Reliability of Digital Image Correlation Techniques for Cementitious Composite Fracture Characterization

Conventional devices used for measuring strain, like strain gauges and LVDTs, typically used as single-point sensors, require enhanced precision of gathered data, encompassing accuracy and consistency. However, these instruments are incapable of generating strain maps. Furthermore, it requires more time and precision during the set-up test. However, this study assesses the reliability of digital image correlation (DIC) methods as a non-destructive and helpful tool for monitoring the development of cracks in cementitious composites by comparing the DIC test and the mechanical test (Machine test) results. In the objective study, three types of mortars were prepared: Normal Strength Mortar (NSM), High Strength Mortar (HSM), and High Strength Mortar with Fly Ash (HSMFA). Steel 13 mm in length and synthetic fibres 19mm and 54 mm in length (short and long) were mixed into the composites in varied volume ratios, ranging from 0% to 1. Pre-notched 40x40x160 mm prismatic specimens were tested in three-point bending while being simultaneously filmed to track the crack's growth. The results showed that the post-cracking behaviour switches from softening to hardening for some types of mortar and certain fibre dosages. To evaluate the reliability of DIC for the characterisation of fracture properties, the vertical displacements for all specimens were analysed using GOM correlate software and compared with machine test data. The use of the DIC approach for the measurement of crack opening and the interpretation of the results in terms of Force-crack mouth opening displacement (CMOD) were made possible by the good agreement between the results regarding vertical deflection for all the employed mortars.