The coupling effect of calcium concentration and pH on early hydration of cement
The coupling effect of calcium concentration and pH on early hydration of cement
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钙浓度与pH值对水泥早期水化的耦合影响
DOI：
10.1016/j.conbuildmat.2018.07.067
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发表时间：
2018-10-10
影响因子：
7.4
通讯作者：
Sun, Wei
中科院分区：
文献类型：
--
作者：
Chen, Heng;Feng, Pan;Sun, Wei
孔隙溶液为水泥水化提供了物理和化学环境，水泥熟料溶解释放的钙、硅和羟基离子在孔隙溶液中转移到水化产物硅酸钙水合物（C-S-H）和氢氧化钙水合物（CH）中。因此，钙离子和pH不仅对水泥熟料的溶解有显著影响，而且对CH和C-S-H的析出也有显著影响。然而，它们如何影响水泥水化动力学，特别是在非常早期的阶段，仍然不清楚。为了探究这种影响，我们分别用草酸钾和草酸分别调节孔溶液中钙的浓度和pH。采用量热法和孔隙溶液分析相结合的方法对不同配方的水泥浆体进行了研究。结果表明，同时去除钙离子和羟基离子可以显著增加诱导期长度，降低量热曲线上硅酸盐反应峰的高度，而单独去除羟基离子或钙离子则不能。通过对alite饱和指数、CH和C-S-H的计算，可知alite在诱导期的欠饱和度与诱导期的长度有很好的关系，同时去除钙离子和羟基离子可能导致alite的欠饱和度降低，诱导期延长，硅酸盐峰出现时间推迟。随着pH的升高，硫酸盐浓度升高，铝酸盐峰升高，硅酸盐峰与铝酸盐峰之间的时间间隔缩短。(C) 2018 Elsevier Ltd.版权所有。
Pore solution provides the physical and chemical environment for cement hydration, in which calcium, silicon, and hydroxyl ions released by dissolution of cement clinker are transferred into the hydration products such as calcium silicate hydrates (C-S-H) and calcium hydroxide (CH). Therefore, both calcium ions and pH not only have significant influence on the dissolution of cement clinker but also on the precipitation of CH and C-S-H. However, how they influence the kinetics of cement hydration, especially at the very early stage, remains unclear. With the attempt to explore this influence potassium oxalate and oxalic acid were used to regulate the calcium concentration and pH within pore solution independently. Cement pastes with different formulations were investigated by the combination of calorimetric measurements and pore solution analysis.The results suggest that simultaneous removal of calcium and hydroxyl ions can significantly increase the length of induction period and reduce the height of the silicate reaction peak in the calorimetric curves, whereas the removal of hydroxyl or calcium ions alone cannot. The calculation of saturation index of alite, CH, and C-S-H indicates that undersaturation degree of alite during induction period is well related to the length of induction period and simultaneous removal of calcium and hydroxyl ions is likely to cause lower undersaturation degree of alite, longer induction period, and postponed time of silicate peak. The increase of pH could result in a higher sulfate concentration and subsequently a higher aluminate peak, and a shorter time interval between silicate and aluminate peak. (C) 2018 Elsevier Ltd. All rights reserved.