The influences of quartz content and water-to-binder ratio on the microstructure and hardness of autoclaved Portland cement pastes

The present paper evaluates the influence of the amount of quartz and water/binder ratio on microstructure development in cement pastes. Samples without quartz and with 10%, 20%, 30%, 40% and 50% cement replacement by quartz and with water/binder ratio of 0.1, 0.2, 0.3, 0.4, 0.5, 0.7 and 1.0 were autoclaved at 220 °C for 8 h under a 2.1 MPa pressure. The microstructure was characterized by elemental distribution X-ray maps, XRD, SEM and FTIR and the hardness and elastic modulus of the cement matrix were determined by dynamic hardness testing. The results showed that a significant fraction of quartz flour reacted under hydrothermal conditions, tobermorite and xonotlite were detected in samples with high quartz content and traces of α-C2SH were present in samples with low quartz content. Samples with a w/b of 0.2 and 30-40% of cement replacement by quartz exhibited the higher values of hardness and elastic modulus.