Study On Mechanical Properties Of Magnesite Concrete Under Sulfate Erosion Environment

With the rapid development of China’s economy,the consumption of national resources is increasing day by day.Magnesite ore is abundant in China,but the utilization rate is low,even low-grade magnesite ore appears to be piled up and idle,which has caused great pressure on the environment.In addition,concrete in the harsh environment,easy to suffer from salt erosion and crystallization expansion erosion,resulting in concrete structure failure damage.Compared with the full immersion method,concrete erosion in dry and wet cycle environment is more complex,erosion reactions are more diverse,and concrete damage is more serious.Therefore,in this thesis,the mechanical properties of magnesite concrete under dry and wet cycle environment of sulfate erosion are studied,and the specific research contents and conclusions are as follows:（1）The results of the comparative tests on the deterioration of C30 and C40 magnesite concrete under natural immersion and dry and wet cycles show that the changes of mass,dynamic modulus of elasticity,compressive strength and splitting strength of magnesite concrete after sulfate erosion show the same trend,all showing a general trend of first growth and then decline,and the greater the density of concrete,the slower the deterioration rate.（2）Dry and wet cycle tests were conducted on C30 concrete with water-cement ratios of 0.41,0.43 and 0.45 and C40 concrete with water-cement ratios of 0.35,0.37 and 0.39,respectively,and the results showed that the trends of mechanical properties were the same for each group,but the concrete with water-cement ratios of 0.45 and 0.39 showed the greatest deterioration and the most obvious damage effect under the two erosion methods.154d At 154d,the mass,dynamic modulus of elasticity,compressive strength and splitting strength lost 0.95%,4.3%,12.6%,19.1%and 1%,6%,14.5%,19.8%.It further shows that the water-cement ratio has a greater influence on the durability performance of concrete against sulfate attack,and the smaller the water-cement ratio,the stronger the concrete against sulfate attack.（3）The SEM and XRD analysis of the microstructure of the erosion cycles of 0d,88d and 154d revealed that the performance of each group of magnesite concrete gradually increased in the early stage and reached the peak at 88d,and the performance started to decrease after 88d until 154d.Based on the results of the microscopic analysis of the three time periods,it was found that the internal structure of the concrete experienced a series of deterioration damage processes,including"initial defect-filling and compacting-further filling and cracking and expansion".The results of the microscopic analysis showed that the internal structure of the concrete underwent a series of deterioration and damage processes of"initial defects-filling-cracking-further filling-cracking and expansion".（4）A modified transport diffusion model of SO₄^2-movement inside concrete based on Fick’s second law was established,and a polygonal random aggregate distribution model Python language subroutine was written and imported into ABAQUS to generate a two-dimensional model containing mortar,aggregate and interfacial transition zone to simulate the diffusion phenomenon of SO₄^2-in specimens,which was finally compared with the experimental measurement results.The results show that this approach can better simulate the diffusion phenomenon of SO₄^2-in the specimens and predict the SO₄^2-distribution and damage changes inside the concrete in the future cycles,which provides a reference for future simulation studies of sulfate erosion.