In this study, the interface between different types of bacteria-embedded self-healing polylactic acid capsules (PLA) and cement paste is investigated. Particularly, the changes in microstructure and mechanical properties of the interface with respect to bulk cement paste were studied. First, nanoindentation was performed to obtain maps of hardness and elastic modulus in the interfaces. Lattice modeling of uniaxial tensile test on the mapped locations was performed then to obtain the overall tensile strength and stiffness of the interface. Moreover, hydrates assemblage and chemical composition around the PLA particles were studied through Backscattering Electron images and Energy Dispersive X-ray Spectroscopy. The ratios between resulting tensile strength and elastic modulus of the interface with respect to bulk paste were obtained for each PLA type. The results suggest that PLA can be tailored to optimize the physico-mechanical properties of the interface and hence, the mechanical behavior and triggering efficiency of the self-healing system.

Soft inclusions, such as capsules and other particulate admixtures are increasingly being used in cementitious materials for functional purposes (i.e. self-healing and self-sensing of concrete). Yet, their influence on the fracture behaviour of the material is sometimes overlooked and requires in-depth study for the optimization of mechanical and/or smart properties. An experimental investigation is presented herein on the role of bacteria-based lactate-derived particles on the fracture behaviour of cement paste in tensile configuration. These admixtures are currently used for the purpose of self-healing. Digital Image Correlation was used to obtain strain contours on the surface of the samples during the test. The influence of soft particles addition and age of the samples on the fracture mechanics of the composite were investigated.