Ceramics-Silikáty 53, (2) 65 - 75 (2009)

Hydration was studied in two cements (CEM I 42.5R and CEM II/A-V 42.5R) cured at temperatures ranging from 4 to 85°C. Hydration was monitored with a number of instrumental techniques: X-Ray Diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Backscattered Electron (BSE) imaging in conjunction with Energy Dispersive X-ray analysis (EDX) and Nuclear Magnetic Resonance (MAS NMR). The mechanical strength of the pastes was likewise determined at different ages, while mercury intrusion porosimetry was used to establish porosity and pore size distribution. The results confirmed that curing cement at higher temperatures tended to increase the early age hydration rate significantly and decrease longterm compressive strength. The decline in 28-day compressive strength in pastes cured at high temperatures was attributed to their higher porosity and less uniform microstructure. The FTIR and MAS NMR findings indicated that polymerization was more intense in the calcium silica hydrate gel (C–S–H) formed in pastes cured at high temperatures than in the gel formed in pastes cured at low temperatures. No substantial temperature-induced differences were found between cements with and without fly ash additions.