Investigation of microstructural damage in shotcrete under a freeze-thaw environment

Shotcrete is extensively used in underground engineering and other fields. In cold regions, the initial shotcrete lining of tunnels is repeatedly frozen and melted several times in a single year when temperatures alternately change. Thus, the freeze-proof durability of shotcrete is significantly impacted by the freeze-thaw cycle. Computed tomography (CT), a non-destructive scanning method, was adopted to demonstrate the process of shotcrete microstructural damage in a freeze-thaw environment. CT scanning results showed that looseness and slippage of the cement mortar became increasingly apparent and that the number of internal micro-pores significantly decreased with increasing number of freeze-thaw cycles. In addition, the axial compressive strengths of the shotcrete prism specimens significantly decreased. After 300 freeze-thaw cycles, the total number of micro-pores in specimens DR1-1 and DR1-2 decreased by 50.32% and 34.20%, respectively, and the axial compressive strength loss reached 63.78%.