Investigation on the transport properties of chlorides in concrete (I) Identification of ITZ

Concrete is a multiphase composite material, in which the mortar, aggregate and interfacial transition zone (ITZ) have important influence on the chloride ions transport. In this research, the thickness ITZ was measured and the concentration distribution of chloride ions in concrete was obtained through electron microprobe analysis. The experiment results that the thickness of ITZ follows a normal distribution and the size of aggregate shows no clear influence on the thickness of ITZ

An experimental study on relationship among water sorptivity, pore characteristics, and salt concentration in concrete

© 2017, Budapest University of Technology and Economics. All rights reserved. In this work, the sorptivity properties of concrete with various types of supplementary cementitious materials (SCMs) cured at three different curing regimes was investigated using the gravimetric method. In parallel, the effects of four different concentrations of sodium chloride solution on the sorptivity of concrete were studied using both gravimetric and electronic methods. The results show that the incorporation of SCMs reduces the sorptivity of concrete when sufficient moisture curing is provided; otherwise, it exacerbates sorptivity. Nevertheless, there exists a strong correlation between the sorptivity coefficient and threshold pore size of concrete measured by mercury intrusion porosimetry. The gravimetric and electronic methods show different trends regarding the effects of liquid properties on sorptivity, probably because the gravimetric method cannot differentiate the weight of water from salts during the measurements.Link_to_subscribed_fulltex

Rust distribution and corrosion-induced cracking patterns of corner-located rebar in concrete cover

© 2017 Elsevier Ltd In this work, the rust distribution patterns and concrete cover cracking behavior of corner-located rebar was studied by means of digital microscopy. The corner-located rebar with various cover thicknesses embedded in concrete specimens was exposed to artificial corrosive environments. The time-dependent evolution of rust distribution profiles around corroded rebar was measured and described by Gaussian models. The results show that for corner-located rebar, when the two side concrete cover thicknesses have the similar value, the onset of rust formation starts simultaneously and its rust pattern can be well described by two or three independent Gaussian functions. At the same level of corrosion, the cracking behavior of corner-located concrete can be considerably different, depending on the rust profiles and dimensional ratio of the two side concrete cover thicknesses.Link_to_subscribed_fulltex

Investigation on the transport properties of chlorides in concrete II Numerical simulation

The chloride ions diffusion in concrete is an important problem inducing the corrosion of reinforcement under marine environment. Based on a parallel transmission model, the diffusion coefficient of chloride ions in ITZ was determined. Thereafter, the measured parameters of ITZ were integrated into a numerical model to simulate the chloride ions diffusion and the reliability of the model was verified by comparing the numerical simulation with the surface scanning results collected from the electron microprobe. The test results show that if the concrete is taken as a threephase composites, the numerical model can reflect the real transmission process of chloride ion more accurately

Influence of flexural loading on chloride ingress in concrete subjected to cyclic drying-wetting condition

© 2015 Techno-Press, Ltd. Chloride ingress implies a complex interaction between physical and chemical process, in which heat, moisture and chloride ions transport through concrete cover. Meanwhile, reinforced concrete structure itself undergoes evolution due to variation in temperature, relative humidity and creep effects, which can potentially change the deformation and trigger some micro-cracks in concrete. In addition, all of these process show time-dependent performance with complex interaction between structures and environments. In the present work, a time-dependent behavior of chloride transport in reinforced concrete beam subjected to flexural load is proposed based on the well-known section fiber model. The strain state varies because of stress redistribution caused by the interaction between environment and structure, mainly dominated by thermal stresses and shrinkage stress and creep. Finally, in order to clear the influence of strain state on the chloride diffusivity, experiment test were carried out and a power function used to describe this influence is proposed.Link_to_subscribed_fulltex

Theoretical and experimental investigation of loading effects on chloride diffusion in saturated concrete

Copyright © 2015 Japan Concrete Institute. In this paper, a comprehensive investigation regarding the loading effects on chloride diffusion in saturated concrete is reported. It involves both theoretical and experimental aspects, towards contributing to the service-life prediction of infrastructure under chloride attack. A revised chloride diffusion model is proposed based on the modified Fick's second law with an emphasis on the loading effects. In particular, this influence is quantified using a newly-introduced damage effect factor defined by tortuosity and constrictivity of damaged concrete. This model is capable of predicting the chloride profiles in concrete under different loading states, regardless of whether it is damaged or undamaged. Meanwhile, a series of experimental studies were extensively operated in order to analyze the influence of loading on chloride diffusion process. Two types of mixtures (i.e. ordinary concrete and ordinary concrete mixed with slag) were investigated for chloride diffusion tests under different natures (i.e. compressive and tensile loads) and magnitudes of loads. Totally four levels of loads were applied to further correlate the relation between chloride diffusivities and associated strain values. Finally, two groups of test data with different tensile strain were adopted to validate the theoretical model. It shows that the model is reasonable and the numerical result is adequately accurate.Link_to_subscribed_fulltex