Performance of natural rubber latex modified bottom ash-based geopolymer stabilized recycled concrete aggregate as a pavement base material

The present research assessed the performance of natural rubber latex (NRL) modified bottom ash (BA)-based geopolymer stabilized recycled concrete aggregate (RCA) as a sustainable pavement base material. Effects of NRL content (0.1, 0.2 %, and 0.3 % by weight of aggregate) and alkaline activator ratios (NaOH:Na₂SiO₃, G/N = 1:1, 1:1., and 1:2) in strength development and microstructure of the stabilized mixtures were evaluated. Unconfined compressive strength (UCS) tests were carried out at 7 and 28 days of curing, and the results were correlated with microstructural analyses using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The findings revealed that the mixture containing 0.1 % NRL and a G/N ratio of 1:1 exhibited the highest UCS values of 4.0 MPa and 5.17 MPa at 7 and 28 days respectively, surpassing the minimum strength requirement for pavement subbase materials. The microstructural analyses confirmed the constitution of a dense and homogeneous geopolymer matrix, with NRL films acting as bridging structures that enhanced the bonding between RCA particles and the matrix. Higher ratios of G/N led to a silica-rich gel that hindered further geopolymerization and strength gain. Meanwhile, a higher ratio of NRL resulted in the formation of thicker NRL films that interfered with the geopolymerization process, resulting in a subsequent strength reduction. The study demonstrates the potential of NRL-modified BA-based geopolymer stabilized RCA as an environmentally friendly and high-performance alternative to conventional cement-stabilized pavement base materials.