Corrosion resistance of SD345 steel, which is mainly used for reinforcing steel in concrete, was investigated by electrochemical measurements in a solution that simulates concrete with Cl-. The protective property of passive film of SD345 steel formed in saturated Ca(OH)2 solution was examined by dynamic anodic polarization and impedance measurements. It is revealed that the passive film growing with immersion time in the test solution improves the corrosion resistance of SD345 steel. However, the stability of passive film decreased in the concrete modified solution including over 0.1 M Cl-. In addition, the influence of passive film properties before corrosion test on the corrosion behavior of reinforcing steel in concrete was discussed by corrosion monitoring of SD345 steels with passive film under wet and dry cyclic environment. With increasing the growth period of passive film in the test solution, changes in the corrosion resistance of SD345 steel decreased during wet and dry cyclic environment.
This study aims to propose the mechanical models of fiber reinforced Porosity Free Concrete (PFC). The compression test, splitting cylinder test, and bending test of PFC specimens were conducted to investigate the mechanical properties of fiber reinforced PFC. The material characteristics of PFC such as the characteristic values for material strength, the compressive stress-strain relationships, and the the tension softening curve were proposed from each material test and the inverse analysis based on the results of three-point bending test, respectively. Furthermore, the size dependence of the flexural strength of fiber reinforced PFC was investigated through the four-point bending test and the finite element analysis with a discrete crack model. Based on the results of this FEM analysis, an equation to predict the flexural strength was proposed for PFC beams with the various height. Moreover, the equivalent specific length of fiber reinforced PFC beam with various height was also determined based on the numerical study using fiber modeling analysis. Finally, the tensile stress - strain relationships were obtained by the use of the equivalent specific length in order to convert the crack width of the tension softening curve into the strain.
In Japan, dehydrated cake discharged from crushed stone quarry is still disposed. To make it possible to recycle a large amount of dehydrated cake, we focused on a high temperature heating production method for recycling construction waste as concrete aggregates, we have been produced coarse aggregates for concrete by using dehydrated cake discharged from crushed stone quarry and investigated their performances. However, to produce dehydrated cake coarse aggregates, we had decided appropriate heating conditions, i.e., temperature and time of dehydrated cake granulated materials through high temperature heating test with different heating conditions. By the trial and error method, since the kinds of dehydrated cake differ depending on the kinds of crushed stone, working efficiency to produce dehydrated cake coarse aggregates decreases. To improve the working efficiency, the objective of this study is to develop an estimation model of heat melting temperature (temperature keeping time: 30 min) of dehydrated cake discharged from crushed stone quarry based on its chemical composition by x-ray fluorescence analysis (XRF). First of all, several kinds of dehydrated cake discharged from crushed stone quarry in the Tohoku region were used and the range of heating temperature and heating time to produce dehydrated cake granulated materials were indicated through high temperature heating test. Next, the performances of melted granulated materials were evaluated and strength properties of concrete using the melted ones was measured. As a result, it was clear that the melted granulated materials can be used as coarse aggregates for concrete. Finally, based on the above results, estimation model of heat melting temperature of dehydrated cake discharged from crushed stone quarry was developed by using neural network back propagation. It was found that the estimated all results were good agreement with the measurement ones.
While it has long been acknowledged that water penetration into RC members under fatigue loading conditions will reduce their fatigue resistance, the influence of such water penetration on RC members subjected to freezing conditions has not yet been explored. This study evaluates the compressive and splitting tensile strength of concrete cylinders, as well as RC beam flexure properties, via static loading and fatigue testing carried out on specimens under controlled ambient temperature and moisture content conditions. The results showed that while dry concrete was unaffected by ambient temperature, water saturated concrete specimens showed reduced static strength as well as a reduction in the number of fatigue failure cycles under normal temperature conditions. However, those same saturated concrete specimens showed an increase in static compressive strength under low-temperature (freezing) conditions, even though no increase in fatigue failure cycle number could be confirmed based on incremental static strength testing. Furthermore, the flexural behavior of RC beams under water saturation conditions showed load carrying capacity and fatigue resistance reductions under normal temperature conditions, but increased load carrying capacity under low-temperature conditions. Finally, while it was revealed that the fatigue resistance of normal and low-temperature specimens were comparatively the same with regard to the number of fatigue failure cycles, there was a change in the fatigue failure mode.
In order to evaluate quantitatively and to measure by a non-contact method for degree of deterioration of concrete surface subjected to freezing and thawing action, this study investigated applicability of an arithmetical mean deviation to measurement of scaling. The arithmetical mean deviation was useful method for quantitative evaluation of measurement of scaling regardless of mix proportion, curing and experimental condition in this study, and also the measurement condition had little effect on the results of the mean, from laboratory experiments and investigation for existing actual structures. Relationships between the mean deviation and distribution of the crack density from the surface to inside of concrete cover were also discussed, thus it was revealed that the micro cracks were propagated up to 30 mm depth from the surface showed scaling. Furthermore, attempts of simplified measuring of the arithmetical mean deviation by using the stereo-camera were carried out. Evaluation of deterioration of concrete surface by using the arithmetical mean deviation was applicable satisfactory from the results of this study.
In response to the aging of social infrastructure, it is required to evaluate deterioration damage of concrete structure due to sophistication of maintenance technology. Authors have been developing a X-ray inspection system using mobile linac X-ray sources for bridge inspection, and trying to evaluate the state of tendons existing inside of a concrete bridge by transmission X-ray inspection. We also intend to inspect the state of grout. We have already carried out X-ray inspection system on actual bridges, but quantifying the relationship between concrete thickness and transmission X-ray imaging capability has become a problem in securing accurate inspection. For this reason, in this research, we investigated the response of X-rays with different thicknesses of concrete, and made basic studies to improve the inspection accuracy. From that, we can specify the applicable concrete thickness of each portable X-ray source. And the performance of the mobile linac X-ray source was evaluated.