Influence of microstructure concrete curing condition on the formation in high-strength

Microstructure of high-strength concrete prepared at low water cement ratio is quite different from that of ordinary concrete. Both steam and autoclave curing applied to high strength concrete also have a large influence on the structure formation of concrete. Heat curing at 250-400 degrees C is applied to manufacture RPC-reactive powder concrete - which is ultra-high strength and ductile properties. In order to study the influence of water cement ratio, curing condition and addition of silica fume on the hydration of cement and microstructure formation, and to discuss the relationship between microstructure and compressive strength, the high strength mortars prepared at W/C=0.25 with S/C=1 cured at 20 degrees C, 250 degrees C, 80 degrees C-steam and 180 degrees C-10atm were characterized and stress-strain properties and clack propagation of high strength mortar were evaluated. By the steam curing, the strength of SFC was remarkably increased through the acceleration of cement hydration and pozzolanic reaction. The strength of mortar after steam-curing was,however, hardly increased though it was additionally autoclave-cured and oven-cured. The linearity of stress-strain curve of mortar under the loading of compressive strength was much improved by temperature-increasing curing. The static modulus of elasticity of the SFC mortar was lower than of NPC mortar especially in temperature-increasing curing. The reason for these phenomena were discussed in relation to the microstructure-related characters including porosity, pore size distribution, crack of mortar, and kind, crystallinity, quantity and rearrangement of produced hydrates.