Techniques for recording self-healing efficiency and characterizing the healing products in cementitious materials

The self-healing mechanism of cementitious materials has been investigated by many researchers in the last two decades. In the journey of this quest, more and more advanced methods of analyzing the efficiency of healing have been employed. These methods are intended to clarify and quantify the healing mechanism. This paper presents five techniques, which are either common in the microstructure and nanostructure study or innovative in this field, which was used in order to identify the healing efficacy. Specifically, the application of scanning electron microscope (SEM) analysis, 3-D ultrasound tomography, nanoindentation, water absorption test (sorptivity), and software development in the Python programming environment for monitoring the crack closure have been used. The main objective of this study was to quantify several parameters, such as the geometry of the cracks, the properties of the healing products, as well as the healing depth. SEM analysis is a well-known technique that can contribute to identify the elements of the healing products and give the morphology of the surface. The methodology for nondestructive 3-D ultrasound tomography of healed specimens clarifies the ability of healing in depth. The nanoindentation technique enables localized contact response, which allows accurate estimates of the nanomechanical properties of the tested areas. The absorption method (sorptivity) is a representative method of recording cracks and open porosity. The software developed in a Python programming environment aimed at quantifying the surface crack closure and is an attempt to minimize the parameters that affect the inaccurate results, usually caused by the program's inability to detect only the crack. In addition, the results of each of the above methods are also presented, and their contribution to the study of healing is analyzed.