Maintaining post-tensioned prestressed concrete bridges in sound condition for continued service increasingly requires the implementation of measures such as reinjection of grout for prestressed concrete and strengthening by external cables to ensure the safety of such bridges as they age. A number of methods of reinjection of grout for prestressed concrete have been developed and are being used in practice, but the specific performance requirements and performance verification methods for reinjection remain to be clarified. In addition, specific criteria for the method of strengthening by external cables, which is often used to strengthen post-tensioned prestressed concrete bridges, have not been defined. Based on the above, the Japan Prestressed Concrete Institute published the “Guidelines for Maintenance of Existing Post-tensioned Prestressed Concrete Bridges”. This paper presents the outline of these Guidelines.

This paper presents an overall picture of ecological concrete and discusses technologies that achieve both the i-Construction goal of labor saving at construction sites and the reduction of CO₂ emissions through the use of ecological concrete. By combining the technology of admixing calcium carbonate powder produced with CO₂ as a component of self-compacting concrete, which contributes to labor saving in compaction work, and the technology of applying CO₂-absorbent concrete to stay-in-place formwork, it is possible to simultaneously achieve labor saving and CO₂ reduction. Furthermore, such technology is expected to reduce the cost of stay-in-place formwork, and the possibility that it may yield considerable shortening of the construction period along with the reduction of CO₂ emissions at a cost comparable to current cost is discussed.

Against the background of numerous reports about deterioration of concrete structures notwithstanding the completion of repair work, the purpose of this study was to verify the validity of the proposed method using by Impact Elastic Wave Method to control the quality of repair works. The proposed method was applied on an experimental basis to a bridge where application of the Section Repair Method was completed in 2016. As a result, outlier points in the bridge were revealed by the Impact Elastic Wave Method and construction faults were found at these points by the coring method. These results indicate that the proposed method can be expected to contribute as an effective measure to prevent deterioration of concrete structures after repair work.

To improve the workability and quality of concrete work during hot weather, the authors developed a new type of hot weather concrete using a special admixed agent with ingredients that maintain fluidity and delay setting time, and subjected it to various studies. As a result, we found among other things that (1) it is appropriate to use an admixed agent containing fluidity-retaining and setting-delaying ingredients to both maintain fluidity and secure allowable time between placements of fresh concrete, (2) the use of a special admixed agent can improve workability by ensuring the same level of fluidity retention time and allowable time between placements as concrete made at standard temperatures of about 20℃, even in environments exceeding 35℃, (3） the use of special admixed agent does not affect the quality of hardened concrete.