Alternative concrete aggregates - Review of physical and mechanical properties and successful applications

Concrete is one of the most widely used construction materials, yet its production is associated with significant environmental impacts. One approach to mitigate such impacts is to use alternative aggregates. However, the limited knowledge about the availability and benefits of these unconventional materials, as well as concerns about their quality and performance, have hindered their adoption. This paper aims to analyse the potential benefits and limitations of using alternative aggregates in concrete by reviewing examples from three primary sources: construction and demolition waste (CDW), end-of-life materials (i.e., tyre rubber, glass, and plastic), and forest and agricultural waste (i.e., rice husk, wood, and hemp). First, the main sources and treatment needs are analysed. Then, a comprehensive macro analysis is provided on the physical and mechanical properties of concrete materials, discussing the results in terms of the aggregate nature and substitution ranges. The collected experimental data are also compared with estimations based on different models from two published codes, suggesting that more specific design-oriented models need to be developed to relate concrete's physical and mechanical properties using different waste-type aggregate replacements. Selected data analyses are presented to help the readers obtain the optimum content for specific structural or non-structural applications. Examples of successful application of alternative aggregates in construction projects and products are also provided and discussed.