Strength variation and cracking behavior of corundum bricks with modified hydrated magnesium chloride Binders

Abstract

This work examined differences between modified and non-modified binders regarding corundum brick cracking and strength variations pre and post-modification. Comparing samples treated with magnesium chloride hexahydrate at 200 °C before and after modification highlighted the importance of basic magnesium chloride in filling corundum gaps and aiding dehydration, affecting initial strength. The transformation from the 518 phase (5 Mg(OH)2·MgCl2·8H2O) to magnesium chlorocarbonate phase (Mg2CO3(OH)Cl·2H2O) enlarged grain size, explaining later-stage strength differences in hydration. TEM analysis after FIB fixed-point cutting of the cracked site of the ninth-day hydrated corundum brick sample indicated that the significant mismatch in lattice spacing between the magnesium chlorocarbonate phase and corundum resulted in the generation of a large number of misfit dislocations at the binding site. Additionally, the transformation from the 518 phase to the magnesium chlorocarbonate phase generated numerous dislocations during structural transformation. The internal stress generated by hydration pushes these dislocations to form a stress field, causing the samples to crack.