Using Ultra-high Performance Concrete Research Articles

An Accelerated repair method for steel girders with severe end corrosion damage

A novel repair method for corroded steel girder ends using ultra-high performance concrete (UHPC) has gained the attention of several departments of transportation. The method involves welding shear studs to the intact part of the web plate and encasing the end region in UHPC. This paper presents the findings of an experimental study on a full-scale girder aimed to assess the feasibility of rapid implementation of the repair. Reducing the construction complexities and time is critical in cases where access to the bridge is constrained or closing the bridge to traffic is not possible. To expedite and simplify repair construction, welded shear studs originally used to transfer loads to the UHPC cast were replaced with steel dowel rods. In place of conventional wooden formwork, a reusable flexible light-gauge sheet of steel was wrapped around the end. Installation of the shear connectors, installation of the form, and casting of the UHPC was completed by two workers within an eight-hour shift. The repaired girder was load tested after the UHPC gained a compressive strength of 96.5 MPa to demonstrate the adequacy of the repair for restoring the capacity of the intact girder end shortly after implementation. It is anticipated that this empirical data encourages the use of this repair technique to address the widespread problem of end corrosion in steel superstructures.

UHPC sandwich panels with GFRP shear connectors tested under combined bending and axial loads

A new design of double wythe insulated wall panels using ultra-high performance concrete (UHPC) and glass fibre-reinforced polymer (GFRP) shear connectors is developed and tested. It consists of two 25 mm thick UHPC ribbed wythes with a 152 mm thick layer of extruded polystyrene (XPS) sandwiched in between. Small diameter (4 mm) GFRP bars were used as reinforcements in the wythes and as diagonal shear connectors. Five 3.0 × 0.61 × 0.2 m panels were tested to failure in flexure (M), under axial compression (P) and under combined loading. Four-point bending was used to simulate wind pressure, while axial compression was applied on one wythe only, representing gravity floor loading. For combined loading, a constant (P) of 16%, 33% or 66% of the axial strength of the wall was applied on three different panels, then transverse loading was applied to failure. The full (P-M) interaction curves, relative to the centroids of a composite and non-composite sections were developed, including both primary and secondary moments from slenderness. The degree of composite action was calculated to be 78% under transverse loading only and was reduced as the axial load increased. Failure was triggered by a progressive fracture of the diagonal GFRP shear connectors, regardless of the M and P combination. The wall design met serviceability requirements at the highest wind pressure based on the 50-year return period as per the National Building Code of Canada.

Precast concrete deck-to-girder connection using Ultra-High Performance Concrete (UHPC) shear pockets

Precast concrete deck systems have been successfully used in Accelerated Bridge Construction (ABC). In most systems, precast concrete deck-to-girder connections use special shear connectors embedded in the girders and projecting into the deck block-outs (pockets or troughs) that are grouted to achieve composite sections. This requires tight production/erection tolerances that complicate deck and girder fabrication and compromises the economics of the precast concrete deck systems. In this paper, a new deck-to-girder connection is developed using ultra-high performance concrete (UHPC) to relax production/erection tolerances for both precast deck panels and girders. Typical girder shear reinforcement remains unchanged but terminated in the haunch below the soffit of deck panels to eliminate any conflict with the deck shear pockets. Loop bars are installed in the shear pockets that are filled with UHPC to provide required interface shear capacity while relaxing production/erection tolerances. Small scale push-off and double shear tests were conducted to evaluate the interface shear resistance of the connection. Full-scale push-off specimens are fabricated and tested to evaluate the structural performance and constructability of the proposed connection. Test results indicated that interface shear resistance of the connection can be predicted using the AASHTO LRFD shear friction model with different cohesion and friction factors that are dependent on the UHPC compressive strength. Also, UHPC fiber stability has a significant effect on the capacity of the proposed connection. Design example and design aids are presented to demonstrate the design of the new connection in a typical bridge.

