Use Of Ultra-high Performance Concrete Research Articles

Study on workability and mechanical strength of low cement ultra-high performance concrete with ultrafine quartz powder as alternative material under high temperature curing

High CO2 emission has been a key issue that needs to be addressed for the widespread use of ultra-high performance concrete (UHPC). In this study, low cement UHPC was prepared by using ultrafine quartz powder (UQP) as a replacement material for cement, and the effects of UQP on workability and mechanical strength were investigated. The TG, XRD, MIP, and SEM methods were used to study the effects of UQP on hydration products and pore structure of UHPC. Results showed that the addition of UQP reduced the fluidity, shortened the setting time, and increased the drying shrinkage of UHPC. Under high temperature curing, when the amount of cement replaced by UQP was 15%, the maximum compressive strength of UHPC at 7 d reached 147.9MPa. Meanwhile, the compressive strength of UHPC at 7 d was still as high as 132.8MPa when the amount of cement replaced by UQP was 75%. Under high temperature curing, Ca(OH)2 in UHPC reacted with UQP to produce more C-S-H resulting in a decrease in total porosity and an increase in gel pores of UHPC. Under the simultaneous guarantee of mechanical properties and sustainability of UHPC, the replacement of cement by UQP for the preparation of UHPC can reduce the consumption of cement to 188kg/m³.

Experimental and numerical investigation on layered UHPC beams incorporated with recycled macro fibers

The high cost of production is a major hindrance to the wider use of ultra-high performance concrete (UHPC). Recently, the authors’ group has proposed to replace expensive steel fibers in UHPC using macro fibers mechanically recycled from the solid waste of glass-fiber-reinforced polymer (GFRP). Such a concept has been justified by a series of tests, whose results indicate that the recycled macro fibers are effective in mitigating the development of cracks. However, a somewhat negative impact on UHPC strength would be generated by macro fibers. To lower the negative effect on concrete strength at the compression area and further increase the added value of macro fibers, this paper attempted to employ the layered UHPC structure, in which only the tension layer was reinforced with macro fibers. A total of 30 layered UHPC beam specimens were prepared and tested. The test variables comprised of the thickness of the bottom layer and the macro fiber volume fraction within the bottom layer. In addition, the fiber re-arrangement analysis was performed. The results revealed that, under the layer thickness of 50 mm, when the macro fiber volume fraction increased from 2 % to 6 %, the flexural toughness increased from 58.87 to 136.59 J (132.02 % enhancement). The maximum fiber efficiency was reached at the group with a fiber fraction of 2 % and a bottom layer thickness of 50 mm. Furthermore, numerical simulation was conducted to evaluate the feasibility of the tensile constitutive relation of UHPMFRC in the layered structure. The results indicated that it could not be directly used as model input in the numerical simulation of layered UHPMFRC structures when a strong fiber alignment effect was exhibited.

Shear behavior of FRP-UHPC composite beams enhanced by FRP shear key: Experimental study and theoretical analysis

To investigate the shear behavior of FRP (fiber reinforced polymers)-UHPC (ultra-high performance concrete) composite beams, four-point bending tests were conducted on seven FRP-UHPC specimens and two FRP-NSC (normal strength concrete) specimens, having different width and depth of concrete flange as well as FRP shear key (FSK) spacing. The slip between FRP profiles and concrete flange was controlled by employing FSK and epoxy resin bonded hybrid connection. The failure pattern, load-deflection/strain curves, and sliding response of composite beams were analyzed to study the influence of concrete type, FSK spacing, width and thickness of concrete slab. The results indicate that FRP-UHPC composite beams exhibited shear failure, while FRP-NSC composite beams experienced bending-shear failure. The composite beams demonstrated shear-lag effect, which became more pronounced with the increasing of the concrete slab width. The use of UHPC, reducing FSK spacing, and increasing the size of cross-section of concrete flange can effectively enhance the shear performance and reduce interface sliding. Formulae were developed to predict the shear capacity and deflection, considering shear deformation. The results predicted by the formulae developed match well with the experimental results.

