Ultra-high-performance Fiber-reinforced Concrete Research Articles

Enhancement of the Shear Capacity of RC Deep Beams with Ultra-High Performance Fiber-reinforced Concrete

This research investigates the shear behavior of Reinforced Concrete (RC) deep beams strengthened with Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC). For this purpose, eight RC deep beams were fabricated and tested for failure. One beam served as a control beam (un-strengthened), while the remaining seven deep beams were strengthened utilizing various strengthening schemes. This experimental study primarily focused on the thickness of the UHPFRC layer, Steel Fiber (SF) volume fraction, and strengthening schemes (jacketing, bilateral layers, and strips exclusively in the shear zone). The experimental findings demonstrated that UHPFRC significantly enhanced the shear capacity, toughness, and stiffness of the RC deep beams. The performance of the strengthened beams exhibited improvements in ultimate shear strength, stiffness, and toughness of about 43.6%, 102.2%, and 171.3%, respectively, higher than that of the un-strengthened deep beam. UHPFRC U-jacketing is a highly effective method for strengthening the RC deep beams. Incorporating SF into the UHPFRC mixture improved the shear properties of the strengthened specimens and delayed fracture propagation. Finally, the shear capacity of the strengthened specimens was compared to the values predicted by the analytical approaches presented in earlier research.

Mechanical anchorage system in retrofitting of RC slabs using CFRP rods and concrete jacket

Over the past few decades, the demand for retrofitting reinforced concrete members has risen dramatically. Retrofitting reinforced concrete slabs with carbon-fiber-reinforced polymer (CFRP) rods and ultra-high-performance-fiber-reinforced-concrete (UHPFRC) jackets is the one of significantly effective techniques. However, the main challenge of employing CFRP rods and UHPFRC jackets technique to strengthen existing reinforced concrete members is the efficiency of using CFRP rods and the debonding issue between old and fresh new concrete jacketing. Debonding mostly occurs between CFRP rods and old concrete, as well as the surfaces of old and new concrete, and is especially prevalent when the slab is subjected to daily repetitive loads such as cyclic loads. In this study, a new retrofitting system utilizing a mechanical anchor system was proposed to improve the bond between the UHPFRC layer and existing slab. This mechanical system incorporates an expandable anchorage bolt and steel plates. Therefore, a benchmark RC slab and two retrofitted RC slabs were experimentally tested under a five-point incremental repeated load (cyclic load) employing the dynamic actuator. The influence of embedded CFRP rods into the jacket of UHPFRC on the performance of system were studied. The experimental results showed that the newly proposed approach was significantly effective in preventing early debonding. In addition, the mechanical system played an essential role by improving the attachment between the jacket and the slab, ensuring better load transfer. A new proposed retrofitting technique improved the capacity of slabs from 164 to 298kN, illustrating an improvement of over 82%. On the other hand, the FE models have been developed to provide both practical validation and deeper analytical insights, ensuring a comprehensive evaluation of the proposed retrofitting system. Experimental data were used to validate the results of the finite-element models, which showed good agreement and high accuracy. Finally, a parametric study was executed to evaluate the impact of various parameters on the performance and efficacy of the new suggested strengthening technique, and to optimize the proposed system parameters, including the diameter of bolts, a normal strength concrete (NSC) jacket with various grades rather than the UHPFRC, applying the proposed retrofitting technique on a compressive side instead of a tension zone, and rebar steel of varying diameters in the jacket instead of CFRP rods. Findings indicated (parametric study) that using anchor bolts with a diameter greater than 12 mm improved the slabs’ ultimate load capacity.

A review of five years’ experience on the effect of fibers on the autogenous healing of Ultra High-Performance Fiber-Reinforced Concrete

A review of five years’ experience on the effect of fibers on the autogenous healing of Ultra High-Performance Fiber-Reinforced Concrete

Abrasion resistant characteristics of UHPC based on high-speed underwater method: Efficiency, process, evaluation, and mechanisms

Abrasion resistant characteristics of UHPC based on high-speed underwater method: Efficiency, process, evaluation, and mechanisms

