Evaluation of hydration mechanism of refractory materials and associated evaluation of horizontal stress from experiments and numerical simulations

Abstract

Ground upheaving occurs in expansive soils as a result of the absorption of water molecules onto the clay surface. Even though it is a different mechanism, the refractory materials deposited underground also expands via the hydration process transforming from magnesium oxide to magnesium hydroxide. The hydration process of magnesium oxide (MgO) causes volume expansion, and this process takes a long time under normal atmospheric pressure and temperature conditions. In this study, visual observation was obtained by accelerating the hydration process of two magnesia particles (Dead Burned Magnesia DBM and Crystal Fused Magnesia CFM) by utilizing conditions of high-pressure high-temperature. The smaller the particles, the wider the area of contact with the water, which leads to a faster hydration reaction. In the case of DBM with relatively small particles, the hydration process was completed within 3 hours, and however for CFM particles, it was not completed for 33 hours even under 220 °C temperature condition. For the analysis of physical behavior of refractory materials, the weight ratio of refractory material in the mixture of sand No.7 including 30%, 50%, and 70% was used for the test under the confining stress 100kPa. During the hydration process, the horizontal stress is observed 9 to 30 times the vertical confining stress depending on the as the weight fraction of MgO in the mixture. While the vertical expansion was still progressing, the horizontal stress reached to a constant value. A numerical simulation was performed under the same conditions as the previous experiment using the Discrete Element Model program (PFC3D, Itasca). The ultimate horizontal stress is measured as 1.7 times the confining stress regardless of the vertical confining stress for the 30% MgO weight fraction, and 1.9 times for the 50% MgO and 70% MgO weight fraction.