Experimental Study On Deterioration Of Mechanical Properties Of Concrete Sulfate Erosion Under Drying-Wetting And Environments

Sulfate erosion is the main cause of premature failure of concrete structures.It is one of the environmental erosions with complex influencing factors and more harmful.Wet-dry cycle environment is the most significant factor affecting the concrete sulfate process.At present,there is no consensus on the unified wet and dry cycle test standards.Domestic and foreign scholars usually use the self-established methods for experimental research,in this case,the research results are often difficult to systemize,leading to a chaotic situation in the field of research,which restricts the development of research on concrete sulfate erosion.In order to explore a scientific and reasonable sulfate drying-wetting cycle system,this paper uses 1d as a cycle to design four dry-wet time ratios?1:1,3:1,5:1,7:1?,and 5%Na₂SO₄ Solution as an erosion solution.Carry out experimental study on the mechanical properties degradation of concrete eroded by sulfate under the drying-wetting cycles and exploring the damage mechanism analysis.Compressive strength,splitting tensile strength,and dynamic elastic modulus are used as mechanical evaluation indexes to characterize the evolution law of the performance of erosion concrete.SEM,XRD and MIP were used to scan and analyze the concrete samples,and the mechanism of sulfate transport reaction was investigated from the micro-level.The main conclusions are as follows:?1?The dry-wet ratio has a significant effect on the sulfate corrosion of concrete,and the mechanical properties of the eroded concrete show a trend of increasing in the early period and decreasing in the later period.The larger the dry-wet ratio,the faster the performance of concrete in the early stages of corrosion;in the later period of erosion,the erosion rate of concrete accelerates.?2?After 150 drying-wetting cycles,the concrete mechanical properties deteriorates most severely when the dry-wet ratio is 3:1.The compressive strength,splitting tensile strength and dynamic elastic modulus of DW3 concrete decreased by39%,50%and 8%compared with the initial values.?3?Deterioration of concrete due to the effects of sulfate attack coupled with wet-dry cycle is caused by fatigue damage.The generation and filling of micro-cracks,micro-voids in concrete are the main reasons for the evolution of concrete performance.In this process,concrete has experienced cyclic damage of"steady state-unsteady state-new steady state".?4?The SEM,XRD,and MIP tests of corroded concrete show that the strength of sulfate chemical attack on concrete is related to the wetting time.The expansion erosion products generated by chemical erosion can fill the pore network,reduce the porosity,and also reduce the capacity of the concrete to accommodate the expansion phase.The stress caused by the crystallization and transformation of sodium sulfate during the drying process further accelerates the deterioration of the concrete.