Effect of rice husk ash content and carbonization curing on lime-stabilized recycled aggregates: mechanical behavior and microscopic mechanism

Abstract The stabilization of recycled aggregates using rice husk ash (RHA) synergized with lime offers both the resource utilization of solid waste and an enhancement in the mechanical properties of recycled aggregates. This study investigated the effects of various percentage RHA contents (0%, 2%, 4%, 6%, and 8%) and carbonation durations (0 h, 12 h, and 24 h) on the mechanical properties of rice husk ash-lime stabilized recycled aggregates (RLA) through a series of unconfined compressive strength (UCS) tests. Additionally, this study used x-ray diffraction (XRD) to analyze the chemical composition and phases of RLA, energy dispersive spectroscopy (EDS) to detect the elemental composition and content of RLA, and scanning electron microscopy (SEM) to observe the surface morphology of RLA. The main findings are as follows: (1) Both RHA and carbonation treatment significantly improve the UCS of lime-stabilized recycled aggregates, with optimal RHA content and carbonation time identified as 6% and 12 h, respectively. (2) RHA and carbonation treatment do not alter the chemical composition of RLA but promote the formation of C–S–H gels and CaCO 3 . (3) The combination of RHA and carbonation treatment enhances the densification of C–S–H gels in RLA; however, excessive carbonation results in decalcification of the C–S–H gel, which reduces the calcium-to-silicon ratio of RLA. (4) Both RHA and carbonation treatment contribute to reducing porosity and improving microstructure of RLA. However, excessive carbonation leads to an increase in porosity and a deterioration of the microstructure of RLA. These findings support the practical application of RHA and carbonation treatment methods in road engineering.