Research On Mechanism Of Concrete Dterioration Under Bittern Environment

Bittern freeze-thaw cycle destruction,bittern dry-wet cycle damage,chloride ion erosion damage are important durability problems faced by concrete structural materials in salt lakes.Cracking,denudation and steel corrosion are macroscopic damages of concrete materials,the phase and pore structure changes are the microscopic performance of concrete materials.In recent years,scholars at home and abroad have done fruitful work to improve the durability of concrete by mixing mineral admixtures in concrete.However,the improvement of durability of concrete can not meet the requirements of concrete under extreme environmental conditions in Salt Lake areas.In this paper,based on the work of predecessors,modifiers are added to further improve the durability of concrete in bittern environment.Three modified concrete specimens were prepared by using nano-SiO₂,XSBRL and LDOs modifiers,simulate the bittern environment of concrete in Salt Lake area,the mechanical properties and durability of modified concrete were studied,which provided a theoretical basis for the practical application of modified concrete in salt lakes.The main work and achievements of this paper are as follows:（1）Under standard conditions,the mechanical properties of concrete mixed with mineral admixtures other than silica fume are lower than those of cement concrete.The mechanical properties of concrete mixed with SL,FA and SF are relatively good.In the modified concrete,with the increase of nano-SiO₂ content,the compressive strength first increases and then decreases.When the nano-SiO₂ content is 2%,the mechanical properties are the best.With the increase of XSBRL and LDOs,the mechanics Performance is declining.（2）Under the action of bittern freeze-thaw cycle and bittern dry-wet cycle,concrete mixed with mineral admixture,composite concrete with SL,FA and SF has less compressive strength and mass loss.Under the same freeze-thaw cycle or wet-dry cycle,the bittern freeze-thaw cycle resistance and bittern dry-wet cycle resistance of nano-SiO₂and LDOs modified concrete first increase and then decrease with the increase of modifier content,when the dosage is 2%,the performance of the two modified concrete is the best.With the increase of XSBRL content（3%¹5%）,the bittern freeze-thaw cycle resistance of the modified concrete and the bittern dry-wet cycle resistance gradually improved.（3）The concrete with three modifiers showed better resistance to chloride ions.The chloride ion diffusion coefficient of concrete decreases with the increase of the amount of concrete mixed with nano-SiO₂ and XSBRL.3%nano-SiO₂ and 15%XSBRL have the lowest chloride ion diffusion coefficient of concrete,diffusion coefficient is 0.42?10^-12m²/s.With the increase of LDOs content,the chloride diffusion coefficient of concrete decreases first and then increases,when the LDOs content is 2%,the chloride diffusion coefficient reaches the lowest value,which is 0.72?10^-12m²/s.（4）Under the conditions of bittern freeze-thaw cycle,bittern dry-wet cycle,the types of corrosion products of nano-SiO₂,XSBRL and LDOs modified concrete are basically the same.It can be seen from the change of microscopic morphology that bittern erosion and freeze-thaw cycle will cause corrosion damage to concrete,and the incorporation of three modifiers hinders the corrosion damage of concrete;Comparing the pore structure of the reference concrete and the modified concrete,it can be seen that the pore size distribution of the modified concrete is transferred from harmful pores to less harmful pores and harmless pores.In summary,it can be seen that the incorporation of the three modifiers improves the mechanical properties and durability of the concrete.