This study investigated the effects of calcium propionate on alkali silicate reaction behaviors of water glass cullet used as model aggregate and natural aggregate under alkaline environment. Further, to clarify the effects of calcium salts on reaction products, calcium chloride and calcium hydroxide were also used. Calcium propionate was found to reduce expansion due to the alkali silicate reaction not only for water glass cullet but also for natural aggregate. Expansion was also reduced in the case of calcium chloride. Calcium ion may have reduced water absorption expansion in the reaction products.

In order to clarify the effect of the reinforcing material on the punching shear strength of PC slabs, including the fracture process, various studies were conducted using existing experimental data and FEM analysis. As a result, it was confirmed that the effect of the reinforcing bar ratio on the punching shear strength of PC slabs is smaller than that for RC slabs, whereas the effect of short fibers is equal to or greater than that for RC slabs. In addition, it was shown that the punching shear strength of PC slabs using fiber reinforced concrete can be evaluated well by adding to the load on the concrete content the load on the short fiber content, taking into consideration the effects of the residual tensile strength and the effective height.

Drying shrinkage of concrete is affected by mix proportions such as unit water content and water-cement ratio. In addition to these, many publications have reported in recent years that aggregate itself also shrinks and that this affects the shrinkage of concrete. The effect of aggregate is qualitatively included in formulas proposed by academic societies such as the Japan Society of Civil Engineers and the Architectural Institute of Japan, however it is still not sufficiently clarified due to its complexity. This study aims to analyze and clarify the effect of aggregate properties on drying shrinkage in concrete by machine learning, which can identify dominant regimes directly from data without explicit programming, and clarify the effects of aggregate properties on concrete shrinkage. The results of the analysis show that the average specific surface area of aggregate has a significant effect and affects shrinkage of concrete in relation to mix proportions.

This study proposes a new approach to interpret and extract dominant regimes from a machine learning model for constructing formulas, and provides a case study of the regression task for drying shrinkage in concrete. The effects of the concrete mix and aggregate properties on drying shrinkage were extracted based on the proposed approach. The results showed complex regimes, such as the non-linear effect of the mixing ratio based on the unit water content and aggregate volume, and the effect of the water absorption of aggregate, which varies with the mixing ratio. These findings were compiled into a formula and it was confirmed that the predicted value calculated by the formula tracks actual shrinkage well and the regression performance is improved especially in regions where data density is low.

The purpose of this study is to develop a reinforcement method for improving shear strength, targeting existing reinforced concrete piers in locations where the application of conventional seismic reinforcement methods is difficult.

Although a post-installed shear reinforcement method has been developed for underground structures whose backs are in contact with the ground, which allows reinforcement from only one side of the member owing to structural constraints, there have been few cases of verification of this method for reinforced concrete supporting beam of highway bridges until now.

A horizontal positive and negative alternating box loading test was conducted on an RC column specimen that simulated a reinforced concrete pier. The reinforcement effect of post-installed shear reinforcement rebar was investigated based on the deformation characteristics and damage status. While the post-installed shear reinforcement rebar was observed to have a shear reinforcement effect in the RC column specimen, no reinforcement effect could be confirmed in terms of deformation performance.

This study was carried out on UHPFRC for repairing concrete slabs that have suffered deterioration. Waterproof properties are required for decreasing LCC. Bending tests, bending fatigue tests and water penetration tests were carried out focusing on crack behavior, especially the microcrack restraint ability in the strain hardening zone of UHPFRC. Significant strain hardening was observed in UHPFRC with 3vol% steel fiber content, with effective crack dispersal and no visually detectable cracks until 1000 μ in bottom strain. Crack width was constrained to less than 0.07 mm in a 4,800,000 cycle bending fatigue test applying 15 N/mm² to 20 N/mm² in bending stress. Most cracks could be healed by the self-healing agent, indicating the possibility of achieving higher waterproof performance. In light of the above, the newly developed UHPFRC can be expected to be of use as a waterproof top layer for RC slabs in future.

