Failure Characteristics And Mechanism Of Chlorine Deicers And Freeze-thaw On Concrete

In order to keep a smooth traffic in snowy weather, the chlorine deicers are widely used on roadsto thaw snow by lowering its freezing point. However, while thawing snow, the chlorine deicers alsobring many negative impacts, such as corrosion and freeze-thaw damage, environmental pollution andso on. Though in the past years, domestic and foreign scholars have studied a lot, technology andtheory problems remaining need to be studied comprehensively and further.In this paper, experiments were conducted to analyze the damage of concrete due to chlorinesalts and freeze thawing, which were focused on three fronts as follows:①The salt heaving damageof cement concrete sample under condition of immersion or dry-wet cycle.②The double effect ofchloride and freezing-thawing on the deicer-scaling resistance of cement concrete.③The damage ofasphalt mixture sample under dry-wet or freeze-thaw cycle due to chlorine salts. Effects of concretestrength grade, types and concentrations of chloride and cyclic number on properties of pavementconcrete were researched in this paper. The hydration products, microstructures were investigated bymeans of XRD and SEM. Failure characteristics and mechanism of concrete exposed to chloride andfreezing-thawing was also investigated. The experimental results showed as follows:（1）The concrete strength increased when the samples were immersed in chloride solution,while under dry-wet cycle condition it firstly ascended and then descended, with the age increased.The diffusion rate in dry-wet cycle condition was larger than that in immersion condition. C50had asuperior erosion resistance to C30. The analytical expression between the content of free chloride ionat different positions of concrete species y and the distance surface x was in the form of exponent, i.e.,y=a*exp(-x/t)+b.（2）Denudations or cracks appeared on the surface of salt-frozen samples. Meanwhile, theweight loss rate increased continuously, relative dynamic modulus of elasticity and strength decreasedwith the increase of freeze-thaw cycles. The deicer-scaling resistance of C50is better than that of C30,and the former can suffer another65freeze-thaw cycles. Reference groups entertained withappropriate amount of silica fume and high-performance air-entraining agent had a betterdeicer-scaling resistance, even if they underwent200cycles, no visible damage was observed. Whenthe concentration of chloride solution was between3%and5%, the damage of concrete issignificantly more, while for the higher concentration (20%), the damage is less.（3）The water stability of asphalt mixture specimens reduced when they were exposed to3%,10%and20%chloride solution under dry-wet or freeze-thaw cycle condition. Higher concentration of salt solution resulted in lower water stability. The Marshall stability and Marshall modulus decreasedwhile flow value incresesed with the increase of dry-wet cycles. The freeze-thaw cycle has a negativeeffect on the freeze-thaw cleavage strength of bituminous mixture.（4）The effect of chloride solution concentration of3%,10%and20%on low temperaturestability of asphalt mixture was also studied through low temperature bending test. The higher theconcentration was, the less the low temperature stability reduced. Along with the treating time passing,the flexural tensile strength and the biggest flexural strain decreased, while the bending strengthdegree modulus increased.（5）The main failure features of concrete were characterized by surface spalling, cracking, andwhite crystal separated out. All these were caused by physical crystallization, temperature effect,chemical reaction of the deicers with the hydration products of cement and alkali-aggregate reaction.