Production of expansive additive to portland cement

The expansive additive was produced from sulfate–calcium component and aluminate clinker, containing 60% Al2O3. The sulfate–calcium component is prepared by flue gas desulphurization gypsum and calcareous raw material mixture burning. The ground sulfate component, mixed with ground aluminate clinker transforms into the effective expansive addition to portland cement. The following main phases were present in this expansive material: anhydrite, calcium oxide and monocalcium aluminate.The expansive substance was added to CEM I 42.5 cement as 7 and 12% addition. The mixtures were subjected to the hydration process; the expansion was measured as a function of varying conditions. The linear changes, as well as the compressive/flexural strength were determined after 1, 3, 7 and 28 days. The initial and final setting time was also measured.The cement with 7% (by weight) expansive additive is a shrinkage-less material, while the mixture with 12% (by weight) expansive additive is an expansive binder.The samples were examined by XRD and SEM-EDS.