Effect of Fly Ash Geopolymer on Layer Coefficients of Reclaimed Asphalt Pavement Bases

Abstract

The utilization of reclaimed asphalt pavement (RAP) material in road construction has gained prominence with the backdrop of sustainability. The present study evaluates the usage of a significant amount of RAP material with virgin aggregates (VA) stabilized with low and high calcium, alkali-activated fly ashes as pavement base materials. The role of a liquid alkaline activator (LAA) on the reactivity of various fly ashes are highlighted. Three distinct fly ashes sourced from different locations were adopted to stabilize the RAP:VA bases. To establish an optimum LAA ratio for these fly ashes, alkaline solutions with varied proportions of Na2SiO3∶NaOH (0∶100, 30∶70, 50∶50, 70∶30, and 90∶10) with a constant NaOH molarity were considered. It was noticed that the strength and stiffness of the mixes at a 28-day curing period were increased with an increase in the LAA ratio. However, in contrary to the existing understanding, the LAA is not a constant ratio (50∶50) for all types of fly ashes. The optimum LAA ratio was found to be 50∶50 for low calcium fly ashes and 70∶30 for high calcium fly ash; however, it depends on the reactive potential of the fly ash. The 60% RAP, 40% VA, and 20% fly ash blended specimens prepared mostly with LAA ratios of 50∶50 and 70∶30 were found to be suitable as pavement base course materials as per design standards. A set of regression models were developed and validated to estimate the base layer coefficients from the corresponding layer’s resilient modulus for various subgrade conditions. Based on the proposed models, a new set of base layer coefficients (a3) were developed for fly ash–stabilized base layers.