The carbonation of concrete is the prime deterioration factor in reinforced concrete (RC) structures. During carbonation, the atmospheric CO₂ penetrates the concrete and lowers its alkalinity. The problem in predicting carbonation is difficult to address, and a reliable probabilistic carbonation assessment is required to consider different variables such as the concrete quality, the chemistry of the reinforcing steel, and the quality of finishing materials. In the present study, we have used different finishing materials on concrete to minimize the effects of carbonation with a field survey and accelerated conditions. In one experiment, the measurement of the thickness of the concrete cover and the application of the finishing materials were done on-site, whereas, in the other experiment, these were done under accelerated conditions. The carbonation depth and the coefficient of silk wallpaper (SWP) were reduced by half in an accelerated 5% CO₂ experiment compared to the plain ordinary Portland cement (OPC), owing to the external physical barrier that reduces the penetration of CO₂ through the pores of the concrete. We found that carbonation did not reach the embedded rebar even after 100 years when SWP finishing material was used. The probability model predicted that 51 years would be required for OPC and water paint (WP) to reach a 30% onset of corrosion initiation through accelerated carbonation, while SWP would require 200 years.

This paper presents the effect of anion exchange resin (AER) on the adsorption of chloride ions in cement mortar. The kinetic and equilibrium behaviors of AER were investigated in distilled water and Ca(OH)₂ saturated solutions, and then the adsorption of chloride ions by the AER in the mortar specimen was determined. The AER was used as a partial replacement for sand in the mortar specimen. The mortar specimen was coated with epoxy, except for an exposed surface, and then immersed in a NaCl solution for 140 days. The chloride content in the mortar specimen was characterized by energy dispersive X-ray fluorescence analysis and electron probe microanalysis. The results showed that the AER could adsorb the chloride ions from the solution rapidly but had a relatively low performance when the pH of its surrounding environment increased. When the AER was mixed in the cement mortar, its chloride content was higher than that of the cement matrix around it, which confirms the chloride ion adsorption capacity of the AER.

The purpose of this study is to understand the complex mechanisms through which the active ingredients of crystalline waterproofing agents change the microstructure of cement-based materials. Microstructural and phase characterization are carried out on cement pastes modified with waterproofing agents through thermogravimetric analysis, scanning electron microscope with energy-dispersive x-ray spectroscopy, and x-ray microcomputed tomography. Two types are investigated—one that is applied onto the surface of existing concrete and another that is incorporated as an admixture into the fresh mix. Samples treated with the waterproofing agents are compared with a sample cured in sodium carbonate solution, one of the key active ingredients. Results indicate that both types of waterproofing agents lead to formation of calcium carbonate. The surface treatment type forms a dense coating, with little penetration into the matrix, whereas the admixture type leads to a measurable decrease in porosity throughout. The sample cured in sodium carbonate solution leads to an increase in porosity due to decalcification shrinkage, which underscores the importance of controlling sodium carbonate content to avoid excessive carbonation.

In this study, γ-dicalcium silicate (γ-C₂S) was incorporated into ordinary Portland cement (OPC) to sequester CO₂ to enhance the carbonation resistance of cement-based composite materials. γ-C₂S can react with CO₂ rapidly to form vaterite and high dense SiO₂ gel which could block the pores off and then inhibit further diffusion of CO₂ into the system. Cement mortar specimens containing 0%, 5%, 10%, 20%, and 40% γ-C₂S as cement replacement were prepared. After water curing for 28 days followed by curing in an environmental chamber for 28 days, the specimens were then exposed to an accelerated carbonation with 5% CO₂ concentration for 28 days. The carbonation depth of the cement mortar with a low replacement rate (5% and 10%) was lower than that of the OPC mortar at all ages due to the sequestration of CO₂ by γ-C₂S. However, the cement mortar with a high replacement rate (20% and 40%) showed less carbonation resistance due to the dilution effect of γ-C₂S replacement and increase in initial porosity caused by nonhydraulic characteristic of γ-C₂S.