Research On The Damage Of Concrete Under Sulfate, Chloride And Flexural Loading

In seaside and slat lake area, where many concrete constructions are severely deteriorated and lost its function only in several years, which is mainly caused by the concentrated salts solutions such as chloride, sulfate, carbonation, magnesium ions and so on. The effects of single factor, double factors and multi-factors with salts solutions lead concrete to deteriorate. In this paper, the most serious and common damage factors are selected to analysis the concrete performance degradation and the reinforced corrosion.A new durability testing research system and loading equipment are established to simulate damage and deterioration process of concretes. The damage law and properties of concrete are systematically investigated under single factor, double factors and multi-factors with sulfate-chloride-flexure loading. Based on durability experimental results, a damage function of the relative dynamic modulus of elasticity (Eed) considering the flexure loading, concentration of sulfate, chloride and types of concrete, is proposed. The steel corrosion of reinforced concrete under the mixture solution of sulfate and chloride is investigated, the effects of flexure loading on steel corrosion is discussed in this paper.The ultrasonic technique is employed to investigate the damage law and properties of concrete, dynamic modulus of elasticity (Ed) reflecting the macro-mechanical damage performance of concrete. Electrochemical methods (corrosion potential and linear polarization resistance) are used to analyze the corrosion state of steel in concrete. There are several conclusions in experiment.(l)The results of single sulfate exposed480d test indicate the sulfate erosion is a chronically process and the evolution of Ed submit to the parabola, early enhancing consistency, keeping and descending further, corresponding with the negative damage mechanics of concrete. The chlorine salt decelerates the damage of concrete by sulfate erosion, whereas the flexural loading accelerates the deterioration of concrete. The degradation of concrete is related to concrete strength and the concentration of sulfate, the lower strength the faster change, the higher concentration the faster change. (2)The variation of the relative dynamic modulus of elasticity of concrete exposure to several attacking condition fit in the same curve, the damage evolution equation of D (damage degree) with/(attacking time):Erd=D=1+Bt+Ct2;B refer to the initial variation rate of concrete Erd, C reflecting the variation rate of deterioration. Experiment data analysis shows that this model can fit the relationship between damage and attacking time well.(3)The corrosion potential of reinforced concrete exposure to the mixture solution of sulfate and chloride deceases as time goes on; the higher strength of concrete posses higher density, the higher the corrosion potential. During the experiment, the corrosion current density increases. Flexure loading promotes the steel corrosion by speeding up the erosion of salt ions, accumulate the concrete cracking. The steel corrosion of the same strength of concrete samples under higher flexure loading is more serious. The results of steel corrosion of cracked concrete under flexure loading shows that, the reinforced itself under flexure loading or not don’t influence the stress corrosion degree.(4) By defining the damage degree of concrete caused by steel corrosion, the relation among the damage degree, corrosion current density and corrosion time-varying was established, which reflected the process of damage evolution.