in RL/L ratios up to 40/60 by weight significantly improved the tensile strength properties of the sand-asphalt mixtures. 6. The values of retained tensile strength after different moisture conditioning methods indicate greater adhesion for mixtures containing rubberized filler up to a RL/L ratio of 40/60 by weight.