Research Of The Compounds Containing Aluminum On Resistance Of Concrete To Sulfate Attack

Sulfate attack can cause the expansion and cracking of concrete and consequently the strength of concrete is reduced, which maybe lead to the failure of concrete. It has been reported that some substances containing aluminum could inhibit alkali-silica reaction?ASR? effectively, but the effect of substances aluminum on sulfate attack resistance of concrete is not clear. So in this research work the effect of Al₂O₃ and Al?OH?₃ on concrete sulfate attack resistance was investigated.According to ASTM C1012 and JGJ/T70-2009, the mortar specimens were prepared and immersed respectively in the solution of 5% Na₂SO₄ and MgSO₄ for 26 weeks.Taking the mass loss rate and compressive strength as the criteria, the effect of Al₂O₃ and Al?OH?₃ on sulfate attack resistance of concrete was studied. The products and microstructure of concrete with Al₂O₃ and Al?OH?₃ were tested by means of X-ray diffraction?XRD?, scanning electron microscopy?SEM? and thermogravimetrydifferential thermal analysis?TG-DTA?. The research results are listed as follows:For the specimens in 5% sulfate solution, the resistance to sulfate attack decreased with increasing the dosage of Al₂O₃ and Al?OH?₃, but when the dosage of Al?OH?₃ was10%, it did not decrease. When fly ash was added with Al₂O₃ or Al?OH?₃ at the same time, the harm to the sulfate attack resistance because of adding Al₂O₃ or Al?OH?₃ could be weakened. The specimens adding Al₂O₃ and Al?OH?₃ had higher resistance to Na₂SO₄ attack than to MgSO₄ attack.Through analysis of microstructure, for the specimens in Na₂SO₄ solution, gypsum and ettringite which were the products of sulfate attack reaction were found in the surface layer of the specimens; for the specimens in MgSO₄ solution, not only gypsum and ettringite but also hydrated magnesium silicate?M-S-H? and Mg?OH?2 were found in the surface layer.