Using Ultra-high Performance Concrete Research Articles

Rehabilitation of reinforced concrete slab using ultra high-performance concrete and fiber reinforced polymer

Rehabilitation the flexural capacity of reinforced concrete structures has been the subject of many studies. However, there is currently limited research on repairing such structures using Ultra-High-Performance Concrete (UHPC) and the combination of UHPC with Fiber-Reinforced Polymer (FRP) materials. This article presents the results of an experimental study on the flexural behavior of 4 specimens: 1 specimen of reinforced concrete (RC), 1 specimen strengthened with FRP sheets, and 02 specimens with the same height as the RC specimen but with a replacement of 3 cm of the protective concrete layer with a UHPC layer, either bonded or not bonded to the existing concrete, with or without the reinforcement of FRP sheets. The experimental results of the 4-point bending tests indicate that, while maintaining the height of the RC specimen constant, replacing the protective concrete layer with a UHPC layer and incorporating FRP in the tension zone led to an increase of approximately 83.35% in flexural capacity, with the deflection at the failure stage rising by only 12.8%. This research opens up a new and promising direction for improving and extending the service life of RC bridges using UHPC and FRP

Quasi-static testing of UHPC cupped socket piers-footing connection and its seismic fragility analysis under near-fault ground motions

Assembly construction is extensively employed in bridge construction due to its ability to accelerate construction and improve quality. To speed the recovery of bridges after major earthquakes, this study proposes an assembled connection for precast piers and footings based on assembly construction. The precast piers are connected to the footings using ultra-high-performance concrete (UHPC) post-cast cupped sockets. Two specimens are tested with a 1:4 scale, namely, the cast-in-place (CIP) specimen and, the UHPC cupped socket pier specimen. Finite element models (FEM) of a continuous girder bridge with cupped socket connections are developed and verified by experimental results. The seismic fragility analysis is conducted to investigate the difference between the cupped socket connection and the CIP connection. The experimental results showed that the plastic hinge was formed on the precast piers and there was little damage to the UHPC sockets. The results of FEA indicate that UHPC cupped socket piers have slightly higher seismic fragility than the seismic fragility of cast-in-place piers. Then, some methods were proposed to reduce the seismic fragility of UHPC cupped socket piers, and their availability was confirmed by comparing them with the seismic fragility of CIP piers. Finally, an example bridge with this connection is introduced to illustrate replacing prefabricated piers after an earthquake.

Experimental and theoretical investigations on the static behavior of low aspect ratio shear stud connectors in ultra high performance concrete

In reinforcement project for early-built orthotropic steel bridge decks (OSDs) using ultra high performance concrete (UHPC), low aspect ratio shear stud connectors in UHPC are required. In present study, push-out tests of six static UHPC specimens with and without reinforcement bars were first conducted. The failure modes, load-slip curves and shear capacity of shear stud connectors embedded in UHPC with an aspect ratio of 1.84 were investigated. Subsequently, the experimental results of shear capacity and load-slip curves were compared with the theoretical calculation results. Finally, a new theoretical model of shear stiffness was proposed for low aspect ratio shear studs based on the energy equivalence theory. The experimental results indicated that the failure mode of all specimens was stud shank failure, while the UHPC slabs without reinforcement bars showed extensive cracks. The effect of reinforcement bars on the behavior of shear studs embedded in UHPC slabs can be negligible. The reinforcement bars mainly affected the internal force flow in the UHPC, thus limiting crack initiation and extension. The compressive strength of the UHPC and the weld collar had significant impact on the shear capacity of short studs in the UHPC. In calculating the load-slip curves of short shear stud connectors in UHPC, the theoretical results calculated using the fractional form equations were in better agreement with the experimental results. The proposed theoretical model neglecting the deformation of shear stud in elastic stage can accurately predict the shear stiffness of low aspect ratio shear stud connectors in UHPC.

