Study of chemical interaction of magnesia cement with high concentration magnesium chloride solutions

V. N. Derevianko, A. A. Maksimenko, A. Biegun, H. Hryshko

Abstract


Problem statement. In activating MgO by electrolyte salts, as a result of formation of non water-resist magnesium silicate hydrate are obtained the durable cement stone having the low water-resist. I. P. Vyrodov considers [9; 5], that magnesia cement curing in mixing with sufficiently concentrated (C > 20 %) solutions MgCl2 is caused with the crystallization of oxyhydrochloride composition: 3MgO∙MgCl2∙11Н2О, 5MgO∙MgCl2∙13Н2О and 7MgO∙MgCl2∙15Н2О. In the lower concentration parts of MgCl2 solution is formed a transitional compound of Mg[(OH)nCl2-n] with isomorphous Mg(OH)2 structure. At very low Cl concentration only Mg(OH)2 is practically formed.

Purpose. The Formation of water-resist magnesium silicate hydrates for obtaining of fast curing and solid structure of the magnesia stone.

Conclusion. The dependence of the formation of the magnesia stone from the ratio (MgO/MgCl2) of the magnesia cement (MgO) and the magnesium chloride solution (MgCl2) of different density has been identified in order to obtain the best content for oxyhydrochloride 3MgO·MgCl2·11Н2О, 5MgO·MgCl2·13Н2О and magnesium hydroxide (Mg(OH)2). In putting into the system MgO∙–∙H2О of the silicic acid or fine ground quartz grains with size of less than 20 – 30 microns, over 1 month for the magnesium silicate hydrates formation is needed, where from 2 to 5 % of the total number of newgrowths are created. The study is proved by the expert opinion, that magnesium silicate hydrates do not have binding properties, unlike calcium silicate hydrates, and the main role in the system curing is played with the Mg(OH)gel recrystallization, which provides the acceptable stone strength (R ≈ 30MPa) in a few years. It has been also established, that in mixing of cement with low concentration MgO solutions of less than 1,5 mol/l (or 13% 1,1g/sm3), the final product in the stone structure is Mg(OH)2. With increasing the sealer (MgCl2 solution) there is formed by turn in structure 3MgO·MgCl2·11Н2О and 5MgО·MgCl2·13H2О. The increase of the sealer concentration to more than 2,5 mol/l (C = 21 % or 1,18 g/sm3) leads to the formation of system MgО∙–∙MgCl2∙–∙H2О consisting of a three phase of pentoxyhydrochloride (5MgО·MgCl2·13H2О), trioxyhydrochloride (3MgO·MgCl2·11Н2О), and remains of non-reacted Mg(OH)2. It has shown in the result of testing that the samples produced from the mixture of cement and bishofit with ρ = 1,28 g/sm3 have the bigges strength.


Keywords


magnesia cement; magnesium chloride; sealer; curing time; crystallization; liquid phase; solid phase; x-ray phase analysis; differential and thermal analysis

References


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