Early age cementitious pastes structuration

Concrete is everywhereshaping our homes, offices, and the streets we walk onthanks to its strength and versatility. Concrete owes its success to its main constituent, ordinary Portland cement (OPC), and boasts an annual production of around 4 billion tonnes worldwide, responsible for significant CO2 emissions. To address this environmental challenge, many alternative and more sustainable construction materials (such as ashes, slag, and calcined clay) have been increasingly studied over the past few decades. Although these alternatives show promise in reducing CO2 emissions, they often present challenges during manufacturingsuch as reduced paste workability and slower strength development. Ensuring these sustainable alternatives meet key criteriasuch as workability, pumpability, mechanical strength, and durabilityis essential for their effective adoption in daily applications. Our research aims to improve the formulation of sustainable concrete by investigating the early-age structuration of cementitious pastesthe processes that occur when the powder contacts water and begins to react, forming the hydration products responsible for setting and developing the final products mechanical strength. Studying the fresh paste of various cementitious materialsfrom classic cement to more sustainable alternativesprovides critical information on how particles are organized at the nanoscale and how they interact over time. To achieve this, the study employs advanced techniques: (a) small amplitude oscillatory shear (SAOS) rheology is used to examine paste properties, such as the elasticity and deformability of the particle network over time; (b) diffusing wave spectroscopy (DWS) is used to observe the dynamics of particle agglomeration and percolation, offering insights into the kinetics of setting. Additionally, the project incorporates shrinkage, creep, and light scattering measurements to monitor the flocculation and reorganization of the particle network from seconds to days after mixing. This approach helps in understanding the development of internal stresses and the potential formation and progression of microcracks, which can compromise the durability of the final material. Our ultimate goal is to evaluate how novel sustainable cementitious materials behave after adding water by estimating the cohesive forces between particles, their network formation, and organization over time. By developing and applying these methodological techniques, the project aspires to control the early-age properties of cementitious pastes for more sustainable concrete.