Study On The Properties Of Alkali-activated Fly Ash Slag Cementitious Materials Under Sulfate Corrosion

For building materials,sulfate corrosion has been a widespread concern at home and abroad.As a new type of building material,alkali-activated fly ash slag cementitious materials have not been fully studied under sulfate attack,and related properties studies are still lacking.Therefore,it is of great significance to promote the establishment and improvement of related production and construction engineering standards to carry out research on the sulfate resistance of alkali-activated fly ash slag cementitious materials.This paper mainly studies the changes of mass loss,compressive strength,microstructure,phase and functional groups of alkali-activated fly ash slag cementitious materials with different alkali activator modulus and silica fume content during the sulfate curing process.The effect of curing temperature and dry-wet cycle on the resistance of alkali-activated cementitious materials to sulphate corrosion is discussed;And,the changes of the mass loss,compressive strength,phase and functional groups of the alkali-activated fly ash slag cementitious materials by different liquid-solid ratios after corrosion in sulfate were studied.The results show that:The erosion damage of Na₂SO₄ solution to the sample of alkali-activated fly ash slag cementitious material is less than that of Mg SO₄ solution to the sample.An increase in the modulus of the alkali-activated（Na OH）solution can enhance the resistance of the sample to sodium sulfate erosion and weaken its resistance to magnesium sulfate erosion.And the increase of curing temperature can effectively increase the sulfate resistance of the sample.The crystallization of Mg（OH）₂ and the decalcification degradation of C-A-S-H gel are the main reasons for Mg SO₄ erosion to destroy the sample.The alkali-activated fly ash slag cementitious materials samples after 28 cycles of wet and dry conditions caused 5 wt.%Na₂SO₄ to damage the samples more than the deionized water eroded the samples.With the increase of silica fume content,the mass loss of the sample decreased after 28 dry and wet cycles in 5 wt.%Na₂SO₄ solution,the compressive strength increased by 19MPa,and the corrosion resistance coefficient increased by 9.4%,indicating that the silicon the increase of ash content can enhance its resistance to dry and wet cycling and sodium sulfate.As the temperature of the solution increases,the resistance to dry and wet cycling and sodium sulfate resistance of the sample are significantly improved.No new substances were produced during the wet-dry cycle of the sample in Na₂SO₄ solution.The alkali-activated fly ash slag cementitious material samples were immersed in acetic acid solution after corrosion in 5 wt.%Na₂SO₄ solution,and the erosion damage was smaller than that in the deionized water.When the liquid-solid ratio increased from 0.25 to 0.31,the mass loss of the samples after corrosion in 5 wt.%Na₂SO₄ solution increased by 0.7%and the compressive strength decreased by 8.0MPa.The corrosion resistance coefficient decreased by15.0%;the mass loss of the sample immersed in acetic acid solution after deionized water corrosion increased by 0.8%,the compressive strength decreased by 18.1MPa,and the corrosion resistance coefficient decreased by 25.5%.This indicates that as the liquid-solid ratio of the sample increases,the destruction of the structure of the sample by acetic acid is promoted.H⁺in acetic acid will cause decalcification and depolymerization of the formed C-A-S-H gel.