Excavation Waste London Clay Utilisation in Concrete Applications ("Ex-Clay")

As part of the biggest infrastructure project in the UK (High Speed 2), enormous quantities of material are being excavated due to tunnelling and other operations, approximately 5,000,000 m3, its majority London Clay. Transportation of the excavated clay for off-site disposal leads to significant carbon dioxide emissions and costs. Current practice for repurposing of the excavated material is regarded as "low value" since it is normally sent to landfill.

An innovative approach for high value repurposing of the excavated clay has been developed, where the excavated London Clay is treated and repurposed in concrete. A method has been established to process and calcine the spoil to use them in specific concrete mixes as a Portland cement replacement. Since Portland cement is the primary contributor of CO2 emissions in concrete, the proposed method offers major improvements in terms of reducing the carbon footprint of the significant concrete volumes that are going to be cast as part of High Speed 2 works and beyond.

For context, Portland cement in project specific concretes can be replaced with up to 70% calcined London Clay while maintaining the onerous requirements for 120-years service life which results in major savings in concrete embodied carbon and promotes high value waste utilisation.

Construction logistics, particularly for projects in dense, urban environments such as London, are complex to execute, challenging to budget and programme, and impact the environment and local surroundings. It is estimated that this pioneering approach reduces the carbon footprint for the concrete and associated disposal operations by up to 70%, revolutionizing the way excavated clay materials can be repurposed towards sustainable infrastructure development with maximised circularity.

Additionally, this technology can be transferred to other major infrastructure projects or mining operations across the UK and beyond where clayed spoils are generated, with immense potential to reduce waste generation while promoting sustainable construction materials development and use, as well as self-sufficiency of the construction sector.

The innovative "Ex-Clay" project presents a pioneering approach towards utilisation of waste clays generated from excavation operations to usable low carbon supplementary cementitious materials for concrete. This is a bold step towards concrete decarbonisation through decreasing the industry's reliance on Portland cement and traditional supplementary cementitious materials, such as fly ash and slag for the production of structural concrete with decreased embodied carbon.

As part of the "Ex-Clay" project, a structural element, e.g., a retaining wall, with 120 service life will be constructed.