CIVIL ENGINEERING 365 ALL ABOUT CIVIL ENGINEERING



AbstractBased on exposure tests in a natural tidal environment, free chloride concentrations in concrete with different fly ash contents and exposure times were tested, and the apparent and instantaneous chloride diffusion coefficients of different fly ash contents were analyzed. Microstructural parameters such as porosity were analyzed using nuclear magnetic resonance (NMR) test results. The time-dependent model and analysis method of stable time for microstructural parameters is presented, and the time-dependent and stable time of microstructural parameters with different fly ash contents were studied. The relationship between stable time for chloride diffusivity and stable time for microstructural parameters was analyzed. Results show that chloride concentrations and chloride diffusion coefficients both have a linearly increasing relationship with exposure time and fly ash content increase. The stable time for chloride diffusion coefficients decreased as fly ash content increased. The total porosity and contributive porosity of large capillary pores (100–1,000 nm) generally decreased with the increasing exposure time, which is consistent with the time-dependent chloride diffusion coefficients. Increasing fly ash content had an obvious effect on reducing the contributive porosity of large capillary pores (100–1,000 nm) in concrete. The stable time for contributive porosity of large capillary pores (100–1,000 nm) decreased with increasing fly ash content. Whether fly ash was added or not, the contributive porosity of large capillary pores (100–1,000 nm) stabilized at first, and the stable time was the most important factor affecting the stable time for instantaneous chloride diffusion coefficient of concrete, providing a reference for predicting the stable process of macroscopic permeability from a microscopic view.



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