Ultra-high performance concrete might be a competitive alternative to normal concrete for some purposes. But despite research efforts during decades, utilisation is still not widespread. Reasons include limited competence and material availability. This paper presents one step of a research initiative aimed at facilitating the use of UHPC in Norway. The step presented here comprises the accumulated results from investigations on the influence steel fibres (content, type, and hybrid combination) have on material strength and deformation behaviour of locally produced UHPC, made with constituents found in southern Norway. 231 specimens were tested, spanning nine UHPC mixes. Digital Image Correlation (DIC) was successfully used to study crack propagation. Compressive strength of 166 MPa and E-modulus of 46 GPa were obtained, not being influenced by fibre content. The flexural tensile strength was found to be strongly dependent on variations in steel fibre properties and mix design. The highest flexural tensile strength was obtained for prisms with micro straight steel fibres alone, or in 50% combination with macro hooked-end fibres. The experimental results are considered in a theory-informed discussion. Suggestions are made on the use of steel fibres in locally produced UHPC, potentially lowering the cost by 30%.

This paper is a presentation of an investigation into the suitability of locally produced ultra-high-performance fiber-reinforced concrete (UHPFRC) for the rehabilitation of deteriorated concrete bridge decks in Norway. Full-scale production was conducted at a conventional ready-mix concrete plant using mostly locally available materials from silos at the plant. Material properties relevant for bridge deck rehabilitation were investigated, including compressive strength, residual flexural strength, E-modulus, shrinkage, and resistance to chloride ion penetration. These results were compared to earlier experiences at laboratory scale. The findings indicate that full-scale production of UHPFRC with locally available constituents is achievable using common facilities for ready-mixed concrete, including mixing, transportation, and pumping in quantities appropriate for industrialized bridge deck rehabilitation. The applied UHPFRC mix design was found suitable for bridge rehabilitation, considering compressive and flexural strength, shrinkage, and durability evaluated by resistance against chloride migration. Up to approximately 3 vol% of micro steel fibers (225 kg/m³) were stepwise added, achieving a castable and self-leveling UHPFRC mix. Self-leveling mixes are not suitable for applications in slopes, which are common for bridge decks. Adjustments to the mix design are necessary to achieve thixotropy. Some additional material properties remain to be evaluated, such as the bond between the old concrete substrate and the new UHPFRC layer. This is being investigated in the next stage of the project.

This paper presents an investigation on substituting the cement content with an inert material, in a typical locally produced UHPC mix. A structured literature review was performed to enrichen the discussion and to benchmark the results towards already reported investigations in the research society. Investigations on cement substitution in UHPC are frequently reported. However, usually the cement is substituted with other binding materials – often pozzolanic by-products from other industries. Reports from investigations on the use of inert materials for cement substitution in UHPC seem scarce. An experimental program that included a total of 210 test specimens was executed. This program included evaluating several questions embedded to the problem on how to substitute cement while keeping all other variables constant. It is concluded that up to 40% of the cement can be substituted with an inert material, without significantly changing the flexural tensile strength or compressive strength of the hardened UHPC. Two preconditions were caretaken: the particle packing was maintained by securing that the substitution material had a Particle Size Distribution (PSD) near identical to the cement and that the water balance was maintained through preconditioning of the substitution material. Suggestions are made for improving benchmarking.

Three-dimensional printed concrete (3DPC) has received growing attention as digital fabrication technologies continue to influence construction workflows. This study presents a systematic review of research published between 2015 and 2026, following PRISMA guidelines. Based on the reviewed literature, six opportunity categories and six challenge categories were identified. The opportunities include design optimization, construction speed, materials innovation, labor reduction, remote area construction, and circular economy. The findings show that material innovation is the most extensively researched category; a substantial proportion of the literature focuses on materials, rheology, printability, and structural behavior, reflecting an emphasis on improving fresh-state properties, interlayer bonding, and mechanical performance. The second most researched opportunity is design optimization, followed by the circular economy. Research in the remaining three categories of construction speed, labor reduction, and remote area construction appears to be limited. The main challenges identified include reinforcement integration, structural performance, mixing and curing, high equipment costs, durability, and the lack of standards. High equipment costs and the lack of standards appear to be the least researched challenges, while the four remaining challenge categories are actively addressed by the research community.

Concrete three-dimensional (3D) printing technology has the potential to significantly reduce on-site labour activities, as 3D-printed concrete eliminates the need for formwork. However, challenges persist in ensuring the quality and strength of 3D-printed concrete. One of the factors likely to impact its strength is the fluctuation of the water-to-binder ratio (w/b) during the printing process. In contrast to traditional cast-in-place concrete, where the mix is prepared at the factory with a fixed water-to-binder ratio, 3D-printed concrete is continuously mixed from a dry mix during printing. The amount of water added to the dry mix is routinely adjusted by the printer operator to maintain optimal consistency. This adjustment affects the water-to-binder ratio, leading to variations in concrete strength. This chapter investigates the extent to which the consistency and strength of 3D-printed mortar may vary while remaining printable using an industrial-scale concrete printer. Using the same dry mix, we observed a difference of approximately 15% in the mean strength for samples cast at the 3D printing site on two different dates. Additionally, there was about a 20% difference in the strength between the thickest and thinnest printable consistencies mixed in the laboratory. This variation must be considered when determining the design strength of 3D-printed concrete.