Research On Chloride Ion Erosion Of Cracked Concrete Under Load

The durability of concrete is a hotspot issue in the field of civil engineering.And chloride erosion is the most serious reason for durability failure of concrete structures.In practical projects,most concrete works with cracks.The generation and development of cracks would change the permeability of concrete and the transmission mode of harmful substances in concrete.The resulting durability problems will have an adverse impact on concrete structures.Therefore,the chloride erosion of cracked concrete in service cannot be ignored.At present,the domestic and foreign scholars have conducted a significant amount of research on the problem.But researches on the chloride erosion problem in concrete fracture process,especially in the crack critical state under load is seldom.Based on this,the cracked concrete was taken as the research object,through the three point bending beam fracture test and the chloride erosion test,the effects of load and load level,chloride erosion time,and maintaining the pore strain state of concrete around cracks on chloride diffusion were studied,the relationship between the concrete stress intensity factor K and the chloride resistance was analyzed.The main research contexts and research conclusions are as follows:（1）Three point bending beam fracture test of unilateral prefabrication incision concrete specimens was carried out,the concrete specimens were loaded to the three load levels of pre-cracking load,cracking load and maximum load,respectively.Some concrete specimens were immediately inserted into the stainless steel wedge at the precast crack when the load completed to keep the pore strain state of the concrete around the crack consistent with the loading state.The concrete specimens after loading were immersed in 8%sodium chloride solution for 30d,60d,90d,120d,150d and 180d respectively.The chloride content at different depths of the concrete specimens was measured by the borehole sampling method,the chloride erosion profile changes of cracked concrete specimens crack section under different erosion times and load levels were observed by silver nitrate method,and the chloride erosion area of crack section was measured.（2）According to the chloride content measured results,the concrete surface chloride concentration C_swere fitting calculated and the chloride diffusion coefficient D_cwere calculated.The influence of load and load level,chloride erosion time and maintaining the pore strain state of concrete around the crack on the chloride diffusion coefficient was investigated.Moreover,the diffusion law of chloride in cracked concrete under load was analyzed.The P-CMOD test curve obtained from the three-point bending beams loading test was used to calculate the stress intensity factor K of cracked concrete specimens.The relationship between the stress intensity factor K and the chloride resistance was explored.（3）The results show that the load have obvious influence on chloride diffusion in cracked concrete.When the crack initiation load of concrete is reached,the chloride erosion rate of concrete fracture section increases significantly,and presents a slow and steady growth trend with the load increasing.Hereafter,the erosion times have become an main factor affecting the chloride contents in cracked concrete.The degree of chloride erosion in cracked concrete is increased when the wedge is inserted to maintain the strain state,and the chloride content is increased with the increasing of erosion times and load levels.When the stress intensity factor K is less than 0.7MPa·m^1/2,the chloride diffusion coefficient D_cof concrete would not increase significantly,and when the stress intensity factor K is greater than0.7MPa·m^1/2,the chloride diffusion coefficient D_cincreases significantly with the stress intensity factor K increasing in the short erosion times.