Abstract: 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.

Key words: steam-cured concrete;metakaolin;compressive strength;capillary water absorption;pozzolanic reaction