Investigation of the influence of magnesium chloride to sulfate corrosion of concrete

Abstract

The paper research subject is to examine whether chlorides of magnesium chloride block the affect of sulphate of magnesium sulfate to the concrete, that is, whether they block the sulfate corrosion of concrete. The cylindrical samples of cement paste measuring 80 × 40 mm of varying water-cement ratio 0.5 and 0.7 (kg H2O / kg of cement) were prepared for implementation of planned research. The samples were immersed and treated for nine months in following solutions: 1% MgCl2, 1% MgSO4, 1% MgCl2 + 1% MgSO4, 5% MgCl2, 5% MgSO4, 5% MgCl2 + 5% MgSO4. In order to study concrete corrosion, the samples were dried, grounded and analyzed by X-ray diffraction analysis (XRD), after being removed from the solutions. Treated cement paste samples in solutions of MgSO4, the concentration of 1% MgSO4 and 5% MgSO4, at both water-cement ratios form ettringite formula 3CaO×Al2O3×3CaSO4×31H2O. Ettringite occurs in reactions of sulfate and aluminate hydrate and could lead concrete structure to a state of destruction. The reaction is also known as sulphate corrosion of concrete. In joint solutions of magnesium salt of concentration of 1% MgCl2 + 1% MgSO4 and 5% MgCl2 + 5% MgSO4, at both water-cement ratios, chlorides with aluminate hydrate form monochloroaluminate hydrate formula 3CaO×Al2O3×CaCl2×10H2O, while sulfates react with calcium hydroxide to gypsum without forming expansive ettringite on samples of the cement paste. Blocking the formation of expansive ettringite verifies the blocking of sulfate corrosion of concrete by chloride from magnesium chloride.