Mechanical and Durability Performance of Concrete Containing Calcined Excavated London Clay

By replacing a large portion of Portland cement with calcined clay, carbon emissions associated with concrete production can be significantly reduced, facilitatingnet-zero targets in construction projects. Vast amounts of soil waste generated from major infrastructure projects could serve as a valuable resource for producing cement replacements or supplementary cementitious materials (SCMs); however, it is largely unknown whether low-purity, low-kaolinite content clays are suitable for producing resilient concrete. This study investigated the use of low-purity calcined clay, derived from excavation operations in the greater London area, as an SCM in the production of concrete. Specifically, the effects of replacing CEM I with calcined excavated London Clay (30 wt.% replacement) or by replacing CEM I with 30 wt.% calcined London Clay plus 15 wt.% limestone on concrete’s performance were explored. Concrete mixes were prepared with a binder content of 360 kg/m ³ and a water-to-binder ratio of 0.5. Mechanical and transport properties were monitored for a curing period of up to 180 days. Additionally, durability performance, including chloride migration and accelerated carbonation, was evaluated. The results revealed that concrete containing excavated London Clay achieved a compressive strength of about 40 MPa after 28 days of curing, exhibiting an increased chloride resistance compared with CEM I concretes. This outcome demonstrates the high potential of utilizing low-purity calcined clay (about 30% kaolinite content) obtained from excavation activities to produce sustainable and durable concretes.