Dissemination of technic for concrete using low-quality recycled aggregate to achieve a sustainable environment: examination on design method and validity of recycled aggregate concrete

Many resources are used in the concrete-related sector to construct civil engineering buildings. Therefore, using the various by-products for resource circulation throughout the lifecycle of the concrete-related sector is critical to building a sustainable society. This study focuses on resource recycling, low carbon emissions, and environmental safety as means to building a sustainable environment in order to reinforce concrete works, particularly in civil engineering buildings. It also presents the examination results of the design method and validity for the active use of low-quality recycled aggregate concrete to decrease waste generation, reduce CO2 emissions, and ensure environmental safety. Consequently, it was confirmed that the water–cement ratio could be set on the basis of safety reasons for the production of recycled aggregate concrete-Class M using the aggregate replacement method at all ready-mixed concrete factories. This was achieved by employing the strength reduction ratio obtained from the difference between the relative water absorption of normal-weight concrete and that of recycled aggregate concrete

Contributions of Concrete Recycling Technology toward Sustainable Development: Standards and Technologies Related to Recycled Aggregate Concrete in Japan

Concrete is durable and can last for centuries. The waste from demolished concrete structures can be reused to reduce the environmental burden during their life cycle and ensure economic use of the construction resources. This study aims to improve the use of recycled aggregates prepared using the aggregate replacement method, effectively reducing both the environmental burden and costs associated with concrete waste. A high-value recycling method should be developed for concrete waste that offers improvements in terms of resource diversion and environmental preservation. New uses of concrete waste should be sought to counter the expected increase in the production of concrete waste with newer construction projects. Concrete waste contains harmful trace elements due to the use of cement, such as hexavalent chromium and lead. The most promising alternative materials are recycled aggregate concrete prepared using the aggregate replacement method, the uses of which are confined to concrete prepared from original mortar and/or original cement paste that contain toxic substances such as hexavalent chromium. The results of this study provide evidence for the effectiveness of using low-quality recycled aggregate concrete, such as of Class L, specified in the Japanese industrial standard (JIS) directive (JIS A 5023)

Expanding the Use of Fly Ash as an Admixture in Concrete in Vietnam

To bolster the drive for economic and social development in Vietnam, 31 coal-fired power plants were constructed to meet the demand for electricity. According to a survey by the Ministry of Natural Resources and Environment, approximately 20.5 million tons of coal ash will be generated in 2020. A part of the generated coal ash was recycled as landfill; however, the rest lies unused or discarded, causing serious environmental pollution. Since fly ash (FA) forms a major component of coal ash, it is necessary to establish methods for the safe, continuous, and effective use of FA. This study compared the Vietnamese National Standards with the Japanese Industrial Standards from the perspective of using FA as an admixture in concrete. Japanese FA was used in the experiments. Consequently, by using suitable amounts of chemical admixtures and adjusting the ratio of FA as a cement replacement and as a fine aggregate replacement, structural concrete can be manufactured, and the required quality can be assured

Performance improvement of recycled aggregate concrete using fly ash and Portland blast-furnace slag cement

Several countermeasures are implemented in the manufacture of construction materials to avoid negative impacts on the environment. Using concrete debris in construction demolition waste as a recycled aggregate to make recycled aggregate concrete (RAC) is one of the countermeasures. Further, the use of recycled construction waste and industrial by-products, such as fly ash and ground granulated blast-furnace slag, in concrete not only promotes resource circulation and reduces CO2 emissions in the cement manufacturing process but also improves concrete performance. In this study, low-quality recycled aggregate was mixed with normal aggregate at various replacement ratios to produce RAC. Additionally, ground granulated blast-furnace slag in Portland blast-furnace slag cement and fly ash were introduced in concrete to improve concrete performance. Applying the relative quality index method for performance evaluation, it was possible to design a mix proportion of RAC that achieved the requisite performance through the application of Portland blast-furnace slagcement and fly ashas a cement substitute or as a fine aggregate substitute

Expanding the Use of Fly Ash as an Admixture in Concrete in Vietnam

To bolster the drive for economic and social development in Vietnam, 31 coal-fired power plants were constructed to meet the demand for electricity. According to a survey by the Ministry of Natural Resources and Environment, approximately 20.5 million tons of coal ash will be generated in 2020. A part of the generated coal ash was recycled as landfill; however, the rest lies unused or discarded, causing serious environmental pollution. Since fly ash (FA) forms a major component of coal ash, it is necessary to establish methods for the safe, continuous, and effective use of FA. This study compared the Vietnamese National Standards with the Japanese Industrial Standards from the perspective of using FA as an admixture in concrete. Japanese FA was used in the experiments. Consequently, by using suitable amounts of chemical admixtures and adjusting the ratio of FA as a cement replacement and as a fine aggregate replacement, structural concrete can be manufactured, and the required quality can be assured

Material Design for Concrete Using Low-Quality Recycled Aggregate

Since the 19th century, concrete has been a fundamental construction material. It is the most popular manmade material in the world because of its more reliable workability, greater durability, and lower cost compared with other construction materials. However, because of its durability, demolishing or renovating old structures generates a huge amount of concrete waste, which, if not properly treated or reused, can adversely affect the environment. Therefore, the development of concrete-recycling technology is a necessary and pressing requirement for all the countries. This study concerns material design with concrete using low-quality recycled aggregates prepared via an aggregate replacement method. To evaluate the quality of the aggregates in recycled aggregate concrete, experiments were conducted using specimen groups characterized by various mix proportions. Accordingly, when low-quality recycled aggregate is used, by employing the relative quality index method for material design, the manufacturing of recycled aggregate concrete with required performance could be achieved