The aim of this research is to reveal the effect of curing conditions on carbonation and chloride diffusion of normal concrete and fly ash replacement concrete. Sealed curing, air curing and curing under the wind and sunlight were compared to normal water curing. As the result, better curing made carbonation depth, chloride diffusion coefficient and void ratio of cement matrix were low, and in case of fly ash replacement concrete, mass transfer resistant was lower by comparison of same void ratio of normal concrete. According to the analysis of binarized concrete CT image by homogenization methods, magnitude relation of tortuosity between normal concrete and fly ash concrete is differ in the difference of water to powder ratio. This fact implies that the mechanism of high mass transfer resistance performance of fly ash concrete is different in differ of pore structure of each solid.
The large drying shrinkage of concrete can cause cracks in concrete structures. For solving the cracking problem, it is required to clarify the relationship between the shrinkage of concrete and the quality of aggregate in it. The main purpose of this study is to obtain data on the drying shrinkage of coarse aggregate available at the stockyard in ready-mixed concrete plants, and its static modulus of elasticity and its compressive strength in order to utilize the coarse aggregate as local resources efficiently. The length change test of concrete and the drying shrinkage cracking test of restricted concrete are also carried out on the three types of concrete mixtures. The results are follows: The quality of coarse aggregate is one of the crucial factors affecting the quality of concrete. The drying shrinkage of the aggregate increases the shrinkage of concrete. The shrinkage of coarse aggregate is also related to the static modulus of elasticity as well as the rate of water absorption. The drying shrinkage of coarse aggregate can be estimated in 3-7days by using the strain gauge method.
This study investigates fatigue characteristics of concrete and reinforced concrete member using easily crushed limestone aggregates and low quality aggregates such as waste roof tiles and melt-solidified slag aggregate derived from municipal solid waste. From the experiments, the following results were obtained : (1) Under repetitive loading, the distribution of fatigue life of plain concrete that used these aggregates also are confirmed to a logarithmic normal distribution as well as concrete with normal aggregate. (2) The compression fatigue strength of concrete varies with type of aggregates used. The compression fatigue strength of concrete with limestone aggregate is higher compared to that of concrete with normal aggregate. It is lower than compression fatigue strength of concrete with normal aggregate although the compression fatigue strength of both concretes with waste roof tiles aggregate and with melt-solidified slag aggregates derived from municipal solid waste is nearly equal. (3) Reinforced concrete beams with these aggregates have shown nearly the same value of fatigue strength. Consequently, it comes into conclusion that the kinds of aggregates used in the concrete have hardly effect on the fatigue strength of reinforced concrete beams.
Various repair methods have been recently applied to not a few concrete structures which had been degraded, in order to prolong the service life of infrastructures. In the Subcommittee on Polymers for Repair and Strengthening (in Concrete Structures) organized in Committee on Polymers in Concrete (Chair : Toyoaki Miyagawa) of the Society of Materials Science, Japan (JSMS), the systematic experiment with the common test procedure on the concrete surface coating systems/materials has been carried out since 2006, in order to propose a common test method which is available to the actual proof and the comprehensive evaluation of the durability of the concrete structures repaired with the concrete surface coating material.In this study, the common test method was focused on the bond performance which has a great influence on the durability of concrete surface coating system. The bond test methods which were able to evaluate the peeling behavior were performed in addition to the popular bond test using uni-axial tension, which often resulted in the similar bond strength due to the fracture of the substrate. The common test results on the concrete surface coating system using both the uni-axial tensile and peeling bond test brought more practical and accurate evaluation for the bond performance of coating films.
In these days, the footings degenerated due to Alkali Silica Reaction (ASR) have been discovered in Japan. To perform an appropriate diagnosis for those footings, a lot of knowledge for the footings degenerated due to ASR have to be obtained, such as the occurrence condition of ASR in footings, the internal degradation conditions. Accordingly, the road administrator can't maintenance them, and this is a big problem to carry on safe road network. So, the long term exposure test has been done under the actual condition up to now, and the crack and strain of the footings, temperature and water level of the exposure environmental have been measured to get those knowledge. At first, we analyzed the difference of the degradation of footings cased by environmental condition, in water, air and under the ground, from measured data, and we examined the reason of the difference. And we showed that the strain of steel is affected by reflection from temperature. Further out, we identified the internal degradation mechanism in footings. Finally, the characteristic value, for example temperature, needed for the occurrence of ASR and the evaluation of the degenerated condition in the footings are revealed.
This paper presents general solutions for anisotropic cylinder using complex stress functions based on Lekhnitskii formalism. Up to now, an analytical solution of isotropic cylinder has been widely used whereas solutions of anisotropic elliptic cylinders subject to arbitrary surface loads have not been derived. The proposed complex stress functions, which are developed by Laurent series, enable to solve conditions under distributed loads like hydro pressures and concentrated loads. The function can also analyze a shear load parallel to longitudinal axis of a cylinder. Analyzed stress distributions are graphically represented.
This study focuses on the method of predicting the fatigue life of materials subjected to random loading. Since random stress is rigorously expressed in frequency domain as stress power spectral density (PSD), the fatigue life should be predicted with the stress PSD. In this article, we propose a method of improving the accuracy of the fatigue life prediction with stress PSD in frequency domain. Although the method proposed by Dirlik is widely used for predicting the fatigue life in frequency domain, it often overestimates fatigue damage caused by large stress amplitude. To avoid this overestimation, we estimate the expected value of maximum stress amplitude from stress PSD and then use the expected value to adjust the probability density function of stress amplitude evaluated using Dirlikﾕs method. The proposed adjustments were applied to the fatigue life prediction in the cases of typical random stresses observed on mechanical products, and as a result, it worked well to improve the accuracy of the prediction. By evaluating fatigue strength against random stress accurately, we can design lightweight and mechanically reliable trains, construction machinery, automotive products, etc.
Flake-polymer composites are commonly used in protection and barrier applications due to its low effective diffusivity. Effective diffusivity through flake-polymer composites depends on the local accelerated transport along the flakematrix interphase. This paper describes analytical models for predicting the effective diffusivity through the flake-polymer composite as a function of flake orientation, volume fraction, aspect ratio, and interphase properties. Estimates of effective diffusivity were also generated using random walk simulations. Results from the two methods agree well with each other. Using model-predicted effective diffusivities, solute penetration depths in systems with flakes aligned either orthogonal or parallel to the diffusion direction are calculated and compared to experimentally obtained penetration depths of acid solutes through glass flake-polymer composites.