Accelerated carbonation curing of concrete masonry units: Process parameters, performance, and CO2 capturing potential

Abstract

Accelerated carbonation curing (ACC) has attracted increasing attention as a curing technique for concrete masonry units (CMUs) because it can simultaneously accelerate strength development and utilize CO₂. Unlike conventional steam curing, ACC introduces controlled CO₂ exposure during the curing stage of freshly formed masonry products, enabling strength development and permanent carbon sequestration. This paper reviews the current research on ACC of load-bearing and non-load-bearing CMUs, including manufacturing methods, mix design, curing parameters, CO₂ uptake, mechanical properties, durability, and industrial implementation. Evidence from laboratory-scale specimens, and pilot- and full-scale block production is examined to identify the governing mechanisms and practical performance trends. The reviewed studies show that ACC can permanently sequester approximately 9–25% of cement mass as CO₂ in OPC-based systems, while reducing curing-energy demand from approximately 2500 kJ/block for steam curing to about 500 kJ/block. Across the literature, the optimum moisture condition consistently corresponded to approximately 4–6% residual moisture or 35–50% mixing-water loss, confirming that moisture pre-conditioning is the dominant process variable controlling carbonation efficiency. The reviewed studies also demonstrate that low-pressure carbonation curing, typically about 0.1–0.5 bar above atmospheric pressure and 2–6 h duration, is generally sufficient for practical masonry production. ACC is shown to provide substantial early-age strength gain and CO₂ uptake, although maximum sequestration and maximum strength do not necessarily coincide under the same curing conditions. The review also shows that post-carbonation hydration is important for later-age performance, and that ACC generally improves dimensional stability and reduces water transport, while long-term durability evidence remains comparatively limited. Alternative and low-clinker binder systems, including recycled-aggregate fines, slag-based, and waste-derived masonry products, further demonstrate the broader potential of ACC, but their scale-up and standardization are less mature than those of OPC-based systems. Overall, ACC is a feasible alternative to steam curing for masonry production. ACC can reduce energy consumption and permanently store CO₂ in masonry products. However, wider industrial application still requires standardized curing methods, long-term durability verification, and optimization of plant-scale curing processes.