Seismic Retrofitting of Corroded Reinforced Concrete Columns Using Ultra-High-Performance Concrete (UHPC) Jacketing

Seismic Retrofitting of Corroded Reinforced Concrete Columns Using Ultra-High-Performance Concrete (UHPC) Jacketing

Predicting strength of non-prestressed concrete I-beams repaired/strengthened in flexure and shear using Ultra-High-Performance Concrete (UHPC)

The applications of Ultra-High-Performance Concrete (UHPC) have been growing significantly in the past two decades because of its superior mechanical and durability properties compared to those of conventional concrete (CC). Using UHPC as a repair and/or strengthening material for beams can offer several advantages, such as: ease of construction, protection against severe environment, high ductility, reduced encasement dimensions, and economy compared to existing repair materials. Limited repair cases were reported in the literature and a few experimental investigations were conducted on rectangular non-prestressed concrete beams repaired with UHPC in flexure and shear. In this paper, these cases and investigations are reviewed and new prediction models for the flexural and shear strength of composite CC-UHPC beams are developed. The paper also presents the testing of three non-prestressed I-beams in flexure: one control beam, and two beams strengthened with reinforced UHPC layer at the beam soffit. Three additional non-prestressed beams tested in shear are also presented: one control beam, and two beams strengthened with unreinforced UHPC layers at the two sides of the web. The construction procedure and structural behavior of the composite CC-UHPC beams up to failure are discussed. Test results showed that the strengthened I-beams achieved significantly higher strength in flexure and shear compared to those of the control beams. The average measured-to-predicted flexural and shear strength using the developed models were 1.08 and 1.32 respectively. In addition, no delamination or cracking was observed between the two materials up to failure indicating the adequacy of the interface shear resistance and design.

Behavior and reasonable design of steel-UHPC composite beams under negative moment

After using Ultra-High Performance Concrete (UHPC), the mechanical properties of the composite beams have significant differences compared to those of the steel-normal concrete composite beams. To investigate the effect of reinforcement ratio on the force behavior of steel-UHPC composite beams, tests on the flexural performance of steel-UHPC composite beams with different reinforcement ratios under negative moments were carried out, and reasonable design of the composite beams was analyzed by using a numerical simulation method. In addition, the existing crack calculation methods for composite beams were validated. The results showed that the failure modes of the composite beams with different reinforcement ratios were similar. Increasing the reinforcement ratio from 2.01% to 2.98%, the ultimate capacity of the steel-UHPC composite beams was increased by 4% and the ultimate deflection was reduced by 7%, while the ductility was reduced by 11%. The cracking load was not enhanced, but the higher reinforcement ratio had a controlling effect on crack development and crack width in the late loading stage. For steel-UHPC composite beams, the appropriate reinforcement ratio should be less than 4%. Furthermore, the crack calculation formulas in the existing steel-concrete composite beam codes do not apply to steel-UHPC composite beams, and the calculation results were much smaller than the measured values. Among the related formulas for reinforced UHPC members, the calculated value of the formula in NF P 18–710 was closer to the measured value but the overall error was still large, so further research is needed.

Deformation-based design of hollow coarse-aggregate ultra-high-performance-concrete beams reinforced with CFRP bars

This study aims to develop a novel type of beams strengthened with carbon fiber-reinforced polymer (CFRP) bars and cast using ultra-high-performance concrete (UHPC) with coarse aggregates (CA-UHPC) to address issues such as poor ductility, extensive cracking, and significant deflection observed in FRP-reinforced concrete (FRP-RC) beams. Six hollow beams were fabricated and tested via a four-point-bending test under cycle loading to study the effects of parameters, including CFRP reinforcement ratios, hollow shapes, and hollow ratio on the deformation performances of the beams. The results show that the deformation of all hollow beams under service loads met the requirements of the GB50610 code for deformation. Increasing hollow ratio had a negative impact on the flexural behaviors of beams, and this effect was more pronounced in beams with higher hollow ratios than in beams with lower hollow ratios. The flexural performances of square hollow beams were better than that of circular hollow beams with the same hollow ratio. Compared to other hollow beams, square hollow beams with a hollow ratio of 44.44% demonstrated superior flexural performance and optimal cost-effectiveness. Ultimately, leveraging the computational framework for steel fiber reinforcement and residual deflection, predictive models for deflection were formulated for CFRP-CA-UHPC beams with various hollow configurations under both static and cyclic loading conditions.

Lumped Plasticity Model and Hysteretic Performance of Ultra-High-Performance Concrete Rocking Pier.

