Ultra-high performance concrete (UHPC) was evaluated as a potential material for future bridge deck designs. Material characterization tests took place to identify potential challenges in mixing, placing, and curing UHPC. Biaxial testing was performed to evaluate behavior of UHPC in combined tension and compression stress states. A UHPC bridge deck was designed to perform similarly to a conventional concrete bridge deck, and a single unit bridge deck section was tested to evaluate the design methods used for untreated UHPC. Material tests identified challenges with placing UHPC. A specified compressive strength was determined for structural design using untreated UHPC, which was identified as a cost-effective alternative to steam treated UHPC. UHPC was tested in biaxial tension-compression stress states. A biaxial test method was developed for UHPC to directly apply tension and compression. The influence of both curing method and fiber orientation were evaluated. The failure envelope developed for untreated UHPC with random fiber orientation was suggested as a conservative estimate for future analysis of UHPC. Digital image correlation was also evaluated as a means to estimate surface strains of UHPC, and recommendations are provided to improve consistency in future tests using DIC methods. A preliminary bridge deck design was completed for untreated UHPC and using established material models. Prestressing steel was used as primary reinforcement in the transverse direction. Preliminary testing was used to evaluate three different placement scenarios, and results showed that fiber settling was a potential placement problem resulting in reduced tensile strength. The UHPC bridge deck was redesigned to incorporate preliminary test results, and two single unit bridge deck sections were tested to evaluate the incorporated design methods for both upside down and right-side up placement techniques. Test results showed that the applied design methods would be conservative for either placement method. / Ph. D.

When compared to traditional concrete, steel fibre reinforced concrete (SFRC) shows several enhancements in performance, including improved tensile resistance, toughness and ductility. One potential application for SFRC is in columns where the provision of steel fibres can improve performance under axial and lateral loads. The use of SFRC can also allow for partial replacement of transverse reinforcement required by modern seismic codes. To improve workability, self-consolidating concrete (SCC) can be combined with steel fibres, leading to highly workable SFRC suitable for structural applications. Recent advances in material science have also led to the development of ultra-high performance fibre reinforced concretes (UHPFRC), a material which exhibits very high compressive strength, enhanced post-cracking resistance and high damage tolerance. In heavily loaded ground-story columns, the use of UHPFRC can allow for reduced column sections. This thesis presents the results from a comprehensive research program conducted to study the axial behaviour of columns constructed with highly workable SFRC and UHPFRC. As part of the experimental program, twenty-three full-scale columns were tested under pure axial compressive loading. In the case of the SFRC columns, columns having rectangular section and constructed with SCC and steel fibres were tested, with variables including fibre content and spacing of transverse reinforcement. The results confirm that use of fibres results in improved column behaviour due to enhancements in core confinement and cover behaviour. Furthermore, the results demonstrate that the provision of steel fibres in columns can allow for partial replacement of transverse reinforcement required by modern codes. The analytical investigation indicates that confinement models proposed by other researchers for traditional RC and SFRC can predict the response of columns constructed with SCC and highly workable SFRC. In the case of the UHPFRC columns, variables included configuration and spacing of transverse reinforcement. The results demonstrate that the use of appropriate detailing in UHPFRC columns can result in suitable ductility. Furthermore, the results demonstrate the improved damage tolerance of UHPFRC when compared to traditional high-strength concrete. The analytical investigation demonstrates the need for development of confinement models specific for UHPFRC.

This research project has been undertaken to produce and characterize the behavior of High Strength Cementitious Mix (HSCM), which has considerably higher compressive strength compared to conventional concrete. Components of HSCM are cement, silica fume, sand, water, and high range water reducer. The material is tested for compressive strength and impact energy absorption capacity while the amount of above mentioned components are varied parametrically. The effect of these parameters are extensively studied and trends are reported. Finally, this research projects attempts to find correlations among compressive strength, compressive toughness, and impact toughness. Limitations of the experimental program are discussed and future direction for improvement and expansion of the research program is suggested.

