The use of AE technique for identifying ductility degradation against cryogenic on flexural performance of UHPC at various temperature conditions

Abstract

This paper reports the flexural performance of ultra-high performance concrete (UHPC) exposure to six temperature conditions, including ambient temperature (A), after exposure to 200 °C (EA), in-situ −170 °C (DC), in-situ −170 °C after exposure to 200 °C (IDC), after exposure to −170 °C (AC), after exposure to 200 °C and −170 °C (AEC). The cracking characteristics of UHPC under the coupling effect of cryogenic and external load is identified with acoustic emission (AE) technology. The results show that DC condition is the most efficient in enhancing flexural strength and toughness due to frozen water and improved bond strength. A nonlinear relationship between first-peak deflection and first-peak flexural strength is observed because of the changed flexural modulus at different temperature conditions. The increasing shear cracks in linear-elastic stage is attributed to the fracture process of frozen water, which can account for the significant increase of first-peak strength at DC and IDC conditions. Cryogenic-induced ductility degradation is observed in the flexural behaviour of UHPCs at DC and IDC conditions, which is attributed to higher energy release rate. Furthermore, pre-exposure to 200 °C reduced the positive influence of cryogenic temperature on flexural performance and the negative effect of cryogenic temperature on ductility because of the initiated cracks around steel fibers.