Carbonation reaction and microstructural changes of metro-tunnel segment concrete coupled with static and fatigue load

Carbonation problems relating to concrete durability cannot correspond to the real engineering service environment, because the degradation of concrete properties is actually affected by load and multiple environment factors for a coupling effect. This paper studies the chemical reaction mechanism, carbonation depth, pH values, and pore-structure changes under a load and carbonation coupling effect. The authors study the time-dependent evolution of carbonation depth under different levels of tensile and compressive loads. The authors then further study the time-dependent evolution of concrete carbonation depth under fatigue bending loads at different stresses levels and cycles. While taking advantage of the microstructure characterization methods, X-ray diffraction (XRD), mercury intrusion porosimetry (MIP) and a pH-value meter were used to analyze the chemical reaction mechanism of the concrete carbonation process, undertake a quantitative analysis of the solid phase composition, and examine the evolution of the pore structure.