Experimental and analytical study on flexural behavior of corroded RC beams strengthened with CFRP rods and UHPC

Recent research confirms that concurrent use of Ultra-High Performance Concrete (UHPC) and Carbon Fiber Reinforced Polymer (CFRP) yields superior strengthening effects on RC structures compared to individual applications. However, this combined strategy is underutilized in research on corroded structure strengthening. This study investigates the flexural behavior of corroded RC beams strengthened with UHPC and CFRP rods through experimental and numerical analyses. A total of 13 RC beams were designed with different corrosion levels (0 %−20 %) and strengthening forms (U-strengthened, T-strengthened). The four-point bending test results indicate a substantial increase in peak moments for the strengthened beams, with U-strengthened beams exhibiting higher bearing capacity than T-strengthened ones. Additionally, the failure mode of the strengthened beams tends to be brittle. Sectional analysis results demonstrate that before the longitudinal reinforcement yield, it mainly governs the sectional moment, while after yielding, CFRP rods control the moment. Moreover, UHPC tensile stress makes a non-negligible contribution to the moment.

Dynamic behaviour of ultra-high performance concrete beams with rectangular openings subjected to impact loads

To facilitate residents’ needs, contemporary building structures often incorporate prefabricated transverse openings in reinforced concrete (RC) beams to accommodate pipeline installations. However, these openings can potentially impact the load-bearing capacity of the beams, particularly as structures increasingly need to consider dynamic loading effects. The use of ultra-high performance concrete (UHPC) has proven effective in enhancing the dynamic resistance of RC beams with openings. This study employs numerical simulations in ANSYS/LS-DYNA to investigate the dynamic response of UHPC beams with rectangular openings exposed to low-velocity impact. The calibrated Continuous Surface Cap (CSC) model is primarily validated through quasi-static four-point loading tests on UHPC beams with openings. Following this validation, numerical simulations of drop hammer impact are carried out to comprehensively analyse the behaviour of UHPC beams with openings. Furthermore, parametric investigations are performed to evaluate the impact response of UHPC beams with large or small openings, considering various design factors such as opening size, opening position, stirrup quantity and UHPC strength level.

A comparative study between ultra-high-performance concrete structures and normal strength concrete structures exposed to fire

The use of ultra-high-performance concrete (UHPC) in civil infrastructure is increasing due to its numerous advantages compared to normal strength concrete (NSC). In this research, thermal analysis of NSC and UHPC beams and columns was developed to understand and compare the fire performance of these structures. A numerical analysis was performed using finite element (FE) modeling with ABAQUS software. Compared to NSC, UHPC structures in some cases have lower fire resistance due to their slender cross-sections and unfavorable thermal properties and mechanical capacity degradation due to temperature effect. The results show that UHPC structures experience significantly higher cross-sectional temperatures when exposed to fire compared to NSC. The results are particularly relevant for high-rise buildings, where fire safety requirements are more stringent and the use of UHPC is attractive, leading to an unprecedented contradiction. Alternative strategies for the application of UHPC, such as the contradictory increases in cross-section or the use of fire protection coatings, must be considered. In some cases, NSC may be more attractive as a structural material than UHPC if structural fire design requirements are taken into account.

Effect of shrinkage-mitigating additive and curing condition on flexural and fracture behavior of ultra-high-performance concrete (UHPC) unnotched beam

The study aims to examine how the flexural and fracture behavior of UHPC is impacted when shrinkage is mitigated by adding shrinkage-mitigating additives. Furthermore, due to the consistent use of UHPC for structural repair and reinforcement throughout the year, including emergency construction in winter, it is necessary to carry out construction operations in winter conditions. Thus, this study adopts the natural cold curing condition of UHPC specimens to mimic real-world outdoor construction settings, while also using the standard curing condition as a comparison. The bending test was performed on three different types of UHPC materials: material 1 without a shrinkage-reducing agent (SRA) or expansive agent (EA), material 2 with 1 % SRA, and material 3 with 1 % SRA and 7.5 % EA. Fracture and flexural behavior of UHPC beams were studied, and Spearman's correlation between shrinkage and flexural/fracture toughness was evaluated. The study revealed that adding SRA/EA decreased the mean flexural tensile strength of specimens cured in standard conditions. Additionally, specimens cured in natural conditions showed less flexural tensile strength when SRA/EA was added. Furthermore, when compared to material 1, the addition of SRA and EA greatly reduced the fracture energy of UHPC, resulting in reductions of 21.9 % and 26.6 %, respectively, for materials 2 and 3. The fracture toughness showed a modest correlation with the shrinkage behavior, and the fracture energy exhibited a high association with the shrinkage behavior. The research findings can provide references for UHPC applications in natural winter conditions when the material contains shrinkage-mitigating additives.