Several connection details have been developed for the connection of precast cap beams to precast columns in Accelerated Bridge Construction (ABC) applications. Currently, the suggested details involve some form of either reinforcement or portion of the precast column to penetrate inside the cap beam. Such details present many challenges in the field, such as necessitating bundling of reinforcement in the cap beam or creating a congested reinforcement arrangement. Furthermore, closer inspection of some of the test data indicates that for currently used details, cap beams could sustain some damages during major seismic events, whereas they are designed to be capacity protected. Additionally, construction of such details demands precision. To overcome these challenges, two new connection details are envisioned. Both details completely eliminate penetrating of column into the cap beam. In the first detail, the rebar of the cap beam and the column are spliced in the column and joined with a layer of Ultra High Performance Concrete (UHPC). The use of UHPC in the splice region allows the tension development of reinforcing bars over a short length. High workability of UHPC and large tolerances inherent with the suggested details can facilitate and accelerate the on-site construction. In the second detail, to confine the plastic hinge with a limited length in the column, two layers of UHPC were employed. Confining the plastic hinge is achieved by sandwiching a desired length of the column, using normal strength concrete (plastic hinge region) in between two layers of UHPC. The most interesting aspect of this detail is the exact location and length of the plastic hinge. The primary goal of this research is to provide a description of the newly developed details, verifying their structural performance and recommendation of a design guide. These goals are achieved through a diverse experimental and numerical program focused on the proposed connections. Results show that both details are equally applicable to seismic applications and able to achieve adequate levels of ductility. Lack of failure in splice region indicated that UHPC can provide a good confinement and shear capacity even when confining transverse reinforcement was not used.

Yes / Super-fine stainless wires (SSWs) with micron diameter and large specific surface area can simultaneously strengthen and toughen reactive powder concrete (RPC) at low volume fraction, so SSW reinforced RPC composites have potential for developing infrastructures bearing fatigue load or with aseismic requirements. In this paper, the uniaxial compressive fatigue characteristics of such composites under high stress levels were investigated, and the modification mechanisms of SSWs to RPC were revealed through failure state and microstructure analyses. The results showed that incorporating only 0.5 vol.% SSWs into RPC enables the fatigue life and energy dissipation capacity to increase by 252.0% and 262.3%, meanwhile, the fatigue limit strength of composites at the failure probability of 50% reaches up to 76.6% of static uniaxial compressive strength, due to the improvement effect on microstructure compactness, inhibiting effect on flaw initiation, and the ability to convert single main crack into radial multiple micro cracks centered on SSWs. Furthermore, the average maximum fatigue strain and residual strain of composites are improved by 73.7% and 87.2%, respectively, which can be ascribed to the bridging, debonding and being pulled-off effect of SSWs. It can be therefore concluded that the incorporation of SSWs endows RPC with excellent fatigue performance, thus further enlarging the application of composites. / The authors would like to thank the National Science Foundation of China (51908103 and 51978127), and the China Postdoctoral Science Foundation (2019M651116) for providing funding to carry out this investigation.

Yes / Utilizing seawater and sea-sand for producing ultra-high performance concrete (UHPC) can substantially reduce raw materials costs and alleviate the current freshwater and river sand resources shortage in coastal and marine areas. However, the corrosion risk to reinforcing fibers inside UHPC caused by chlorides in seawater and sea-sand cannot be ignored. In this study, a new type of sustainable UHPC composed of seawater and desalinated sea-sand (UHPSSC) reinforced with stainless profile, super-fine stainless wire (SSW) was developed. Its mechanical properties and chloride content were studied. The research results show that SSWs do not rust after immersion in seawater. The flexural and compressive strengths of UHPSSC incorporating 1.5% SSWs are 13.8MPa and 138.6MPa, respectively, and the flexural toughness of UHPSSC is increased by 428.9%, reaching the basic mechanical requirements of UHPC. The high specific surface area of SSW and enrichment of silica fume on its surface enhance the interfacial bond between fiber and matrix, further promoting the full play of the SSWs’ reinforcing mechanisms as proved by the decrease of the Ca/Si ratio at the SSW surface. The C-S-H gels with a high Ca/Si ratio within the ITZ as well as Friedel’s salt are conducive to immobilize chlorides, blocking the migration of chlorides through the matrix and further mitigating the risk of long-term chloride corrosion of SSWs. Overall, utilizing seawater and desalinated sea-sand in combination with SSWs can produce UHPC with improved strength and toughness, making it a suitable choice for applications where high durability and long-term mechanical performance is required.

