297 / 2023-02-17 16:04:01

Effect of early carbonation and hydration on high temperature performance of cement blocks

Early-age carbonation,Further hydration,Elevated temperature,Cement paste,Calcium Carbonates

Early-age carbonation can accelerate the curing process of cement-based materials. This technology holds several benefits, such as improved engineering properties and CO₂ capture, and thereby garners increasing attention from academics and industry experts with an aim to further develop low-carbon construction materials. Previous studies well demonstrate that proper and complete hydration after early-age carbonation curing is crucial for the development of mechanical properties at a later age and beneficial for the recovery of pH in maintaining the long-term durability of concrete.



In this study, the effect of early carbonation coupled with further standard curing (CS) on the performance of cement blocks subjected to different high temperatures was investigated. The change in mechanical properties was investigated in terms of residual compressive strength and microhardness. The impact of elevated temperatures on microstructure evolution was also analyzed using backscattered electron microscopy and thermogravimetric analysis.



The experimental results showed that the strength of all samples increased after exposure to 200 and 400°C (Fig. 1), owing to the fact that heating temperature can accelerate the hydration of unreacted clinker (Fig. 2). In addition, the micro-hardness continuously increased before 400°C, which was associated with the dehydration of calcium silicate hydrate (C-S-H) (Fig. 3). However, compared to those cured with single carbonation (C) or standard curing (S), the cement pastes with CS curing showed a higher residual compressive strength and thermal stability with a lower apparent cracking at 600°C. The microstructure results revealed that the CaCO₃ skeleton prevented matrix cracking by restricting the range of volume shrinkage of the C-S-H gels. Meanwhile, the C-S-H formed after carbonation adhered to the CaCO₃ skeleton after dehydration, which further enhanced the skeleton system (Fig. 4). However, the carbonated layer was transformed to a weaker layer when CaCO₃ was decomposed into lime at 800°C, resulting in a 70% loss (e.g., CS curing samples) in compressive strength. This study successfully develops a novel method for simultaneously ensuring good residual mechanical properties and maintaining the integrity of cement-based materials at elevated temperatures.