Influence of aluminum impurity for recycled concrete and inspection method

Abstract

Recycling of construction and demolition waste, especially concrete recycling has become more important for the establishment of sustainable society due to the depletion of natural resources and the lack of final disposal area. However, recycled aggregate made from demolished concrete could bring about several problems, one of which is the various impurities contained in the recycled aggregate, i.e. plastic, wood, wastepaper, tile, ceramics, brick, etc. that may cause the performance degradation of concrete. Therefore, it is significantly important to determine the influences of some impurities on concrete performance because perfect removal of all impurities is impossible. Though the upper limits of impurities contents in the recycled aggregate was enacted as JIS A 5021 and 5022 (Recycled aggregate for concrete-class H and M), those for metal impurities have not been specified yet. This paper evaluated the properties of concrete containing two types of metal impurities, i.e. aluminum and iron. The effects of those on concrete performance were tested through various experiments. As the result, it was found that aluminum contained in recycled aggregate adversely affects both mechanical properties and durability even with very low content. This paper also suggests a simple inspection method to reduce the risk of the aluminum impurity in recycled aggregate.