Utilization of low-cost celestite ore in the production of high-quality calcium-strontium aluminate refractory cement

Calcium-strontium aluminate cement (CSAC) has been successfully prepared for the first time from celestite mineral and corundum (α-Al2O3) via solid-state reaction. Various mixing compositions containing 40–70 wt% celestite and 60–30 wt% alumina have been sintered at firing temperatures between 1550 and 1650 °C with an interval of 50 °C. Among these sintered mixes, four cement specimens (CA101-1600, CA101-1650, CA201-1600 and CA201-1650) were selected as the optimal mixes for CSAC preparation based on their physico-chemical and mechanical characteristics. These cement mixes were ground to form a very fine powder with a particle size of less than 4.85 μm and a specific surface area of greater than 3629 cm2/g. Upon mixing these cement mixes with water, they consumed mixing water within a range of 19–27 wt% to form workable cementitious pastes. The initial and final setting times of these four cement mixes were in the range between 80 to 90 min and 290–379 min, respectively. An average compressive strength of approximately ~62 MPa was reached after curing of these cement cubes in a 100% humidity cabinet for 28 days. The main hydration products detected in the cement pastes were strontium aluminate hydrates such as 3SrO·Al2O3·H2O (Sr3A.H2O) and 5SrO·Al2O3·11H2O (Sr5A.11H2O) along with a minority of calcium aluminate hydrate 4CaO·3H2O·3H2O (C4A3.3H2O) and aluminium hydroxide Al(OH)3. The obtained physico-mechanical results of the four cement samples have met the international standard requirements; demonstrating the high-susceptibility of celestite mineral to be utilized as a potential feedstock in the production of CSAC on an industrial scale.