Kinetics of Heat Release of Mechanically Activated Cement-Sand Composition

Introduction . Mechanical activation of the dry components of cement composites is utilized in order to increase the initial strength, improve the rheological characteristics of the mixture, as well as to reduce the setting time by increasing the reactivity of the binder. Heat release kinetics of components of cement composites modified by means of mechanical activation methods has been insufficiently investigated and studying its changes is an urgent task. In order to describe heat release kinetics, well-known equations are used relating a degree of hydration and a relative heat release. The aim of this study is to examine heat emission of a mechanically activated cement-sand composition as well as to identify parameters of equations describing heat release kinetics. Materials and Methods . The investigated mechanically activated composition consists of cement and sand with a weight ratio of 1:2.14, with a specific surface area of 3690.8 cm2/g. Using an isothermal calorimeter, a calorimetric analysis of a mechanically activated cement-sand composition, as well as non-activated cement, was conducted, and heat flux data were obtained. Research Results . The cement in the composition of the mechanically activated composition was found to be moderately thermal in terms of heat release, with heat release values of 247 J/g and 281 J/g at the age of 3 and 7 days, respectively. During preliminary mechanical activation of the cement-sand composition, the time of the induction period and that to reach 50% of the maximum heat release of cement are reduced by 1.34 and 1.76–1.79 times, respectively. Discussion and Conclusion. In the course of the study, the heat release kinetics of a mechanically activated cement-sand composition is described. A decrease in the induction period of the hydration process during mechanical activation of cement has been identified confirming the efficiency of mechanical activation of initial dry concrete components. The results can be practically applied in plants for producing dry building mixtures and concretes while introducing the technology of mechanical activation of concrete composite components.