Development of a New Rubber Buckling-Restrained Brace System for Structures

Buckling-Restrained Braces (BRBs) are widely utilized in structures as an anti-seismic system to enhance performance against lateral excitations. While BRBs are designed to yield symmetrically under both tension and compression without significant buckling, their effectiveness is often limited to moderate seismic events. During high-intensity earthquakes, repetitive yielding can lead to core failure, resulting in the loss of BRB functionality and potentially causing structural collapse. This study proposes an innovative design for BRBs to improve energy dissipation capacity under severe seismic activity. The new design incorporates Ultra-High-Performance Fiber-Reinforced Concrete (UHPFRC) filler and hyper-elastic rubber components as primary load-bearing elements. Through extensive testing and simulation, the proposed Rubber Buckling-Restrained Brace (RBRB) was developed and manufactured by integrating hyper-elastic rubber between the concrete and core to enhance the device’s strength. Additionally, a prototype of the conventional BRB device was fabricated to serve as a benchmark for evaluating the performance of the RBRB. Experimental testing of both the conventional BRB and the proposed RBRB prototypes was conducted using a heavy-duty dynamic actuator to assess the RBRB’s performance under applied loads. Based on the experimental results, an analytical model of the proposed RBRB was formulated for use in finite element modeling and analysis. Furthermore, a specialized seismic design procedure for structures equipped with the RBRB was developed, according to the performance-based design method. This procedure was applied to the design of a seven-story steel structure, and the impact of the RBRB on the seismic response of the structure was investigated through finite element simulations. The analysis results demonstrated that the RBRB significantly improves the loading capacity and energy dissipation capabilities of structures, thereby enhancing their overall performance against earthquake excitations.

Influence of Modified PVA Fiber on Ultra-High Performance Concrete and Its Enhancing Mechanism.

In this study, the properties of ultra-high-performance concrete (UHPC) were enhanced by adding modified polyvinyl alcohol (PVA) fibers. The specimens with different curing ages were evaluated in various aspects to investigate the effects of different dosages, lengths, and surface treatments of PVA fibers on the performance of UHPC. The performance was compared with that of steel fiber-reinforced UHPC with the same ratio and multiple dosages. At the same time, the distribution of fibers and the morphology of fibers were observed by a scanning electron microscope, and the mechanism of fiber reinforcement was discussed. The results showed that the mechanical properties were significantly affected by the fiber dosage, length, and surface treatment. Based on the test results, the optimum PVA fiber addition can increase the compressive strength and flexural strength by 12.0% and 6.0% compared to the control UHPC without fibers. A comprehensive evaluation was carried out and indicated that the optimum PVA fiber addition has the potential to replace 0.5% steel fiber in certain conditions.

UHPFRC structural analysis from a geometrically exact Extended Lumped Damage Mechanics approach

The use of ultra-high-performance fibre-reinforced concrete (UHPFRC) has significantly increased in the recent years. However, the accurate mechanical behaviour modelling of this complex material is still a challenge in the present. Because the materials high load-bearing capacity and the presence of fibbers, this type of problem experiments large displacements before the failure. In this study, the material damage description has been performed by the Extended Lumped Damage Mechanics. Additionally, an approach based on the nodal positions of the Finite Element Method has been utilised, which makes the formulation geometrically exact. Thus, this study evaluates the failure of structures composed of UHPFRC, accounting for the effects of material and geometric nonlinearities computed by the Extended Lumped Damage Mechanics and the Finite Element Method based on positions, respectively.

Numerical study on the flexural and shear behavior of steel fiber and high‐strength steel combination in ultra‐high‐performance fiber‐reinforced concrete beams under cyclic loading

AbstractFiber‐reinforced concrete consists of hydraulic cement, water, aggregate, and discrete fibers, making it a composite material. These fibers, available in different shapes, sizes, and materials such as steel, polymer, glass, and natural fibers, are commonly utilized in structural applications. The tensile strength of conventional concrete tends to decrease as micro‐cracks develop rapidly under applied stresses. However, incorporating closely spaced fibers can hinder the progression of micro‐cracks, leading to a substantial improvement in both tensile and flexural strengths of concrete. Furthermore, fibers can delay the initiation of tensile cracks, effectively enhancing concrete's ability to withstand tensile strains before failure. As a result, fiber‐reinforced concrete exhibits increased durability and enhanced resistance to impacts compared to plain concrete. This study aims to evaluate and compare the cyclic flexural behavior of a cantilever beam constructed from ultra‐high‐performance fiber‐reinforced concrete (UHPFRC) using reinforcing bars made of high‐strength steel (HSS). The beams contain varying relative proportions of longitudinal reinforcement and steel fibers. Various key performance parameters of the cantilever beam were thoroughly examined, such as load capacity, flexural ductility, failure mode, hysteresis response, energy dissipation, and hardness. The study demonstrated that UHPFRC beams with HSS exhibit good cyclic flexural performance prior to failure.

