Volume 4, Issue 3 (March 2007)
Effect of Chemical Admixtures on Rheology of Cement Paste at High Temperature
Placement of cement-based materials in hot weather conditions encounters many problems due to the rapid evaporation of mixing water and the accelerated hydration of cement. Such materials are also adversely affected at elevated temperatures by an increased water demand, shorter setting time, and more rapid slump loss. These problems can be mitigated using adequate chemical admixtures. However, technical data on such admixtures are commonly developed at normal temperatures, and there is a real need to investigate their performance at hot temperatures. In the current research, the rheological properties of portland cement pastes with a water-cement ratio (w/c) of 0.35 and 0.50 are investigated at different temperatures in the range of 20 to 45°C using an advanced shear-stress/shear-strain controlled rheometer. The influence of water-reducing and retarding admixture, polycarboxylate, naphthalene sulfonate, and melamine-based high-range water-reducing admixtures (HRWR) in addition to mid-range water-reducing admixtures (MRWR) on the rheological properties of cement paste at various temperatures was also examined. The paper aims at formulating recommendations for the effective use of chemical admixtures at high temperature, which should enhance the rheological properties of cement-based materials in hot weather conditions.