Stabilization of Demolition Materials for Pavement Base/Subbase Applications Using Fly Ash and Slag Geopolymers: Laboratory Investigation

The use of recycled construction and demolition (C&D) materials in unbound and cement stabilized pavement base/subbase applications has generated growing interest in recent years. C&D materials consisting of crushed brick (CB), recycled crushed aggregate (RCA), and reclaimed asphalt pavement (RAP) have been investigated in unbound and cement stabilized pavement base/subbase applications. However, the high carbon footprint of using cement for pavement base/subbase stabilization has led to this research to seek alternative low-carbon binders. This study evaluates the behavior of C&D materials when stabilized with geopolymers. Fly ash (FA) and ground granulated blast furnace slag (S) were used as pozzolanic binders and a different alkaline activator solution to pozzolanic binder ratio was tested. A maximum of 4% of dry weight of soil was used for geopolymer stabilization of the C&D materials. The binders used were either 4% FA, 2% FA+ 2% S, or 4% S. The geotechnical engineering and strength properties of these geopolymer-stabilized C&D materials were evaluated to ascertain their performance for pavement base/subbase applications. Elastic modulus, compressive strength, and resilient modulus of the blends were tested and analyzed in this research. Both the resilient modulus of the C&D materials and compressive strength were found to increase as a result of geopolymer stabilization. Geopolymer stabilization was found to be most effective for RCA. Higher compressive strength will be achieved by slag-based geopolymer stabilization when compared with fly ash-based geopolymer stabilization. The effect of alkaline activator to pozzolanic binder ratio on the enhancement of geotechnical properties of C&D materials was also analyzed. The performance of the geopolymer-stabilized C&D materials was furthermore compared with that of traditional cement-stabilized C&D materials. Geopolymer-stabilized RCA and RAP were found to be a viable and sustainable option for the stabilization of future pavement bases/subbases.