C_4A_3$-CaSO_4-CaO体系在硅酸盐水泥浆体中的膨胀机理

Expansion Mechanism of C_4A_3$-CaSO_4-CaO in Portland Cement Paste

对C_4A_3$-CaSO_4-CaO体系(CCC体系,C_4A_3$为4CaO·3Al_2O_3·SO_3)的膨胀机理进行探讨。X射线衍射谱、水化放热历程和封闭环境下的体积变化测试结果表明:CCC体系中CaO的水化活性显著大于其它两者,CaO在水化早期表现出剧烈的水化放热行为,并产生剧烈而短暂的膨胀;CCC体系水化的目标产物是氢氧化钙和钙矾石,但生成钙矾石不是产生宏观膨胀的充要条件,适宜的钙矾石生成位置可以使其在C4A3$颗粒表面,通过钙矾石生长过程中产生的颗粒互斥效应产生膨胀;钙矾石生成过程的膨胀机理,除了吸水肿胀和结晶生长外,还有孔隙形成机理。CCC体系中CaO和CaSO_4的存在有利于保障钙矾石的生成位置。使用CaO-SO_3^-Al_2O_3三元相图表征了CCC体系的组成与水化产物之间的关系,并给出了适宜组成的CCC体系在三元相图中的存在区域。

The expansion mechanism of C4A3$-CaSO4-CaO （CCC system, C4A3$is4Ca O·3Al2O3·SO3） was discussed. Based on the results obtained by X-ray diffraction, hydration heat releasing process and volume change during hydration, it is manifested that the reactivity of CaO overwhelms that of C4A3$ and CaSO4, and introducing CaO to cement paste results in an intensive hydration heat releasing behavior and an expansion in early hydration period. Producing ettringite cannot guarantee the expansion of cement paste because ettringite forming location is also a decisive factor. The suitable forming location of ettringite should be on the surface of C4A3$ particle, and the growth of ettringite results in expansion. The expansion mechanism of CCC system could be due to the porosity enhancing other than the swelling and the crystal growth. From the thermodynamic and kinetic point of view, it is manifested that the existence of CaO and CaSO4 in CCC system promotes the forming tendency of ettringite on the surface of C4A3$ particle. CaO-SO3-Al2O3 three phases diagram was used to character the relationship between the composition of CCC system and its hydration products. The suitable region of CCC system in the three phases diagram was recommended.