Enhancing the mechanical properties and microstructures of geopolymeric recycled aggregate concrete by waterborne epoxy resin incorporation

Abstract Geopolymeric recycled aggregate concrete (GRAC) emerges as an alternative to ordinary concrete, presenting promising prospects in practical engineering due to its exceptional performance and eco-friendly attributes. Nevertheless, GRAC exhibits deficiencies in toughness and brittleness. To address this concern, this study investigates the potential of waterborne epoxy resin (WER) in enhancing the properties of GRAC. Experiments were conducted using WER and recycled aggregate (RA) content as variables, focusing on the setting time, fundamental mechanical strengths, stress–strain response and microstructure of GRAC. The findings indicate that the increase in the RA content results in an overall deterioration in the mechanical performances of GRAC. Nevertheless, the addition of WER effectively mitigates the adverse effect of RA substitution, enhancing the splitting tensile and flexural strengths of GRAC. The addition of WER leads to a growth in compressive toughness, and the post-peak stress–strain curve of GRAC exhibits a flatter trend, indicating enhanced ductility. WER interacts with C-A-S-H, forming a compact organic–inorganic interpenetrating network structure, which strengthens the GRAC matrix. Moreover, the incorporating 4% WER content leads to a reduction of 31.2% in the total porosity of GRAC, in contrast to GRAC without WER. Drawing from experimental results and prior researches, a refined stress–strain model is presented to provide comprehensive depiction of the compressive stress–strain curve of GRAC considering differing dosages of RA and WER. Finally, Life Cycle Assessment (LCA) of GRAC results demonstrate its superior environmental performance as a low-carbon material relative to ordinary concrete.