Study On Damage Of Concrete Properties Under Solar Irradiation And Dry-wet Cycle Of Chloride Solution

The damage of concrete caused by solar irradiation and cyclic action of chlorine solution is an important research direction of durability of Marine engineering concrete.This paper focuses on the damage of concrete volume stability,mechanical properties and impermeability under the action of solar irradiation and chlorine salt solution dry-wet cycle.The specific results are as follows:(1)The effects of solar irradiation and the dry-wet cycle of chlorine solution on the volume stability of concrete were studied.By studying the changes of internal temperature,humidity,mass,cracking and surface strain of concrete in the process of solar irradiation,the reason of concrete cracking under the action of solar irradiation was revealed.Concrete was in a state of fatigue due to solar irradiation.When the fatigue stress exceeds 84%of the concrete tensile strength,the concrete cracks.The continuous hydration of unhydrated cement particles in concrete was accelerated by solar irradiation and the carbonization of concrete was intensified.The dry-wet cycle method adopted in this paper was"solar irradiation 12h-Na Cl solution immersion for 12h".Under the action of dry-wet cycle formed by solar irradiation and Na Cl solution,the internal humidity of concrete was greater than 95%.Under the condition of dry-wet cycle,the maximum fatigue stress of concrete surface was only 51%of the standard tensile strength of concrete,which is the reason why concrete does not crack.The continuous hydration of unhydrated cement particles in concrete was significantly enhanced by the wetting and drying cycle,and the content of F salt in concrete increases gradually.(2)The effects of solar irradiation and the dry-wet cycle of chlorine solution on the mechanical properties of concrete were studied.By studying the macroscopic elastic modulus of concrete,it was found that the macroscopic elastic modulus of concrete is almost not affected by solar irradiation,and the change of elastic modulus is consistent with that of the control group.The microhardness of cement on concrete surface was reduced by 39.62%at most under the influence of solar irradiation.The macroscopic elastic modulus of concrete was not affected by the wetting and drying cycle,and the change of elastic modulus was consistent with that of the contrast sample.The microhardness of cement on concrete surface decreased by 46.04%at most under the influence of the wetting and drying cycle of chloride solution.The characterization methods of the micromechanical properties of cement were studied.The application conditions of Nanoindentation in cement were discussed.The appropriate number of lattice(more than 225)and probe pressure(more than 150μN)were determined.The change of hydration product volume rate showed that the internal microcracks of cement are caused by solar irradiation,which leads to the decrease of microhardness.Similarly,the decrease of microhardness of cement stone was influenced by the dry-wet cycle of Na Cl solution,which is due to the dissolution of CH,the increase of F salt content in cement stone,the increase of pores,and the decrease of CSH gel content.(3)The influence of solar irradiation and the dry-wet cycle of chlorine solution on the impermeability of concrete had been studied.According to change of concrete volume resistance,it was concluded that with the growth of concrete age,the volume resistance of concrete will gradually increase.However,the concrete volume resistance was negatively affected by solar irradiation,which leads to a decrease in concrete compactness.The negative effect of solar irradiation on concrete compaction degree was not only due to the cracking behavior of concrete,but also due to the ITZ width change in concrete caused by solar irradiation.By studying the strain of ITZ during solar irradiation,it was found that ITZ is in a fatigue state under solar irradiation,and this fatigue stress leads to the increase of ITZ width.According to the ITZ width determined by Nanoindentation,it ccould be seen that the ITZ width in C60,C45,C30 concrete increases by 5.5 times,2 times,and 7.7%under the effect of40 times of irradiation,which leads to the decrease of the impermeability of concrete.The width of concrete ITZ is also negatively affected by the wetting and drying cycle formed by solar irradiation and Na Cl solution.The ITZ width of C60,C45,C30 concrete increased by 2.5 times,1.7 times,and 15.4%under 40 cycles of wetting and drying,which is the main reason for Cl~- invasion accelerated by wetting and drying cycles.