Thermal-dependent brittleness effect of ultra-high performance concrete exposed to cryogenic flexural loads by acoustic emission evaluation

Abstract

Ultra-high Performance Concrete (UHPC) exposed to cryogenic temperatures typically fails in a brittle fashion, with a failure mode that is undesirable and catastrophic. In this study, the Thermal-dependent Brittleness (TDB) concept and its utilization for the evaluation of UHPCs exposed to different cryogenic temperatures were undertaken. Herein, flexural load-deflection curves of UHPC specimens and the absorbed energy evolution mechanism were analyzed. Moreover, the deformation and failure of UHPC specimens were also monitored utilizing changes in the Acoustic Emission (AE) signal. Results showed that whereas one-cycle flexural strength of UHPC specimen generally increased as test temperature reduced from 20 °C to −170 °C, a mixed effect on the toughness index was observed. The highest and lowest flexural toughness indexes were recorded for tests conducted at −110 °C and −170 °C, respectively. Moreover, the brittleness of UHPCs tested within −170 °C was accurately estimated by the newly proposed TDBall index. Finally, AE signals indicated that while tensile cracks exceeded shear cracks in specimens tested between 20 °C and −80 °C, there is a preponderance of shear cracks in specimens tested at −110 °C and −140 °C.