Mechanical properties and damage evolution of sprayed ultrahigh performance concrete under uniaxial compression

Abstract

To investigate the effects of the spraying process and different fibers on the mechanical properties and failure patterns of ultrahigh performance concrete (UHPC), three types of fibers were used. These fibers were formed using both spraying and molding methods. Uniaxial compression tests were conducted, and two nondestructive monitoring techniques, acoustic emission (AE) and digital image correlation, were employed to monitor the uniaxial compression tests. The results indicated that the compressive strength of UHPC with single steel fibers and hybrid fibers increased by about 19% and 14% compared with those of UHPC with polyoxymethylene fibers. In comparison with molded UHPC, sprayed UHPC showed a slight improvement in compressive strength. Specimens containing steel fibers exhibited better post-cracking ductility, whereas those with only polyoxymethylene fibers displayed a certain degree of brittle failure. In sprayed UHPC, the onset of significant internal damage was delayed, which was related to the redistribution of internal fibers. The failure of UHPC was characterized by primary tensile cracks, supplemented by shear cracks. The spraying process can better restrict the development of tensile cracks in UHPC. Sprayed UHPC typically exhibited multiple crack developments leading to failure, whereas molded UHPC generally failed in the form of a single main crack penetrating the specimen. The addition of steel fibers delayed the occurrence of local stress concentration zones, aligning well with AE monitoring data.