Challenges in the study of fresh sustainable construction materials

Abstract

Concrete construction is responsible for substantial CO2 emissions due to the vast consumption of cement, the most used man-made material worldwide. Cement shows exceptional mechanical properties, it is low cost and accessible globally. The majority of emitted CO2 is linked with its production stage (i.e., limestone decomposition during calcination). The use of sustainable alternative binders is indeed becoming increasingly urgent, requiring the adoption of advanced measurement techniques. On a material level, new sustainable formulations enable to partially or completely replace classical cement, bringing an additional complexity at the physico-chemical level of the pastes, requiring innovative characterization tools such as small oscillatory rheology (SAOS). SAOS has been used to describe the viscoelastic behavior of sustainable cementitious pastes in time, providing macroscopic information about physico-chemical mechanisms occurring at the microscopic scale, otherwise challenging to access experimentally through direct measurements. Indeed, it has been shown that the evolution of the storage modulus (G’) with time, imposing a deformation within the paste linear viscoelastic regime, tracks the development of interaction forces inside pastes and quantifies their cohesion. Our findings on sustainable alternative cementitious pastes with different chemical composition (clay, slag, recycled concrete, recycled bricks), confirm small oscillatory rheology as a powerful macroscopic tool to measure interactions at the microscopic scale. Moreover, SAOS open a path to quantify the reactivity of these more sustainable binders in order to optimize their use in new recipes, thus reducing cement content.