Early age cementitious pastes structuration – EarlyCem

Concrete is the most widely used building material in the world for its availability, durability and mechanical strength. Nevertheless, we do not have a fundamental understanding of the early age formation of a network of cement particles, and of the evolution of their mechanical properties when time elapses. This is particularly relevant to develop new cementitious formulations that are less costly in terms of CO2 emissions.
We wish to use a combination of light scattering and mechanical techniques in order to reach a rationale concerning the early-age cement paste flocculation. This will allow us to obtain better foundations for cement paste formulations and for the ones in which cement is partially or totally replaced by another component, on order to reduce its carbon footprint. In particular: (i) limestone calcined clay cement (LC3) for partial substitution and (ii) alkali-activated slag (AAS) for total substitution. The overall objectives of this project are thus the following:
1- the development of new methodological tools allowing for a quantitative description of the early-age cement paste behavior and the kinetics of formation of a flocculated network,
2- the study of cement paste formulations that are alternative to ordinary Portland Cement (OPC), either based on partial or full replacement of clinker, on view of reduction of their Global Warming Potential.

We will use the methods below:
1- Small Amplitude Oscillatory Rheology (SAOS) : rheological mechanical characterization of fresh cementitious pastes (ie structural buildup, paritcule interactions, deformation and cohesion).
2-Light scattering techniques : (i) MultiSpeckle Diffusing Wave Spectroscopy (MSDWS) to characterize the dynamics of very early age pastes and (i) Laser Speckle Imaging (LSI) to monitor the crackling dynamics at early ages.
3-Shrinkage mechanical testing (chemical, autogenous and plastic drying) and creep measurements. Two new setups will be built for chemical and autogeneous shrinkage.
4- X-ray powder diffraction (XRPD) : phase composition of hardened pastes
5- Isothermal calorimetry : heat of hydration of fresh cementitious pastes

This research project should lead to the following outputs:
1- SAOS and MSDWS measurements on cements , LC3 and alkali)-activated slags (AAS) will allow the non-perturbative study of the floculation dynamics of very early age, from seconds to hours after mixing, of the hydrating pastes.
2- Shrinkage, creep and LSI measurements will resolve the dynamics of the particle network forming during hydration, from hours to days after mixing, including the formation and evolution of micro cracks.
the initial floculation and later micro cracks formation will give an overall description of cementitious systems evolutions, fundamental to the development of better sustainable formulations.