Review of Behavior Flexural Strengthened RC Beams Using Ultra-High Performance Concrete

The use of ultra-high performance concrete (UHPC) to reinforce existing reinforced concrete (RC) structures in flexure has made great strides in research recently. In addition to creating an experimental archive, the research provided a thorough technical literature review. The effectiveness of UHPC strengthening schemes for RC beams was assessed by examining the effect of size on the flexural strengthening performance of RC members with UHPC. Various dimensions of RC elements were considered in order to understand any possible size-related effects. Factors like material strength and stiffness of the current RC members were considered because they could affect the strengthening's overall effectiveness. To comprehend how the strengthening of the UHPC would impact the overall. In order to find the most successful strategy, various UHPC strengthening configurations were examined. prior to applying the UHPC, the concrete substrate must be prepared. The experimental results from the studies under review indicate that UHPC is a promising reinforcement that can successfully provide RC beams flexural strength. The plain overlay's bending capacity increased by 20% to 60% when the thickness of the UHPC overlay was increased within the range of 30 to 50 mm. In contrast to plain overlays, the reinforced overlay resulted in a notable 40%–85% increase in flexural capacity. To assist stakeholders in making decisions, a cost comparison of UHPC with other strengthening techniques, such as carbon fiber reinforced polymers (CFRP), was provided. The study concludes by highlighting the potential of UHPC as a workable option for flexural strengthening of existing RC structures and offers insightful information for furthering the advancement and application of this technology in the building sector.

Experimental and simulative analysis of flexural performance in UHPC-RC hybrid beams

With high strength, excellent durability, and cracking resistance, ultra-high-performance concrete (UHPC) has gradually become popular. In this study, a novel hybrid beam was designed to fully harness the cracking resistance and tensile strength of UHPC. A series of experiments were conducted to investigate the influence of UHPC layer depth and steel bar diameter on the flexural performance of UHPC-RC hybrid beams. The experimental results indicated that the use of UHPC in the tensile zone of UHPC-RC hybrid beams can significantly improve the bearing capacity, crack resistance, and ductility of the structure. Based on the application of cohesive zone model (CZM), a finite-element (FE) model was proposed to simulate the mechanical behavior of the UHPC-RC hybrid beams, and the cohesive elements were used to represent the potential fracture surfaces of UHPC (concrete) and the rebar-concrete interface. A constitutive model for potential fracture of UHPC, taking into account the bridging effect of fibers, has been proposed. This FE model can reflect the fracture behavior of UHPC-RC hybrid beams. The simulation results demonstrate that the proposed model can accurately simulates the mechanical response and fracture behavior during the whole fracture process. Based on the results obtained from the experiment and simulation, a theoretical method for predicting the bearing capacity of UHPC-RC hybrid beams was developed, which can provide the reference for the design of similar structures.

Pull-out behavior of cluster stud-post pouring UHPC connectors in prefabricated steel-concrete composite beam

