Evolution of silica gel during post‑carbonation hydration of calcium silicates and its effect on mechanical strength of carbonated matrix

Accelerated carbonation of the alkaline industrial wastes as building products has attracted increasing attentions, but the studies on post‑carbonation hydration of the unreacted calcium silicate in these building products remain limited. This study investigates the evolution of silica gel during post‑carbonation hydration of calcium silicates and its effect on mechanical strength. The results indicate that the compressive strength of γ-C₂S compacts remains unchanged after 28 d of post‑carbonation hydration whereas that of β-C₂S compacts display a rapid decrease in strength. This is attributed to the dissolution of silica gel into the pore solution with high pH value and the formation of cracks in the carbonated matrix. For C₃S, the gradual accumulation of C-S-H leads to a continuous increase in compressive strength. These findings provide insights into the mechanism of mechanical strength evolution in outdoor exposed building products made from carbonated industrial solid wastes.