Flexural behavior of GFRP and steel bars reinforced lightweight ultra-high performance fiber-reinforced concrete beams with various reinforcement ratios

Flexural behavior of GFRP and steel bars reinforced lightweight ultra-high performance fiber-reinforced concrete beams with various reinforcement ratios

Incorporating Limestone Powder and Ground Granulated Blast Furnace Slag in Ultra-high Performance Concrete to Enhance Sustainability

While ultra-high performance concrete (UHPC) offers numerous advantages, it also presents specific challenges, primarily due to its high cost and excessive cement content, which can pose sustainability concerns. To address this challenge, this study aims to develop cost-effective and sustainable UHPC mixtures by incorporating ground granulated blast furnace slag (GGBFS) and limestone powder (LP) as partial replacements for portland cement. Eight fiber-reinforced UHPC mixtures were investigated, with a water-to-cementitious materials (w/cm) ratio of 0.15. In four of the UHPC mixtures, 25% of the cement was replaced with GGBFS, and further, LP was added as a mineral filler, partially substituting up to 20% of the cement. In the remaining four mixtures, cement was replaced with only LP up to 20% (without GGBFS). The 28-day compressive strength of the UHPC mixture with 25% GGBFS and 20% LP was 149 MPa, 3.50% lower than the mixture without GGBFS. Its 28-day flexural strength decreased by 30%. Increasing LP replacement reduced drying and autogenous shrinkage, with a 29% shrinkage reduction at 20% LP replacement. Moreover, UHPC mixtures with GGBFS exhibited lower shrinkage compared to those without GGBFS for all LP replacements up to 20%. For evaluating the sustainability of UHPC mixtures, the cement composition index (CCI) and clinker to cement ratio (CCR) were determined. For 20% LP replacement with 25% GGBFS, CCI was 3.6 and the CCR was 0.5, 38% decrease from the global clinker to cement ratio. Overall, 20% LP replacement UHPC mixtures with and without GGBFS can produce UHPC class performance and reduce the environmental impact.

Structural Behavior of Full-Depth Deck Panels Having Developed Closure Strips Reinforced with GFRP Bars and Filled with UHPFRC

The adoption of prefabricated elements and systems (PBES) in accelerating bridge construction (ABC) and rapidly replacing aging infrastructure has attracted considerable attention from bridge authorities. These prefabricated components facilitate quick assembly, which diminishes the environmental footprint at the construction site, alleviates delays and lane closures, reduces disruption for the traveling public, and ultimately conserves both time and taxpayer resources. The current paper explores the structural behavior of a reinforced concrete (RC) precast full-depth deck panel (FDDP) having 175 mm projected glass-fiber-reinforced polymer (GFRP) bars embedded into a 200 mm wide closure strip filled with ultra-high-performance fiber-reinforced concrete (UHPFRC). Three joint details for moment-resisting connections (MRCs), named the angle joint, C-joint, and zigzag joint, were constructed and loaded to collapse. The controlled slabs and mid-span-connected precast FDDPs were statically loaded to collapse under concentric or eccentric wheel loading. The moment capacity of the controlled slab reinforced with GFRP bars compared with the concrete slab reinforced with steel reinforcing bars was less than 15% for the same reinforcement ratio. The precast FDDPs showed very similar results to those of the controlled slab reinforced with GFRP bars. The RC slab reinforced by steel reinforcing bars failed in the flexural mode, while the slab reinforced by GFRP bars failed in flexural-shear one.