The use of ultra-high performance concrete (UHPC) as a connection material for cluster studs of prefabricated steel-concrete composite beams can achieve higher connection strength and less space for reserved holes. However, in addition to bearing the shear force, the studs need to bear the pull-out force to counteract the vertical relative separation between the steel and concrete. The pull-out behavior for cluster stud-post pouring UHPC connectors is complex and has not been clarified completely. Thus, a total of 30 cluster stud pull-out tests in 10 groups were carried out in this study, and the interface type, length-to-diameter ratio of the stud, transverse spacing of stud group, dimensions of the reserved holes, and type of post pouring concrete were considered. The results showed that the pull-out behavior of the cluster studs was different from that of studs embedded in cast-in-place intact UHPC slabs due to the UHPC conical integrity having been reduced significantly by the old-to-new concrete interface. The rough groove interface and UHPC as a post pouring material significantly improved the pull-out capacity and stiffness of the cluster studs. The stud fracture belongs to ductile failure, whereas UHPC and normal concrete (NC) cone failures are brittle. The bearing capacity of the UHPC cone is observed to increase with the effective embedment depth of the stud, the transverse spacing, and the dimensions of the reserved holes. The angle of the UHPC conical failure surface is 70° based on 3D laser scanning. Finally, the theoretical equations for predicting the pull-out capacity of stud-post pouring UHPC connectors with a rough groove interface were proposed, and the critical length-to-diameter ratio of the stud was calculated for different combinations of stud and UHPC strength.

Seismic performance of precast concrete sandwich walls with bolt-steel plate connection

The bolt-steel plate connection stands as a dry connection method in precast structures characterized by its simplicity, high efficiency, ease of assembly and disassembly, and environmental protection. Five precast concrete sandwich walls (PCSWs) with glass fiber-reinforced polymer (GFRP) to connect the interior and exterior concrete wythes were designed and tested to investigate the seismic performance of such walls under cyclic loads. Ultra-high performance concrete (UHPC) was used to strengthen the bolt-steel plate connection joint. This study investigated the effect of the sandwich wall between the two bolt-steel plate connection joints, opening, and UHPC on the seismic performance of PCSWs. The findings revealed that the sandwich wall between the two bolt-steel plate connection joints, UHPC, and the interface between UHPC and ordinary concrete had a significant influence on the failure modes, including four failure modes: shear failure of bolt-steel plate connection joint, concrete crushing at the wall toe and through-crack of the shear oblique cracks and horizontal joint, shear failure at the interface between the solid and sandwich walls, and shear failure typified by a "Keyway" configuration. The use of UHPC to strengthen the bolt-steel plate connection area could significantly improve the load-bearing capacity and peak drift ratio. Whether the sandwich wall was used in the non-bolt-steel plate connection area in the horizontal joint zone had minimal influence on both the load-bearing capacity and peak drift ratio. For the walls without UHPC strengthening, the ultimate load and ultimate drift ratio could be increased by using the sandwich wall between the two bolt-steel plate connection areas, however, it was the opposite when UHPC strengthening was used. The paper also compared the sandwich walls with the solid walls, and the results showed that the sandwich wall with bolt-steel plate connections had good seismic performance.

Finite element analysis of progressive collapse resistance of precast concrete frame beam-column substructures with UHPC connections

Compared with reinforced concrete structure, precast concrete structure is prone to progressive collapse due to its poor continuity. The use of ultra-high performance concrete (UHPC) provides a feasible solution. To this end, investigate the influence of UHPC on the progressive collapse resistance of precast beam-column substructures, the finite element model of precast beam-column substructures with UHPC connections was established. The model was validated using available experimental data. Specifically, the cohesive-Coulomb friction model was used to simulate the interface behavior between precast concrete and cast-in-place concrete, and the metal ductile damage model was used to simulate rebar failure. The finite element simulation results show good agreement with experimental results, with an average error of less than 5 %. Additionally, five sets of full-scale analysis models were designed to analyze the effect of cast-in-place UHPC on the progressive collapse resistance of precast beam-column substructures. The results indicated that UHPC enhances the compressive arch action (CAA) capacity and catenary action (CA) capacity of precast beam-column substructures. Parametric analysis was conducted based on these models. The results indicated that the increase of UHPC strength grade can improve the CAA capacity of the structure, but reduce the CA capacity. Interface roughness has a certain effect on CAA capacity, but has no obvious effect on CA capacity. Finally, the accuracy of existing analytical models in predicting the CAA and CA capacity of UHPC-connected precast beam-column substructures is evaluated. The research results can provide reference for the design and application of precast concrete structures connected by UHPC.

