偏高岭土对蒸养混凝土强度和毛细吸水性的影响

采用偏高岭土等矿物掺合料等量取代30%水泥研究了蒸养混凝土强度和毛细吸水性，并通过热重、差热分析和电镜探讨了作用机理。结果表明，偏高岭土对提高蒸养混凝土的脱模强度效果显著，复掺10%粉煤灰和20%偏高岭土的蒸养混凝土脱模强度比空白蒸养混凝土强度高23%，比复掺粉煤灰和矿渣的高17%；掺入粉煤灰、矿渣和偏高岭土都降低了混凝土的毛细吸水性，且掺偏高岭土混凝土试件的早期水吸附速率及总的吸水量均为最低；热分析和电镜观察表明，在蒸养60℃温度的热激发下，偏高岭土早期与水泥水化产物氢氧化钙发生火山灰反应是脱模强度高的主要原因，火山灰反应消耗了氢氧化钙，生成了更多的水化产物，混凝土更为致密。

Effect of Metakaolin on Compressive Strength and Capillary Water Sorptivity of Steam-cured Concrete

The compressive strength and capillary water absorption of steam-cured concrete with 30%replacement of cement by metakaolin and other mineral admixtures were investigated. The mechanism was also analysed using differential analysis( DTA) , thermogravimetric analysis ( TGA) and scanning electron microscope( SEM) . Results show that the presence of metakaolin( MK) is greatly beneficial in increasing the demoulding compressive strength of steam-cured concrete. The demoulding compressive strength of steam-cured concrete containing 10% fly ash( FA) and 20% MK is 23% higher than that of the blank concrete incorporating no MK, and 17% higher than that of the concrete incorporating FA and ground granulated blast furnace slag ( GGBS) . Use of FA, GGBS and MK as cementitious materials remarkably decrease the water sorptivity. For the steam-cured concrete containing MK, both the capillary sorptivity coefficient and the total mass of water absorption are the lowest. Thermal analysis and SEM images indicate that the main cuase for the improvement of demoulding compressive strength is the pozzolanic reaction between MK and Ca( OH) 2 liberated from cement at early ages due to thermal activation under 60 ℃ steam curing conditions. The consumption of Ca ( OH ) 2 and the formation of more hydration products are observed, thus the concrete become denser.