Calcium leaching resistance and mechanism of early-age mortar with combined incorporation of glass powder and sodium sulfate under leaching condition

Shotcrete is exposed to groundwater after application and prone to calcium ion leaching. Glass powder (GP)+sodium sulfate(SS) incorporation is expected to enhance calcium leaching resistance of early-age concrete, but the effect and mechanism remain unclear. Therefore, leaching tests on early-age mortar incorporating GP+SS were conducted. Calcium leaching resistance was analyzed through leached calcium, soluble calcium, and leaching depth, while mechanism was revealed by TGA, MIP, and SEM. Combined with compressive strength, the optimal mix was determined. Results show that within 28 days, GP+SS incorporation effectively enhanced calcium leaching resistance of early-age mortar. Calcium ion concentration in leachate of 40%GP+6%SS mix was reduced by 42.79% compared with reference group, exhibiting the best resistance. GP+SS incorporation reduced soluble calcium and Ca(OH)2 through the dilution of GP and calcium fixation of SS within 7 days, and the pozzolanic reaction of GP and activation of SS during 7~28 days. GP+SS incorporation alleviated pore deterioration caused by GP through AFt and C-S-H filling, reducing porosity and leaching coefficient. Combined with compressive strength, optimal mix was selected as 10%GP+6%SS. Leaching delayed activation of SS, enlarged pore size, and formed ink-bottle pores. The findings provide references for enhancing calcium leaching resistance of shotcrete and recycling waste glass.