Size-independent fracture energy in plain concrete beams using tri-linear model

► The present study is aimed to obtain size independent fracture energy and the length of the fracture process zone in concrete, using acoustic emission technique. ► The bi-linear boundary effect model using AE data has already been used to estimate the size independent fracture energy in concrete. ► The tri-linear model based on the observations made in the acoustic emission data in front of the notch, on a plain concrete beam tested under three point bend condition to estimate size independent fracture energy. ► The tri-linear model appears to showcase a more accurate energy distribution along the ligament length and facilitates a better estimate of size independent fracture energy. ► From this model, the fracture process zone length is estimated using event histogram from AE data. The boundary effect or the size effect on the fracture properties of concrete has been studied assuming a bi-linear model for the distribution of local fracture energy concept. Boundary effect is observed not only near the back boundary but also near the notch tip, where a fictitious boundary seems to exist, separating the linear and non-linear fracture zones. In this paper a tri-linear function is assumed for the local fracture energy distribution along the ligament and expressions relating RILEM fracture energy and the size-independent fracture energy are developed. Transition ligament length measurements based on the acoustic emission (AE) histogram of events are used to obtain size-independent fracture energy. Length of the fracture process zone is identified in the AE histogram and compared with the value obtained from softening beam model. There seems to be a good agreement between the results.