The durability of alkali-activated slag grouting materials (AASGMs) has attracted significant research attention. This paper investigated the mechanical properties and microstructure of AASGMs mortars and pastes immersed in a flowing 5% ${\mathrm{NaHCO}}_3$ solution. Compared with the strengths of AASGMs immersed for 3 days, the flexural and compressive strengths of AASGMS immersed for 56 days increased by 11.1% and 37.8%, respectively. The leaching depth of AASGMS immersed for 56 days was 0.627 mm. The AASGMs had good antiflowing ${\mathrm{NaHCO}}_3$ solution deterioration performance. The leaching process of AASGMS in flowing ${\mathrm{NaHCO}}_3$ solution was divided into three stages: (1) neutralization of residual alkali in gel pores; (2) decalcification of calcium aluminate silicate hydrate (C-A-S-H) gels in the surface and intermediate layers to form calcium carbonate and silica gels; and (3) leaching of calcium and silicon in surface layers from calcium carbonate and silica gels.