Using photographs of earthquake damage that contain many characteristics of shear failure of RC partial walls, fine tuning of a pre-trained CNN model was performed to generate classifiers that classify the damage index into four levels (II and below, III, IV, and V) based on photographs of earthquake damage to shear-failing RC columns. We checked the learning conditions that affect the estimation accuracy in generating the classifiers. One of the generated classifiers was able to estimate the damage index to shear columns with an 85.3% accuracy rate. By using the damage index estimated by the classifier, the remaining seismic capacity of two damaged buildings was generally evaluated appropriately.

In this study, a method for estimating the compaction completion range of low-slump dam concrete mixtures compacted by large-diameter hydraulic internal vibrators is proposed, and this estimation method is put into practical application for compaction quality control through visualization. The compaction completion range was estimated from the relationship between the vibration energy propagation in concrete and the compaction completion energy measured with a prototype device considering the maximum size of coarse aggregate. Then the estimated range values were verified by the quality of the hardened concrete. The results show that the compaction completion range of low-slump dam concrete can be estimated accurately using the compaction completion energy. Furthermore, by using this compaction estimation method, a system that enables quantitative evaluation by visualizing the compaction state inside the dam concrete was constructed and applied it to the construction work. As a result, it was found that measuring the compaction degree can contribute to the enhancement of quality control and the improvement of productivity.

The objective of this study was to clarify the spall-suppressing performance of slurry infiltrated fiber concrete (SIFCON) with fine straight steel fibers and to develop an efficient blast-resistant member using SIFCON. In the first part of this work, contact detonation tests were performed on 80 mm thick SIFCON slabs under the explosive charges of 130 g to 170 g. As a result, it was shown that the scaled concrete thickness of the spall limit can be reduced by almost 55% by using SIFCON as a replacement for normal concrete. In the second part of this work, experimental investigations were conducted regarding blast resistance of double-layered slabs composed of SIFCON on the back side and pre-packed concrete (PPC) on the detonation side. The results showed that an effective blast-resistant design can be achieved by counting on the effect of the SIFCON layer to capture the spall fragments generated in the PPC layer, rather than the effect of SIFCON to resist spall failure.

The purpose of this study is the development of an RC joint structure for connecting precast PC slabs used for replacement of the deteriorated RC slabs of a steel girder bridge, wherein the anchor length of the reinforcing bar in the bridge span direction is shortened by using mechanical anchorage with a nut at an end of the bar. The applicability of that joint to actual bridge structures has already been confirmed by the moving wheel loading test. In this paper, the pull-out test is conducted on reinforcing bars with nuts at their ends to clarify the anchor properties, and the applicability of the existing bond-slip-strain relationship considering the behavior of the nut and the reduction of the effect of strain of reinforcing bar is confirmed.

The Nam Ngiep 1 (NNP1) Hydropower Project in Lao PDR has constructed a 167 m-high roller compacted concrete (RCC) dam. Class C fly ash (FA) procured from the Mae Moh coal-fired power plant in Thailand has been selected as a supplemental cementitious material for the NNP1 RCC dam, to control hydration heat generation and improve workability. Though rarely used globally for RCC, it was found that the Class C FA was acceptable for the NNP1 RCC because it did not undergo a large temperature rise in its early age and because of the relatively high compressive strength of the concrete as the age in the medium-term and long-term as compared with general features of the concrete with Class C FA. To clarify the reaction mechanism for Class C FA, factors affecting the above features of Class C FA are analyzed and evaluated by observing FA particles and concrete core specimens of NNP1 RCC through a variety of devices, including Field Emission-Electron Probe Micro Analysis (FE-EPMA). This paper clarifies the reaction mechanism of the concrete with Class C FA and demonstrates its applicability for RCC dam and other structures. Herein, this article is a Japanese translation from the scientific paper on “Study on Application of Class C Fly Ash for RCC dam in Nam Ngiep 1 Hydropower Project in Lao PDR,” Volume 20, 30-42, January 2022.