Fiber alignment and its effect on mechanical properties of UHPC: An overview

Ultra-high performance concrete (UHPC) is attracting increasing interests worldwide due to its excellent mechanical properties and durability. Securing fiber alignment corresponding to the direction of principal tensile stress can greatly enhance the mechanical performance, especially flexural and tensile properties of UHPC. In this paper, an overview on fiber alignment and its effect on mechanical properties of UHPC is presented. The changes in flow patterns of mixture and the assistance of electromagnetic field during casting can lead to a higher improvement in fiber orientation (up to 80%) compared to other fiber alignment methods. Quasi-static flexural strength, toughness, and tensile strength can be enhanced by 10%-80%, 20%-100%, and 30%-90%, respectively, for UHPC with fiber alignment compared to those with random fiber orientation. This can enable up to 2% reduction in fiber volume needed to secure a similar mechanical performance. Such fiber alignment can increase the dynamic compressive strength and flexural strength by up to 20% and 50%, respectively. Moreover, fiber alignment can lead to the reduction of electrical resistance and improvement of self-sensing ability of UHPC due to the formation of a more complete conductive network. To promote the research and application of fiber alignment in UHPC, the alignment of flexible fibers that can bend in mixtures and the alignment of fibers in mixtures containing coarse aggregates where fiber alignment can be interfered should be further investigated. Furthermore, practical applications of fiber alignment in UHPC structural elements should be advanced. (C) 2021 Elsevier Ltd. All rights reserved.