As an energy-intensive industry, cement manufacturing is a significant contributor to CO₂ emissions. Simultaneously, the increasing volume of construction waste has also exerted significant pressure on the environment. Recycling demolished concrete has been proposed as a strategy to address the depletion of aggregate resources. In addition, it facilitates the disposal of construction waste and reduce carbon emissions. A particularly promising approach is the recycling of waste concrete powders (WCP) as a supplementary cementitious material (SCM), which has garnered significant attention. However, the high absorption and low reactivity of WCP pose a challenge to its direct use as SCM. Accelerated carbonation of WCP produces calcium carbonate (CaCO₃) and amorphous silica gel. These products enhance the reactivity of WCP and facilitate the effective sequestration of CO₂. This process not only promotes the high-quality utilization of WCP but also helps to mitigate the environmental and energy burdens associated with cement production.

This study reviews the properties of carbonated waste concrete powder (cWCP) and provides an in-depth analysis of the carbonation process of WCP. It covers various carbonation methods, the regulation of carbonation degree and the prperties of carbonation products. Furthermore, the review evaluates the influence of cWCP on the performances of cement-based materials, including rheology, hydration behavior, mechanical properties, and impermeability.

The carbonation products of cWCP are influenced by the carbonation conditions. In turn, cWCP influences the properties of cement-based materials through the properties of these carbonation products. The primary products of cWCP are CaCO₃ and amorphous silica gel. Their composition, morphological characteristics, chemical properties, and relative distribution depend significantly on the carbonation method and conditions used. The reaction environments and carbonation kinetics of dry and wet carbonation processes differ significantly, resulting in variations in both the degree of carbonation and the polymorphs of products. By optimizing these carbonation conditions, it is possible to improve the degree of carbonation of cWCP while also controlling the polymorphs of CaCO₃ and polymerization degree of silica gel. Furthermore, the influence exerted by these carbonation products on cement-based materials primarily stems from their surface characteristics combined with various effects. Surface properties include both geometrical and surface electrochemical characteristics of CaCO₃ in diverse polymorphs, as well as the hydrophilicity of the silica gel. The effects of carbonation products include the filler effect, nucleation effect, chemical reaction with C₃A, and the pozzolanic effect attributed to silica gel. Notably, improvements in rheological properties are not significantly influenced by either the filler effect or surface electrochemical characteristics of CaCO₃. Instead, more pronounced negative influences arise from the hydrophilicity of silica gel and the fibrous geometry of aragonite. These factors contribute to a significant deterioration in rheological properties, with hydrophilicity being the primary mechanism behind this deterioration. When the degree of carbonation is sufficiently high, the combined positive effects of the filler effect, nucleation effect, chemical reaction, and pozzolanic effect can surpass the negative influence of dilution effect. As a result, the incorporation of cWCP accelerates the hydration, improves the microstructure, and enhances the compressive strength and impermeability.