Multiscale deterioration of recycled aggregate gel network via solar irradiation: Reaction molecular dynamics and experiments

Abstract

Nowadays, the efficient recycling of construction waste and the sustainability of recycled concrete have faced challenges due to the reduced performance of recycled aggregate (RA). One significant factor impacting the performance of RA is solar irradiation, which occurs throughout the entire service life of a construction project. However, the analysis of the effect of solar irradiation on hardened cement paste has not been fully addressed. This research presents a comprehensive investigation of the multi-scale deterioration of RA caused by solar irradiation. The dynamic evolution of the atomic and chemical structure of synthetic Calcium Silicate Hydrate (C-S-H) gel, the morphological changes in tricalcium silicate (C3S) hydration products, and the alteration of pore structure in the cement paste are unveiled through the combination of reactive molecular simulation and experimental approaches. The results indicate that solar irradiation disrupts the structure of C-S-H, leading to the migration of water molecules from the interlayer spaces of C-S-H to the pore spaces. This prompts the formation of a new, denser gel. However, as a consequence, more capillary pores are formed within the cement paste. The research outcomes provide a bottom-up, multi-scale insight into the reduced performance of RA under solar irradiation. Furthermore, the transmission mechanism of deterioration information at various scales is established, facilitating comprehension of the correlation between gel characteristics and macro-performance. This research paves the way for strategies to ameliorate the sustainability of recycled concrete, addressing the challenges associated with solar irradiation and enhancing the overall performance of recycled aggregate in concrete applications.