Yes / This paper numerically investigates flexural performance of Ultra-High Performance Concrete (UHPC) beam reinforced with Steel-Fibre-Reinforced Polymer (FRP) Composite Bars (SFCBs) in terms of flexural stiffness, moment capacity, deflection, ductility and energy dissipation. The effect of various parameters, include the inner steel core area ratio of SFCB, yield strength of inner steel core, elastic modulus and ultimate strength of outer-wrapped FRP, reinforcement ratio, type and strength of concrete were studied. The results demonstrate that the inner steel core area ratio of SFCB, reinforcement ratio and the elastic modulus of SFCB's outer FRP have significant effect on the overall flexural performance of SFCB reinforced UHPC beam. The overall flexural performance of SFCB reinforced UHPC beam is slightly improved by increasing the yield strength of inner steel core of SFCB, but not affected by the ultimate strength of SFCB's outer FRP when specimen occurred compression failure. The results also exhibit that the flexural performance of UHPC beam reinforced with SFCBs is significantly improved when compared to those of reinforced high strength concrete (HSC) beam and normal strength concrete (NSC) beam. The flexural stiffness and the moment capacity of SFCB reinforced UHPC beam at the ultimate point were 2.0 and 2.4 times, respectively, of those of reinforced NSC counterpart. / Natural Science Foundation of Jiangsu Province, China (BK20201436), the China Postdoctoral Science Foundation (2018M642335), the Science and Technology Project of Jiangsu Construction System, China (2018ZD047, 2021ZD06), the Science and Technology Project of Gansu Construction System, China (JK2021-19), the National Natural Science Foundation of China (51678514), the Science and Technology Innovation Fund of Yangzhou University, China (2020-65), the Open Foundation of Jiangsu Province Engineering Research Center of Prefabricated Building and Intelligent Construction, China (2021), the Science and Technology Cooperation Fund Project of Yangzhou City and Yangzhou University, China (YZU212105), the Practice and Innovation Plan for Postgraduates in Jiangsu Province, China (SJCX21_1589), the Blue Project Youth Academic Leader of Colleges and Universities in Jiangsu Province, China (2020) and the Deputy General Manager Science and Technology Project of Jiangsu Province, China (FZ20200869). References

Yes / Ultra-high performance concrete (UHPC) is an innovative cementitious composite, that has been widely applied in numerous structural projects because of its superior mechanical properties and durability. However, ensuring the safety of UHPC structures necessitates an urgent need for technology to continuously monitor and evaluate their condition during their extended periods of service. Self-sensing ultra-high performance concrete (SSUHPC) extends the functionality of UHPC system by integrating conductive fillers into the UHPC matrix, allowing it to address above demands with great potential and superiority. By measuring and analyzing the relationship between fraction change in resistivity (FCR) and external stimulates (force, stress, strain), SSUHPC can effectively monitor the crack initiation and propagation as well as damage events in UHPC structures, thus offering a promising pathway for structural health monitoring (SHM). Research on SSUHPC has attracted substantial interests from both academic and engineering practitioners in recent years, this paper aims to provide a comprehensive review on the state of the art of SSUHPC. It offers a detailed overview of material composition, mechanical properties and self-sensing capabilities, and the underlying mechanisms involved of SSUHPC with various functional fillers. Furthermore, based on the recent advancements in SSUHPC technology, the paper concludes that SSUHPC has superior self-sensing performance under tensile load but poor self-sensing performance under compressive load. The mechanical and self-sensing properties of UHPC are substantially dependent on the type and dosage of functional fillers. In addition, the practical engineering SHM application of SSUHPC, particularly in the context of large-scale structure, is met with certain challenges, such as environment effects on the response of SSUHPC. Therefore, it still requires further extensive investigation and empirical validation to bridge the gap between laboratory research and real engineering application of SSUHPC. / The full-text of this article will be released for public view at the end of the publisher embargo on 28 Dec 2024.

Yes / In order to promote the utilization of high strength materials and application of prefabricated structures, flexural behaviour of section steel-precast UHPC (Ultra-High performance concrete) slab composite beams prefabricated with bolt shear connectors are numerically simulated by the finite element (FE) software ABAQUS. The model is verified by three prefabricated steel-concrete composite beams tested. Numerical analysis results are in good accordance with experimental results. Furthermore, parametric studies are conducted to investigate the effects of strength of section steel and concrete of precast slab, thickness of section steel, width and height of precast concrete slab, diameters of steel bars and bolt shear connectors. The flexural behaviour of composite beams, in terms of bearing capacity, deflection, ductility and energy dissipation, are compared. The numerical results indicate that the improvement of strength of section steel results in a decrease of ductility, but a significant increase of the ultimate load and energy dissipation. Compared with composite beam made of section steel with thickness of 10 mm, the ultimate load of beams made of section steel with thickness of 14 and 18 mm improve by 29.0% and 58.8%, respectively, the ductility enhance by 2.8% and 8.3%, respectively, and the energy dissipation improve by 8.0% and 12.3%, respectively. With the increase of concrete strength, the ultimate load, deflection and energy dissipation gradually increase. The ductility of steel-UHPC composite beam is the highest, that of steel-HSC composite beam is the lowest. The effect of reinforcement ratio of concrete slab and diameter of shear bolts on the ultimate load of composite beam is limited. Simplified formulae for two different sectional types of proper-reinforced section steel-precast UHPC slab composite beams occurred bending failure are proposed, and the predicted results fit well with the simulated results. The results can be taken as a reference for the design and construction of section steel-precast UHPC slab composite beams.

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