Concrete is regarded as a material that places a burden on the global environment owing to the large amount of CO₂ that is emitted during the manufacturing process of cement, one of its constituent materials. Recently, however, various types of less environmentally burdensome concrete have been developed and put into practical use, ranging from concrete that reduces CO₂ emissions to concrete that offsets CO₂ emissions through absorption to such an extent that it becomes carbon negative. Such types of concrete are called environmentally considerate concrete. This paper outlines the mechanism by which concrete emits CO₂, classifies environmentally considerate concrete according to differences in characteristics, and explains each technology. Further, it discusses future prospects based on the evaluation of initiatives related to CO₂ reduction.

In March 2022, the Architectural Institute of Japan published the “Guidelines for Design and Construction of Reinforced Concrete Buildings Using Hot-dipped Galvanized Rebars”. This paper presents the background and history of the establishment of these Guidelines, as well as an overview. Besides touching upon planning matters and design methods based on structural design and durability design, these Guidelines cover construction practices including construction work, quality control, and inspection, and constitute a compendium of practical content in line with the latest JIS standards and the current JASS 5 specifications and durability design framework.

The technology of colored concrete having been applied mainly to concrete of general strength thus far, studies on the application of this technology to high-strength concrete with low water-binder ratio are scant. Therefore, focusing on the mortar portion, which determines the surface color of colored concrete, we decided to study the effects of changes in the water-binder ratio of mortar on the compressive strength and color changes of mortar mixed with pigment for coloring. We found that it is possible to produce beautifully colored high-strength mortar with compressive strength of about 140/mm², and that color fading over time can be suppressed by lowering the water-binder ratio.

This paper reports on the characteristics of concrete using a special paraffin emulsion, which was developed as a new technology for the restraint of frost damage, and describes an example of concrete construction using this new technology. The freeze-thaw resistance of concrete was significantly improved by the use of the special paraffin emulsion. This is attributed to the aggregation in concrete of paraffin particles forming aggregate bodies ranging in size from 20 μm to 200 μm, which reduce expansion pressure during freezing, an effect similar to that obtained from the entrainment of fine air bubbles. Concrete mixed with the special paraffin emulsion was applied to an actual structure. It was confirmed that such concrete can be manufactured in an actual plant like ordinary concrete, and that it remains sound even two years and five months after construction.

The cement industry utilizes large amounts of waste material during clinker firing, contributing significantly to extension of the life of final disposal sites. On the other hand, in recent years, the use of blending components in cement has been increasing as part of efforts to achieve a carbon-free society, and there is concern that the resulting decrease in the amount of waste material received by the cement industry will negatively affect the remaining life of final disposal sites. Therefore, a study was conducted to better understand the effect of the cement industry on extending the remaining life of final disposal sites. As a result, it was found that the remaining life of final disposal sites is shortened by one to three years for every 10％ increase in the production ratio of blended cement. It was also shown that even when the clinker composition is not changed, the impact of a 5％ increase in the amount of trace additives is equivalent to a 10％ increase in the production ratio of blended cement.

For the purpose of quantifying the chemical prestress introduced by expansive concrete and demonstrating its estimation method, we verified the consistency between estimated expansive strain calculated under the assumption of constant workload and measured expansive strain using a full-scale specimen of a road bridge with full-scale slabs and wall rails on steel girders. The results confirmed that, by using the assumption of constant workload, the expansive strain and chemical prestress introduced into the structure can be quantitatively evaluated with constant accuracy, regardless of whether or not the structure is axisymmetric. This suggests that the proposed estimation method is effective as a method for grasping in advance the amount of chemical prestress that is effective for suppressing cracks in structures.