摘要
热力学计算表明,碱—碳酸盐反应的AG_(298)~0=-12.19kJ。这是去白云石化反应得以进行的化学推动力。文中列出了计算所得的白云石稳定区和不稳定区的范围。由此得出,溶液中的pH愈高,CO_3^(2-)浓度愈低,则白云石愈不稳定。这就从理论上阐明了为什么水泥中碱含量愈高,碱—碳酸盐反应愈烈,膨胀破坏作用就愈大。混合材掺量很高时,才能显著降低水泥石液相中的pH值,从而缓和碱—碳酸盐反应。这再一次证明碱—碳酸盐反应与去白云石化密切相关。实验和理论证明,碱—碳酸盐反应是由于去白云石化在原地产生,这种局部化学反应和结晶压是引起膨胀的根本原因。要抑制碱—碳酸盐反应,防止混凝土工程遭受破坏,最根本的途径是采用高混合材掺量的低碱水泥。
Thermodynamical calculation demonstrated that the △G_(298)~0 of the alkali-carbonate reaction (ACR) equals -12.19KJ. Which is the chemical driving force to make the dedolomitization occur. In this paper, the stable and unstable areas of dolomite are given by thermodynamical calculation. From this, it is concluded that the higher the pH value and the lower the CO_3^(2-) concentration in solution, the more unstable the dolomite. It explains theoretically the reason why the higher the alkali content in cement, the heavier the ACR, thus the more serious the deterioration due to the expansion. The pH value of the liquid phase in cement paste could be significantly reduced only by adding a great amount of mineral admixtures, so that ACR could be alleviated. This confirms again that the expansion due to ACR is closely related to dedolomitization. Both experimental results and theoretical analyses show that the reaction of dedolomitization is carried out in situ, and both the topochemical reaction and the pressure of crystallization of brucite growing are the essential causes of the expansion due to ACR. In order to restrain the ACR and to prevent the concrete structures from deteriorating, the basic measure is the application of a low-alkali cement with a high content of mineral admixtures, so as to minimize the progress of the reaction of dedolomitization as far as possible.
