白云石微粉对水泥早期水化性能的影响及其机制

Effects of dolomite powders on the early hydration properties of blend cement and its mechanism

为探究白云石微粉在水泥混凝土中安全和高效应用途径,以石灰石微粉为参照,采用水泥标准试验方法和等温量热法,研究白云石微粉取代量和细度对水泥凝结和放热特性的影响及其机制。结果表明:细度大于水泥的白云石和石灰石微粉均增加混合水泥用水量。与石灰石微粉对初凝时间无明显影响、小幅延长终凝时间不同,白云石微粉明显延缓初、终凝时间,且取代量和细度愈大,缓凝现象愈显著。白云石微粉与石灰石微粉均可加速早期水化和降低累计放热量,润湿期的放热速率随白云石微粉用量增加而降低,却随石灰石微粉用量增加而升高。决定混合水泥需水量变化的主要因素是碳酸盐粉体引入而致堆积密度的改变;混合水泥的缓凝主要与体系的堆积密度和微粉颗粒表面所带电位有关。润湿期放热速率差异性主要是粉体表面荷电量不同所致。

For exploring the high efficient and safe application of dolomite powders in cement and concrete,the early hydration properties,including setting and hydration heat release of cement blended with dolomite powders at various replacement levels and fineness were studied by standard cement testing method and isothermal calorimetry with limestone powder as the reference. Results showed that both limestone and dolomite powders finer than cement increased the water demand of blend cement. Contrary to limestone powder,which showed no obvious effect on initial setting and slightly prolongs the final setting,dolomite powders showed a stronger retarding effect on both initial and final setting,and the phenomenon was more pronounced with the increase of its replacement levels and fineness.Both limestone and dolomite powders accelerated the early hydration,and reduced accumulative heat release of blend cement. However,the heat release rate in the pre-induction period decreased with the increasing of dolomite content,and increased with the increasing of limestone powder. The variation of water demand was determined by the changes in the packing density of the blend cement caused by the incorporation of carbonate powders. The retarding behavior of blended cements was mainly due to their differences inpacking density and surface zeta potential of two carbonate powders.The differences in the zeta potentials of the carbonate powders resulted in the distinct behavior in the heat release rate in the pre-induction period of the blend cements.