Quasi-static tests and seismic fragility analysis of RC bridge piers with high-strength steel bars and high-strength/ultra-high performance concrete

The use of high-strength steel bars (HSSB), high-strength concrete (HSC) and ultra-high performance concrete (UHPC) in bridge piers can obviously improve bearing capacity and save material consumption. However, the use of high strength materials may detrimentally affect the seismic performance of reinforced concrete (RC) piers. This paper tries to study the seismic performance of RC piers with HSSB and HSC/UHPC by quasi-static tests and seismic fragility analysis. Three RC piers, solid pier with normal strength steel bars (NSB) and normal strength concrete (NSC), solid pier with HSSB and HSC, and hollow pier with HSSB and UHPC, were designed and tested under quasi-static loading. The failure mode, hysteretic performance, stiffness degradation and residual displacement of three specimens were compared and analyzed. A fiber-based beam-column finite element model (FEM) was developed to simulate the nonlinear response of RC piers with HSSB and HSC/UHPC. On this basis, the seismic fragility analysis was performed to study the effects of high-strength materials on the seismic performance of RC piers. Research results show that, compared with NSC piers, HSC piers reinforced with a small amount of HSSB still exhibited slightly larger lateral bearing capacity but lower deformability due to the higher brittleness of HSC. The UHPC hollow pier presented obviously larger deformation capacity, and more slow decline speed of lateral stiffness than NSC and HSC solid piers. Meanwhile, the matching use of UHPC and HSSB in hollow pier can improve the elastic deformation, and then reduce residual displacement of RC piers. The proposed fiber-based finite element model (FEM) can simulate the nonlinear response of RC piers with different high-strength materials with reasonable accuracy. Fragility results demonstrate that, HSC pier presents lower seismic fragility than NSC pier at different damage states except for collapse due to lower ductility of HSC pier. The UHPC hollow pier with HSSB has lower seismic fragility than NSC and HSC solid piers at the same seismic intensity. Overall, the hollow pier with HSSB and UHPC can maintain good seismic performance while greatly saving material consumption.

Assessing durability properties of ultra-high performance concrete-class materials

Ultra-high performance concrete (UHPC) is a class of concrete materials that has received significant attention from the infrastructure community due to its favorable mechanical and durability performance. As the use of UHPC in infrastructure projects is becoming more common, there is an increasing interest in identifying appropriate testing techniques to assess the durability properties of UHPC-class materials. The dense microstructure of UHPC-class materials and the presence of a high concentration of fiber reinforcement have made it difficult to rely on existing standard testing approaches for concrete durability assessment. This study explores the application of various conventional-concrete durability test methods to UHPC, including electrical resistivity (American Association of State Highway and Transportation Officials (AASHTO) TP 119-22), freeze–thaw (ASTM C666), water absorption (ASTM C1585), and rapid chloride migration test (NT BUILD 492). The selected tests are meant to qualify and quantify the microstructural penetrability of UHPC to ions and fluids, a surrogate property commonly used as an indicator of durability. The findings from this study indicate that electrical resistivity can be used as a durability indicator for UHPC-class materials. Moreover, strong correlation between electrical resistivity and the chloride migration coefficient is identified, a potential benefit given that chloride migration can be used to estimate service lives of UHPC-class materials. Other tests, including freeze–thaw and water absorption, although identifying the favorable performance of UHPC relative to conventional concrete, were unable to provide insightful information through which the performance of individual UHPCs could be differentiated.

Degradation Mechanism of Ultra High-Performance Concrete under Coupling Erosion of Salt and Frost

Abstract With the use of ultra high-performance concrete (UHPC) in frozen areas, UHPC structures suffer from severe erosion under the interaction of salt ions and frost, resulting in significant performance degradation of UHPC structures. However, the performance degradation mechanism of different compositions and structures of UHPC under the coupling erosion of salt and frost is still unclear at present. In order to study the degraded behavior and mechanism of UHPC under the coupling erosion of salt and frost, various UHPCs were prepared and exposed to freeze–thaw (F-T) cycles and salt–freeze–thaw (S-F-T) cycles. The mass and compressive strength of the UHPCs before and after the F-T and S-F-T tests were compared to evaluate the performance degradation of UHPCs. The SPSS software correlation method, scanning electron microscope, and mercury intrusion porosimetry tests were used to analyze the mechanism of the coupling erosion of salt and frost on the UHPCs. Results indicate that UHPC with a lower water–binder ratio (WBR) and higher superplasticizer content exhibits better resistance to the coupling erosion of salt and frost. The resistance of UHPC to the coupling erosion of salt and frost will decline with the rise of WBR, and the WBR is the most significant factor affecting the coupling erosion of salt and frost for UHPC. The coupling of salt and frost decreases the compressive strength and leads to cracking of UHPC, which can be ascribed to the larger average pore size and higher cumulative pore volume caused by the salt ions. The hygroscopicity of salt ions increases the moisture in pores, and salt crystallization generates pressure in the pores, further aggravating the damage of UHPC.

