The meta-kaolinite content of the calcined clay source impacts the mechanical and durability performance of blended Portland concrete

This study evaluated the mechanical and durability performance of CEM I and CEM I plus limestone blended concrete produced with calcined clays (CC) with a varying meta-kaolinite content (70, 50 or 20 wt%). Results revealed that concrete with >45 MPa can be produced with a CC with only 20 wt% meta-kaolinite. Increased compressive and flexural strengths were obtained using higher meta-kaolinite content CC. Limestone addition did not significantly change the concretes' transport or durability properties when compared to binary mixes, despite the reduced clinker factor. CC-containing concretes exhibited excellent chloride resistance, but reduced carbonation performance compared with CEM I. Using a CC with higher meta-kaolinite content enhanced the concrete's carbonation resistance, when evaluated for 650 days of natural exposure. This suggests that generalising the impact of CC addition on concrete performance can be misleading, as bespoke concrete, compliant with specific exposure class requirements, can be produced by appropriate clay selection.