Physical, thermal, and microstructural effect of CO₂ in carbonic acid on mortar

Existing studies have shown current methods of carbon dioxide infusion are limited to slow carbonation rates and lack of carbon dioxide penetration. This study aims to tackle these problems by proposing a new method of infusion by adding carbon dioxide via liquid directly during mixing process. This study also investigates the thermophysical behaviour of mortar subjected to liquid-phase CO₂ infusion, focusing on its effects on mechanical strength, hydration, and carbonation processes. Mortar specimens were prepared and infused with carbonic acid during mixing, followed by compressive strength testing, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The results indicate that liquid-phase CO₂ infusion increases calcium carbonate (CaCO₃) formation, as confirmed by SEM observations of calcite crystallisation. Compressive strength measurements showed that 100% infusion CO₂ mortar does surpass normal mortar mixture showing potential in this method. TGA revealed that the amount of CO₂ retained or released is highly dependent on the mixing and curing conditions, but higher infusion does results in high amount of calcite form, with hydration dynamics significantly influencing the final strength. This is supported by SEM results showing more calcium carbonate formed for all samples but also the formation of pores due to high water content inside mortar.