Effect of competitive adsorption between specialty admixtures and superplasticizer on structural build-up and hardened property of mortar phase of ultra-high-performance concrete

This study aims to enhance structural build-up of ultra-high-performance concrete (UHPC) without influencing the initial flowability, which is critical in repair applications (e.g., use of UHPC in thin bonded overlays for bridge deck rehabilitation). Specialty admixtures, such as a viscosity-modifying admixture (VMA), have been used to enhance the structural build-up at rest. However, the use of specialty admixtures can increase superplasticizer (SP) demand to maintain proper flowability; the synergistic effect of these admixtures on structural build-up is not well understood as the coupled admixture content can reverse the net effect on yield stress, viscosity, and thixotropy. In this study, VMAs including welan gum (WG), diutan gum (DG), and cellulose ether (CE) were used. Styrene-butadiene rubber (SBR) and acrylic ester (AE) latex polymers (LPs) that can enhance structural build-up and bond strength were also incorporated. The competitive adsorption between these specialty admixtures and SP and its effect on structural build-up, early-age hydration, compressive and pull-off strengths, porosity and entrapped air content of UHPC mortar (i.e., without fiber) were systematically investigated. Test results indicated that the incorporation of anionic WG and DG that exhibited high competitive adsorption with SP led to a 275%–450% enhancement in structural build-up despite the 55%–135% increase of SP demand. Such increase was limited to 130% when using CE, SBR, or AE that cannot effectively adsorb onto cement particles in the presence of SP. This was because the high competitive adsorption between specialty admixtures and SP strengthened the particle flocculation and promoted the cement hydration in the first hour; the latter resulted in 20%–40% enhancement in non-reversible component of structural build-up. Furthermore, the use of LP at low and moderate dosages secured high bond strength to normal strength mortar despite 8%–33% decrease in compressive strength given the increased capillary porosity. The use of VMAs increased the entrapped air and resulting 5%–15% lower compressive strength, while the bond strength was not influenced.

Advanced Study of Columns Confined by Ultra-High-Performance Concrete and Ultra-High-Performance Fiber-Reinforced Concrete Confinements

The need for concrete with ‘super’ strength and ‘super’ ductility for greater sustainability has been answered by the existence of ultra-high-performance concrete (UHPC) and ultra-high-performance fiber-reinforced concrete (UHPFRC). Over the last decades, UHPFRC has been implemented in actual concrete structures, as well as used to retrofit structural elements, including columns. However, the use of UHPC and UHPFRC confinement to strengthen normal concrete columns is still limited. Therefore, this research aims to investigate the advanced performance of columns using UHPC and UHPFRC confinement in the context of the strength and ductility of such columns, such as load capacity, stress–strain behavior, and the crack pattern in the failure mode. This research is an advanced study of several investigations previously carried out by other authors on the characteristics of UHPC and UHPFRC, as well as columns confined by UHPC and UHPFRC. The methods used in this research are experimental and analytical. The experimental results were compared to analytical calculations for validation. This research produced 12 short-column specimens confined by UHPC (CF0 series) and UHPFRC (CF1 and CF2 series) that contained 0%, 1%, and 2% fiber and were also tested for axial loading and various eccentricities as follows: e = 0, 35, and 70 mm. The results found that the normal strength concrete (NSC) columns confined by UHPC and UHPFRC could sustain a higher maximum load and stress, and also sustain greater vertical deformation and strain compared to the control specimens. It was noted that specimen CF2-35 had the highest load capacity, vertical deformation, maximum stress, and maximum vertical strain compared to specimen C-0 (control column with no confinement). The specimen CF2-35 (column confined by UHPC with a 2% fiber volume with an eccentricity of 35 mm) also exhibited a ductile failure mode and very minor cracks. It was also found that 75% of the specimens had 0–39% errors and 25% had 0–13% errors. The research proved that the addition of a volume of 2% fiber to the UHPFRC minimizes the crack of the failure mode and prevents confinement spalling of the column. This research has led to the conclusion that UHPC and UHPFRC confinements will increase the strength and ductility of columns.

