Effects of high-pressure/temperature curing on reactive powder concrete microstructure formation

Reactive powder concrete (RPC) comprises cement with quartz sand, superplasticizer, silica fume, and water which is processed by heat curing and/or pressure. This paper presents the effect of treatments (static pressure of 8 MPa and heat curing at 240 °C for 48 h) on microstructure formation. Results indicated that pressure decreased the total pore volume, but increased the capillary pore volume due to the movement of grains. The space created could allow additional C-S-H growth during hydration (and later pozzolonic reaction). Heat treatment accelerated the propagation of microcracks (formed during shrinkage) due to thermal expansion of the solid phases, volumetric expansion of the air and increased pressure within entrapped voids. It induced further crystalline hydrate formation inside the capillary pore network. Pressure following by heat curing treatment firstly increased the capillary pore volume and then accelerated both the hydration and pozzolonic reactions with subsequent increased in skeletal density.