Concrete containing a large amount of mineral admixture has excellent characteristics in terms of low heat generation and chloride penetration resistance, and it is advantageous for allowing the utilization of industrial by-products and low-quality aggregate. Further, it is expected to reduce the environmental impact of concrete through the use of a large amount of mineral admixture having lower unit emission of CO2 than Portland cement. Despite these promises, widespread use of such concrete remains to be achieved. Having been commissioned to consolidate the known characteristics of such concrete and issue recommendations for its use, the Concrete Committee of the Japan Society of Civil Engineers established a research subcommittee for this purpose, and in September 2018, it published “Recommendations for Design and Construction of Concrete Structures Containing High-volume Mineral Admixtures”. It is hoped that these Recommendations will promote increased use of this type of concrete, and thereby lowered impact on the environment and more effective use of resources, as well as improvement of the durability of concrete structures.
Active use of fly ash as a concrete admixture holds promise for the reduction of CO2 emissions and the eff ective utilization of resources, and the accumulation of technical knowledge regarding the application of fly ash based concrete to building construction works is desirable as instances of such application are still few in number. When concrete using a large amount of fly ash is applied to a building structure, there are issues such as fresh properties, change in air content over time, concrete strength correction value, exothermic characteristics, and carbonation resistance. This paper about a construction project where concrete using a large amount of fly ash was applied describes, among other things, a preliminary test that determined concrete strength correction value 28S91 equivalent to fly ash cement type C to be 0, the results of quality control tests on the fly ash used and the produced concrete, which exceeded 30000m3 in volume, as well as the temperature measurement results for the actual structure.
This paper reports experimental data on concrete temperature and quality at unloading presented in the “2018 Manual for Application in Hot Weather Concreting” revised and published by the Kinki Branch of the Architectural Institute of Japan. In recent years, with the rise of outdoor air temperatures, the temperature of concrete at the time of acceptance tends to be higher, and the possibility of said concrete temperature exceeding 35℃, which is specified in JASS 5 and other standards as the highest allowable temperature, is increasing. Based on experimental data, this paper examines whether the quality of concrete is adversely affected when the temperature of the concrete at acceptance exceeds 35℃, and finds that no major problems arise as long as the temperature of concrete at acceptance does not exceed approximately 38℃.
In response to deterioration and damage in structures using aggregate evaluated to be “harmless” under Japanese Industrial Standards (JIS) as a measure against the alkali-aggregate reaction of concrete, East Japan Railway Company has taken the lead since November 2011 in developing a new approach for the use of aggregate in blended cements and the like based on a finer reactivity classification of aggregates. The introduction of this approach for actual construction faced various challenges related to the supply of materials, the production of ready-mixed concrete, construction, and so on. As a pilot project, a continuous multi-level crossing construction project using concrete mixed with fly ash near Niigata Station was selected for the introduction of this new approach. Various aspects, including the effect of various fly ash mixing ratios in terms of ASR suppression, the construction of a ready-mixed concrete supply system, and measures for quality assurance during construction were investigated, and the applicability of the proposed approach was verified through actual application to said construction project.