Experimental Study On Freeze-thaw Damage Characteristics Of Concrete Materials With Pre-crack

In the practical engineering application,concrete usually works with cracks,and the generation and development of cracks is the main reason for the decrease of bearing capacity and durability of concrete structure;in the cold region,the freeze-thaw damage of concrete structure aggravates the deterioration of concrete performance.Therefore,the research on the freeze-thaw deterioration and damage characteristics of the pre-crack concrete material has reference value for the construction of cold area engineering.In this paper,through the freeze-thaw cycle test and mechanical property test,the influence of cracks on the frost resistance of concrete specimens is studied.The specific research contents and results are as follows:(1)Through the rapid freeze-thaw cycle test,174 concrete prisms with the size of 100 mm×100 mm×300 mm were tested.The influence rules of the pre-crack on the frost resistance index of the specimen are obtained.With the increase of the crack angle,the relative dynamic elastic modulus of the specimen decreases significantly at first,then slows down and finally increases slightly;with the increase of the crack length,the relative dynamic elastic modulus of the specimen decreases.(2)For the specimens with different fracture parameters,it is found that the change rule of local damage of crack growth occurs under the action of freeze-thaw.Based on the analysis of the expansion of pre-crack under the action of freeze-thaw cycle,two modes of the expansion of pre-crack are obtained,namely coplanar expansion and horizontal expansion.According to the damage mechanics theory,the damage evolution model of concrete under the action of freezing-thaw cycle and load coupling is derived.Through the analysis,it is found that the damage degree of the pre-crack specimen is obviously greater than that specimen without pre-crack.(3)Through the mechanical tests of concrete specimens after the freeze-thaw cycle tests,the influence of different crack parameters on the mechanical properties of concrete specimens under freeze-thaw cycles is found.On the basis of previous studies,considering the influence of crack parameters,the calculation formula of relative peak stress(strain)of specimens with different crack parameters under the action of freeze-thaw is established by introducing the initial damage coefficient k of concrete,the influence coefficient T?,S?of inclination angle and the influence coefficient T_a,S_a of length.Compared with ordinary concrete,the rising section of the stress-strain curve after freeze-thaw shows a concave trend,while the pre-crack increase the concave degree of the curve.According to the stress-strain curve model of concrete after freeze-thaw proposed by Xu Shanhua,the reference values of the constitutive parameters of concrete with different crack parameters after the freeze-thaw cycle are given.