Sustainable infrastructure development through use of calcined excavated waste clay as a supplementary cementitious material

Major infrastructure development projects in London produce large quantities of London clay and use significant volumes of concrete. Portland cement (CEM I) in concrete is normally partially replaced by supplementary cementitious materials such as ground granulated blastfurnace slag or pulverised fuel ash. The supply of supplementary cementitious materials is critical to the production of sustainable concrete. This study has investigated use of waste London clay as a supplementary cementitious material. The optimum calcined clay was produced at 900°C and concrete made with 30 wt.% of CEM I replaced by calcined clay had 28-day strengths greater than control samples. Compressive strengths of concrete containing calcined London clay were similar to concrete containing ground granulated blastfurnace slag and pulverised fuel ash. The production of calcined London clay emits 70 kg CO2/tonne and this is 91% lower than CEM I. 30 wt.% replacement of CEM I by calcined London clay therefore produces concrete with 27% lower embodied carbon. London clay can be calcined to form a technically viable supplementary cementitious material and use of this in concrete would enable major civil infrastructure projects to contribute to a circular economy.