Rocking piers using ultra-high-performance concrete (UHPC) have high damage-control capacity and self-centering characteristics that can limit the post-earthquake recovery time of bridges. To study the hysteretic behavior of UHPC rocking piers, a lumped plasticity model is proposed that comprises two parallel rotational springs and which can accurately calculate their force-displacement hysteretic behavior. Three states of the rocking piers, decompression, yield, and large deformation, are considered in this study. The model is verified based on existing experimental results, and the hysteretic characteristics of the UHPC rocking piers, such as strength, stiffness, and energy dissipation, are further analyzed. The research results show that the lumped plasticity analysis model proposed in this study can predict the force-displacement hysteretic behavior of the rocking piers accurately. Moreover, the hysteretic performance of the UHPC rocking piers is better than that of rocking piers using normal-strength concrete. An increase in the energy dissipation reinforcement ratio, pre-stressed tendon ratio, and initial pre-stress improves the lateral stiffness and strength of the UHPC rocking piers. However, the increase in the pre-stressed tendon ratio and initial pre-stress reduces their energy-dissipation capacity.

Rehabilitation of Corroded Steel Bridge Girder Ends using Partial-Height Ultra-High-Performance Concrete Encasement

Beam end corrosion is one of the most prominent types of deterioration on simple-span steel bridges. To address this concern, the Connecticut Department of Transportation and the University of Connecticut have jointly developed a repair method for corroded steel girder ends using ultra-high-performance concrete (UHPC) encasement. In this repair, shear studs are welded to the undamaged portion of the web and encased in UHPC to create an alternate load path for bearing and shear forces. This novel repair method has been implemented in multiple states. The widespread promotion of steel girder end repair with UHPC demonstrates the need for literature on field implementations and alternative designs. This paper advances the findings from a field implementation completed in Connecticut in October 2021, which was the first instance of a partial-height repair in the country, the first application of the repair to a weathering steel bridge, and the first use of flange studs to restore shear capacity at the junction of the web and bottom flange. Two of the girder ends were fully instrumented to collect data on the performance of the repaired locations. The paper presents an overview of the bridge, discusses the design and implementation of the repair, provides short-term monitoring data showing its successful activation, and discusses lessons learned throughout the process. It is anticipated that the findings put forward provide support for the use of UHPC encasement as a promising method for the repair of corroded steel girder ends.

Behavior of Ultrahigh-Performance Concrete Plates Encasing Steel H-Piles

Steel H-piles are exposed during their service life to wet-dry cycles in combination with salts, such as deicing, that may result in corrosion, leading to cross-sectional loss and reduction in axial load-carrying capacity. This paper proposes an innovative repair method for corroded steel H-piles using ultrahigh-performance concrete (UHPC) plates. The UHPC plates are reinforced with carbon fiber-reinforced polymer (CFRP) grids. The UHPC plates bridge the corroded segment so that the axial force bypasses the corroded segment. The UHPC are bolted to the steel H-pile using high-strength bolt connectors (HSBCs). Eleven steel H-piles bolted with UHPC plates were investigated experimentally under push-out loading to quantify the axial force that can be transferred from a steel H-pile to UHPC plates through HSBCs. The examined parameters were the UHPC plate thickness, the diameter of HSBC, and the number of CFRP grid layers. The results were compared with those predicted using different design codes and guidelines. The UHPC plates attached to the steel H-pile could transfer axial loads ranging from 35% to 98% of the steel H-piles’ ultimate axial capacity. Further, the installation of the UHPC plate on a steel pile can be completed in about 2 h with minimal equipment, making it a promising repair candidate in real-world applications.

Experimental and numerical investigation of seismic performance of prefabricated double-column piers used in accelerated bridge construction

The socket connection has been considered to be an effective connection for accelerated bridge construction (ABC) due to its promising advantages, i.e., higher construction tolerance rate, simpler connection method, easier quality control method, and better seismic performance when the socket depth is sufficient. To further facilitate the promotion of socket connections, a novel double-column piers system with socket connection was proposed, and the prefabricated piers and adjacent elements are connected using Ultra High-Performance Concrete (UHPC) grouting. Three 1:3 scale double-column pier specimens using novel type socket connection, ordinary grouted corrugated duct connection, and cast-in-place connection, respectively, were subjected to pseudo-static tests, aimed to compare the effects of connection methods on the damage development, failure mode, strain distribution, and seismic performance of the double-column pier. The test results indicate that all three double-column piers with three different connection forms exhibit good seismic performance, with the failure mode being the fracture of the longitudinal rebars of the piers. Compared with the piers fabricated with the other two connection forms, the piers with socket connection feature less residual displacement, and the damage is mainly concentrated at the bottom of the pier. Additionally, numerical analysis models were developed and validated for the socket-connected double-column piers to facilitate further research in this area.

