The “Design and Construction Guidelines for Repairing Concrete Structures Using Lithium Nitrite” were published by the Japan Concrete Maintenance Association（ JCMA） in April 2020. These Guidelines are basically comprised of two parts: A general section and a construction method-specific manuals section. The general section describes the material properties of lithium nitrite and the concept behind the selection of a repair method using lithium nitrite. The construction method-specific manuals section describes the design, construction, and construction management standard for each of various methods including the surface impregnation method, the cross-section repair method, the crack injection repair method, and the pressurized injection method. This paper gives an overview of the main parts of these latest Guidelines.

Sometimes it is not possible to place concrete continuously due to problems or issues at the construction site. In such a case, the appearance of the concrete is inspected after formwork removal, and while color differences across the interface of layers are judged acceptable, the occurrence of cold joints is judged to be a concrete casting defect that requires repair. However, when it is difficult to objectively make a clear judgment, for example in the absence of a significant color difference, or in the case of an intermediate or mixed state between color difference and cold joint, determination of the necessity of repair tends to be left to the subjective judgment of the supervisor. Therefore, in this study, we conducted tests on specimens and cored specimens of concrete placed with a placement interval up to three hours and examined the relationship between the non-destructive test results and the loading test results.

The prevention of initial defects caused by the time interval between the placement of the various concrete blocks that make up the structure to be built is a fundamental issue in construction management. On the other hand, concrete placement plans are formulated based on the experience of field engineers, and it is considered necessary to automate the formulation of placement plans in order to promote the automation of concrete work. Therefore, in this study, we investigated a method to calculate the order of placement to achieve the shortest or quasi-shortest time limit to completion of placement of each block, and we created a system to assist with the formulation of placement plans. Then, using this system, the order of placement, the placement start position, and the number of placements were examined, and it was confirmed that placement plans that include these items could be evaluated objectively.

Independently of newly constructed concrete structures and elder ones, the geological survey on the aggregates used in concrete may be inevitable to clarify their alkali silica reactivity, however, there has never been carried out such a survey as the daily work in Japan. This technical report represents the relationship between the geological characteristics of reactive aggregates used and their alkali-silica reactivity in the Chubu district, in which there coexist so-called “Early-expansive and Late-expansive Aggregates”. Furthermore, the countermeasure of fly ash concrete in controlling the alkali-silica reaction（ ASR） in the Chubu district is also discussed.