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Ultra-high performance concrete (UHPC) combines advanced fibrous and cementitious material technologies to achieve high strength and exceptional durability. The material tends to have microscopic pores that prevent harmful substances such as water, gas, and chlorides from entering. UHPC can also achieve compressive strengths above 200 MPa and tensile strengths above 20 MPa. It also shows significant tensile strain hardening and softening behavior. Owing to all these characteristics, UHPC has excellent performance, making it a potentially attractive solution for improving the sustainability of construction components. Despite UHPC’s outstanding mechanical properties, superior toughness and ductility, and extraordinary durability, various challenges prevent its widespread use. At the same time, several challenges are currently being faced in the applications of UHPC, which include i) design aspects such as material properties; ii) production technology for large-volume and/or long-span elements with low workability, high spalling, and high shrinkage strains; and iii) unknown durability characteristics after the appearance of long-term concrete cracking. With a lack of industry experience, UHPC specialists face additional challenges in spreading hands-on practice to concrete industry professionals so that the latter can be well versed in applying this sophisticated concrete technology. For these reasons, a comprehensive literature study on recent development trends of UHPC should be conducted to determine its current status and prospects. This article scientifically reviews the current status, carbon capturing capabilities, sustainability aspects, challenges and limitations, and potential applications of UHPC. This state-of-the-art review is aimed at helping scientific researchers, designers, and practitioners widen the use of UHPCs in advanced infrastructure applications. This review will help specialists to develop the design guidelines to enable the widespread application of sustainable UHPC. In doing so, design engineers will be provided with an assurance to fully exploit the high strength and other special properties of UHPC and develop models that can efficaciously estimate the ultimate bearing capacity of UHPC sections under various loading conditions.

Composite floor systems with fin-plate connections are widely used in multi-storey buildings, but there is currently no reported research on the development of a component-based model of a fin-plate connection at the beam-column interface that includes the effect of slab continuity above the fin-plate connection. In this research, a component-based model is developed to simulate a composite fin-plate connection. The component-based composite fin-plate connection model is able to simulate the slab continuity when installed at the beam-to-column interface of a composite floor system model. Fracture criteria for the plates and bolts of the fin-plate connection are adopted in the model to simulate connection failure. The component-based composite fin-plate connection model has been implemented in the software Vulcan, and is validated against a range of existing results, covering tests of individual fin-plate connections at ambient and constant high temperatures, subjected to combinations of tensile force, shear force and moment. The element is also used to simulate a test in which fin-plate connections were implemented at both ends of a composite beam with slab continuity, and subjected to elevated temperatures. The Vulcan modelling results show good comparison with the test results. The proposed component-based composite fin-plate connection model is shown to be a reliable tool to enable the performance-based finite element modelling of full-scale composite beams with fin-plate connections under fire conditions. Subsequently, parametric studies are carried out to investigate the influence of the key parameters, axial restraint stiffness and reinforcement ratio, on the behaviour of the composite beam and the connection force distribution, as well as to compare the very dissimilar structural responses of bare-steel and composite beams with the same geometries and loading conditions in fire.

Building and infrastructure damages, such as tunnels, have become a more important issue because of the continuous expansion of rural and urban constructions. It is well-known that when high-strength concretes (HSCs) are exposed to high temperatures; it is more likely to experience explosive fire-induced spalling than conventional strength concrete. Spalling might result in catastrophic loss of life and damage to nearby critical infrastructure. The exposure of reinforcement bars to elevated temperature, decreased permeability, higher density, moisture transfer, and brittleness of the HSC contribute to spalling. The concrete on a structural member's surface may be violently ripped apart by a high and fast rising temperature during a fire. Despite being a non-combustible material, the physics-chemo-mechanical properties of concrete deteriorate when subject to high temperatures. The magnitude and duration of a fire in a concrete structure define the severity of the fire. The resistance to fire spalling of HSCs under different fire conditions, extremes, and tendencies must be explored urgently. Cementitious materials exhibited a positive impact as an alternative to cement in HSC because they are known as environmentally friendly concrete materials with superior fire-resistant properties. In addition, the inclusion of fibers as an additive reinforcement is adopted to prevent and mitigate fire spalling in HSCs. Therefore, the establishment of appropriate fire-safety measures is a fundamental requirement in building design to ensure the safety of its inhabitants. While the process of fire spalling for HSC during a fire has not yet been completely understood. For this reason, a critical literature study on recent developments in HSC fire-resistance performance should be conducted to determine the present fire spalling behavior of HSC in the event of high temperatures and/or a fire. This article systematically reviews the mechanisms, influential factors, and types of fire spalling. This literature also reviews the behavior, fire spalling modelling, and strategies to prevent spalling in HSC applications. Given the advantages of the research subject, several hotspot research topics for scientific investigations are also suggested to facilitate the widespread use of HSCs in advanced construction applications.

