Cement reactions in hydrothermal conditions
Fundamental processes of cement hydration were studied at elevated temperatures, between 100 and 200oC at saturated steam pressure, using hydrothermal curing. Initial investigations centred on treatments on Ca3SiO5 and -Ca_2SiO_4, synthesised in the laboratory, having compositions similar to those which occur in cement clinker. Their reaction products, either separately or with blending agents such as quartz or silicic acid, were identified by x-ray diffraction. Further characterisation data were obtained for tobermorite, xonotlite, hillebrandite, gyrolite, truscottite, kilchoanite, calciochondrodite, -dicalcium silicate hydrate and tricalcium silicate hydrate using scanning electron microscopy, infrared spectroscopy and nuclear magnetic resonance spectroscopy. The current postulated structures of hillebrandite and tricalcium silicate hydrate were reassessed. The factors affecting compressive strength development of cement pastes were reviewed. Theoretical volume changes were calculated for the formation of hydrothermal calciumsilicate hydrates. These may be a useful aid in assessing the suitability of a particular phase and estimating the likely consequences of phase changes on strength. The nature of the silica source affects the type of products obtained. A more detailed study of the reaction between Ca3SiO5 and various blending agents was undertaken in order to correlate between formulation, mineralogy after hydrothermal treatment, compressive strength and porosity. Actual cement blends were studied using a typical class G oilwell cement and various blending agents. In short term tests the mineralogy and compressive strength were determined with varying compositions and temperatures. It is hoped that this information will be an aid in predicting optimum compositions by correlating properties with the nature of the materials and their chemistry. Class J cement hydration and class G cement blends were also studied by infrared and nuclear magnetic resonance spectroscopy.