Experimental Study On The Damage Characteristics Of Concrete Under The Multiple Interactions Of Fatigue Loading And Freezing-thawing Cycles

The concrete dams,bridges,roads and buildings in the north have to bear the combined effects of load and freeze-thaw cycle during their service.Therefore,it is necessary to carry out researching on the damage properties of concrete under fatigue loading and freeze-thawing cycle.In this study,the single fatigue loading,single freeze-thawing cycle and fatigue-freeze in the damage tests of single interaction and multiple interactions are performed on 82 specimens.The damage characteristics of concrete under single and interaction factors are studied.The relation between fatigue loading and freeze-thawing cycle is illustrated by introducing the overlay effect variables-K and the microscopic angle.The main tasks include:(1)The damage characteristics of concrete under the action of single factor are studied by fatigue loading and freeze-thawing cycle respectively.The effects of different fatigue times and fatigue load on relative dynamic modulus,compressive strength,peak strain and stress-strain curve of concrete are analyzed.The results show that the relative dynamic modulus of elastic decline is the first to slow down,the compressive strength is increased and the peak strain and damage variables are reduced.Under the same fatigue load times,the mean value of 0.2fc and 0.3fc have no significant difference in damage performance.The effects of freeze-thawing times on concrete quality,relative dynamic elastic modulus,strength and deformation properties are also analyzed.The results show that the quality of the specimens increased and then decreased with the increase of freeze-thawing cycle times,the relative dynamic elastic modulus continue to decrease,the reduction rate of compressive strength,peak strain and the increase rate of damage variables increase obviously after 50 freeze-thawing cycle.(2)The damage properties of concrete under the interaction of fatigue and freeze-thaw are studied.The fatigue-freeze-thaw interaction was compared with the damage performance of single factor freeze-thaw,and the effects of fatigue load on the damage performance were analyzed.The results show that the quality of the samples increases and then decreases with the increase of the test cycle.Compared with single-factor freeze-thawing cycle and fatigue-freeze interaction,the mechanical properties of concrete are significantly affected by multiple interactions.The quality,relative dynamic modulus,peak stress and peak strain of the sample change rapidly with the increase of the test cycle,and the more the test cycle,the larger variation of the experimental curve.To some extent,the increase of fatigue loading value accelerated the damage of the specimens under many interactions,but the promotion effect not be obvious.(3)The effects of fatigue loading and freeze-thawing cycle on the performance of concrete are discussed.The relation between single factor and double factors is analyzed by introducing superposition effect variable K.It is concluded that the fatigue loading and the freeze-thawing cycle interaction are positive effects,and the damage variables are greater than the superposition values under any test periods.The increase of fatigue loading has only a slight effect on the growth of damage variables,but the effect is not obvious.The microstructure of fatigue loading and freeze-thawing cycle under different damage conditions was compared,and the characteristics of mechanical property deterioration under multiple interactions were revealed.