Although a novel inorganic family of geopolymer concrete (GPC) is a promising building material. The need for understanding its resistance against fire at high temperatures is considered essential to ensure its long-term durability. Physical examinations of the degree of cracking, spalling, brittleness, and loss of strength in GPC upon exposure to high temperatures and during fires provide an indicator of their resilience to such conditions. The addition of recycled fibers (RFs) to GPC has been reported as a strategy for overcoming these limitations and preventing concrete microstructure deterioration. Therefore, the development of RF-reinforced GPC (RF-RGPC) to resist fire has become research imperative. The use of RFs derived from industrial wastes provides additional benefits, such as waste reduction, resource conservation, reduced processing costs compared with virgin fibers, and the elimination of waste disposal in landfills. Moreover, RF-RGPC is an inorganic polymer binder made through the alkali activation of reactive aluminosilicate materials that comprise RFs, which increase its structural reliability. In this regard, conducting a critical literature review of current updates related to the fire performance of RF-RGPC subjected to elevated temperatures and during fires is urgently necessary. This study provides critical reviews on the type of RFs, spalling mechanism, physical inspection and properties of RF-RGPCs. It also comprehensively demonstrated the influence of fire on the properties of RF-RGPC after high temperature exposure. The major findings of this study are expected to introduce this unique, cutting-edge, accessible, and environment-friendly RF-RGPC as a promising, durable and heat- and fire-resistant building material for the current infrastructure and sustainable construction industries.

Conductive nanocomposites, enabled by their piezoresistivity, have emerged as a new instrument in structural health monitoring. To this end, studies have recently found that electrical resistance tomography (ERT), a non-destructive conductivity imaging technique, can be utilized with piezoresistive nanocomposites to detect and localize damage. Furthermore, by incorporating complementary optimization protocols, the mechanical state of the nanocomposites can also be determined. In many cases, however, such approaches may be associated with high computational cost. To address this, we develop deep learned frameworks using neural networks to directly predict strain and stress distributions -- thereby bypassing the need to solve the ERT inverse problem or execute an optimization protocol to assess mechanical state. The feasibility of the learned frameworks is validated using simulated and experimental data considering a carbon nanofiber plate in tension. Results show that the learned frameworks are capable of directly and reliably predicting strain and stress distributions based on ERT voltage measurements.

High strength construction materials are now attractive owing to their economic and architectural advantages. The higher the material strength, the smaller member size is required. Ultra-high strength concrete (UHSC) encased columns are being developed for the erection of high-rise buildings due to their higher load bearing capacity and smaller cross section size compared to normal strength concrete encased columns. When the UHSC is subject to elevated temperature, explosive fire-induced spalling is more often observed than in normal strength concrete. The consequence of spalling could cause serious life loss and damage to the close key infrastructure. Spalling is mostly due to the UHSC increased density, lower permeability and brittleness. Most of the previous studies show that polypropylene fibres have been found\ud effective in preventing fire spalling. The aim of this experimental study is to discover the minimum polypropylene fibre dosage to control the fire spalling of steel fibre reinforced concrete of 115-135 MPa strength. The experimental study was carried out on 15 concrete specimens with different parameters and two fibre-reinforced concrete encased columns exposed to ISO 834 fire. The study indicates that a polypropylene fibre dosage of 1.365 kg/m3 can prevent the 115-135 MPa ultra-high strength concrete from explosive fire spalling. This polypropylene fibre dosage is lower than that proposed in Eurocode 2, which is 2 kg/m3. The proposed lower polypropylene fibre dosage can potentially bring sustainability (use less polypropylene fibres that are made of crude oil) and economy, as well as improve constructability by improving the workability of fresh concrete. It is also found steel fibres may relieve the fire spalling but not adequate to prevent spalling. Moreover, there is no significant effect of the size and inner temperature of the centre of the concrete specimen on spalling

