Papers by Author: Jin Xia Xu

Abstract: In order to evaluate more accurately the corrosion condition of reinforcing steel in chloride contaminated concrete, it is significant to investigate the error level in the linear polarization resistance measurement caused by IR drop. Concretes with eight levels of chloride ions (ranging from 0% to 2.0% by mass of cement) by adding different amounts of sodium chloride in the mixing water were prepared. Linear polarization measurements with and without IR compensation, were applied to determine the error level. Besides, half-cell potential method was employed to detect the corrosion condition of reinforcing steel. The results indicate that the error level is so low (less than 5.0%) that the IR drop can be negligible when the chloride content is relatively lower (0.6% or less by mass of cement). However, the error level is increased with the increase of chloride content. The IR drop is suggested to be compensated when the chloride content is relatively higher (more than 0.6% by mass of cement). At this time, the onset of active corrosion of reinforcing steel is also found.

Abstract: Non-structural cracking of concrete is a serious problem and the underlying phenomena, namely, shrinkage and creep, need to be better understood. Much research has been devoted to this complex problem. However, despite major successes, the phenomenon of autogenous shrinkage is still far from being fully understood. The paper discusses the main aspects of concrete shrinkage, with a focus on autogenous shrinkage, which are especially important in low water/binder ratio concrete. These aspects include the theories of physical mechanism, prediction models and future research trends. Shrinkage of concrete due to moisture changes, which result in surface and capillary tension, was reviewed. The mechanisms often cannot be directly linked to the macroscopically observed dilatation/contraction. An overview of recent model developments is also presented.

Abstract: In this article, some empirical and theoretical models accounting the relationship between the strength and pore structure of cement-based materials is reviewed and analyzed. From the literature review and analysis, it can be found that the total porosity can be singly used to characterize the relationship between compressive strength and pore structure, but can not be applied into describe the relationship between pore structure and tensile strength. Another major parameter of pore structure - pore size distribution, will have a major impact on strength; the relationship between pore structure and tensile strength is for most models of cement paste, without the consideration of aggregate, and the application of the model must comply with the relevant assumptions. The research on the relationship between the tensile strength of concrete is still at a preliminary stage, requiring more theoretical and experimental study.