Recycled aggregates

Recycled aggregates are materials recovered from construction and demolition (C&D) waste, industrial by-products, or other discarded resources, and repurposed for infrastructure applications, such as road base, concrete, and asphalt. Their use reduces the demand for virgin materials, minimises environmental impacts, and diverts waste from landfills, contributing to resource efficiency and sustainability. However, challenges remain, including variability in material quality, lack of standardised specifications, and limited market acceptance, which can hinder large-scale adoption.

A number of recycled aggregates are described below.

Recycled crushed concrete & Recycled brick

Derived from crushed C&D waste, these aggregates are commonly used in road construction, earthworks and non-structural concrete, offering an alternative to virgin materials. Their market maturity is high, with established processing technologies and specifications.

Reclaimed asphalt pavement

Derived from milled end-of-life asphalt or plant returns, reclaimed asphalt pavement is widely reused in new asphalt mixes and road construction. Its market maturity is high, driven by its cost-effectiveness and environmental benefits.

Recycled crumb rubber

Crumb rubber is derived from shredded and crumbed end-of-life tires and is used in asphalt and sprayed seals. It can be added via dry mix processes, as an aggregate replacement, though is also used as a binder modifier. Market maturity is high, though can be hindered in some environments by processing and adoption challenges.

Recycled glass

Produced by crushing post-consumer and industrial glass waste, recycled glass is used in road bases, asphalt, bedding, and concrete applications. Its market maturity is moderate, with applications that are growing but remain niche.

Recycled/reused ballast

Recovered from old railway tracks, this cleaned and graded aggregate is primarily reused in rail projects. Recycled ballast can also be further processed to produce aggregates of various sizes for use in earthworks, pavement, and concrete applications. Its market maturity is moderate, with applications in other infrastructure sectors still emerging.

Bottom ash

A granular by-product of coal combustion in power plants, bottom ash is used in road construction and concrete. Market maturity is moderate but constrained by quality variability and environmental regulations.

Recycled plastic

Aggregates made from shredded or melted plastic waste are used in asphalt, lightweight concrete, and geotechnical applications (e.g. incorporate into geosynthetics). Market maturity is emerging, with potential limited by processing costs and performance awareness.

Slag aggregate

A by-product of steel and iron production, crushed slag is used in road construction, concrete, and cement. Market maturity is high, with well-established applications and markets.

Biochar

Biochar aggregates are lightweight materials derived from the pyrolysis of biomass waste, used in concrete and soil stabilisation. Market maturity is emerging, with applications mainly in research and pilot stages.

Piles of recycled aggregates
References
  1. Hall, B, Grenfell, J, Pandelidi, C, Yaghoubi, J, Chaudry, U, Lyons, M, O'Connor, G, Harrison, J & Feigen, D 2022, Best practice expert advice on the use of recycled materials in road and rail infrastructure: part A technical review and assessment.
  2. Hall, B, Grenfell, J, Pandelidi, C, Yaghoubi, J, Lyons, M, O'Connor, G, Harrison, J, Feigen, D & Xue, S 2022, Best practice expert advice on the use of recycled materials in road and rail infrastructure: part B sustainability impacts report.
  3. Main Roads Western Australia 2022, Recycled and Sustainable Materials at Main Roads, Reference Guide, Document No: D21#13639.