Calcium leaching resistance and mechanism of early-age mortar with combined incorporation of glass powder and nano-silica under leaching conditions

After application, shotcrete is immediately subjected to erosion by surrounding rock water, and calcium leaching is prone to occur in early-age concrete under leaching conditions. The combined incorporation of glass powder (GP) and nano-silica (NS) is expected to enhance the calcium leaching resistance of shotcrete; however, the improvement effect and mechanism of GP-NS incorporation in early-age concrete under leaching conditions remain unclear. In this study, leaching tests were conducted on early-age mortar specimens with GP-NS incorporation. Calcium leaching resistance was analyzed through measurements of leached calcium, soluble calcium, and leaching depth, and its mechanism was elucidated using TGA, MIP, SEM, and EDS. Finally, compressive strength tests were conducted to determine the optimal mix ratio. Results show that GP-NS incorporation improves the calcium leaching resistance of early-age mortar throughout the 28d leaching process, with the concentration of leached calcium ions in the 40 % GP-9 % NS group being 30.97 % lower than that of the control group at 28d. The dilution and pozzolanic effects of GP and NS act synergistically to reduce soluble calcium sources. Compared with the control group, the 40 % GP-9 % NS group exhibited a 68.66 % reduction in soluble calcium per unit mass at 28d, and the 25 % GP-9 % NS group showed a 6.04 % lower total CH content percentage. The incorporation of NS mitigates the deterioration of pore structure in early-age mortar under leaching conditions induced by GP, thereby blocking calcium ion leaching pathways. The porosity of the 25 % GP-9 % NS group was 7.11 % lower than that of the 25 % GP group. The activity stages of the externally incorporated materials are effectively connected in sequence: NS's secondary hydration occurs from 7 to 14d, while the pozzolanic effect of GP develops from 14 to 28d. The incorporation of NS effectively compensates for the deficiency in early strength of GP alone. The 40 % GP-9 % NS group showed a 34.75 % improvement in compressive strength at 7 d compared to the 40 % GP group. Under leaching conditions, the optimal mix ratio for the GP-NS incorporation is 25 % GP-6 % NS. The calcium leaching process increases mortar porosity, with pore morphology evolution characterized by pore enlargement, pathway extension, and the formation of numerous ink-bottle pores due to local pitting corrosion. These findings provide a reference for mitigating calcium leaching in tunnel shotcrete and promoting the resource utilization of glass solid waste.