Durability and long term performance of geopolymer stabilized reclaimed asphalt pavement base courses

Utilization of reclaimed asphalt pavement (RAP) materials in pavement base courses has proven to be a viable alternative not only to conserve the natural resources but also to reduce the environmental pollution and landfilling. Recent studies demonstrated that untreated RAP is inefficient to be used as a pavement material unless blended with virgin aggregates (VA) and/or stabilized with additives, because of their inferior gradation and bonding characteristics. Most of the design guidelines limit the amount of RAP in the base course up to 30% by weight of the virgin aggregates, in lieu of the aged bitumen coating present on the RAP aggregates and lack of understanding of the long term performance of the material. Hence, in this study it is proposed to promote a high percentage of RAP in the base course by stabilizing the RAP:VA mixes with a fly ash. However, the presence of the aged bitumen over the RAP aggregates may affect the long term strength and durability of the design mixes. Hence, to attain the desired design strength, the fly ash is activated in an alkali environment to form a geopolymer by triggering the unreacted polymeric compounds present in the fly ash. However, exposure of these mixes to the severe moisture and temperature variations may alter the cementation. This process may lead to strippage of the asphalt coating from the RAP aggregates and leach out the stabilizer from the mixes. Hence, the present study verifies the suitability of these mixes in terms of their initial compressive strength and the corresponding retained strength after exposure to the alternate wet/dry cycles in the severe laboratory environment. The permanency of the stabilizer/activator is also verified through leachate studies. Variation in the hydration products and oxide contents of the mixes are verified at every stage using X-ray diffraction (XRD) and X-ray florescence (XRF) studies. The comprehensive test results indicated that the strength loss of RAP:VA mixes is very minimal and are found suitable for the base course applications.