Recycling of waste concrete as aggregate

Abstract

The construction industry persists in a massive over production of primary aggregates. This has caused the depression of primary aggregate prices which in turn leads to the serious under-utilization of secondary and recycled aggregates - valuable resources which are simply being wasted. Currently, C & D waste generated on our islands is managed through its landfilling. With the large amount of other wastes, and an assured increase of waste in the future, landfilling has become a major problem, particularly considering the scarcity of land. With an increase in our environmental consciousness, together with economic considerations, the construction industry is coming under intense scrutiny and pressures. We will soon be dealing with the problem of the depletion of the supply of natural aggregates. This has compelled the author to investigate the possibilities of recycling demolished concrete structures as aggregate in the production of new concrete. Following an extensive literature review, the limitations of producing this recycled aggregate, as well as the resulting environmental and economic benefits are discussed. The demolition process is described and various recommendations made for the local scenario. The first obstacle which is inevitably encountered is that of removal of reinforcement, but one must bear in mind that the added cost which this process involves is immediately counteracted by the reduction in landfilling costs and the conservation of natural resources. Waste concrete was acquired and crushed to the desired particle size in the laboratory. After the basic properties of both natural and recycled aggregates were established, a number of laboratory investigations were carried out. These concluded that the compressive strength of recycled aggregate concrete could be higher than that of conventional concrete produced locally. Flexural strength was found to be equal to that achieved by conventional concrete, and may be increased if the strength of the original concrete is also increased. In fact, mechanical strength is influenced by the grade of the original concrete. Workability is reduced with the use of recycled concrete fines, but this may be solved with the introduction of an admixture. This study serves as useful background to further research on the possibilities of recycled concrete aggregate produced locally.