Experimental study on fracture and acoustic emission properties of internally cured concrete with super absorbent polymer subjected to high temperature

Abstract

The three-point bending experiment was conducted on notched beams containing five different SAP contents to investigate the influence of high temperature on the fracture performance of Superabsorbent Polymer (SAP) concrete. Acoustic Emission (AE) technology was employed to monitor real-time crack propagation, and scanning electron microscopy (SEM) was utilized to analyze the micro-pore structure. The experimental results reveal the following findings. After exposure to high temperatures, the peak strength of SAP concrete continuously decreases. Compared to specimens at 20 °C, the strength loss after exposure to temperatures of 200 °C, 400 °C, and 600 °C is approximately 11%, 55%, and 87%, respectively. However, the introduction of SAP can reduce the proportion of strength loss in the concrete. Additionally, SAP improves the toughness of the concrete, with an increase in ductility coefficient ranging from 4.0 to 6.8 times as the loading temperature increases. Similar to the strength variation pattern, the initial fracture toughness of SAP concrete exhibits a significant decrease with increasing heating temperature. The loss in initiation toughness after exposure to temperatures of 200 °C, 400 °C, and 600 °C is approximately 11%, 42%, and 85%, respectively, while the loss in unstable fracture toughness is 11%, 46%, and 74%. Based on the experimental results, this study proposes two temperature-dependent fitting models for the peak strength and fracture toughness of SAP concrete, which are compared and validated with the experimental results. SEM analysis reveals a loose and porous internal structure in SAP concrete. Through the analysis of AE signals at different temperatures, the fracture process is elucidated based on the b-value method. Moreover, RA-AF analysis indicates that an increase in temperature reduces the proportion of tensile-type cracks in specimens with the same SAP content. From the temperature loaded results spanning 20 °C–600 °C, the proportion of tensile cracks decreases from 80% to 50%, indicating a transition in the failure mode from tension to shear. However, this trend is not significantly affected by the temperature increase, suggesting that the failure mode of the specimens is primarily determined by the internal pore structure of the concrete rather than the temperature load. The research findings provide experimental evidence for the application of SAP concrete in engineering projects.