International Concrete Abstracts Portal

This paper addresses first the generation of construction waste in Japan, the extent of recycling, and the shortage of landfill capacity. Second, it chronicles the trend of recycling concrete rubble from 1970 until today. Third, it discusses methods of manufacturing recycled concrete aggregate and introduces the recently developed equipment and methods to produce good aggregate for concrete. Fourth, the problems associated with the use of recycled concrete aggregate are mentioned. Also, the utilization of concrete fines, eco-concrete, and slurries from ready-mix concrete plants are addressed. Land in Japan is very scarce and resources limited. These conditions are similar to those faced by Europeans and Scandinavians. Therefore, this paper should be of interest to those countries and their efforts to build closed-loop material cycles.

The paper consists of an overview of the development of techniques for recycling concrete. Demolition, processing and the recycling of the resulting materials are often analyzed separately. "High quality" recycling of concrete waste does not always correspond to production/use of the product with the highest value, but rather the most feasible product in a specific project or region. It is by analyzing the whole disposal/supply-chain, including the substituted material, that the best effects of recycling can be achieved. Overviews of methods for environmental evaluations as well as economic considerations are presented. Integrated demolition waste management in Kosovo and an analysis of the potential market in Hong Kong are presented as examples of the worldwide market for recycled materials. Issues regarding the handling of polluted materials will be discussed from a practical point of view. Moreover, some aspects to soncsider regarding future demolition when producing new concrete products are presented.0

This study investigated the reactivity of concrete containing recycled concrete aggregates (RCA) that had shown distress due to alkali silica reaction (ASR). The investigation evaluated several mitigation techniques to control ASR in concrete containing potentially reactive RCA. Mitigation work was done with three different aggregate types; an igneous fine-grained quartzite aggregate locally called blue rock, a non-reactive limestone, and RCA containing blue rock aggregate. These aggregates were used to investigate various mitigation techniques to prevent ASR from occurring in concrete containing RCA. The mitigation strategies include the use of class F fly ash, ground granulated blast furnace slag (GGBFS), lithium nitrate, silica fume blended cement and low alkali cement. These materials were incorporated into concrete mixes by cement substitution and direct application. These mitigation strategies showed potential in controlling ASR distress in RCA concrete. Mortar bars and concrete prisms were used to investigate the mitigation strategies by following standard and modified versions of ASTM C 1260 and ASTM C 1293 specifications to evaluate expansion caused by ASR. The modified versions of ASTM C 1260 were found effective in evaluating potential ASR expansion using conventional aggregates.

Recycled concrete aggregate (RCA), when used appropriately, is an excellent substitute for natural aggregates in highway construction. RCA has been used successfully in unbound applications such as base course and fill, and in bound applications as aggregate in new concrete. However, a significant amount of concrete debris is still disposed of in landfills. Barriers to concrete recycling include regulatory and policy issues, economic disincentives, environmental concerns and technical questions. This paper reviews current obstacles to concrete recycling and discusses recent developments and research that will help overcome these barriers.

The reduction and utilization of waste and by-products is one of many challenges facing mankind in the modern world. This paper consists of an overview of the handling of the world's concrete waste and is concerned with unbound applications of blended construction and demolition (C&D) rubble for pavement bases and sub-bases in road construction. The problems of recycling mixed wastes are considered and global perspectives are presented on the use of C&D rubble. The paper proposes that studies should be carried out in order to research the technical properties of blended C&D rubble, which the authors believe would be economically and environmentally justifiable in promoting the widest possible range of recycled products for road construction.