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

Through a Change Proposal by Facca Incorporated, the Ontario Ministry of Transportation (MTO) approved the replacement of the as-tendered steel H-piles by newly designed prestressed/precast Ultra-High-Performance Concrete (UHPC) piles for supporting the west abutment of the Lily River Detour Bridge. The 300 mm (~12”) deep UHPC piles were designed and installed at the west abutment based on the previous successful development and testing of a tapered H-shaped pile at Iowa State University. The east abutment, as tendered, was designed to be supported by six steel H-shaped battered piles driven to bedrock. For the west abutment, six UHPC piles were produced and installed using the same batter. Since the site contained occasional boulders and the design intent to drive the piles to bedrock, the UHPC piles were fitted with steel shoes for the first time. All piles were successfully installed to reach the targeted load bearing capacities. After the replacement bridge was constructed, the detour bridge was removed and the UHPC piles were extracted to examine the conditions of the piles. This presentation will provide details of the innovative design of the piles, fabrication and driving of the piles, and lessons learned from analyzing the driving data and removal of the piles. Fellowship and Scholarship recipients. With the help of generous donors from the concrete community, the ACI Foundation awards high-potential undergraduate and graduate students in engineering, construction management, and other appropriate curricula.

This study focuses on evaluating the mechanical, microstructural, and durability properties of 3D printing mortar (3DPM), with a specific emphasis on the influence of incorporating recycled fine aggregates (RFA). These RFA are produced from construction and demolition waste (C&DW) in Belgium and are sieved to a maximum particle size of 2 mm [0.08 in].

Cast and printed samples of mortar containing 100% RFA, with a sand-to-cement ratio of approximately 1:1 and a water-to-cement ratio of 0.29, were subjected to mechanical tests, including flexural, compressive, and tensile strength, at 2, 7, 28, and 56 days. The possible anisotropic behavior of the printed material was also investigated. The results show that using RFA does not significantly affect the mechanical properties of the mortar, and some anisotropic behavior was observed based on the compression test results. The end goal of the project is to print non-reinforced urban furniture; in order to assess its durability, only freezing and thawing (F-T) behavior was investigated. The F-T behavior was analyzed based on the quantity of spalling particles after 7, 14, 28, 56, and 91 F-T cycles. The results show that up to 91 F-T cycles, no significant surface damage occurred.

The addition of supplementary cementitious materials (SCMs) to low-carbon concrete mixtures has been investigated in recent years as part of the sustainability of the concrete sector. Recently, most traditional SCMs, such as fly ash and blast furnace slags, have become unavailable in several developed countries, mostly due to environmental restrictions. Consequently, several new by-products from fast-growing sectors are being considered as potential replacements for traditional SCMs. However, the durability of these new by-products in low-carbon concrete has not been thoroughly explored. As a result, this paper presents the first part of a project related to an extensive experimental characterization, in which low-carbon concrete with high compactness, paste optimization, and partial cement replacement by the addition of waste by-products from the agricultural, metallurgical, paper, and glass industries is studied. Alternative SCMs including rice husk ash, biomass fly ash, rock wool residues, or waste foundry sand are incorporated into corresponding mortar matrices and the results concerning the mechanical properties (flexural and compressive strength) and durability (capillary water absorption, surface electrical resistivity, and carbonation resistance) are presented and analyzed. The outcomes indicate that it is possible to reduce the Portland cement content without compromising the mechanical and durability properties of the concrete.

It is known that the use of recycled coarse aggregates (RCA) can raise a variety of problems, which are mainly due to the porosity of the old mortar contained in RCA. One of the simpler ways to solve these problems is the pre-wetting of RCA, which allows not only to minimize disadvantages but also to obtain the advantages associated with the effect of internal curing. Undoubtedly, the strongest positive effect of pre-wetted RCA is on the rheology of recycled concrete. But there are also possible positive effects of internal curing for strength and durability of blended cement concretes, which require longer curing times compared to normal Portland cement concrete. In this paper, we mostly study the influence of porous RCA on the rheology of cement paste, based on slag cement with a 75% slag content. For this purpose, the absorption properties of RCA of different sizes were studied. From this, mathematical dependences of the workability of cement systems on w/c and time could be obtained. These further underline the positive effect of pre-wetting of RCA with regard to retaining the workability of cementitious systems. This lays the basis for a broader study of pre-wetting RCA on the rheology of mixtures, strength, and durability to be covered in future publications.