Micro-Chemo-Mechanical Characterization of a Limestone-Calcinated-Clay Cement Paste by Statistical Nanoindentation and Quantitative SEM-EDS

To address the sustainability concerns associated with Portland cement clinker production, the ternary blend of limestone, calcined clay and cement (which was named LC³) has recently been demonstrated to be an efficient solution. This work aims to contribute to the development of this promising material by applying latest techniques to characterize the chemo-mechanical properties of the complex heterogeneous microstructure of an LC³ paste by combining statistical nanoindentation and quantitative SEM-EDS techniques (SNI-QEDS). The results showed that the mechanical properties of LC³ come from a complex microstructure assemblage of C-A-S-H, Al-rich hydrates and anhydrous grains. Thus, the LC³ microstructure is composed by large anhydrous grains (clinker and calcined clay) embedded in a cementitious paste made of hydrates incorporating finely graded grains of anhydrous calcined clay, limestone and quartz. Moreover, the partial reaction of the calcined clay, limestone and Portlandite formed C-A-S-H and other Al-rich hydrates (likely including carboaluminates). Notably, the latter exhibited higher mechanical properties than those of C-A-S-H. Finally, the present work provides new knowledge for better understanding the complex LC³ microstructure towards advanced modelling and mix design optimization.