水泥-硅灰/粉煤灰体系强度、收缩性能与微观结构研究

为研究硅灰及粉煤灰对不同养护龄期的水泥浆体强度及收缩性能的影响,以水胶比为0.29的水泥浆体为基体,设计制备了五种硅灰及粉煤灰掺量的复合水泥浆体,借助量热仪和压汞仪测试表征了不同复合水泥浆体的水化放热特性以及孔结构组成,分析了水化放热量、孔隙率等参数随硅灰和粉煤灰掺量增加的变化规律,建立了复合浆体抗压强度与孔结构以及水化特性与收缩应变之间的量化关系。结果表明,掺入粉煤灰会大幅降低水泥净浆早期抗压强度,但对减小自收缩应变和干缩应变极为有利。掺入硅灰能明显提高净浆3 d抗压强度,但当硅灰掺量超过10%(质量分数)后,净浆3 d自收缩应变及28 d干缩应变增加极为明显。掺入硅灰会使水泥水化诱导期开始和结束的时间提前,还会增加水化反应级数和各阶段的反应速率常数值,导致水泥-硅灰复合浆体的水化放热总量和放热速率相较于水泥-粉煤灰体系大幅增加。粉煤灰和硅灰的掺入均能有效细化水泥浆体内部孔结构,提高凝胶孔比例,大幅降低大孔比例。复合浆体的72 h水化放热总量和3 d自收缩应变呈现正相关关系,而孔隙率和抗压强度呈现明显的负相关关系。

Strength,Shrinkage Performance and Microstructure of Cement-Silica Fume/Fly Ash System

To investigate the effect of adding silica fume (SF) and fly ash (FA) on the strength and shrinkage performance of cement slurries at various curing ages, five different composite cement slurries (water-binder ratio of 0.29) with different content of SF and FA were designed.The hydration heat release characteristics and pore structure composition of different composite cement slurries were characterized by calorimeter and mercury porosimeter tests, and the changes of hydration heat release and porosity with the increase of SF and FA content were analyzed. The relationships between compressive strength and pore structure, hydration characteristic and shrinkage strain were also established. Results show that FA greatly reduces the early compressive strength of cement pastes, while it is beneficial to reduce the autogenous shrinkage strain and dry shrinkage strain at the same time. The 3 d compressive strength of the cement pastes can be improved obviously by adding SF. However, the autogenous shrinkage strain at 3 d and dry shrinkage strain at 28 d of cement pastes increase significantly once SF content exceeds 10% (mass fraction). The addition of SF advances the start and end time of the induction period of cement hydration, and increases the hydration reaction order and the constant value of reaction rate at each stage, which leads to a significant increase of total hydration heat release amount and heat release rate of cement-silica fume in comparison with cement-fly ash system. SF and FA not only effectively improve the internal pore structure of cement slurries, but also increase the proportion of gel pores and reduce the proportion of large pores. It is found that the total hydration heat release amount of composite slurries at 72 h has positively correlation with 3 d autogenous shrinkage strain, and porosity has negatively correlation with compressive strength of composite slurries.