Effect of UHPC jacketing on the shear and flexural behaviour of high-strength concrete beams

Ultra-high performance concrete (UHPC) is an advanced material which shows high compressive strength, tensile resistance, toughness and durability when compared to conventional concrete. One of the potential applications of UHPC is in the retrofit of ageing or deteriorated reinforced concrete structures. However, limited research exists on the use of UHPC to strengthen higher strength concrete members (with compressive strength exceeding 80 MPa). This paper examines the ability of UHPC to improve the shear and flexural performance of high-strength concrete (HSC) beams. As part of the tests two shear-deficient HSC beams built without stirrups, and having 15M or 20M bars (steel ratios of 1.6% and 2.4%), were retrofitted with a thin UHPC jacket and tested under four-point bending. The results are compared to a control set of HSC beams built with and without stirrups. The effect of steel ratio in the retrofitted beams was also investigated. The results show that the UHPC jacketing significantly increased the shear capacity by 40–125% in the shear-deficient HSC beams, allowing the beams to reach their full flexural resistance. The UHPC retrofit also allowed for improved flexural performance, with increases of 80–85% in stiffness, 20–35% in flexural strength and 40–180% in ductility when compared to the control beams built with stirrups. The failure mode and ductility in the UHPC retrofitted beams was affected by the longitudinal steel ratio, with the failure transitioning from bar fracture to concrete crushing as the steel ratio in the reference HSC beams was increased from 1.6% to 2.4%. To supplement the engineering case, finite element modelling is used to study the influence of other retrofit types, as well as the shear-span-to-depth ratio.

Comprehensive sustainability strategy for the emerging ultra-high-performance concrete (UHPC) industry

The concrete industry is facing significant challenges in substantially reducing CO2 emissions, recycling waste materials and limiting the use of resources. Using ultra-high-performance concrete (UHPC) is one of the many possible solutions to reduce the environmental impact of the concrete industry. Numerous approaches have been applied to meet the challenges of making and utilising UHPC more environmentally friendly; however, an overall approach is lacking. This study aims to fill this gap by constructing a strategy for more sustainable use of UHPC. The strategy is developed by first evaluating measures known from the conventional concrete industry concerning transferability to the UHPC industry. Subsequently, the approach is enrichened with measures targeting the special composition and properties of UHPC. The strategy suggested in the conclusion consists of the following tools: efficient use of cement, efficient use of steel fibres, circularity: utilise by-products, local production, and efficient use of UHPC in structures.

Electromagnetic method field test for characterizing steel fibers in ultra-high performance concrete (UHPC)

The use of ultra-high performance concrete (UHPC) has been growing in the construction industry due to its excellent flexural, tensile, and compressive strengths. The flexural and tensile strength of UHPC is often augmented by the addition of steel fibers. However, the strength of UHPC is highly dependent on the density and orientation distribution of those fibers. Failure to properly distribute the fibers can lead to failures. As a result, steel fiber distributions need to be characterized post-fabrication. Among available testing methods, an electromagnetic technique based on induction sensing had shown significant promise. However, there has been no field experiments to verify fiber density and orientation in real UHPC fabrication. This paper studies the effectiveness of the electromagnetic technique on field-fabricated UHPC. The measurements from our electromagnetic sensor are validated from cores studied with a computed tomography (CT) scan. We demonstrate a 98% correlation between our electromagnetic method and the CT scan results for the orientation, and a root mean square error (RMSE) of 0.295% for the density of the fibers.