Study of the effects of CaCl2 salt on hydration of MgO in aluminous concrete.

Reference	Presenter	Authors (Institution)	Abstract
09-057	Raquel Gomes Araujo	Sousa, R.E.(Instituto Federal do Maranhão); Paiva, A.E.(Instituto Federal de Educação do Maranhão); Araujo, R.G.(Instituto Federal do Maranhão);	Magnesium oxide (MgO) is an excellent refractory material because it has a high melting point (Tf = 2800 ° C) and high resistance to attack by basic slag. As a consequence, this oxide is widely used as raw material in basic refractory castables used as coating in Martin furnaces with basic procedure, electric furnaces and cement kilns. MgO is also widely used in alumina refractories (Al2O3-MgO system), which, through the reaction between these two oxides, produces the spinel-like crystalline structure (MgAl2O4), responsible for giving the concrete a good resistance to thermal shock, high refractoriness and resistance to slag. Due to these properties of spinel (MgAl2O4), research on the optimization of this process and the incorporation or formation of this phase have been carried out over the years. One of the barriers to optimization of this process is precisely in the hydration of the MgO during the concrete curing process, which in contact with water (liquid or vapor), magnesium oxide rapidly hydrates to form magnesium hydroxide (Mg (OH) 2), also known as brucite. This phase is extremely expansive, increasing approximately three times the initial volume of alumina concrete samples containing MgO. In this context, the objective of this work was to alleviate the deleterious effects caused by the formation of the brucite phase during the hydration of the alumina concretes containing MgO by the addition of the CaCl2 salt. The characterization was carried out by means of the tests of apparent volumetric expansion (EVA), mechanical resistance to compression, apparent porosity and X-ray diffraction (XRD). The results showed that the increase of the calcium chloride content decreased the apparent volumetric expansion and increased the mechanical strength of the analyzed concretes.
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