矿物掺合料对UHPC性能的影响

传统超高性能混凝土(UHPC)的硅灰用量一般都比较高,导致其制作成本较高,而且自收缩比较大,对实际工程应用造成了一定的影响。本文用粉煤灰和矿粉部分或全部替代硅灰制备UHPC,并对其工作性能、力学性能、自收缩及孔结构特征进行了试验研究。结果表明:采用粉煤灰或矿粉替代硅灰可以改善UHPC拌合物的流动性,替代率越高,拌合物的流动度越大;当采用粉煤灰或矿粉替代50%(质量分数)硅灰时,在标准养护下,对28 d抗压强度的影响较小,而在高温蒸养下,则会导致28 d抗压强度下降,当替代率达到100%(质量分数)时,无论是标准养护还是高温蒸养,都会显著降低28 d抗压强度;采用粉煤灰或矿粉替代硅灰能降低细孔的占比,增大孔径,减少自收缩,且粉煤灰对于自收缩的抑制效果优于矿粉。

Influences of Mineral Admixtures on UHPC Performance

For traditional ultra-high performance concrete (UHPC), the dosage of silica fume is generally high, resulting in high production cost and large autogenous shrinkage, which has a certain impact on its practical engineering application. In this paper, UHPC was prepared by partly or completely replacing silica fume with fly ash and mineral powder. The working performance, mechanical properties, autogenous shrinkage and pore structure characteristics of UHPC were studied. The results show that the replacement of silica fume by fly ash or mineral powder improves the fluidity of UHPC mixture. The higher the replacement rate is, the greater the fluidity of the mixture is. When 50% (mass fraction) silica fume is replaced by fly ash or mineral powder, the influence on 28 d compressive strength is small under standard curing, while for high temperature steam curing, the 28 d compressive strength decreases. When the replacement rate reaches 100% (mass fraction), the 28 d compressive strength is significantly reduced under standard curing or high temperature steam curing. Fly ash or mineral powder instead of silica fume reduces the proportion of fine pores, increases pore size and reduces autogenous shrinkage, and the inhibitory effect of fly ash on autogenous shrinkage is better than that of mineral powder.