The combined effects of carbonation and chloride attack can accelerate the degradation of reinforced concrete (RC) structures. In this study, the effect of natural carbonation on the chloride binding behaviours in Ordinary Portland cement (OPC) paste was investigated. The phase-equilibrium model for the dissolution/precipitation reactions and the surface complexation model for the ionic adsorption of C–S–H were adopted. An experiment from the literature was used as the benchmark. The results indicate that Kuzel's salt is produced when OPC paste is exposed to a mild chloride attack. During the natural carbonation process, Kuzel's salt is converted into Friedel's salt. As the carbonation continues, the Friedel's salt disappears. Complete natural carbonation results in a total loss of chemical binding capacity, and only a partial loss of the physical binding capacity in cement-based materials. This completely differs from the accelerated carbonation commonly used in the laboratory, which can cause complete loss of both chemical and physical binding capacity. Therefore, the durability design of RC structures vulnerable to the combined attack of chloride and carbonation based on the results of the accelerated carbonation is conservative.@en

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.@en

Numerical study on crack propagation are of great importance for structure design and assessment. In this contribution, the floating node method (FNM) is combined with the symplectic analytical singular element (SASE) to form a new crack-tip element. The four node quadrilateral crack-tip element contains a SASE for the crack tip area to account for the singularity issue. Floating nodes are used to form a smooth transition mesh to full fill the other area of the element automatically once the SASE has been generated. Delaunay triangulation is used to guarantee the quality of the transition elements. Strong discontinuity resulted from complex crack networks with multiple cracks is treated by the FNM. Criteria for crack nucleation, propagation angle and length of new crack segment are given. Interaction between cracks and between crack and defect can be readily modelled without any prior knowledge of crack path. The fracture process of crack propagation can be modelled without remeshing. Inherited from the FNM, the proposed crack-tip element is especially suitable to be implemented in the form of a user defined element. Completed fracture processes with crack nucleation, propagation and interaction are modelled in the numerical examples.

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