THERMODYNAMICAL STUDY OF HYDRATION AND CHEMICAL SHRINKAGE OF CEMENT CONTAINING SLAG

Over the recent decades, understanding fundamental aspects of cement chemistry has advanced. Due to the recent developments in the eld of cement for improving and reducing the negative environmental impacts of cement production, it is necessary to model or simulate hydration reactions of the cementitious materials. The process in which the cementitious materials form is of great importance. Hence, employing thermodynamic science properly is important. This knowledge gives a powerful insight into developing links between the mineralogy and engineering properties of hydrated cement paste and, therefore, anticipates improvements in its performance of cement production. The hydration process is dramatically in uenced by cement chemistry and microstructures, as a slight change in cementitious generic ingredients can create great differences in the hydration products. Usage of supplementary cementitious materials has considerable in uence on the amount and kind of hydrates formed and thus volume, porosity and durability of cementitious systems. In this paper, blast furnace slag of Esfahan Steel Company with the replacement percentages of 10 to 80 was used to make several thermodynamical models at constant temperature of 20C. Thermodynamic modeling was based on the method of minimizing Gibbs free energy to calculate the composition of the pore solution and solid phase's developments. It is ideal for better understanding reactions' mechanisms during the hydration process. GEM software was applied for thermodynamical modelling. The formed phases assemblage, concentration of pore solution and chemical shrinkage of models were examined. Thermodynamic calculations indicate that slag consumes portlandite and increases calcium silicate hydrates. It also reduces the pore solution volume that results in higher chemical shrinkage and increases the amount of hydrotalcite. Overall, the ndings of slag replacement in cement are higher volume of hydrates, improvement of mechanical properties and, enhanced durability of concretes with cementitious materials.