An Experimental Study On The Diffusion Characteristics Of Chloride Ions In Early Age Concrete

An experimental study on the mechanical properties and chloridediffusion characteristics of cement paste and concrete is conductedsystematically in this thesis. The effects of the curing age, water/cementratio, aggregate volume content, maximum aggregate diameter and fly ashcontent on them are analyzed. Finally, the prediction method of the chloridediffusivity of ordinary concrete and the chloride diffusivity of interfacialtransition zone (ITZ) are discussed.The experimental results show, as the curing age increases, thecompressive strength and elastic modulus of cement paste and concreteincrease but the chloride diffusivity decreases sharply at early ages andslowly at later ages. As the water/cement ratio increases, the compressivestrength and elastic modulus decrease but the chloride diffusivity increases.The addition of fly ash has a certain influence on the mechanical propertiesand chloride diffusivity of cement paste and ordinary concrete. At earlyages, fly ash decreases the compressive strength and elastic modulus butincreases the chloride diffusivity. At later ages, fly ash has a beneficialeffect in increasing the compressive strength and elastic modulus and in decreasing the chloride diffusivity. As the aggregate volume content andmaximum aggregate diameter increase, the compressive strength andelastic modulus of ordinary concrete increase but the chloride diffusivitydecreases. The aggregate gradation has a certain influence on themechanical properties and chloride diffusivity of concrete, but the extentsto which it influences the compressive strength, elastic modulus andchloride diffusivity are different.Finally, the prediction method of the chloride diffusivity of ordinaryconcrete is discussed. By comparing with the experimental results, thevalidity of the method is verified. The chloride diffusivity of ITZ isobtained using the numerical inverse method. It is found that the ITZchloride diffusivity increases with an increase in water/cement ratio, butdecreases by increasing the curing age.