Study On Sulfate Resistance Of Admixture Concrete Under Dry And Wet Circulation

Reinforced concrete was building material which was widely used.The reinforced concrete is made into building structures due to the advantage of low cost and easy obtained and fire resistance.It's found that the damage of concrete in condition of wetting and drying had a great impact on the durability of reinforced concrete structure.For example,the concrete structure near sea-level likely was damaged.Moreover,the most extensive and common form of chemical erosion of concrete was sulfate attack.The studies that combine two factors have important engineering significance on the durability of reinforced concrete structure.This paper mainly studies the anti-sulfate corrosion performance of concrete under sulfate attack and wetting and drying cycle.The test method was cyclic accelerated sulfate corrosion.One cycle include soak in 3 days by etching solution and dry in 4 days.The admixture of concrete was erosion damaged in different ranks.The apparent and mass and compressive strength and microscopic appearance of concrete after corrosion are studied.The influence of water-binder ratio?w/b=0.35,0.45,0.55?and fly ash content?10%,30%,50%?and admixture types?fly ash,slag,silica fume?and mixed mineral admixtures on the erosion resistance of concrete were studied under the dry and wet cycling of 5%Na₂SO₄ solution.The change of anti-sulfate corrosion performance of concrete was obtained by each specifications of different sulfate solution.The anti-sulfate corrosion performance is set up with a main target at sulfuric acid root ion concentration?0.5%,2.5%,5%?,sulfate solution type?5%Na₂SO₄,5%MgSO₄?,composite salt solution types?5%Na₂SO₄+3.5%NaCl,5%MgSO₄+3.5%NaCl solution?.The microscopic structure and influence mechanism were analyzed.The micro-structural changes of admixture concrete after50 times of wetting and drying cycle were observed by the SEM?scanning electron microscopy?observation technique.The sulfate radical invasion of concrete in different sulfate solutions was tested by spectrophotometer.It provided the basis for analyzing the mechanism of sulfate resistance of admixture concrete.The main results of the study are as follows:?1?With water-cement ratio increased,the amount of water per unit volume decreases and the internal microstructure was compacted and the pore contentis reduced and the anti-sulfate corrosion performance of concrete was promoted.The effect of fly ash content on the anti-sulfate corrosion performance of concrete was observed.With fly ash content increased,the anti-sulfate corrosion performance of concrete was strengthened.?2?The influence of compound material on the anti-sulfate corrosion performance of concrete were compared:The anti-sulfate corrosion performance of mixed concrete from good to bad was silica fume and fly ash and slag and no admixture.The anti-sulfite erosion performance of mixed concrete under compound mixing conditions were compared:15%fly ash+30%slag+5%silica fume>20%fly ash+10%silicon>20%fly ash+30%slag.The pore structure of microstructure and monoclinic mixed admixture concrete was observed.It could get that the pore structure had been improved.a lot of acicular and clusters of Stringier were generated.?3?The anti-erosion ability of the mixed concrete with different concentrations of sulfate ion solution was compared:the larger concentration of sulfate,the smaller corrosion resistance of the concrete.The Na₂SO₄ solution and MgSO₄ solution at the same concentration was compared.To the MgSO4 solution,the anti-erosion ability of admixture concrete to was poor.The erosion ability of sulfate solution were weakened when addition NaCl of 3.5%.The anti-erosion ability of different sulfate solutions fromhightolowwas5%Na₂SO₄+3.5%NaClsolution>5%Na₂SO₄solution>5%MgSO₄+3.5%NaCl solution>5%MgSO₄ solution.?4?The admixture concrete in different sulfate environments was analyzed by SEM experiment results and spectrophotometry.Compared with the high concentration of sulfate ion solution,the penetration depth and intrusion amount of the concrete sulfate were decreased and the amount and length of calcium alum were reduced in the small concentration of sulfuric acid root ion solution.The formation of concrete erosion was different in different environments of sulfate.The calcium silicate was replaced by magnesium hydrated silicate in the environment of magnesium sulfate solution.The structure became loose.The concrete strength was significantly influenced.The sulfate that had penetrated into the concrete was decrease due to the NaCl was joined in the sulfate environment.