Ultra-high performance concrete (UHPC) is a state-of-the-art cementitious composite. Since the concept of this novel concrete mixture emerged in the 1990s, significant advancements have been made with numerous benefits such as high strength, flowability, high post-cracking tensile resistance, improved durability, reduced maintenance, and extended longevity. Currently, UHPC is employed around the globe alongside recently published practice guidelines. Although numerous research projects were undertaken to examine the behavior of UHPC-incorporated structures, there still are many gaps to be explored. Of interest are the development of robust and reliable mixtures and their application to primary load-bearing members for bridges and buildings, including various site demonstration projects that would promote the use of this leading-edge construction material. This Special Publication (SP) contains nine papers selected from three technical sessions held in the ACI Spring Convention in March 2022. All manuscripts were reviewed by at least two experts in accordance with the ACI publication policy. The Editors wish to thank all contributing authors and anonymous reviewers for their rigorous efforts. The Editors also gratefully acknowledge Ms. Barbara Coleman at ACI for her knowledgeable guidance. Yail J. Kim, Steven Nolan, and Antonio Nanni Editors University of Colorado Denver Florida Department of Transportation University of Miami

The efficacy of ultra-high performance concrete (UHPC) overlays holds great promise for mitigating chloride-induced corrosion in reinforced concrete bridges. This research examines the corrosion resistance of a bridge structure through the application of simulation techniques to better understand the effectiveness of ordinary concrete and UHPC overlays. To represent the three-dimensional microstructure of ordinary concrete and UHPC, the Virtual Cement and Concrete Testing Laboratory (VCCTL) program is utilized. Additionally, an agent-based model is developed to investigate chloride penetration mechanisms within the concrete overlays. Furthermore, the structural response of the overlayed bridge under a corrosive condition is studied.

This paper presents the prediction of bond strength between ultra-high performance concrete (UHPC) and fiber reinforced polymer (FRP) reinforcing bars using an artificial neuronal network (ANN) approach. A large amount of datasets, consisting of 183 test specimens, are collected from literature and an ANN model is trained and validated. The ANN model includes six variable inputs (bar diameter, concrete cover, embedment length, fiber content, concrete strength, and rebar strength) and one output parameter (bond strength). The model performs better than other models excerpted from existing design guidelines and previously published papers. Follow-up studies are expected to examine the individual effects of the predefined input parameters on the bond strength of UHPC interfaced with FRP rebars.

Lightweight and high-performance materials have become necessary for infrastructure with advanced construction and performance requirements. One of the major challenges with structures made of these materials is their performance under natural and man-made hazards, such as wind, fire, and blast. Therefore, in this study, the performance of ultra-high-performance concrete (UHPC) and UHPC coated with foamed concrete (UHPC-Foamed) and polyurea (UHPC-Polyurea) is investigated under blast load. A finite element model is developed to assess the behavior of UHPC and coated UHPC panels under far-field and near-field blast scenarios. The constitutive behaviors of UHPC and foamed concrete are considered using the concrete damage plasticity model with respective parameters. The polyurea is modeled as a hyperelastic material with the Mooney-Rivlin model. Moreover, the effectiveness of the additional coatings, i.e., foamed concrete and polyurea, on the blast resistance of each panel is presented. The finding of the study shows that both foamed concrete and polyurea enhance the blast resistance of the UHPC concrete panels. Moreover, a comparison between the blast resistance of UHPC-Foamed and UHPC-Polyurea is conducted under far-field and near-field blast scenarios. Also, the effectiveness of foamed concrete and polyurea coatings with different thicknesses to UHPC panels is assessed under both blast scenarios.

Ultra-high-performance concrete (UHPC) features tensile strain-hardening behavior and a high compressive strength. Existing studies on the shear behavior of UHPC structural members have been focused on prestressed UHPC girders. More experimental data of the shear behavior of non-prestressed UHPC beams are necessary to quantify the safety margin of shear designs for structures. Moreover, while the UHPC members in most studies did not contain coarse aggregate to strengthen their microstructure, the inclusion of coarse aggregate has been shown to substantially reduce the autogenous shrinkage and enhance the elastic modulus for UHPC materials, which is beneficial for structural applications of UHPC. This study experimentally investigated the shear failure behavior of eighteen non-prestressed rectangular UHPC beams. The experimental variables included the volume fraction of fibers, shear span-to-depth ratio of the beams, and coarse aggregate. The detailed shear failure responses of the UHPC beams were discussed in terms of the damage pattern, shear modulus, shear strength, shear strain, and strain energy. The test results showed that the inclusion of coarse aggregate increased the beam shear strength, and its enhancement became more significant with a higher volume fraction of fibers and a lower shear span-to-depth ratio of the beam. In addition to the experimental investigation, a shear strength model for non-prestressed rectangular UHPC beams that accounts for the interactive effect of the key design parameters was developed. An experimental database of the shear strength of the UHPC beams in existing studies was established to assess the performance of the proposed model. It was shown that the proposed model reasonably predicted the shear strength of the UHPC beams in the database with a higher accuracy and lower scatter compared to the results of existing models.