Effect of a Multicomponent Composite Material System on the Carbonate Attack Resistance of Tunnel Lining Concrete

Tunnel lining concrete exposed to groundwater rich in carbonate species can deteriorate under the combined action of CO2, HCO3−, and CO32−. An L9(33) orthogonal experiment evaluated the effects of the water-to-binder ratio (FA), slag powder content (FB), and composite formulation level (FC) on concrete resistance to carbonate attack using compressive strength, the rebound value, and carbonation depth as response indicators. During 56 d of simulated CO2–HCO3− corrosion, compressive strength generally increased initially and then decreased, whereas the rebound value increased or fluctuated upward because of its sensitivity to surface carbonation. Carbonation depth increased continuously, with fitted carbonation coefficients ranging from 0.236 to 0.417 mm/d. Range analysis showed the largest response ranges of compressive strength and carbonation depth for FA, while FC produced relatively larger ranges for the rebound value and carbonation depth at later ages. However, none of the three factors reached statistical significance in analysis of variance (ANOVA) at α = 0.10. Among the nine directly tested mixtures, mixture 3# (A1B3C3) exhibited the most favorable mean response over the full corrosion period, with a mean compressive strength, rebound value, and carbonation depth of 67.4 MPa, 40.7, and 1.37 mm, respectively. Averaging the responses at each factor level over the full corrosion period identified A1 and C3 as the most consistently favorable levels for FA and FC, respectively. Differences among the FB levels were comparatively small; B1 was retained as the balanced level because it exhibited the highest mean compressive strength and rebound value, together with a lower mean carbonation depth. The results provide separate mixture level and factor level evidence for evaluating tunnel lining concrete under carbonate corrosion conditions.