Flexural performance and patterns identification of UHPC subjected to alternating elevated and cryogenic attacks with acoustic emission characterization.

• Study performance of UHPC after alternating elevated and cryogenic attack (AECA) • Flexural Cracking behaviour of UHPC after AECAs is identified by acoustic emission. • AECA has dual effect of enhancement and deterioration on flexural property of UHPC. • Empirical equations are proposed to estimate flexural toughness and load of UHPC. This paper investigates the flexural performance of ultra-high-performance concrete (UHPC) subjected to a simulated lunar ground temperature environment between 200 °C and −170 °C termed as alternating elevated and cryogenic attack (AECA). Additionally, the cracking behavior during the failure process was characterized by acoustic emission (AE) technique. Compared with unexposed UHPC specimens, those exposed to AECA up to five cycles still exhibit superior flexural performance. The AE results imply that tensile cracks are mainly generated by the failure of cement matrix, and shear cracks are mainly attributed to the steel fiber–matrix debonding and steel fiber pull-out behaviour. AECA exhibits the dual effect of enhancement and deterioration on the flexural performance of UHPCs, and there is even a competitive relationship between the two effects. Due to the dual effect, cement matrix strength and bond strength between cement and steel fiber show different responses to AECA. Finally, four prediction equations that matched excellently with the experimental results are proposed to estimate the residual flexural load and compute the flexural toughness directly according to Newton-Leibniz law instead of integrating the area under the load–deflection curve. [ABSTRACT FROM AUTHOR]