Seismic response of precast bridge columns with composite non-proprietary UHPC filled ducts ABC connections

Accelerated bridge construction (ABC) utilizes advanced planning, new construction techniques and innovative detailing to expedite construction of new bridges or rehabilitation and replacement of old deteriorated bridges. ABC has been widely used in low seismic regions and mostly implemented in the superstructure elements but much less considered for substructure elements such as column-base connections, especially in moderate and high seismic regions. While robust seismic ABC connections have been developed using ultra-high performance concrete (UHPC), sole sourcing of robust commercial UHPC mixes is causing bidding issues and limiting the wide adoption of such seismic ABC connections. Thus, validating alternative solutions that use non-proprietary materials could help overcome such challenges. This paper presents experimental and analytical investigation of the structural and seismic behavior of precast bridge columns with non-proprietary UHPC-filled ducts column-to-footing connections. For this study, a recently developed non-proprietary UHPC mix at the University of Nevada, Reno (UNR) is used. Two large-scale column models, varied only in reinforcement debonding, were tested at UNR under combined axial and cyclic lateral loading to evaluate their seismic performance. The column models were compared with reference cast-in-place column models and another column model incorporating proprietary commercial UHPC-filled duct connection from previous studies. The test results showed that the column models were emulative of conventional connections. Analytical modeling for the two tested columns was also conducted and shown to successfully reproduce the local and global behaviors of column models with acceptable accuracy when bond-slip and bar debonding effects are properly considered.

Characterization of toughening mechanisms in UHPC through image correlation and inverse analysis of flexural results

The nature of cracking in flexural specimens made using ultra-high-performance concrete (UHPC) is studied in the context of mechanisms of enhanced strength and ductility. The effect of fibers on the suppression of cracking and the attendant toughening mechanisms are addressed at two different fiber contents to elucidate the strain-softening and strain-hardening responses. Results indicate that the first crack strength is directly related to the fiber content, with fibers extending the stable crack growth region at high fiber contents such that flexural strengths as high as 20 MPa are obtained. Fiber bridging results in resistance to crack growth, stabilization, as well as multiple crack formation, all of which contribute to toughening. Using a combination of experimental results, digital image correlation (DIC) measurements of crack extension, and an analytical model for the flexural response, the stress and strain distributions across the depth of the specimens are determined, leading to stress-crack width relationships, and consequently, the relationship between tensile and flexural stresses in fiber-reinforced UHPCs. The results are also used to determine the tensile and compressive strain and stress distributions. Using back-calculated tensile properties from the flexural response and the 3-D DIC results, crack width profile and the stress-crack width relationship in tension are obtained for UHPCs, leading to a comprehensive understanding required for the structural design using such high-ductility materials.

A Numerical Study on Structural Performance of Railway Sleepers Using Ultra High-Performance Concrete (UHPC).

This numerical study investigates the structural performance of railway sleepers made of ultra high-performance concrete (UHPC). First, numerical concrete sleepers are developed, and the tensile stress-strain relationship obtained from the direct tension test on the UHPC coupons is used for the tensile constitutive model after applying a fiber orientation reduction factor. The numerical sleeper models are validated with the experimental data in terms of the force and crack-width relationship. Second, using the developed models, a parametric study is performed to investigate the performance of the UHPC sleepers while considering various design/mechanical/geometrical parameters: steel fiber contents, size of the cross-section, and diameter and strength of prestressing (PS) tendons. The simulation results indicate that the size of the cross-section has the most impacts on the performance, while the effect of yielding strengths of PS tendons is minimal among all the parameters. Engineers need to pay attention to efficiency and an economical factor when using a larger cross-section, since sleepers with larger cross-sections can be an over-designed sleeper. This study suggests an economical design factor for engineers to evaluate what combination of parameters would be economical designs.

Experimental study on concrete filled steel tubes to footing connection using ultra-high performance concrete

Concrete filled steel tubes (CFSTs) provide improved structural strength and ductility in addition to eliminating the need for column formwork. This research proposes new connection details for column-to-footing connection using ultra-high performance concrete (UHPC). Two connections consisting of an embedded and an encased layer of UHPC were selected for the experimental program. In these details, the CFST is embedded in a layer of UHPC located near the plastic hinge zone of the column and steel dowels from the footings are used for force transfer. The sequence of construction and detailing allows the use of these connection details for accelerated bridge construction (ABC) applications. Two columns were tested under a combination of constant axial and incremental cyclic lateral load. The embedded type connection failed by fracture of the tube while the encased type connection induced damages in the UHPC encasement. Both connections exhibited high levels of ductility and did not show significant loss of lateral load capacity. The load hysteresis of the embedded connection showed higher energy dissipation for the embedded connection when compared to the encased connection due to damages in the UHPC encasement. The capacity protected footing did not show any signs of cracking.

