Prediction Of The Chloride Diffusivity Of Concrete And The Time To Surface Cracking

It is very crucial to the durability design and assessment of reinforcedconcrete structures located in a marine or de-icing salt environment todetermine the chloride diffusivity of concrete and the time to surfacecracking. The former determines the initiation time of reinforcementcorrosion in concrete to a great extent and the latter is a measure of theservice life of reinforced concrete structures.The intention of this paper is to predict the chloride diffusivity ofconcrete and the time to surface cracking. Based on a three-phasecomposite circle model, a two-dimensional finite element method ispresented for predicting the chloride diffusivity of concrete. The validity ofthe proposed method is verified with experimental results. Based on thenumerical results, the effects of the maximum aggregate diameter, thechloride diffusivity of ITZ, the ITZ thickness and the aggregate gradation on the chloride diffusivity of concrete are evaluated in a quantitativemanner. Since the ITZ is the weakest link in concrete, interfacial crackswill be induced by factors like bleeding, shrinkage, thermal gradient,freeze-thaw, alkali-aggregate reaction and external forces. By introducinginterfacial cracks in the three-phase composite circle model, the effect ofinterfacial cracks on the chloride diffusivity of concrete is studied. Theeffects of the subtended angle of interfacial cracks and the mesostructuralparameters of concrete on the chloride diffusivity of concrete arequantitatively evaluated. By considering the softening characteristics ofconcrete and introducing the concept of smeared cracks, a finite elementmethod is developed for the cracking analysis of a concrete cover. The timeto initial cracking, the time to complete cracking and the corrosion-inducedexpansive force at any time are obtained. The validity of the developedmethod is verified with experimental results. The effects of the elasticmodulus of concrete, the tensile strength of concrete and the cover depth onthe maximum corrosion-induced expansive force and the time to completecracking are discussed.