Experimental And Numerical Study On Mechanical Properties Of Concrete Under Different Loading Rates And Freeze-thaw Cycles

In the cold region of Northwest China,repeated freezing and thawing has caused irreversible damage to the mechanical properties and durability of concrete materials.Exploring the damage mechanism of concrete under freeze-thaw environment to improve its mechanical properties is the key to solve such engineering problems.In addition,concrete materials are not only subjected to static loads,but also to dynamic loads such as seismic forces during service.Dynamic loads and freeze-thaw cycles result in reduced service life and irreversible damage of concrete materials.Therefore,it is very important and indispensable to study the dynamic mechanical properties of concrete materials under freeze-thaw cycles.Especially,this study is of great significance to bridges and dams in cold regions of northern China.The works carried out in this paper are as follows:(1)The freeze-thaw cycling test and dynamic mechanical properties test of concrete blocks with size of 100 mm x 100 mm x 400 mm were carried out.According to the results of mechanical tests,the variation of ultimate flexural strength,load-displacement curve and dynamic flexural strength of concrete under freeze-thaw cycles was summarized and analyzed.(2)With the help of ABAQUS finite element software,the temperature field of concrete blocks with the size of 100 mm × 100 mm × 100 mm was numerically simulated.Under different freeze-thaw cycles,the relationship between the temperature field of concrete and the temperature stress of the joints in the upper,middle and lower positions of concrete was studied.(3)The finite element model of concrete specimens under the coupling action of freezethaw cycles and dynamic loads was established using ABAQUS software and CDP model.Under the same loading rate,the effects of freeze-thaw cycles on damage characteristics and mechanical properties of concrete were studied.Comparing the simulation results with the experimental data to verify the reliability of the model.The results show that under the same loading rate,the accumulation of plastic strain damage of concrete is positively correlated with the number of freeze-thaw cycles.(4)Based on the finite element model of temperature field and uniaxial compressionestablished by ABAQUS software,the dynamic mechanical properties of concrete specimens under freeze-thaw cycles were simulated and analyzed in terms of varying parameters.The effects of freeze-thaw cycles and loading rates on the mechanical mechanism,failure modes and ultimate compressive strength of concrete specimens were further discussed.By observing the actual crack diagram and the simulated strain diagram,it is found that the failure crack of concrete is "X" type.