Effects of Precuring Conditions on Carbonation Degree, Material Microstructures, and Chemo-Mechanical Properties of Cement Paste

The early carbonation curing phase of cement paste enables substantial CO 2 uptake, offering a promising route for reducing greenhouse gas emissions. However, when applying this technique at scale, particularly with flue gas instead of high-purity CO 2 , several technical challenges arise, including lower CO 2 concentrations. Therefore, further investigation is needed to assess the feasibility and efficiency of carbonation curing under such practical conditions, particularly under diffusion-limited carbonation conditions. In this study, various precuring conditions including differences in precarbonation hydration duration, free water removal, and elevated temperature were experimentally examined to determine their influence on carbonation performance. Carbonation curing of cement paste was implemented by injecting a 20% concentration of CO 2 gas through a nonpressurized flow-through chamber without vacuum pretreatment. The results indicated that cement paste could reach a carbonation depth of 9.7 mm and a carbonation degree of 12.8% based on mass gain and 32.5% based on thermogravimetric analysis (TGA). CH consumption and CaCO 3 after carbonation curing were confirmed by X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images. According to mercury intrusion porosimetry (MIP) results, carbonation improved pore structures, which led to a noticeable increase in early strength gain. The final compressive strength of mortars and concrete improved by 28% to 34% and 27.8%, respectively. Additionally, modified microstructure enhanced durability properties, reducing water absorption by 10.5% after 24 h submergence and increasing electrical resistivity by 118.9% at early age. Under low CO 2 concentration and ambient pressure conditions, early-age carbonation efficiency is governed primarily by the precuring-controlled moisture state, which regulates CO 2 diffusion and reaction extent and thereby controls carbonation kinetics.