The costs and benefits of combining recycled aggregate with steel fibres as a sustainable, structural material

More than 26.8 billion tonnes of normal concrete is used globally every year, which in turn creates an overwhelming amount of construction and demolition waste. Although recycled aggregate is well recognised as a sustainable material that offers solutions to this problem, it is regarded as inferior to natural aggregate in terms of its structural properties. By adding steel fibre to recycled aggregate, a structurally sound material can be obtained. But the cost effectiveness of the optimum combination, when compared to natural aggregate, is unknown. This research aims to analyse the cost effectiveness of recycled aggregate and steel fibre in its optimum combination for a secondary beam. Firstly, an experimental study was conducted to determine the optimum combination, which was followed by a cost benefit analysis to discover the direct/indirect costs and benefits of recycled aggregate. Interviews were undertaken with practitioners of six recycling plants in Sydney. The optimum combination found through the experiment was 30% recycled aggregate replacement with the addition of 0.6% steel fibre. The cost benefit analysis showed that the savings per beam due to recycled aggregate replacement was nearly 2.5 times high when compared to the cost increase due to steel fibre addition in the considered typical beam design. These results confirmed that the additional cost increase of utilising steel fibre could be offset considerably by the quantified sustainable benefits of recycled aggregate in the optimum mixture. The research reported in the paper is scientifically significant due to the introduction of a new structural material, which has considerable sustainable and cost benefits. This study offers recommendations for all parties concerned in recycled aggregate processes such as policy makers, recycling facilities, builders, clients and designers to promote this new material.