Investigating UHPC in deck bulb-tee girder connections, part 2: Full-scale experimental testing

Deck bulb-tee girders constitute an excellent precast concrete bridge element system for medium- to longspan bridges. The precast concrete girders are transported to the jobsite, where they are placed adjacent to each other. The girders are connected using field-cast longitudinal joints. When required, a continuity diaphragm over the pier is used to create moment continuity; however, there is a risk of cracking of the field-cast joints and construction can be difficult when adjacent girders have different camber profiles. Given these challenges, adoption of the deck bulb-tee girder systems has been limited. Analytical investigation performed in part 1 of this series of papers indicated that using ultra-high-performance concrete (UHPC) can improve the performance of the field-cast joints and help overcome construction difficulties. This paper describes full-scale experimental testing performed as a follow-up to the analytical investigation. Longitudinal joints grouted with UHPC were tested under a combination of thermal and live load. A continuity diaphragm with partial UHPC was also tested under positive and negative moments over the pier.

The feasibility of using ultra-high performance concrete (UHPC) to strengthen RC beams in torsion

To explore the feasibility of using ultra-high performance concrete (UHPC) to strengthen reinforced concrete (RC) beams in torsion, pure torsion tests on 9 specimens have been conducted in this study, including one RC beam without strengthening (referred as control beam) and 8 UHPC-strengthened beams. The variables considered for investigation included the wrapping form of UHPC layer, thickness of UHPC layer, shape of steel fibers added in UHPC layer, UHPC-RC interfacial treatment, and reinforcement ratio of UHPC layer. The overall torsional behavior, torque–twist curves, torque-principal strain curves, cracking pattern and UHPC-RC interfacial slippage for all specimens were obtained based on the torsion tests. Results show that the cracking and ultimate torsional moments of all strengthened beams were higher than those of the control beam, with maximum increases of 488.5% and 593.2%, respectively. When the RC beam cannot be fully wrapped, which is the preferred strengthening scheme, 3-sided wrapping form is also an acceptable choice, but the 2-sided strengthening scheme should be avoided. The determination of the thickness of UHPC layer should comprehensively consider the strengthening effect, cost for strengthening and requirements for RC beam's dimensions after strengthening. RC beam surfaces should be fully roughened before casting UHPC to ensure that the UHPC layers and the RC beam persistently act together as a whole to resist torsional loads. The UHPC layers are recommended to be equipped with steel bars, which could substantially improve the torsional capacity and ductility of the strengthened beam on the premise of limited increase in the cost. Finally, the effectiveness of torsional strengthening using UHPC was compared with that using fiber reinforced polymer (FRP) in terms of increase in cross-sectional area, increases in cracking and ultimate torsional moments, increase in torsional stiffness, failure mode and long-term performance.

Experimental and Numerical Investigation of Prefabricated Concrete Barrier Systems Using Ultra-High-Performance Concrete

The functionality and crashworthiness of concrete barriers in bridge systems can be affected by the deterioration of the connection between bridge decks and concrete barriers. A set of details for barrier-to-deck connections for accelerated bridge construction (ABC) applications are proposed. Component-level testing was carried out on a conventional cast-in-place (CIP) detail and two versions of connections using ultra-high-performance concrete (UHPC). The use of UHPC allows for shorter development length and lap splice length for dowel bars and the material characteristics provide strength and durability to the connection. Two connection details were proposed: (1) UHPC connection within the barrier segment (U-shape connection) and (2) UHPC connection in a recess inside the bridge deck (recessed connection). Besides simplified details, the construction sequence of the proposed recessed connection is suitable for ABC applications. It is observed that the proposed U-shape connection detail is emulative of the equivalent CIP concrete barrier system. However, the recessed connection system can undergo significantly larger deflections at ultimate load compared with the CIP barrier system and exhibits a preferred mode of failure while the deck does not undergo significant damage. The results of the component testing were used to calibrate non-linear finite element models. Using validated models, numerical analyses were performed to investigate the structural performance of conventional 15 ft long barrier modules connected to the deck overhang using the recessed connection. The model was subjected to the end-loading configuration and it was found that the proposed barrier system meets the strength requirement for the corresponding test level.

