Calcium leaching performance of cementitious materials: Nanoindentation results and model predictions

The study is related to the EU 7th Framework Programme CODICE (COmputationally Driven design of Innovative CEment-based materials). The main aim of the project is the development of a multi-scale model for the computer based simulation of mechanical and durability performance of cementitious materials. This paper reports results of nanoindentation testing on fully calcium leached cement paste in relation with the prediction from the latest computer model developed in the CODICE research project. Using the statistical nanoindentation technique, intrinsic properties of different hydrate phases after leaching has been studied. In order to perform reliable nanoindentation experiments a very smooth and flat sample surface is required. Due to the -very porous and weak microstructure of fully-leached cement paste resin impregnation has to be used to produce satisfactory and representative specimens for the nanoindentation experiments. Extensive trials with different low stiffness resins (Young’s modulus < 0.5 GPa) were performed to obtain a sample preparation procedure capable to achieve the required low surface roughness. The results of statistical nanoindentation experiments and computer simulations indicate that Young’s modulus and hardness values of the individual C-S-H phases decreased significantly with the calcium leaching. In contradiction to previous published results, the results presented in this paper showed only a very small difference in degradation performance of LD C-S-H and HD C-S-H. Furthermore, the results clearly show a difference in the calcium leaching performance between the two commercially available Portland cements.