Stabilization of Recycled Demolition Aggregates by Geopolymers comprising Calcium Carbide Residue, Fly Ash and Slag precursors

This paper presents the results of the evaluation of Recycled Asphalt Pavement (RAP) and Fly Ash (FA) blend as a sustainable pavement material. The strength characteristic of RAP-FA blend was determined by Unconfined Compression Strength (UCS) test. The effect of wetting-drying (w-d) cycles on the strength and microstructural changes of this material was also investigated. The micro-structure of the compound pavement material was analyzed using X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The leachability of the heavy metals is measured by Toxicity Characteristic Leaching Procedure (TCLP) and compared with international standards. Test results show that the compacted RAP-FA blend can be used as a base course material as its UCS values meet the minimum strength requirement specified by national road authorities of Thailand. The durability test results show that the UCS of RAP-FA blend increases with increasing the number of w-d cycles (C), reaching its peak at 6 w-d cycles. The XRD and SEM analyses indicate that the increased UCS of RAP-FA blend is due to stimulation of the chemical reaction between the high amount of Calcium in RAP and the high amount of Silica and Alumina in FA during w-d cycles leading to production of more Calcium (Aluminate) Silicate Hydrate [C-(A)-S -H]. For C > 6, the significant macro- and micro-cracks developed during w-d cycles cause strength reduction. The TCLP results demonstrate that there is no environmental risk for RAP-FA blend in road construction. The outcome from this research confirms the viability of using RAP-FA blend as alternative sustainable pavement materials.