In the test method for estimation of compressive strength of structural concretes by Impact elastic wave method, the velocity of elastic wave is measured and the compressive strength of concrete is estimated from the relational expression which is calculated by relation between the velocity and the compressive strength. In this paper, firstly, to discuss method for calculating the relational expression in structural concretes, the relation between the velocity and the compressive strength in 66 kinds concretes with different mix proportions were investigated. Secondly, to discuss the effect of the measured velocity in established concrete structures, a comparison of various test results was carried out. From the results these experiments, the measuring method for velocity of elastic wave which is applicable to established concrete structures and the correction method for estimated compressive strength of structural concretes were devised. In addition, it was verified that the compressive strengths of structural concretes were estimated within around 15 percent range of error by this devised method.
Crack width is sometimes used for evaluation of deterioration grade of concrete structures. Therefore, for crack opening weight loss of corrosion or the relationship between weight loss and crack width, many studies have been carried out. However, various results were reported, and at this point these results have not been arranged systematically with several parameters such as cover thickness, bar diameter, or concrete strength yet. It would be because influence of corrosion products have not been investigated. About 20 kinds of steel corrosion products have been found, and each products have its own density and volumetric expansion ratio. Therefore, it can be thought that difference of corrosion products will have large influence on crack opening weight loss of corrosion. Then, in this paper, at first influence of environment on corrosion products was investigated, and next influence of difference of corrosion products on crack opening weight loss of corrosion was investigated.
Using the specimen which imitated ASR, experimental tests were performed to investigate the failure mechanism of stirrup, degradation of appearance, and deformation characteristic due to ASR. In this experiment, type of stirrup, ratio of stirrup, amount of expansion, and bend radius were used as parameters with the specimen, imitating the existing structure to one fourth scale. The hollow section, in which expansive concrete was used, was prepared in specimen. As a result, it was verified, concentration of appearance damage did not arise by fracture of one reinforcing bar in current experimental tests, and the progress of degradation of reinforcing bar with large initial damage was larger. It became clear that there was no relationship between fracture of stirrup and its physical-properties.
X-ray CT is a powerful tool to examine the fracture behavior of the construction material, because X-ray CT can measure three dimensional interior of a material without any intrusion into the material. However, it is difficult for the standard industrial X-ray CT system to measure the three dimensional interior of the construction material under a heavy load condition which usually act on the material. We have developed a new industrial X-ray CT system which can measure three dimensional interior of the construction material under 300kN compression load condition. The developed X-ray CT system is the Amsler type testing system in which the X-ray tube and the imaging sensor rotate around the test specimen. The developed X-ray CT system was applied to the compression test of the polymer concrete. And the internal behavior of the polymer concrete under compression conditions is analyzed by the image processing technique and the particle image velocimetry. The results indicate that the cracks of the coarse aggregate are generated by a localized compression of polymer
It is known that rebound of shotcrete varies according to internal pressure of a hose and spray distance. Internal pressure of a hose is determined by air flow that conveys concrete. Thus I evaluated relationship of rebound and air flow of a hose. As for spray distance, forms of rebound vary according to it, so I evaluated rebound classifying them according to its form splashes and drops. These results lead to a fact that shotcrete velocity and diffusion area influence on causes of rebound. Therefore I calculated energy of concrete projected by a nozzle by measuring its velocity. As a result, it shows that rebound can be controlled by setting up air flow and spray distance properly.
Three-dimensional mesoscopic simulations of anchorage performance under multi-directional reinforcement conditions were conducted in this study to evaluate the effect of hook and mechanical anchorage, transverse bars and the clearance of reinforcements in congested reinforcement area on the anchorage capacity and crack propagation. Discrete analysis method, Rigid Body Spring Model (RBSM), was adopted to present the cracking directly. The rib of reinforcement bars were modeled to simulate the crack from rib and splitting cracking. Analysis reasonably reproduced the confinement effect of the transverse bars on the pull out capacity as well as the cracking pattern observed in the experiments. Furthermore, vulnerability was introduced to the area where the reinforcements were closely arranged to consider the heterogeneity and worse compaction of concrete. This assumption successfully evaluated the anchorage performance in the congested rebar arrangement area. Three-dimensional internal crack propagation was simulated reasonably according to the reinforcement arrangement and the anchorage type.
Shear strength of reinforced concrete beams with shear reinforcement is evaluated by two-dimensional nonlinear finite element analysis. The shear span to effective depth ratio of beams is varied between 1.5 and 3.0 and the amount of shear reinforcement is increased to 2.0% in order to investigate the effect of the high shear reinforcement ratio on the shear strength. It is confirmed that the beams with a large amount of shear reinforcement have lower shear strength than the predicted strength by the design equations. The beams with a large amount of reinforcement fail by localized compression fracture of concrete, while the strength calculated by the design equations is determined by the yield strength of shear reinforcement. The upper limit for the amount of shear reinforcement in the design equation is proposed in this report.
Recently, it was reported that deflection continued to extend far beyond the predicted value at the time of the design in PC bridge. In this study, in order to develop an analytical method to estimate the long-term deflection of PC bridge, an frame model considering time dependent behavior on each part of the section was proposed. In addition, long-term concrete shrinkage model was formulated based on FE analysis for various types of size and shapes. By using this frame model, long-term deflection of existing two PC bridges was calculated. As a result, it was verified that long-term deflection could be approximately evaluated.