Mechanisms underlying the long-term reaction in high-volume glass powder cement system

Waste glass powder (GP), as a sustainable alternative to cement clinkers in concrete production, contributes to the strength gain and durability enhancement at a suitable replacement ratio normally lower than 20 %. However, there still exists an insufficient understanding of the potential benefits and challenges of using highvolume GP in cement systems, particularly regarding its long-term reaction mechanisms. In this study, the hydration and pozzolanic reactions in high-volume GP cement system with a GP replacement ratio up to 60 % were systematically monitored and assessed for up to a year from the perspectives of hydration heat, phase assemblage, pore solution, microstructure, and compressive strength. The results demonstrate that the incorporation of GP accelerates the early hydration kinetics in terms of initial ionic dissolution, silicate, and aluminate reactions, thereby resulting in a higher early hydration degree of clinker phases. Moreover, the high alkalinity of the pore solution, highly dominated by K* and Na* concentrations, initially increases, while decreasing at later ages due to alkali uptake by secondary C-(N)-S-H gels. Compared to the pure cement system, incorporating GP could result in the formation of secondary C-(N)-S-H gels with a higher Na/Si ratio but a lower Ca/Si ratio. As a result, the chain length of these gels in the GP cement system evolves differently over time, starting with a longer chain length at the early age and stabilizing to a shorter chain length at the later age. Furthermore, these gels contribute to the microstructure refinement with a higher proportion of gel pores, thereby beneficial for the continuous enhancement in late strength of the GP cement system. This study provides insight into the long-term reaction mechanisms in high-volume GP cement systems, beneficial for the maximum resource utilization of waste glass in sustainable construction materials.