Carbonation and related behaviors of hardened cement pastes under different hydration degrees
Carbonation and related behaviors of hardened cement pastes under different hydration degrees
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DOI：
10.1016/j.cemconcomp.2023.105079
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发表时间：
2023-05
影响因子：
10.5
通讯作者：
Y. Xu;Xuhui Liang;C. Wan;Hongyu Yang;Xiaming Feng
中科院分区：
文献类型：
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作者：
Y. Xu;Xuhui Liang;C. Wan;Hongyu Yang;Xiaming Feng
本文研制了一种成型圆盘试样，研究了不同水化程度下硬化水泥浆体的碳化及相关行为。水泥浆体的重量和长度随时间的变化进行了监测，在一个多步骤的过程中，包括碳酸化，干燥，再润湿，再干燥。采用X射线衍射（XRD）和热重分析（TGA）相结合的方法对碳酸盐水泥浆体的矿物组成进行了鉴定和定量分析。水泥净浆的CO2吸收能力与水化时间呈指数关系，表明水泥净浆的CO2吸收能力在水化初期急剧下降，随着水化时间的延长，其吸收能力保持相对稳定。揭示了这一发现的两个原因：i）碳酸化产物的碳酸化和碳酸化后反应之间的平衡，即，二氧化硅-氧化铝凝胶; ii）通过阻碍碳酸化的水合产物来细化孔结构。提出了较为清晰的碳酸化区域划分，初步建立了CO2吸收空间分布方程。通过对不同水化龄期水泥浆体的碳化和干燥行为的监测，发现碳化降低了水泥浆体的干燥收缩，特别是对于早龄期样品，而干燥则增加了碳化收缩。通过考察C-S-H凝胶碳酸化过程中水的变化，发现C-S-H凝胶碳酸化过程中几乎没有水的释放。新提出的模型对碳化收缩机理提供了新的认识。
This paper develops a kind of molded disc samples to investigate the carbonation and related behaviors of hardened cement pastes under different previous hydration degrees. Weight and length changes of cement pastes over time are monitored during a multistep process including carbonation, drying, rewetting, and redrying. The combination of X-ray diffraction (XRD) and thermogravimetric analysis (TGA) is used to identify and quantify the mineral compositions of carbonated cement pastes. An exponential function between CO2uptake capacity and hydration time of cement pastes is established, which shows that the CO2uptake capacity of cement pastes decreases dramatically at the very beginning days of hydration and then remaining relatively stable as hydration time is prolonged. Two reasons for this finding are revealed: i) the equilibrium between the carbonation and the post-carbonation reaction of carbonation product, i.e., silica-alumina gel; ii) refining of pore structures by hydration products which hinders carbonation. A clearer zonation of carbonation areas is proposed, and the spatial distribution equations of CO2absorption are initially established. By monitoring carbonation and drying behavior of cement pastes with different hydration ages, it is revealed that carbonation reduces drying shrinkage of cement pastes especially for early-age samples, whereas drying increases carbonation shrinkage. By investigating the water changes during the multistep process, it is found that water is little released during the carbonation of C–S–H gels. New insight into mechanism of carbonation shrinkage is provided by a newly proposed model.