The effect of curing temperature on sulphate-resistant cement hydration and strength

This paper describes the behaviour of sulphate resistant cement paste hydrated at temperatures ranging from 4 to 85 °C. A number of techniques and methods were used to study hydration: compressive strength, thermogravimetry, X-ray diffraction, mercury intrusion porosimetry, backscattered electron imaging in conjunction with energy dispersive X-ray analysis and nuclear magnetic resonance (NMR). Early age compressive strength was found to be higher in cement pastes cured at 40 and 85 °C than in the materials hydrated at 4 and 22 °C, due to the formation of larger quantities of hydrated product in the former. The MAS NMR findings showed that this higher early age strength was related to increased CSH gel polymerization rates, and a concomitantly larger average number of units in the SiO4 chains. The formation of CSH gels with very long chains at early ages hindered the uptake of further hydration products, however. This in turn generated more porous and less cohesive structures, causing a decline in mechanical strength, as confirmed by the backscattered electron imaging and porosity results.
Dr. I. Elhadiri participated in this study under a Spanish Agency for International Cooperation (AECI) Grant. The research was funded by the Spanish Ministry of Education and Science under Project CTM2004-06619-C02-01. The authors thank Professor Antonio Aguado (Polytechnic University of Catalonia) and M. Palacios for their comments and support. They are likewise grateful to J.L. García, A. Gil, M.M. Alonso and J. Llueca for their assistance with the mechanical, spectroscopic and microscopic tests and I. Sobrados and M. Palacios for the NMR studies.