Abstract
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.
Highlights
In recent decades, increasing number of islands and reefs, which are generally far from the mainland, have been constructed to meet the needs of rapidly developing of marine industry
The developed numerical model for the reactive transport in coral aggregate concrete (CAC) is capable of predicting the variations in the hydrate phases, the concentrations of free ions in the pore solution, and the amounts of ions bound by calcium silicate hydrate (C−S−H) with time and space
Considering that the [Cl−]/ [OH−] ratio in the pore solution determines the corrosion initiation of reinforcing steel embedded in CAC, the numerical results related to chloride and pH are presented and discussed, including the results of the free chloride concentration and pH in the pore solution, the content of chloride bound by C−S−H, and the amount of Friedel’s salt
Summary
In recent decades, increasing number of islands and reefs, which are generally far from the mainland, have been constructed to meet the needs of rapidly developing of marine industry. When external chloride ions penetrate CAC, it produces new Kuzel’s and Friedel’s salts, causing an increase in the their content This is considered to be a result of the precipitation reactions of the species (such as SO42-, Cl−, Al(OH)4-, OH−, and Ca2+) in the pore solution, which is accompanied by other dissolution and precipitation reactions between cement hydrate and pore solution. The hydrated cement compounds and concentrations of species in the pore solution are necessary to solve the reactive transport model in cement-based materials and can be obtained from experiments or calculation of GEMS (Kulik et al, 2013; Lothenbach and Winnefeld, 2006; Lothenbach and Zajac, 2019). The period for simulating chloride ingress for CAC was setas 360 days, giving 36 time steps of 10 days
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