Long-Term Performance Of Concrete Under Axial Compression Coupled Effects Of Sulfate Attack

Any kind of concrete structures bear loads including self weight experiencing environmental effects at the same time,the properties of concrete materials and structure is under the coupling effects of the load with environmental factors should be studied.Due to the change of loading concrete structure,loading and unloading process are also important factors to be considered.The long-term performance of 138 cube concrete specimens under coupling effect of axial compression load of various stress ratios(0,15%,30% and 45%)and sodium sulfate solution with different concentration(0,5% and 10%)were investigated in this paper.Two different immersion ways which are the full immersion and the semi-immersion were used,and the loading and unloading effect were considered.The main results are as follows:1.With the increase of the age of erosion,the surface morphology of the specimen under axial compression load of 45% stress ratio exhibits the characteristics of gradual deterioration.The saturated surface dry water absorption rate of the specimen under full immersion method is greater than that of the semi-immersion method.The surface of the specimen under axial compression load of 30% stress ratio or less presents the characteristics of gradual deterioration after compaction,and the damage degree of non-immersed zone is greater than the immersed zone.The saturation surface dry water absorption rate of the specimens shows a trend of decreasing first and then increasing,and the higher the stress level is,the more obvious the increasing trend is in middle and later stages.The damage of non-immersed zone is more serious than that of the immersed zone of concrete.2.The deterioration rate of the relative dynamic elastic modulus of the non-immersed zone is significantly greater than that of the immersed zone,and the semi-immersion method has obvious effect on the deterioration of strength of concrete.The coupling effect of axial compressive load of high stress ratio and sulfate erosion has obvious effect on the deterioration of relative dynamic modulus and strength of concrete.Under the axial load of 45% stress ratio,the relative dynamic elastic modulus and strength value show the trend of decreasing with the increase of erosion age.Under the axial load of 30% stress ratio or less,the relative dynamic elastic modulus and strength value show the evolution law of decreasing after increasing.The direct coupling effect of the axial load of 30% stress ratio and 5% sodium sulfate solution has significant inhibitory effect on the deterioration of relative dynamic modulus and strength.3.Under the axial load of 30% stress ratio,the deterioration process of interface transition zone under the effect of sulfate attack can be divided into two phases.In the first stage,the internal pores of concrete substrate are filled because of the formation of ettringite and gypsum and filling,which increases the compactness of concrete;In the second stage,the expansion stress of ettringite and gypsum in the concrete matrix is greater than the tensile strength of concrete,which results in microcracks and further deterioration of the concrete.Under the coupling of axial load of 45% stress ratio and sodium sulfate solution,the microstructure of concrete shows the evolution law of gradual deterioration in the process of sulfate erosion.The deterioration process of the interfacial transition zone is the lowest under 30% stress ratio,and the most serious damage of 45% stress ratio.With the increase of the age of erosion,the filling compaction effect of ettringite and gypsum on the microcracks is relatively small,and the deterioration of micro-cracks in the transition zone of concrete interface is gradually increasing.