Experimental Research Of Fresh And Precast Concrete In The Condition Of Sulfate Corrosion

Compressive strength of fresh and precast concrete in conditions of sulfate corrosion was mainly studied. Two types of corrosion medium, Na2SO4 and MgSO4, were considered. The concentration of Na2SO4 solution respectively is 5000 mg/L and 50000 mg/L, and the concentration of MgSO4 solution respectively is 4225 mg/L and 42250 mg/L. Full immersion test method was adopted. The compressive strength and rebound value in different corrosion ages(30d,90 d, 180 d, 270 d, 360 d, 540 d, 720 d, 900 d and 1080d) were respectively determined corresponding to the content of fly ash(0, 15%, 20%, 25%, 30% and 35%). The Concentration of corrosive mediums, content of fly ash, preparation of specimens, corrosive environment and corrosive mediums are the considerations. Based on the corrosion model of precast concrete, the corresponding one of fresh concrete mixed with corrosive solution was established. In addition,evaluation of comprehensive strength of corrosive concrete by rebound method was proposed.The results show that the compressive strength of concrete is in a downward trend after rising at starter phase under the condition of sulfate corrosion through the whole test and correlated with solution concentration, mixing percentage of fly ash, corrosive medium and corrosion environment. High concentration of corrosive medium solution has a negative effect on the performance of sulfate corrosion resistance, while a certain admixture of fly ash is beneficial to the improvement on it. The degree of corrosion is more serious in magnesium sulfate solution than sodium one, and the sulfate resistant of precast concrete is better than that of fresh concrete.The relationships, between corrosion resistant coefficient and age, compressive strength and age, compressive strength and the rebound value with corrosion layer thickness, were set up according to corrosion models. In addition, evaluation of comprehensive strength of corrosive concrete by rebound method was validated so that the relational expression for it is effective to predict strength. The calculated values are in agreement with the experimental data so that compressive strength of corrosive concrete can be well predicted by the corresponding age and hardeness.