The role of Pre-Heating and mineral additive modification on Long-Term strength development of calcium aluminate cement mortars

Strength development of Calcium Aluminate Cement (CAC) under various environmental conditions is an interesting subject of topic that pay attention of researchers for a long time. This special cement usually preferred in applications where quick setting ability, high early strength and resistance to chemical attack is required. However, uncertainty in the hydration process and long-term strength problems, due to conversion reactions in combination with high initial material cost, limit the application of this cement. In order to propose a solution to the above-mentioned problems, blended mortar mixtures were prepared by replacing CAC with variable amounts of microsilica, anhydrite CaSO4 and Portland cement within the scope of this study. The compressive strength development of mortar specimens up to 400 days were investigated under semi-dry curing conditions at 20 ± 5 °C and 60 ± 20% RH. During the initial stages of hydration, a distinct pre-heating based curing procedure was applied to the conjugate specimens. Preliminary stabilization of the unstable hydration products is targeted by this pre-heating method. Accordingly, the crystal structure of the hydration products of specimens was analyzed with the support of microstructural studies (XRD, DTA-TGA, SEM-EDS). The pore size distribution and sub-capillary porosity of specimens were also determined by mercury intrusion porosimetry. The effectiveness of the mineral modification and pre-heating based curing method (exposure to 50 ± 1 °C heating for 21 days) on the long-term strength development of CAC is discussed with the aid of microstructural analysis results. The results showed that it is possible to stabilize the hydration process of CAC and its strength becomes predictable in the long term, if appropriate mineral additives in proper replacement ratios are employed in the mixture design.