Degradation of Mechanical Properties and Chloride Ion Transport Properties of Concrete Exposed to Transient Fatigue Thermal Shocks

Concrete structures of rocket launch towers in marine environments are subjected to transient fatigue thermal shocks during launches and corrosive chloride-rich atmospheres, inducing accelerated steel corrosion and structural degradation. To address these challenges, this study systematically investigated the deterioration of mechanical properties and chloride ion transport in concrete exposed to transient fatigue thermal shocks, simulating rocket launch conditions using a quasisteady-state approach. Experimental methods, including uniaxial compression tests, mercury intrusion porosimetry, and chloride ion transport analyses, were employed to evaluate changes in compressive strength, elastic modulus, pore structure, and chloride ion diffusion coefficients under varying thermal conditions. Empirical models were derived to correlate damage levels with amplified chloride diffusion factors, and a chloride transport model incorporating transient fatigue thermal damage was developed. After 150 cycles at 500°C, compressive strength and elastic modulus decreased by 33.02% and 71.73%, respectively, with elastic modulus showing higher sensitivity to transient thermal fatigue shocks. Microstructural analysis revealed pronounced pore coarsening, especially at high temperatures and after 30 thermal cycles, with porosity increasing from 9.73% before thermal shock to 16.65% after 150 cycles at 500°C. Thermal fatigue damage accelerates chloride ion transport, showing an initial rapid increase followed by stabilization.