Study On Concrete Performance Degradation Under Scour And Sulfate Erosion

Sulphate is widely distributed in the Yellow River basin in China,and hydraulic buildings in the basin are damaged by sulphate erosion,resulting in loose spalling of the concrete surface and serious internal damage,and due to reservoir regulation requirements during the flood season,the sand-laden water flows produces scouring damage to concrete,which seriously threatens the durability of concrete.Volumetric sediment content of water and scouring velocity are important parameters affecting the scouring damage of concrete.The current research of single-factor scouring abrasion is very detailed,while there is also part of research on concrete scouring abrasion damage under the role of two factors（such as the combination of freeze-thaw cycles,H₂SO₄corrosion,chloride ion diffusion,etc.）.However,there are few studies on the interaction between sulphate erosion and sediment flow erosion,the two-factor coupling system is mostly a simple successive superposition,which does not present the effect of scouring on concrete eroded by sulphate.Therefore,this study developed an alternating cycle system of dry-wet sulphate cycle erosion and sand-laden water scour according to the hydrological and climatic characteristics of the basin of the Yellow River.Five sets of tests were designed to investigate the deterioration of the concrete mechanical properties using the volumetric sediment content of water and scouring velocity as parameters.Mass change,washout abrasion rate,compressive strength corrosion resistance factor,and relative dynamic modulus of elasticity were used as macroscopic performance evaluation indicators to investigate the deterioration mechanism of concrete properties.SEM,XRD,and pore structure analysis were used to observe and analyze the microscopic morphology,physical phase changes,and pore structure evolution of concrete.The main conclusions are as follows:（1）Concerning the circular scouring method and taking into account a large number of specimens and the many mechanical parameters to be measured in this study,a concrete scouring tester was designed to meet the test requirements of this study,which can compensate for the limitations of the circular method in terms of number and form of specimens,while retaining the main indicators of the circular scouring method to the maximum extent.（2）Volumetric sediment content of water and scouring velocity have a significant effect on concrete sulphate erosion,and the mechanical properties of concrete tend to increase and then decrease with the number of"erosion-scouring"cycles.The high volumetric sediment content of water or the high scouring velocity leads to an earlier time of decline in its mechanical properties.High volumetric sediment content of water and sulphate attack have a positive feedback relationship on concrete performance.The low scouring velocity and low volumetric sediment content of water slowed down the rate of concrete sulphate erosion damage to a certain extent,i.e.disrupting the continuity of sulphate erosion.The compressive strengths of the S5L10 group and the L15S1 group in Cycle 8 increased by 13.5%and 38.7%,respectively compared to the initial test,while the compressive strength of the sulphate only concrete increased by only 3.6%compared to the initial test.In practical engineering,reducing the sand content of the drainage water body can reduce the degree of damage to hydraulic buildings caused by sulphate erosion.（3）Under the action of"erosion-scouring",the negative impact of the volumetric sediment content of water on the mechanical properties of concrete is more obvious than that of the scouring velocity,and the cumulative scouring abrasion rate of concrete increases as a quadratic function of the volumetric sediment content of water and increasing as a power function exponentially less than1 with the scouring velocity.The greatest deterioration in concrete performance occurred when the scouring velocity was 15m/s and the volumetric sediment content of water was 9.5%,with the mass,compressive strength corrosion resistance factor,and relative dynamic modulus of elasticity decreasing by 2.7%,51%,and 47.7%,respectively compared to the initial time.（4）Combining scour abrasion theory and test results,the empirical model developed can predict the cumulative scour abrasion rate of concrete effectively under"erosion-scouring".