Study On Dynamic Properties Of Sulfate Attacked Concrete Under High Strain Rate

The concrete structures in service are not only subjected to static loads,but also dynamic loads.In addition,the concrete structures facing durability problems which leads to degradation of mechanical properties of cement-based materials.In the region of coastal and saline-alkali,sulfate attack is one of major duability problems of concrete structures,and the concrete structures are inevitably suffered both the dynamic load and sulfate attack.The coupling effect will complicate the properties of concrete materials,and sulfate attack will accelerate the deterioration of materials,which ultimately leads to the failure of concrete structures during service life.Therefore,it is of great significance to study the dynamic mechanical properties of sulfate attacked concrete materials under high strain rates.The dynamic mechanical properties of concrete under high strain rates were simulated by mesoscale models.According to the established polygonal aggregate model based on CT statistical information,the influence of aggregate shapes and aggregate content on the dynamic mechanical properties of concrete were analyzed.What's more,the contribution of end friction effect,inertia effect and free water on the strain rate effect of concrete materials was carried out.The results show that under the condition of aggregate content and loading strain rate,the influence of aggregate shape on the dynamic strength of concrete is negligible,but the effect on crack failure mode is obvious.The higher the aggregate content and load strain rate,the higher the dynamic strength of concrete.The dynamic strength increases with the increase of friction coefficient,and then remains unchanged.The inertial effect is more obvious with a larger aspect ratio and higher strain rate.The existence of free water will result in an increase in the dynamic strength of the concrete under high strain rate.The experimental investigations of dynamic mechanical properties of sulfate attacked concrete under high strain rate were studied by using a Split Hopkinson Pressure Bar(SHPB).The failure patterns,relationship between the strain rate and time,stress-strain curves of the specimen were analyzed.The dynamic strength increase factors of concrete under different sulfate attack conditions were obtained.The results show that the failure pattern of concrete is mainly affected by the loading speed,while sulfate attack has little influence.The strain rate first increases with the increase of time,and then decreases after a platform.The stress-strain curves of the specimen first dramatically rise to the peak stress,and then decrease.The peak strain of specimens after immersed for 60 days and 90 days is slightly larger than that of the specimens unattacked and immersed for 120 days.A case study with L-shaped concrete numerical model was carried out.The dynamic mechanical properties of L-shaped members at different loading speeds and different scales were analyzed.The influence of sulfate attack on the failure pattern of L-shaped models was studied.The results show that with the increase of loading speed,the the area of failure zone of L-shaped members increases gradually.Compared to homogeneous model,the failure pattern of mesoscale L-shaped member presents an envelope type,otherwise having branches.The deterioration of specimens increases as immersion time.