Study On The Durability Of Concrete Suffer Coupling Effect Of Uniaxial Compressive Loadand And Freeze-thaw Cycles

The deterioration of durability of the reinforced concrete structure is usually coupled with various factors.Especially in the northern coastal area of China,the concrete structure is not only affected by their own load,but also suffer the effect of freeze-thaw cycles and chloride ion.At present,the study on the coupling effect of load and freeze-thaw is not uniform in the loading device and the evaluation index,that can not provide a good basis for accurately reflecting the actual project.Based on this,two kinds of loading devices are designed to simulate the actual engineering under the pressure load.The experimental results are the changes of capillary absorption and pore structure of concrete which w/c ratio is 0.35 and 0.53 under the coupling effect of no load,30% ultimate stress(0.3fc)or 50% ultimate stress(0.5fc)and rapid freezing and thawing cycles.The main results are as follows:(1)The device 2 was chosen as the loading device of the subject considering the actual situation of the axial compression of the concrete.By testing the mass loss rate and the relative dynamic elastic modulus of concrete,it is found that the lower the strength grade of concrete,the faster the mass loss rate and the larger the decrease of relative elastic modulus.After 150 cycles of freeze-thaw cycles,the two types of concrete did not meet the freeze-thaw damage criteria and the requirements of frost resistance.(2)Firstly,the damaged concrete specimens were cut into four parts,such as internal cut("i")and external cut("o").Then by capillary absorption test and the chlorine salt erosion test,the capillary water absorption capacity and capillary absorption coefficient of concrete were tested.The study found that with the increase of the applied stress level,the permeability of the concrete decreased first and then increased.(3)Through analysied the pore structure of concrete after coupling effect of loading and freeze-thawing,found that with the increased of the applied stress level,the proportion of the harmless pore in the concrete increased and then decreased;the porosity of the concrete first decreased and then increased.