This paper presents test results of pull-out behavior of short fiber (PP fiber and steel fiber) subjected to monotonic and cyclic loading. In the case of PP fiber, pull-out resistance under cyclic loading was slightly decreased comparing to that of monotonic loading. In some cases, load was suddenly dropped due to split crack due to cyclic loading. In addition, bending of PP fiber induces a damage due to compression action in the test. In the case of steel fiber, frictional bonding behavior was observed in both tensile and compression phases.
An integrated heat transfer analysis of manhole and soil was conducted to predict hydrothermal condition and condensation in manhole, which affects deterioration process of manhole for information network. It was verified that time-dependent change of temperature in manholes in various region in Japan can be simulated. Based on the results of heat transfer analysis, occurrence of condensation was predicted. Water content was calculated by moisture transfer analysis in concrete, in which capillary suction of condensed water. It was clarified that condensation likely occur in manhole in winter and accordingly water content in concrete become higher in winter, which might accelerate corrosion of reinforcement in concrete.
A prediction method for reinforcing bar corrosion in concrete was developed to assure efficient maintenance of concrete manholes for information network. An equation for corrosion rate of reinforcement in concrete of manholes was proposed, which took into account the effect of moisture content of concrete, temperature and supply of oxygen to reinforcement. Corrosion of reinforcement of manholes under various conditions were calculated as a function of time based on prediction results of hydrothermal condition in manhole by integrated heat transfer analysis of soil and structure. It was verified that tendencies of deterioration process of manholes due to reinforcement corrosion in various region in Japan can be predicted considering differences in regional climatic conditions.
Near Surface Mounted (NSM) method using Carbon Fiber Reinforced Polymer (CFRP) rods of ultra-high modulus is suitable to strengthen cantilevered deck slab subjected to negative bending moment. The NSM technique has some advantages such as negligible increase of dead-load and no corrosion of reinforcement. However, the most concern is low bond strength of the ultra-high modulus CFRP rods without shear-resistant ribs. This study focuses on the bond improvement method of the ultra-high modulus CFRP rod embedded in concrete or mortar which is a filling material for NSM. The pull-off test of CFRP rod embedded in concrete or mortar was conducted to examine bond performance. The test result confirmed that the attachment of Glass Fiber Reinforced Polymer (GFRP) rib to the CFRP rod is relatively effective to improve the bond performance. This paper presents the best dimensions of the GFRP rib to effectively improve bond performance of the ultra-high modulus CFRP rod.
In this study, the same mortar chip specimens were exposed to estimate airborne salt environment in 101 places in Japan.
The conversions of the chloride content of the specimen into the surface chloride concentration were carried out. The revised distance was calculated using the distance between specimen and shoreline, the altitude of specimen, the wind direction and the wave energy of exposure test place.
From the regression analysis, the estimation method of the surface chloride concentration of the concrete at various environment using the revised distance was formulated.
In design phase, drying shrinkage strain of concrete is often obtained by a prediction equation. In the prediction formula of the current Japan society of civil engineers, a coefficient α indicating the influence of aggregate quality is introduced. It is said that the prediction formula can predict approximately ±50% with respect to the actual measurement values of the concrete drying shrinkage strain. The coefficient α representing the influence of the quality of the aggregate is substituted into the prediction expression by the value of 4 to 6, but the value is not determined by the type of aggregate or the like. In this research, we analyzed that the actual values of coefficient α expressing the effect of aggregate quality by using data of concrete using coarse aggregate including quality other than Japanese industrial standard. In addition, we modified the prediction equation as a function consisting of the each water content in mortar and coarse aggregate. Moreover, we proposed a formula for calculating the coefficient α’ representing the influence of the quality of the coarse aggregate.
The main required performance of repair adhesives is adhesion, and the change of the material properties on the adhesion surface is important in the durability evaluation. However, it has been difficult to directly evaluate the change in strength of adhesive surface part so far. Therefore, we analyzed the surface strength change accompanying the deterioration of epoxy resin by using surface / interface cutting analysis system. By using the surface / interface cutting analysis system, it became clear that the way of being affected by water absorption and drying changed depending on the kind of curing agent. In the accelerated degradation test with alkaline solution, it became clear that the surface strength greatly decreased initially, then became slow as the immersion time prolonged, and the deteriorated form changed with time. Furthermore, deterioration of the adhesive was dominant by alkali, but it was confirmed that it is also susceptible to water influence at the initial stage. The evaluation of the mechanical properties of the micro area on the surface using the surface and interface cutting analysis device can quantify the progress of deterioration, and is considered useful for evaluating the durability of the adhesive.
In concrete dams, the control of thermal stress caused by hydration heat of cement is an important issue. For that reason, various studies have been conducted for thermal crack control for a long time. In recent years, with the development of analytical methods, it has become possible to examine the thermal stress in the design and construction stages in detail. On the other hand, it has been made clear that, even with lean mixed dam concrete, autogenous shrinkage should not be ignored depending on the type of cement and mix proportion. In this study, the effect of the autogenous shrinkage strain on thermal stress in construction stage of concrete gravity dams was experimentally and analytically investigated. As a result, it has been made clear that autogenous shrinkage strain can be a cause of thermal cracking in concrete gravity dams during construction stage.
As a fundamental study to establish a method for evaluating the scaling resistance of concrete in a short period of time based on the analysis of drilling powder, the correlation between the scaling resistance of cement paste and mortar and the pore volume evaluated by drilling powder was investigated. The pore volume in the drilling powder was measured by mercury intrusion porosimetry. For cement paste, the scaling resistance sharply decreased when the pore volume evaluated with drilling powder exceeded around 0.20 mL/mL, regardless of the water to cement ratio or the entrained air volume. In addition, for mortar, a method for evaluating the pore volume of the cement paste portion in the hardened matrix by applying heat treatment and acid dissolution treatment to drilling powder was proposed. As a result, it was observed that the scaling resistance of mortar specimen sharply decreased when the pore volume of the cement paste portion which were evaluated by proposed method exceeded around 0.18 mL/mL. These results suggest that the scaling resistance of cementitious materials can be estimated even from fine drilling powder.