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In this paper, a chloride diffusion model of coral aggregate concrete under an extremely hot and humid marine environment was studied, and nine mix ratios of coral aggregate concrete were analysed and researched. Utilising Fick's second law, a chloride diffusion model for coral aggregate concrete was established. It considers the impact of the temperature, humidity, erosion time, compressive strength of coral aggregate concrete, fly ash content, and basalt fibre content on the chloride diffusion coefficient in the extremely hot and humid marine environment of the South China Sea. Furthermore, the impact of sulfate ions on the chloride diffusion was considered, and the degree of damage to the coral aggregate concrete was defined. A relationship between the relative chloride diffusion coefficient and the degree of concrete damage was established, thereby successfully incorporating sulfate erosion damage into the chloride diffusion model. Finally, an analysis was conducted on the values of the parameters in the diffusion model. The established chloride diffusion model was used to calculate the chloride concentration distribution under different erosion environments, and the experimental values were compared and analysed to verify the accuracy of the diffusion model. The results show that the calculated results are in good agreement with the experimental results. The establishment of the model can provide a theoretical basis for the durability design and life prediction of coral aggregate concrete under extremely hot and humid marine environments.

This paper studied the effect of sulfate on chloride diffusion behavior in coral aggregate concrete (CAC) in marine tide zone. Three water/binder ratios of CAC were designed for experimental analysis, and the mechanism of the effect of sulfate on chloride transport was investigated by different microscopic experimental methods. The test results show that the chloride content decreases with the decrease of water/binder ratio of CAC. At an equal number of drying-wetting cycles, the chloride content under the combined action of chloride and sulphate is lower than that under the sole action of chloride. The change of peak chloride content with time showed a linear function with the square root of erosion time, while the chloride diffusion coefficient gradually decreased with erosion time. Adding silica fume to CAC effectively reduced the chloride diffusion coefficient, with a decrease of 26.1%∼46.2%. The attenuation coefficient of CAC under chloride erosion was 16.4%∼38.1% higher than that under the combined action of chloride and sulfate. The chloride diffusion model was established, and the error between the calculated value of the model and the experimental value was within 16%. Microscopic observations revealed that in the early stage of erosion, the sulfate erosion products ettringite and gypsum had a compacting effect on the CAC, but in the late stage of erosion, they produced expansion cracks, which accelerated the deterioration of CAC.

In this paper, the chloride diffusion behaviour of coral aggregate concrete (CAC) exposed to marine submerged, tidal, and salt spray zones was investigated, and the effect of the fly ash (FA) content on the chloride diffusion was explored. The chloride concentration was measured using the potentiometric method, and the Ca(OH)₂ content in the CAC was calculated using the thermogravimetric method. The results show that the chloride concentration in the submerged zone decreases with an increasing erosion depth; meanwhile, in the tidal and salt spray zones, the chloride concentration showed a two-stage distribution pattern. The depth of the convective zone gradually increases with an increasing erosion time, and the depth of the convective zone in the salt spray zone is larger than that in the tidal zone. The chloride diffusion coefficient exhibits a power-function attenuation relationship with erosion time when exposed to different corrosion zones. The attenuation coefficient of the chloride diffusion coefficient increases with an increasing FA content. Moreover, the attenuation coefficient is the highest in the salt spray zone with it being 10.8% to 28.5% higher than that of the tidal zone. In addition, the Ca(OH)₂ content in the tidal zone is not only the lowest, but also gradually decreases with an increasing erosion time.

This paper investigates the deterioration progress of coral aggregate concrete (CAC) under the coupling action of sulfate, chloride and drying–wetting cycles. Three strength grades (C25, C30, C40) of CAC specimens were designed for experimental analysis. In addition, ordinary aggregate concrete (OAC) specimens were prepared as the reference group. The relative dynamic elastic modulus and the relative compressive strength of CAC increases first and then decreases with increasing exposure time, while the mass loss rate shows the opposite trend. The CAC with high strength grade has strong corrosion resistance, and the corrosion resistance of CAC is obviously lower compared to OAC at same strength grade. The addition of basalt fiber into CAC can delay the cracking and maintain the integrity. With increasing exposure time, the damage depth increases exponentially. The chloride concentration can be divided into two phases: first increase and then decrease. Basalt fiber can significantly reduce the chloride diffusion coefficient of CAC. The erosion products are ettringite and gypsum for OAC and CAC; in addition, Friedel’s salt is also found in CAC.

Utilizing coral aggregate concrete (CAC) for construction on remote islands can significantly reduce construction cost and period, CO2 emission, and consumption of non-renewable energy. The durability of reinforced CAC structures is critically influenced by their resistance to chloride attack. In this study, a reactive transport modelling was developed to investigate chloride ingress in CAC, in which a COMSOL-PHREEQC interface based on MATLAB language was established. The experiment from the literature was taken as a benchmark example. The results show that the developed numerical model can accurately predict chloride transport in CAC. Differing from ordinary aggregate concrete (OAC), Kuzel’s salt does not appear in cement hydrate compounds of CAC during chloride ingress. The numerical results indicate that the penetration depth of chloride in CAC gradually increases as the exposure time is prolonged. When CAC is exposed to an external chloride solution, the decrease in the pH of the pore solution affects the precipitation of Friedel’s salt, which is detrimental to the chemical binding of chloride.