An Experimental Study On The Degradation Of The Tensile Properties Of Leached Concrete

The degradation of the tensile properties of leached concrete of different mixture proportions with leaching time is studied through experiment.In this experiment,the leaching depth,the water ratio at the saturated surface-dried condition,and the parameters of pore structures are used as the leaching level indexes of concrete,while the axial tensile strength,the elastic modulus,and the peak tensile strain are used as the tensile property indexes of concrete.By combining the modes of failure with the leaching level indexes,the variations of tensile properties with leaching time are explained.The effects of the water/cement ratio and the aggregate volume fraction on the tensile properties of leached concrete are analyzed.Based on the experimental results and the theoretical models,the main conclusions can be made as follows:(1)The leaching depth of concrete is proportional to the square root of leaching time.For a given aggregate volume fraction,the larger the water/cement ratio is,the larger the leaching rate is.For a given water/cement ratio,when the aggregate volume fraction is smaller than55%,the leaching rate is basically invariable.However,when the aggregate volume fraction is larger than 55%,the leaching rate increases significantly.(2)The water ratio at the saturated surface-dried condition increases continuously with leaching time.For a given leaching time,the larger the water/cement ratio and the aggregate volume fraction are,the larger the water ratio at the saturated surface-dried condition is.(3)With increasing leaching time,the tensile strength and elastic modulus of concrete increase but the peak tensile strain decreases.Compared with the elastic modulus and tensile strength of concrete,the peak tensile strain is more sensitive to leaching.(4)The water/cement ratio and the aggregate volume fraction are the key factors that affect the tensile strength,elastic modulus,and peak tensile strain of concrete.The larger the water/cement ratio and theaggregate volume fraction are,the more quickly the tensile strength and the elastic modulus decrease but the more slowly the peak tensile strain increases.(5)The leaching damage variable is proportional to the tensile strength,elastic modulus and peak tensile strain of concrete.(6)Through comparing unleached concrete with leached one measured with the electron microscope,it is obviously shown that the structure of leached concrete is degraded,and for a given leaching time,the larger the water/cement ratio is,the more serious the degree of degradation is.(7)Through analyzing the pore structures with mercury injection apparatus,it is shown that,with increasing leaching time,the porosity of concrete increases and the pores are connected with each other.The dissolution of hydrate starts with CH.When all the CH is dissolved,part of C-S-H starts to be dissolved.(8)A theoretical model of the porosity of leached concrete is introduced.Based on this model,a model for predicting the axial tensile strength of leached concrete is given.The validity of this model is verified with experimental results.