Experimental study of compatibility between chemical admixtures and Portland cement in cementitious mixtures by calorimetry

摘要

Chemical admixtures, increasingly used in construction, have been an important role in cementitious materials technology by modifying some behaviors of cementitious mixtures, such as workability and delay or acceleration of the setting time of cement. The wide variety of admixtures available requires knowledge of their compatibility when used with different cementitious compositions, considering the type of admixtures, the dosage content and type of cement used. Thus, this study aims to analyze a compatibility of the interaction between cements and additives through calorimetric curves generated from a semi-adiabatic calorimeter. The analysis will be performed by the production of pastes resulting from the composition of mixtures between two types of Portland cement (CPIV and CPV) and five water reducing admixtures, four classifieds as plasticizers and one as a superplasticizer, from different manufacturers, and water. The mixtures have a water/cement ratio (w/c) set at 0.40 and different dosage levels of admixtures: 0.0, 0.4, 0.6, 0.8 and 1.0. The results showed that the presence of admixture in the cement pastes influences in the hydration heat and in the initial and final setting time of cement pastes. The maximum temperature decreases and a considerable delay at initial setting time occurs when the quantity of plasticizer admixture in the mixtures is increased, whereas for the pastes produced with superplasticizer admixture this expressive reactant was not registered.