Effect of notch location on flexural and fracture behaviors of UHPGC notched beam based on four-point bending test and acoustic emission monitoring

Abstract

Ultra-high performance glass sand concrete (UHPGC) is a new composite material with superior mechanical properties and durability made by replacing quartz sand in traditional ultra-high performance concrete (UHPC) with environmentally friendly and economical glass sand recycled from waste glass. This study investigated the flexural and fracture characteristics of UHPGC notched beams with prefabricated notches at three different locations (mid-span, 100 mm off mid-span and 145 mm off mid-span) using four-point bending tests. Meanwhile, the damage evolution processes of notched beams under flexural load were monitored in real time and characterized by acoustic emission (AE) technology. Fracture modes were automatically classified based on Gaussian mixture model (GMM) and support vector machine (SVM) of rise angle (RA) and average frequency (AF). Outlier analysis of b-value were applied to provide a warning prior to complete failure of UHPGC notched specimen. The results revealed that notched position presents significant effects on flexural strength, flexural toughness and fracture energy, and exhibit considerable influence on AE parameters and cracking patterns. The farther the notch is away from the mid-span, the greater the flexural strength, flexural toughness and fracture energy exhibit due to the weakened stress concentration. As it takes longer to gather enough strain energy at the tip of the notch to crack, AE monitoring shows that higher amplitude and hysteretic nature of AE parameters such as accumulated energy and information entropy, etc., can be recorded as notch position away from the mid-span. The farther the notch is away from mid-span, the more shear cracks predominate at the later stages of damage. Cumulative AE energy and fracture energy throughout the damage process are found to exhibit a favorable exponential relationship. In addition, the b-value outlier analysis can provide failure warning for UHPGC notched beams. This study is of great significance in exploring the fracture behavior of UHPGC and providing reference for engineering applications related to UHPGC failure.