The shear characteristics of RC beam specimens strengthened with carbon fiber grid plates fixed at their edges by carbon fiber bundles were investigated in terms of the tensile strength of the carbon fiber bundles and the compressive strength of PCM. As a result, strengthening with the proposed method was found to be very effective for shear strengthening of existing RC members. Further, it was established that the carbon fiber bundles used for edge anchoring should have tensile strength at least 1.0 times the tensile strength of the tendons of the carbon fiber grid plate used for shear reinforcement. It was also established that PCM with compressive strength of 50 N/mm2 or more should be used. Finally, the formula proposed for the estimation of shear capacity of the strengthened beams was verified to be valid.
The out-of-plane bending performance of composite slabs consisting of RC and CLT joined with shear connectors (lag screws) was examined. Firstly, single shear testing was performed. The lag screws showed good slip performance. Secondly, bending testing was performed. The test revealed that the bending performance was higher with a narrower interval of shear connectors. A way of applying the conventional γ-method to determine the initial stiffness and yield load of composite slabs was then proposed. As a result, a good correlation was found between the calculation results and the experimental data.
The concrete waste generated when dismantling concrete structures is used as a roadbed material. However, the elution amount of hexavalent chromium derived from cement clinker may increase due to the progress of carbonation during storage. Therefore, in this study, we evaluated the effectiveness of the use of ground granulated blast furnace slag as one of the measures to suppress the elution of hexavalent chromium by elution tests and X-ray absorption fine structure measurements. As a result, we confirmed the reduction of hexavalent chromium eluted from the hardened cement by the reducing substance contained in the ground granulated blast furnace slag as the hydration reaction proceeded. Furthermore, the reducing effect of ground granulated blast furnace slag was maintained for a long period of time compared with other reducing substances. From the above results, we confirmed that ground granulated blast furnace slag is effective as a measure against the elution of hexavalent chromium.
We proposed a "curing plan planning method based on hydration analysis of cement" based on the positioning of curing in the current standard specifications for concrete. In the proposed method, first, the target hydration rate to satisfy the characteristic values of concrete is set. Then, a curing plan is designed so that the hydration rate of the cement obtained by the hydration analysis reaches the target hydration rate. This paper introduces the basic concept of the proposed method and the method of planning a curing plan. Furthermore, it shows examples of curing plans for various portland cements. The feasibility of rationally formulating a curing plan according to the structural conditions, concrete conditions, and construction environment conditions was confirmed.
This study aims to develop a non-destructive test for the detection of invisible cracks in concrete covered with fiber reinforcement polymer (FRP) sheets using electrical impedance variation and phase transition. The fundamental test was performed considering the hypothesis that the concrete exhibits inductive and resistive properties. Some FRP-covered concrete specimens with an artificial crack were prepared. The study examined the frequency characteristics of impedance and phase under AC voltage with frequencies ranging from 1 kHz to 8 MHz. These frequency characteristics were examined using an impedance analyzer controlled by a computer. The impedance and phase were measured using a probe with two electrode terminals. The test results confirmed that in the range of approximately 3 MHz to 4 MHz, the capacitive phase property of cracked concrete changes to exhibit inductive characteristics. It was revealed that invisible cracks in FRP-covered concrete can be detected by measuring the frequency at the impedance local maximum value and the phase transition property.