Hydrophobic materials, superplasticizer and microsilica effects on setting of cement pastes at various temperatures

The use of hydrophobic materials, superplasticizers and microsilica by the concrete industry in hot weather regions is increasing substantially. This paper investigates the influence of these materials on the setting times of cement pastes. Seven mixes with different component proportions were made to demonstrate the uncombined as well as the combined effects of these materials on both the initial and final setting times at 20, 35 and 50°C. The test results indicated that the hydrophobic material had a retardation effect. The efficiency of either the hydrophobic material or the superplasticizer in retarding setting is lower at high temperatures. Most interesting is that when combining the hydrophobic material with the superplasticizer, the resulting product gave an acceleration effect. The inclusion of microsilica in the mixture as a cement replacement material retarded both the initial and final settings.