Basic creep and autogenous shrinkage of Limestone Calcined Clay Cement (LC3)

The use of supplementary cementitious materials (SCM) to lower the clinker factor of cements is now commonplace, for it benefits performance, economics and ecology. This thesis focuses on ternary blends of limestone and calcined kaolinitic clays, two very promising SCM thanks to their worldwide availability. In particular, this research aims to get an insight on the delayed strains in sealed condition of such binders, christened LC3 for Limestone - Calcined Clay Cement. Delayed strains refer to time-dependent deformations undergone by the material during its lifetime, such as shrinkage and creep. This work evaluates the impact of the calcined kaolinite content of the clay - which can vary in accordance with the origin of the clay - on the autogenous shrinkage and basic creep properties of LC3. Compressive creep tests on mature paste samples indicated that the presence of limestone and calcined clay dramatically reduced creep compliance. This reduction is significant even with lower grade clays and does not depend on the clay purity if it has at least 40% of calcined kaolinite. A two-dimensional finite elements model was used to simulate the creep response of the tested microstructures in order to try to determine whether the compliance reduction originated from a different phase assemblage or a higher viscosity of the C-S-H. The outputs pointed towards a different rheology of C-S-H gel. Autogenous shrinkage measurements on LC3 binders showed that these ternary blends had a lower or comparable shrinkage to plain cement reference during the two first months of hydration. Shrinkage rate and amplitude was found to be close for LC3 mixes usingmedium to high grade clays of natural origin. A study of the evolution of microstructure with shrinkage demonstrated that if the calcined clay contained enoughmetakaolin to consume most of the available portlandite, the porosity and desaturation of the microstructure were very similar regardless of the clay. As these features play a large role on the origin of shrinkage force, the macroscopic response is comparable among these specific mixes.