Direct shear strength of UHPC-based gravity-type grouted sleeve connection members

This study aims to clarify the shear mechanism and strength of a new gravity-type grouted sleeve connection using ultra-high performance concrete (UHPC). Direct shear tests were conducted to investigate the shear performance of the UHPC-based connection. The test results showed that the shear strength of the UHPC-based connection is at least 50% higher than that of the traditional connection. Also, the failure mode of the UHPC-based connection is more like that of the cast-in-place (CIP) specimen than the traditional one. Based on the analysis of the shear mechanism, the formulas were proposed to predict the shear strength of the UHPC-based connection. The shear strengths obtained from the proposed formulas are in good agreement with the experimental data. To further verify the proposed formulas and investigate the shear performance, the finite element (FE) modeling method was also developed for the UHPC-based connection. It was found that the numerical results are consistent with the experimental data and the analytical results derived from the proposed formulas, indicating the applicability of the proposed formulas and FE modeling method. Parametric studies indicated that the shear strength is more sensitive to the axial load level than concrete strengths and reinforcement ratios.

Experimental testing of RC shear wall seismic retrofit using selective weakening, self-centering and Ultra High performance concrete

Traditional retrofit methods often focus on increasing the structure's strength, stiffness, or both. This may increase seismic demand on the structure and could lead to irreparable damage during a seismic event. This paper presents a retrofit method, integrating concepts of selective weakening and self-centering (rocking) to achieve low seismic damage for non-code compliant reinforced concrete shear walls. The proposed method involves converting traditional cast-in-place concrete shear walls into rocking walls, which helps to lower the shear demand, while allowing re-centering. Two large-scale lateral load tests were performed to validate the retrofit concept on a concrete shear wall designed according to pre-1970s standards. The design parameters investigated were amount of energy dissipating reinforcements and confinement enhancement. Two different methods using Ultra High Performance Concrete (UHPC) were investigated to provide additional confinement to boundary elements of older shear walls. Observations from the tests showed minimized damage and enhanced recentering in the retrofitted wall specimens. Use of UHPC in the boundary elements of the retrofitted walls provided additional confinement and reduced damage in the rocking corners.

Cyclic performance of severely earthquake-damaged RC bridge columns repaired using grouted UHPC jacket

The bridges constructed in high seismic zones may suffer one or more earthquake shocks of certain scales during their service life. Some of them could be severely damaged during a catastrophic earthquake event. How to quickly and economically restore bridge service functions and traffic lifelines has always been the concern of bridge owners and engineers. In this study, a method for repairing seismically damaged reinforcement concrete (RC) bridge columns using ultrahigh performance concrete (UHPC) materials was developed. Seven down-scale RC bridge column specimens with three different reinforcement ratios and two different heights were designed according to the seismic design code for RC bridges. For three of the specimens, the reinforcement around the plastic hinge area were artificially corroded through chloride ion penetration method to simulate the strength degradation effect of reinforcement erosion that could occur in many aging bridge columns. All seven specimens were tested by applying cyclic loads until their plastic hinge became severely damaged, which were then repaired following the proposed procedure and with different jacket thicknesses. The cyclic tests were re-conducted for these repaired specimens. The testing results were analyzed by comparing to those from the test for the non-seismic-damaging specimens one by one with respect to their seismic performance in order to validate the seismic rehabilitation effect using UHPC materials. Additionally, an ABAQUS software based finite element model was developed for numerically simulating the hysteretic behaviors of the columns repaired using UHPC jacket. The resulting hysteretic curves for the repaired columns with different reinforcement ratios and heights well matched those from the corresponding cyclic tests. This model can be further used for seismic performance prediction and UHPC jacket design for the repaired bridge columns that have different dimensions and reinforcement configurations. All of these experimental and analytical results show that the seismic performance of the repaired bridge columns can be effectively restored in a relatively fast and low-cost manner.

