Contribution of reactive aggregates towards the performance of in-service asphalt pavements

Abstract

This paper presents an assessment of the contribution of reactive aggregates on performance of asphalt pavements in service in order to better understand how to mitigate likely asphalt pavement failures resulting thereof. A petrographic and mineralogical analysis was done on rocks that were used in the asphalt mix as well as their mineral composition. Also, a visual condition survey, deflection testing and coring of the asphaltic surfacing for further analysis and testing were conducted to establish the extent of the distresses. Results showed that though aggregates tested were meeting the criteria required of a good quality asphalt concrete in relation to mechanical properties, they did not satisfy the other criteria in relation to their mineralogical composition and adhesion. Aggregates were found to be reactive and contained pyroxenes and feldspar which were responsible for deterioration in form of ‘blows ups’ and indentations observed on the pavement surface. Pyroxenes oxidised when they combined with atmospheric components due to their high iron content to form hydrated iron oxides. Feldspars experienced a hydrolytic reaction when they reacted with water to form clay minerals, potassium ions, and silica in solution. Continued exposure of reactive aggregates through water and air permeating into the open textured and cracked asphalt surface will result into total transformation of the pyroxenes into erodible iron oxides and hydroxides hence leading to further deterioration of the asphalt pavement. It is recommended that engineers consider conducting petrographic and mineralogical analysis when sourcing quarries for production of aggregates to be used in asphalt mixes.