Environmental challenges for construction materials: potential use of calcined clay in cement

Concrete is the most widely used construction material for infrastructures and buildings. Cement, concrete’s key ingredient, has a dramatic carbon footprint as clinker production is responsible for about 7% of the world’s CO2 emissions. For this reason, European Standard EN 197-5 was updated in 2021 to allow formulation of new cement type containing from 50% to 64% of clinker, while previous versions allowed at minimum 65% of clinker, the main responsible for CO2 emission. This is made possible by a combination of limestone and calcined clay to replace partial clinker content. The properties of the new Limestone Calcined Clay Cement (LC3) have been studied over the last few years in terms of chemistry and hydration, showing that this material exhibits promising properties concerning cement reactivity and sustainability. However, workability studies on calcined clay cements showed that higher amount of admixture is required to provide rheological properties comparable to Ordinary Portland Cement (OPC), with drastic influence on mechanical properties. Analysis of literature studies and technical gaps that need to be further investigated will be presented to the scientific community to give an overview of the advances in construction materials, also providing some results from ongoing experimental research.