Study On Mechanical Behavior Of Corrosion Products Under Different Environments

When the steel corrodes in concrete structures,the volume of rust is almost several times than the original,thus,induce an internal pressure on the surrounding confining concrete.With the production of more quantities of corrosion products,this pressure will generate tensile stress around the concrete and crack it.Since corrosion products grow between the concrete and the steel,before cracking of the concrete cover,the rust actually participates in the mechanical interaction induced by its volume expansion between concrete cover and steel.Therefore,the mechanical behaviors of the rust should be well known.It is important for not only analyzing the stress in the concrete cover due to corrosion during the phase from corrosion initiation to the cracking process,but also predicting the time of concrete cracking due to corrosion.Based on the earlier study and basic principles of chemistry and material science, the main work in this paper can be summarized as follows:1.Corrosion products formed in eight different environments were investigated by X-ray diffraction(XRD).Thermal analysis was used to calculate the content of two types of corrosion products.Based on the expansion coefficient and volume percent of every corrosion compound,the expansion coefficient of eyery rust sample can be obtained by weighted average.Thereby,the relation between the level of different environmental factors and the modulus of rust was discussed,to apply the suggested value of the rust expansion coefficient for the rust layer in real structures. Thus,the bridge of environmental effect,the component of rust and the expansion coefficient had been built up.2.The oedometer tests were used to receive the load versus the deformation of powder rust samples formed in natural environments and accelerated corrosion tests. Considering the way of loading,the "momentary Young's modulus" was defined to analyze the mechanical behavior of rust samples,the modulus of two types of rust were then deduced by Hertz' contact theory.From the results,for rust samples with different sizes,differences of the mechanical and material behavior were summarized. 3.Cycle loading tests under low stress were conducted for flaky rust samples. Compared with the earlier research,a constitutive model of rust was developed by the first loading curve.Then the modulus of different flaky rust samples was tested by the cyclic low-compression;based on the tested data,an equation of the modulus considering the influence of the volume of samples and the ratio between height and area was proposed.Finally,the modulus value of rust applied in concrete cover cracking model is inferred.