Butt weld connection is one of the most commonly used connection types in steel structures, and its post-fire mechanical property is crucial for the estimation of the residual mechanical capacity of steel structures after building fires. To study the mechanical properties of butt weld connections after being exposed to high temperatures, Q235 and Q345 butt weld specimens were designed, heated to various high temperatures between 400 °C and 800 °C, and then naturally cooled to room temperature. Tensile tests were conducted on these butt weld specimens to obtain the force–displacement curves and relevant mechanical properties (yield and ultimate strengths) at various temperatures. The following conclusions were obtained from the test results: (1) The post-fire mechanical properties of the butt weld specimens were affected by material grade and heating temperature; (2) when the temperature exceeded 600 °C, the yield and ultimate strengths of the Q235 and Q345 butt weld specimens began to decrease; the strength reduction of the latter was greater than that of the former; (3) when the temperature was 800 °C, the yield strength and ultimate strength of Q235 decreased to 87% and 91% of the ambient-temperature yield and ultimate strengths, respectively; and (4) the yield and ultimate strengths of Q345 decreased to 83% and 87% of those at room temperature. Computational formulas for the yield and ultimate strengths of the butt weld specimens at high temperatures were also fitted and verified with test data to provide a safety evaluation method for steel structures after a fire.

PurposeMüller cells, a major type of glial cell found in the eye, are postulated to play an important role in many retinal diseases, including diabetic retinopathy (DR). Complement is an integral part of innate immunity, and the activation of complement has been associated with retinal diseases. However, the role of complement in the regulation of Müller cell function remains unclear. We were trying to address these issues in this study.MethodsUsing primary human Müller cells and a spontaneously immortalized human Müller cell line, we examined the expression of complement receptor C5aR both at mRNA and protein levels. Regulation of C5aR expression on Müller cells by prostaglandin E2 and by hyperglycemia, both of which are integrally involved in DR, were studied. Significance of C5aR on Müller cells was also investigated by examining relevant cytokine productions and their impacts on retinal endothelial cell proliferation/permeability after ligating the receptor using its ligand, C5a.ResultsC5aR is constitutively expressed in human Müller cells. Prostaglandin E2 and hyperglycemia individually and synergistically upregulate C5aR expression in Müller cells. Signaling through C5aR on Müller cells upregulates production of IL-6 and VEGF, which promotes the proliferation of human retinal endothelial cells and increases their permeability.ConclusionsThese results indicate that complement can regulate Müller cells through C5aR, which may contribute to the pathogenesis of retinal diseases, including DR.

Background. Routine culturing of patients in intensive care units (ICUs) for methicillin-resistant Staphylococcus aureus (MRSA) identifies unrecognized carriers and facilitates timely isolation. However, the benefit of surveillance in detecting prevalent and incident carriers likely varies among ICUs. In addition, many assessments underestimate the incidence of acquisition by including prevalent carriers in the at-risk population. Methods. We performed a retrospective cohort study using accurate at-risk populations to evaluate the range of benefit of admission and weekly surveillance cultures in detecting otherwise unrecognized MRSA in 12 ICUs in 5 states. Results. We assessed 142 ICU-months. Among the 12 ICUs, the admission prevalence of imported MRSA was 5%-21%, with admission surveillance providing 30%-135% increases in rates of detection. The monthly hospital-associated incidence was 2%-6%, with weekly surveillance providing 7%-157% increases in detection. The common practice of reporting incidence using the total number of patients or total patient-days underestimated incidence by one-third. Surgical ICUs had lower MRSA importation but higher MRSA incidence. Overall, routine surveillance prevented the misclassification of 17% (unit range, 11%-29%) of "incident" carriers, compared with clinical cultures, and increased precaution days by 18% (unit range, 11%-91%). Conclusions. Routine surveillance significantly increases the detection of MRSA, but this benefit is not uniform across ICUs, even with high compliance and the use of correct denominators. © 2006 by the Infectious Diseases Society of America. All rights reserved.