Enhancing the toughness of bonding interface in steel-UHPC composite structure through fiber bridging

Using Ultra-high performance concrete (UHPC) to replace normal strength concrete (NSC) can greatly reduce the weight of steel-concrete composite structures. However, the bonding interfaces between steel and UHPC in composite structures are prone to brittle failure, and the introduction of ductile fibers can effectively enhance the interfacial toughness. In this study, helical fibers and steel wire mesh fibers were stably embedded in UHPC and epoxy matrix to prepare the steel-UHPC bonding specimen. The interfacial shear properties were studied based on a modified direct shear test method, and the effects of fiber size, fiber number, and fiber direction were considered. Meanwhile, the interfacial properties of bonding specimens with two types of ductile fibers were compared with those of epoxy direct bonding interface and quartz sand particle embedded interface. The results indicated that the toughness enhancement of steel wire mesh fiber on the bonding interface of steel-UHPC composite structure is the best among all interfaces, and its maximum fracture energy Gτ is 25.5 times that of epoxy direct bonding interface. Meanwhile, the toughening mechanism of steel wire mesh fiber on steel-UHPC interface is highly related to its arrangement direction. The interface failure began with the shear fracture of steel wire mesh fiber and ended in the failure of epoxy matrix, when the steel wire mesh was transversely arranged. Only tensile fracture of steel wire mesh fiber occurred, and the failure of the epoxy matrix was not observed when the steel wire mesh was longitudinally arranged. Finally, the shear capacity calculated by the proposed model based on two toughening mechanisms showed good agreements with the experimental results. The feasibility of fiber bridging to enhance the toughness of bonding interface in the UHPC-OSD system is confirmed via the finite element analysis.

Using the two optimization algorithms (BBO and FDA) coupling with radial basis neural network to estimate the compressive strength of high-ultra-performance concrete

Using Ultra-High Performance Concrete (UHPC) as the highly resistant material is widely advised in constructing sensitive structures to enhance safety. The utilization of eco-friendly contents such as fly-ash and silica-fume replacing cement can decrease the pollution rate in the production process of concrete and improve the compressive strength (CS) factor. There are many ways to appraise the CS of concretes as empirically and mathematically Artificial Neural Networks (ANN) as the high-accurate model is used in the present study. In this regard, Radial Basis Function (RBF) coupling with Biogeography-Based Optimization (BBO) and Flow Direction Algorithm (FDA) created the two high-accurate frameworks: BBO-RBF and FDA-RBF. Enhancing the accuracy of RBF to predict the CS and decreasing the ANN net complexity leads to having better results evaluated by various metrics. Therefore, using the proposed frameworks, the correlation index of R2 to model the CS in the training phase for FDA-RBF was calculated at 0.9, although BBO-RBF could get 0.85, with a 0.5% difference. However, the RMSE of FDA-RBF was 9 MPa, and for BBO-RBF, this index was calculated at 10 MPa the former model has about three percent more accuracy than the latter.

Ultrahigh Performance of Concrete using Manufactured Sand

The resistance and durability of concrete structures can be improved by using ultra-high performance concrete (UHPC). A crucial component of energy conservation and concrete cost reduction is the use of locally available materials. In this study, the effects of a common type of locally accessible manufactured sand (MS) on the characteristics of UHPC were investigated from both a physical and chemical standpoint. The main objective of the current study is to use locally available materials to create a UHPC with a compressive strength of 100MPa. The impact of fine materials, binder type and content, mixer type, steel fibres, and curing regimes on the concrete’s compressive strength was examined in this study. The use of high strength concrete has various benefits, including a reduction in the size of beams and columns and an increase in the height of buildings with multiple stories. In recent years, high strength concrete has seen increased use in civil engineering. By minimising non-homogeneity, porosity, and micro-cracks in the concrete and its zone of transition, high strength is made achievable. Super plasticizers and additional cementing substances such granulated blast furnace slag, silica fume, and natural pozzolana can be used to achieve it. Concrete with a high modulus of elasticity is strong. On cement, fine aggregate, and coarse aggregate, preliminary studies have been conducted. In the current study, 920KK is employed as a chemical admixture and silica fume is used as a mineral admixture. For M100 concrete, the w/c ratio is taken to be 0.25. The mix proportion for M100 grade concrete can be calculated by following the design process suggested by the ACI Method as 1:0.454:1.527.