Available online at www.CivileJournal.org Civil Engineering Journal (E-ISSN: 2476-3055; ISSN: 2676-6957) Vol. 7, No. 08, August, 2021 1290 Effect of Fiber, Cement, and Aggregate Type on Mechanical Properties of UHPC Esmail Shahrokhinasab 1* , Trevor Looney 2 , Royce Floyd 3 , David Garber 4 1 Research Assistant, Department of Civil and Environmental Engineering, Florida International University, Miami, FL 3317, USA. 2 Graduate Research Assistant, Department of Civil Engineering and Environmental Science, University of Oklahoma, Norman, OK 73019, USA. 3 Associate Professor, Department of Civil and Environmental Engineering Science, University of Oklahoma, Norman, OK 73019, USA. 4 Associate Professor, Department of Civil and Environmental Engineering, Florida International University, Miami, FL 33174, USA. Received 12 April 2021; Revised 25 June 2021; Accepted 08 July 2021; Published 01 August 2021 Abstract Ultra-High Performance Concrete (UHPC) is a new class of concrete that differentiates itself from other concrete materials due to its exceptional mechanical properties and durability. It has been used in structural rehabilitation and accelerated bridge construction, structural precast applications, and several other applications in the past decades. The mechanical properties of UHPC include compressive strength greater than 124 MPa (18 ksi) and sustained post cracking tensile strength greater than 5 MPa (0.72 ksi) when combined with steel, synthetic or organic fibers. Proprietary, pre-bagged mixtures are currently available in the market, but can cost about 20 times more than traditional concrete. This high price and the unique mixing procedure required for UHPC has limited its widespread use in the US and has motivated many researchers to develop more economical versions using locally available materials. The objective of this study was to investigate the effect of different proportions of typical UHPC mixture components on the mechanical properties of the mixtures. Particle packing theory was used to determine a few optimal mixture proportions and then modifications were made to investigate the effect. A compressive strength of around 124 MPa (18 ksi) was achieved without using any quartz particles in the mixture design. Keywords: Non-Proprietary UHPC; Steel Fibers; Particle Packing Analysis. 1. Introduction After water, concrete (made of aggregates, cement, and water) is the most widely used material on Earth. Conventional concrete has been one of the primary construction materials since the invention of Portland cement in 1824. During this time, there have been numerous research efforts to improve the strength, cost efficiency, and durability of concrete, and still, there are many ongoing studies to address different issues accompanied by concrete technology. One relatively recent solution for improving upon conventional concrete is ultra-high performance concrete (UHPC). The definition of UHPC has been evolving over the past few years. Based on Federal Highway Administration (FHWA) guidelines [1], UHPC is concrete with more than 150 MPa (21.7 ksi) compressive strength at 28 days, a maximum water-to-cementitious materials ratio (w/cm) of 0.25, and containing internal fiber reinforcement to achieve post-cracking tensile strength above 5 MPa (0.72 ksi). Other researchers [2] are proposing lower required strengths (124 * Corresponding author: eshah004@fiu.edu http://dx.doi.org/10.28991/cej-2021-03091726 © 2021 by the authors. Licensee C.E.J, Tehran, Iran. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC-BY) license (http://creativecommons.org/licenses/by/4.0/).