Lime-activated fly ash cementitious materials are widely used as masonry cement and autoclaved building materials. This study investigated the effects of MgO on the microstructure and properties of the fly ash/cement-based pastes under hydrothermal conditions. The activator (i.e., CaO + MgO) was fixed at 17 wt%, and CaO was replaced with MgO at 0–30 wt%. The properties assessed were compressive strength, linear expansion, fluidity, porosity and pore size distribution. The microstructure was investigated by means of XRD, TG-DSC and SEM. Experimental results show that the compressive strength depended on the autoclave temperature, time and MgO content. Overall, as the MgO/(MgO + CaO) ratio was less than about 20, 15 and 12% at 140, 180 and 210 °C, respectively, MgO contributed to improve the compressive strength. In addition, appropriately extending the autoclave time or raising the autoclave temperature was in favor of strength development. The lower MgO content had a little influence on the expansion, but once the MgO/(MgO + CaO) ratio exceeded 20%, the expansion remarkably increased. Microstructural analyses demonstrated that MgO promoted the formation and crystallization of tobermorite likely through a solid phase or liquid-solid reaction mechanism. Besides, the micro-morphology of tobermorite tended to be slender in the presence of MgO.

石灰活化的粉煤灰水泥材料被广泛用作砖石水泥和高压灭菌的建筑材料。这项研究调查了在水热条件下MgO对粉煤灰/水泥基浆料的微观结构和性能的影响。活化剂（即CaO + MgO）固定为17 wt％，CaO替换为0-30 wt％的MgO。评估的性能为抗压强度，线性膨胀，流动性，孔隙率和孔径分布。通过XRD，TG-DSC和SEM研究了显微组织。实验结果表明，抗压强度取决于高压釜温度，时间和氧化镁含量。总体而言，由于MgO /（MgO + CaO）的比例分别在140、180和210°C下分别小于20％，15％和12％，MgO有助于提高抗压强度。此外，适当延长高压釜时间或提高高压釜温度有利于强度的发展。较低的MgO含量对膨胀几乎没有影响，但是一旦MgO /（MgO + CaO）比超过20％，则膨胀显着增加。微观结构分析表明，MgO可能通过固相或液固反应机制促进了硅钙石的形成和结晶。此外，在MgO存在下，雪铁矿的微观形貌趋于细长。微观结构分析表明，MgO可能通过固相或液固反应机制促进了水辉石的形成和结晶。此外，在MgO存在下，雪铁矿的微观形貌趋于细长。微观结构分析表明，MgO可能通过固相或液固反应机制促进了硅钙石的形成和结晶。此外，在MgO存在下，雪铁矿的微观形貌趋于细长。