Globally, the rising concern over the concentration of atmospheric carbon dioxide (CO) has pushed the academic and industry parties to alleviate such emissions. One of the most promising means is to directly mineralize the CO from flue gas via fixing carbon in cement/waste-based construction products. Industrial flue gas (∼20 % CO) emitted with inherent heat and water vapor can be utilized to optimize the efficiency of CO sequestration. For this purpose, this study investigated the carbonation behavior of cement compacts subjected to CO temperatures from 80 to 140 °C with a relative humidity (RH) range of 2–90 %. The experimental test results demonstrated that mechanical strength was enhanced with increasing curing temperature and RH up to 120 °C and 60 % RH, owing to a dense matrix with refined pore structure by the highest reaction products. Phase assemblage transitions and microstructural evolution were further studied via examining the BSE images at different depths. A reaction annulus that evolved from hydrates (inner layer) towards stable carbonates (outer layer) was found in samples exposed to temperatures ≤ 120 °C. At 140 °C, a direct carbonation of calcium silicate was observed. These findings lay a basis for optimizing the carbonation temperature and RH for a further in-situ application strategy.

中文翻译：

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通过二氧化碳固化水泥压块进行碳封存：优化烟气固有热量和水蒸气

在全球范围内，人们对大气中二氧化碳（CO）浓度的日益关注促使学术界和工业界致力于减少此类排放。最有前途的方法之一是通过在水泥/废物基建筑产品中固定碳来直接矿化烟气中的二氧化碳。工业烟气（~20% CO）与固有热量和水蒸气一起排放，可用于优化 CO 封存效率。为此，本研究调查了水泥压块在 80 至 140 °C 的 CO 温度和 2-90% 的相对湿度 (RH) 范围内的碳化行为。实验测试结果表明，随着固化温度和相对湿度升高至 120 °C 和 60% RH，机械强度得到增强，这是由于最高反应产物所形成的致密基体和细化的孔结构。通过检查不同深度的 BSE 图像，进一步研究了相组合转变和微观结构演化。在暴露于 ≤ 120 °C 温度的样品中发现了从水合物（内层）向稳定碳酸盐（外层）演变的反应环。在 140 °C 时，观察到硅酸钙的直接碳酸化。这些发现为优化碳酸化温度和相对湿度以进一步实现原位应用策略奠定了基础。