Taketo Uomoto

Evaluation of fatigue damage in reinforced concrete slab by acoustic emission

The applicability of acoustic emission (AE) technique for evaluation of fatigue damage in reinforced concrete (RC) slabs under cyclic loadings in both laboratory and as a structure in service is studied. The fundamental test performed in laboratory shows that the cracking process can be practically monitored by the measurement of AE signals. Analysis of the relationship between loading phase and AE activity indicates that the final stages of the fracture process can be evaluated by detecting AE signals generated near the minimum loading phase. Comparison of the results from the structure and that from the laboratory specimen demonstrates that AE energy can be an effective parameter for the evaluation of fatigue damage in RC slabs in service.

Concrete composites in the construction field

Many new concrete composites are now being used in the construction field. In this report, the lessons learned from the development of cement and concrete composites reinforced with short fibers and continuous fibers, fiber reinforced plastic reinforcements, and concrete polymer complexes used as construction materials, are discussed along with future perspectives of concrete composites.

Effect of Curing Temperature and Humidity on Strength of Concrete Containing Blast-Furnace Slag Admixture

This paper will discuss the compressive strength of blast furnace slag concrete containing slag/(cement + slag) ratios of 0, 0.3, 0.5, and 0.7 was followed by changing the curing conditions. The specimens were cured in air or water at 10, 20, or 40 C, and the strength development after 1, 4, 8, 13, and 26 weeks was determined. Equations were developed for strength based on maturity, curing, method, age of concrete, and amount of slag.

Radar Image Processing for Detection of Shape of Voids under Concrete Slab

Deterioration of pavements or tunnels results primarily from the existence of voids under the pavements or tunnel linings. To detect these voids effectively by non-destructive tests, a method using radar was proposed. In this research, it is investigated to detect the shape of voids by radar image processing. The experiments were conducted to detect voids under concrete slab. From the results, the fundamental algorithm for tracing the voids, improving the horizontal resolution of the object image and detecting shape of objects, was verified. Introduction The ability to survey a broad area with relatively high speed is one of the main advantages of ground penetrating radar. However, the analysis of radar response image on concrete or civil structures can be still regarded as very difficult. This is probably due to the fact that, compared to the situation in the ground, concrete structures have more complicated boundary conditions and constituents, for example, voids, layer thickness, etc, which affect radar response image simultaneously. Additionally, the attenuation of electromagnetic wave and the non-homogeneity of sub-surface materials give rise to a reduction in quality of the radar image. Therefore, it is very important to detect quantitatively voids in concrete structures. But, in order to meet these requirements, it is necessary to develop image processing or reconstruction techniques for the special purpose of detecting objects in concrete structures. In this study, for the sake of facilitating the process of analysis, the fundamental algorithm for tracing voids, improving the horizontal resolution and detecting the shape of objects were verified by the proposal. The experiments were conducted or simulated to detect voids under concrete slab. Theoretical background Detection of shape of voids. It is known that output signal of radar propagates widely with a certain beam width. So, the radar image reflected from objects spreads broader than the original shape and size of objects. This phenomena can be explained as when the output signal from an oblique or normal direction is reflected from the objects, the direction of the reflected signal is changed in accordance with geometric condition of radar and objects. As shown in Fig. 1, the radar image obtained from void with circular cross-section shows that reflected signal from an oblique direction of thick line is plotted in line direction of vertical dotted line. Accordingly, a reflected radar image of a void with circular cross-section spreads broader, as shown in Fig. 2. At this time, if the direction of maximum change of image shades indicates reflected signal direction from a certain point of void surface, the original shape of void can be traced from the radar image by the relationship between gradient vector of image and circular transform of vertical direction signal. This new proposal algorithm for shape recovery of the voids can be explained as follows[1][2][3]: First, as shown in Fig. 2, a circle is drawn with a radius of depth yn in each of x coordinates which range from n=0 to m, where the centre coordinate is (xn, 0). This can be expressed by Eq.1. Key Engineering Materials Online: 2004-08-15 ISSN: 1662-9795, Vols. 270-273, pp 1556-1561 doi:10.4028/www.scientific.net/KEM.270-273.1556

EVALUATION OF TIME-DEPENDENT PROPERTIES OF FIBER REINFORCED PLASTIC RODS

FRPロッドのプレストレストコンクリート用緊張材としての適用性を検討するための基礎的な研究として, ガラス繊維, アラミド繊維, 炭素繊維を用いたFRPロッドの疲労試験およびクリープ試験を行い, 平均応力, 応力振幅, 持続載荷応力の影響について検討するとともに, これら時間依存性を有する特性の破壊機構について検討を加えた. 疲労破断繰返し回数は平均応力および応力振幅の増大とともに減少し, ガラス繊維を用いたFRPロッドに対しては, 平均応力および応力振幅を用いることにより疲労破断繰返し回数を推定することが可能であることを示した. クリープによる破断時間は, 載荷応力の増大とともに減少するが, 応力比を用いることにより, 破断時間の予測が可能であることを示した.