The Properties of Slag Cement and its Influence on the Structure of the Hardened Cement Paste

Abstract

A ground blast-furnace granulated slag used in the production of construction materials and items differs in its chemical composition, dispersion, the quantity of amorphous phase and so on, which leads to the change of properties of the blended cement consisted of CEM I and supplemented with different amount of slag. The chemical and mineralogical composition of portland cement, the conditions of its maturing, activators and others also influence on the properties of the blended cement. The acid slag is not binding in contrast to the basic one, but due to the pozzolanic properties it interacts with the calcium hydroxide to form an additional amount of a low-basic hydrated calcium silicate in a hardened cement paste structure. The strength of the blended cement with increasing dosages of slag varies in different ways - small amount of slag in the cement even increases slightly the compressive and flexural strength in comparison with the blended cement without an additional CEM I. Increasing the dosage of slag in the blended cement, its compressive strength decreases slightly, especially at an early stage, and the flexural strength remains at the same level by increasing the dosage up to 70-80% of blended cement slag mass. Besides the CEM I dilution effect, the increase of the mixture water demand with the increased slag dosage influences the strength of mortar samples of equally and easily workable mixtures. A true water-binder ratio is increased significantly if the content of slag is over 70%.The conducted studies have shown that the substitution of CEM I with 70% of slag is optimal both from the perspective of the impact on the technical characteristics of the resulting rock and from the economic point of view.The rock structure obtained from the blended cement differs in terms of high concentration of amorphized low-basic hydration products and the decrease in its content of Са(ОН)2. The last is proportional to the number of slag additive and affects significantly the phase composition of the rock and its properties.