Study On Durability Of High-volume Mineral Admixture Concrete In Saline Soil Area

In saline soil area,the concrete foundation of transmission lines may suffer from chloride salt corrosion,sulphate chemical corrosion,salt crystallization corrosion,or salt-freezing,which seriously affect the service life of concrete.In this condition,the part of concrete foundation subjected to dry-wet cycles（adsorption area）was usually corroded most seriously,so this paper studied the resistance of high-volume mineral admixture concrete（HVMAC）to sulphate salt crystallization/chloride salt corrosion,the long-term performance deterioration and corrosion mechanism of HVMAC half immersed in different sulphate and chloride solutions,and the salt-freezing resistance of HVMAC in different sulphate and chloride solutions,so as to develop a type of HVMAC with good durability under salt corrosion.The main contents of this paper are as follows:（1）Through chloride ion diffusion coefficient test,electric flux test,and dry-wet cycles test in sulfate solution,the effect of 20%,35%fly ash,35%,55%slag,and 20%fly ash+35%slag on salt corrosion resistance of concrete was studied.The results show that slag and fly ash can both improve the resistance to chloride ion penetration of concrete,and slag is more obvious than fly ash;55%slag or 20%fly ash+35%slag can significantly improve the resistance of concrete to sulfate crystallization corrosion,but it is the opposite for 35%fly ash.（2）Combined with dry-wet cycles,three types of HVMAC were half immersed in sodium sulfate solution,20%fly ash+35%slag concrete（C40F20K35）was half immersed in different sulphate and chloride solutions.Then the corrosion damage,the deterioration of physical and mechanical properties such as mass loss,relative dynamic elastic modulus and strength were studied,the corrosion degree of HVMAC above and below the solution level was also compared,microscopic testing methods were used to reveal the salt corrosion mechanism of HVMAC.The results show that in 10%Na₂SO₄ solution,the corrosion degree of C40K55 concrete（55%slag content）and C40F20K35 concrete is the lowest,due to the crystallization corrosion and chemical corrosion intensification,all the specimens above the solution level are seriously corroded;the corrosion degree of C40F20K35 concrete in the five salt solutions was:10%MgSO4 solution>10%Na2SO4 solution>（10%Na2SO4+10%MgCl₂）composite solution>（10%NaCl+5%MgCl₂）composite solution>20%NaCl solution.（3）C40 ordinary concrete and C40F20K35 concrete were treated with the method of accelerated freezing-thawing in 10%NaCl solution,5%MgSO₄ solution,5%Na2SO4+5%MgCl2 solution respectively.After 300 freezing-thawing cycles,the performance degradation such as mass loss,relative dynamic elastic modulus and strength,were studied,XRD and SEM tests were used to reveal the salt-freezing destruction mechanism of concrete.The results show that in fresh water,the damage of the two types of concrete are the most serious,and the salt-freezing resistance of the concrete is improved because the salt solution has lower freezing point;in fresh water and 10%NaCl solution,the salt-freezing resistance of C40F20K35 concrete is higher than that of C40 concrete,but the poorer performance in 5%MgSO₄ solution;in（5%Na₂SO₄+5%MgCl₂）composite solution,the two types of concrete have almost no damage;the damage of concrete is mainly caused by freezing-thawing damage,the chemical corrosion is small.