Effect of different fiber combinations and optimisation of an ultra-high performance concrete (UHPC) mix applicable in structural elements

Abstract

In this study, Ultra-High Performance Concrete (UHPC) mix was optimised to expand its use in large-scale applications. Using alternative curing methods instead of heat treatment, it was aimed that UHPC will meet the required strength and workability criteria and thus be presented applicable solutions for widespread use of UHPC in engineering applications. Therefore, effect of aggregate type, fiber content, curing method, compacting method, cement type, water/cement ratio and aggregate granulometry on mechanical properties of UHPC was investigated. Compressive strength, flexural tensile strength, splitting tensile strength, pull-out behaviour, modulus of elasticity and toughness values of the UHPC series were determined. Standard water curing (compared to wet hessian application) increased the compressive strength by 11.2% and the flexural tensile strength by 19%, while the inclusion of hybrid fibers (compared to the use of a single type of fiber) increased the compressive strength by 16.7% and the flexural tensile strength by 48%. Type of aggregate was found very effective on flexural tensile strength as well, and it provided additional ductility by increasing the matrix strength. In cases where heat treatment is not available, it was observed that the required strength criteria can be met with standard water curing as well. UHPC with a compressive strength of 170 MPa, which has excellent workability, was developed. As a result of the study, optimum solutions were proposed for the widespread use of UHPC in the precast industry.