Improved mechanical and microscopic properties of ultra-high-performance concrete with the addition of hybrid alkali-resistant glass fibers

Improved mechanical and microscopic properties of ultra-high-performance concrete with the addition of hybrid alkali-resistant glass fibers

Effects of specimen thickness and fiber length on tensile and cracking behavior of UHPFRC: Uniaxial tensile test and micromechanical modeling

Effects of specimen thickness and fiber length on tensile and cracking behavior of UHPFRC: Uniaxial tensile test and micromechanical modeling

Triaxial compressive behavior of 3D printed PE fiber-reinforced ultra-high performance concrete

Triaxial compressive behavior of 3D printed PE fiber-reinforced ultra-high performance concrete

Two-lift concrete pavement with advanced fibre reinforced concrete as the top lift and roller compacted concrete as the bottom lift

Roller Compacted Concrete (RCC), developed for pavements and dams due to its low cement content, is constrained by limited fatigue resistance, making it suitable only for low-traffic pavements. This study aims to develop a high-fatigue-resistant Two-lift Concrete Pavement (TLCP) incorporating RCC, with three primary objectives: (i) constructing TLCP with a two-thirds RCC bottom layer and a one-third ultra-high-performance fiber-reinforced concrete (UHPFRC) or engineered cementitious composites (ECC) top layer, (ii) conducting fatigue testing on 225 specimens, and (iii) analyzing fatigue data using statistical methods to determine the best approach. Results showed that TLCP specimens had higher compressive and flexural strengths than RCC, though lower than UHPFRC or ECC. A graphical method was found most accurate for predicting fatigue life. TLCP with UHPFRC achieved 3.85–7.5 times greater fatigue life, while TLCP with ECC showed 2.63–5.96 times higher fatigue life than RCC, with ECC offering significant cost savings.

Punching shear behavior of ultra-high-performance fiber-reinforced concrete and normal strength concrete composite flat slabs

Punching shear behavior of ultra-high-performance fiber-reinforced concrete and normal strength concrete composite flat slabs

Fire resistance of 3D printed ultra-high performance concrete panels

Fire resistance of 3D printed ultra-high performance concrete panels

Experimental and analytical investigations on bond–slip behavior of steel reinforcement inUHPFRCconsidering yielding

AbstractThe bond behavior between ultra‐high‐performance fibre‐reinforced concrete (UHPFRC) and steel rebars plays an important role in the load‐bearing capacity and serviceability of structural members. A suitable bond–slip model is essential for predicting the load resistance and deformation capacity of members, after cracking of the UHPFRC. This paper studies the bond strength between ribbed steel bars and the surrounding UHPFRC before and after yielding of the steel reinforcement. To determine the corresponding bond–slip relationship, pull‐out tests, with varying embedment lengths of the reinforcement, namely 2 times and 10 times the rebar diameter, and diameter of reinforcing bars ranging from 10 mm to 16 mm were conducted. The bond stress, strain and slip along the embedment length of the steel rebars were measured by strain gauges and displacement transducers. Based on the test data, a bond stress–slip model was derived before (elastic stage) and after (inelastic stage) yielding of the reinforcement. The slip at the yield point is suggested through theoretical equations. The post‐yield bond–slip model is based on yield bond stress and frictional bond stress. The two‐part model was validated through iterative procedures and is able to predict the applied force, bond stress and strain distribution along the reinforcing bar. A comparison between the test data and analytical results demonstrates a good predictive capacity on the bond behavior of reinforcement in UHPFRC both before and after yielding of the reinforcement.

Surface electrical properties of UHPFRC with graphene

Surface electrical properties of UHPFRC with graphene

Experimental characterization of indented dry connections for precast double‐curved concrete shells

AbstractThis paper presents the experimental validation of a connections system to connect segmented precast long‐span thin‐shell structures made with lightweight ultra‐high‐performance fiber‐reinforced concrete (UHPFRC). The work comprises the segmentation of the large‐span ultra‐thin shell to meet the requirements of prefabrication (construction and transport limitations), and the design and characterization of the connections. Once the assembling of the shell required the use of post‐tensioned unbonded prestressing, an indented dry connection was chosen. The connections are experimentally characterized with in‐plane and out‐of‐plane shear tests for different prestressing levels. The results are presented and discussed, demonstrating the balanced behavior of the indented dry connection under shear loading. The connections exhibited high ductility in shear, capitalizing on the use of a UHPFRC to fabricate the shell. The prestressing also demonstrated its efficacy, significantly enhancing both the stiffness and the capacity of the indented dry connection.