Investigation of carbonation on the compressive strength development of Portland Limestone Cement (PLC) concrete

Portland Limestone Cement (PLC) is increasingly promoted as a low-carbon alternative to Ordinary Portland Cement due to its reduced clinker content and associated environmental benefits. However, uncertainties remain regarding its mechanical performance and durability under carbonation exposure, particularly across different mix qualities and curing conditions. This study investigates the influence of carbonation on the compressive strength development of PLC concrete produced at water/cement (w/c) ratios of 0.30, 0.50, and 0.70. Cube specimens were subjected to three curing regimes: continuous water curing, air curing, and accelerated carbonation curing, and compressive strength was monitored up to 182 days. Carbonation depth was measured using phenolphthalein indicator, and statistical analyses were conducted using mean strength, standard deviation, and coefficient of variation. Results show that water curing provided steady strength development and served as a performance benchmark, while air curing led to significant mid-age strength reductions of up to 19% due to premature moisture loss. In contrast, carbonation curing produced progressive late-age strength enhancement, with strength gains of 7–12% relative to water curing at 182 days, particularly in higher w/c concretes. Carbonation-cured specimens also exhibited lower coefficients of variation, indicating more uniform and reliable strength development. Carbonation depth increased with exposure age and w/c ratio, and a positive relationship was observed between carbonation depth and strength gain, confirming the role of carbonation-induced pore refinement and matrix densification. The findings demonstrate the dual nature of carbonation in PLC concretes: while it may pose durability risks for reinforced applications due to alkalinity reduction, controlled carbonation curing can be beneficial for plain and precast PLC concretes by enhancing both strength and consistency. Overall, the study provides experimental evidence supporting carbonation curing as a viable and sustainable strategy for selected cement-based applications, contributing to ongoing efforts in carbon utilization and low-carbon construction materials.