Interaction between low-grade magnesium oxide and boric acid in chemically bonded phosphate ceramics formulation

A hard-burner low-grade MgO (LG-MgO) is used to formulate a chemically bonded phosphate ceramic (CBPC) instead of pure MgO. This by-product is 10 times cheaper than pure MgO. The use of this by-product reduces the cost of the final material and therefore an economical construction material could be obtained. This would reinforce the criteria of sustainability and recyclability. In addition, the inert phases contained on LG-MgO act like inorganic fillers, improving the mechanical properties of this CPBC, which can be considered as a mortar. A range from 55% to 65% of LG-MgO is studied, and boric acid is added in order to improve workability and setting times. Design of Experiments (DoEs) approach enabled the evaluation of the influence of each component and the interactions between them. According to the setting times and compressive strength results, a formulation range is proposed.