Xian Xiangping, Logan Chad, Shao Yixin
Department of Civil Engineering, McGill University, 817 Sherbrooke Street West, Montreal, QC H3A 2K6 Canada.
Mater Struct. 2022;55(3):94. doi: 10.1617/s11527-022-01926-8. Epub 2022 Mar 29.
Early-age carbonation curing of concrete is receiving more interest in terms of performance improvement and emission reduction. However, the volume change of cement-based products subject to carbonation curing may become a concern because of the potential carbonation shrinkage and its related shrinkage cracking. The purpose of this study was to investigate the dimensional stability of cement paste and concrete subject to the early-age carbonation curing. It was found that the carbonation curing introduced first an initial shrinkage due to water evaporation upon gas injection and then generated an expansion due to CO uptake and carbonate precipitation. As carbonation proceeded, the deformation was switched to a secondary shrinkage after expansion. The residual deformation due to carbonation curing was shrinkage in cement paste samples and expansion in concrete samples. This was because the relative expansion due to carbonate precipitation in paste was not large enough to compensate for the shrinkage caused by water loss. However, for concrete samples, the introduction of aggregates reduced the pore spaces in concrete, leading to an expansion owing to the limited precipitation. The results of carbon dioxide uptake, XRD, and SEM analysis confirmed that calcium carbonate formation played a critical role in the relative expansion. The study also showed that cement-based products were more resistant to weathering carbonation after the early-age carbonation curing. After 61-day weathering carbonation exposure, both paste and concrete samples exhibited carbonation shrinkage as a result of carbonation of hydration products. However, the magnitude of shrinkage was much smaller in carbonation curing than in weathering carbonation because of the short period of exposure. Both carbonations did not significantly affect the compressive strength of carbonated products. Carbonation curing likely makes concrete products more dimensionally stable in the long-term service.
混凝土的早期碳酸化养护在性能提升和减排方面正受到越来越多的关注。然而，由于潜在的碳化收缩及其相关的收缩开裂，经历碳酸化养护的水泥基产品的体积变化可能会成为一个问题。本研究的目的是调查水泥净浆和混凝土在早期碳酸化养护下的尺寸稳定性。研究发现，碳酸化养护首先由于气体注入时水分蒸发而产生初始收缩，然后由于二氧化碳吸收和碳酸盐沉淀而产生膨胀。随着碳酸化的进行，变形在膨胀后转变为二次收缩。碳酸化养护引起的残余变形在水泥净浆样品中为收缩，在混凝土样品中为膨胀。这是因为净浆中碳酸盐沉淀引起的相对膨胀不足以补偿水分损失导致的收缩。然而，对于混凝土样品，骨料的引入减少了混凝土中的孔隙空间，由于沉淀有限而导致膨胀。二氧化碳吸收、X射线衍射和扫描电子显微镜分析结果证实碳酸钙的形成在相对膨胀中起关键作用。该研究还表明，早期碳酸化养护后的水泥基产品对风化碳化更具抵抗力。在61天的风化碳化暴露后，净浆和混凝土样品由于水化产物的碳化都出现了碳化收缩。然而，由于暴露时间短，碳化养护中的收缩幅度比风化碳化中的小得多。两种碳化都没有显著影响碳酸化产品的抗压强度。碳酸化养护可能使混凝土产品在长期使用中尺寸更稳定。
