A novel energy-based method to evaluate indentation modulus and hardness of cementitious materials from nanoindentation load–displacement data

In this study, we propose an energy-based method to extract the nanomechanical properties such as indentation modulus and hardness for cementitious materials within the framework of contact mechanics that relies on more accurate and realistic interpretation of the load–displacement data. Such interpretation allows us to evaluate both the initial unloading stiffness and the hardness—two main input parameters for the Sneddon’s solution to indentation of an elastic half-space—directly as the functions of indentation works. Specifically, we show that while the initial unloading stiffness may be expressed in terms of normalized elastic work, the hardness may be evaluated from the total work done using the modified work-of-indentation approach. Results from nanoindentation on hardened cement paste show that the proposed energy-based method provides the indentation modulus and the hardness in agreement with the Oliver and Pharr method for all the nanomechanical phases of the paste considered. Two main advantages associated with the proposed method include: it circumvents the need of fitting the unloading response by a power-law and computing the area of contact between indenter and specimen. As the method described herein is simple and easy to use, it could be employed as a potential alternative to the conventional Oliver and Pharr method for a heterogeneous material like cement paste.