Experimental Behavior of Steel-Concrete Composite Girders with UHPC-Grout Strip Shear Connection

This paper develops a new type of shear connection for steel-concrete composite bridges using Ultra-High Performance Concrete (UHPC) as the connection grout. The UHPC-grout strip shear connection is fabricated by preforming a roughened slot in the concrete deck slab, welding an embossed steel rib longitudinally to the upper flange of the steel girder, and casting the strip void between the slot and the steel rib with UHPC grout. The structural performance of the new connection was validated by two sets of experimental tests, including push-out testing of shear connectors and static and fatigue testing of composite beams. The results of push-out testing indicate that the UHPC-grout strip shear connection exhibits a significant improvement of ductility, ultimate capacity, and fatigue performance. The interface shear strength of the UHPC-grout strip connection is beyond 15 MPa, which is about three times that of the strip connection using traditional cementitious grouts. The ultimate capacity of the connection is dominated by the interface failure between the embossed steel and the UHPC grout. The results of composite-beam testing indicate that full composite action is developed between the precast decks and the steel beams, and the composite action remained intact after testing for two million load cycles. Finally, the trail design of a prototype bridge shows that this new connection has the potential to meet the requirements for horizontal shear.

Experimental investigation of seismic behavior of UHPC connection between precast columns and footings in bridges

The lack of seismic capacity of piers leads to bridge collapse in recent earthquakes, such as the 1994 Northridge (USA), 1995 Kobe (Japan) and 2008 Wenchuan (China) earthquakes. For precast bridge piers, the performance of pier connection determines the seismic capacity of the whole bridge. Therefore, a new connection between precast bridge column and footing using ultra-high performance concrete (UHPC) is developed in this paper. The precast column and footing are connected by longitudinal rebars of the column and the footing anchored into the UHPC-filled cage. The connection allows force to be transferred from the column rebars to UHPC, then to the footing rebars by bond effects. To investigate the seismic behavior of precast bridge piers with this new UHPC connection, cyclic tests with two large-scale (1:2.5) models are carried out. One is the precast reinforced concrete (RC) specimen using the proposed new connection, and the other is the cast-in-place (CIP) RC reference. The results show that the failure modes of the specimens are similar, both denoted by crushing of the core concrete above the connection segment. No obvious damage is observed in the connection region, which demonstrates that the precast bridge pier with the proposed connection is emulative of the CIP pier. Furthermore, a finite element model is developed to simulate the cyclic response of the precast column with proposed connection. The deviation between the calculated and measured force–displacement relationships is about 5%, which indicates that the numerical model used herein can be effective to capture the performance of the precast pier with new UHPC connection.

Fatigue performance evaluation for composite OSD using UHPC under dynamic vehicle loading

A novel composite orthotropic steel deck (OSD) using ultra-high performance concrete (UHPC) is comprised of an OSD and a thin UHPC layer that are connected through shear connectors. The innovative composite OSD system has been increasingly applied to long-span bridges in China to overcome the defect of conventional OSD that frequently suffers from fatigue cracking. However, the fatigue performance of the composite OSD system is usually evaluated with the deterministic analysis in previous studies, which may lead to inaccurate evaluation as many uncertainties, including the statistical properties of dynamic vehicle loadings and fatigue-prone details, have not been considered rationally. In this paper, the fatigue performance of the composite OSD using UHPC was investigated using the reliability-based fatigue analysis and compared with the fatigue performance of conventional OSD system. A three-dimensional vehicle-bridge coupled system was adopted to obtain the stress time histories of fatigue-prone details in the bridge decks under the action of dynamic vehicle loading. The vehicle model was determined based on the fatigue load pattern adopted in the AASHTO standard specifications and finite element models (FEMs) of both the conventional OSD and the composite OSD using UHPC were built based on a girder segment adopted from the HuMen Bridge in China. Four key influence factors, namely, the road surface condition (RSC), length of bridge deck FEM, vehicle speed, and overloading, were taken into consideration. The fatigue life of six typical fatigue-prone details in these two deck systems was evaluated and compared. The results show that the composite OSD using UHPC can effectively extend the fatigue life of OSD by at least 60% and even eliminate the risk of fatigue cracking for most fatigue-prone details. Compared to the reliability method, the fatigue life of OSD determined based on the deterministic method would be overestimated by 65–110% if the very poor RSC is considered. Besides, the composite OSD using UHPC exhibits a better fatigue performance than the conventional OSD system under the action of overloaded trucks. The results from the study can provide a reference for the design and maintenance of the composite OSD using UHPC.

Design and performance of low shrinkage UHPC for thin bonded bridge deck overlay

The service life of bonded overlay materials used for bridge deck rehabilitation is affected by shrinkage of the overlay and bond between the overlay and substrate. There is a growing interest in using ultra-high performance concrete (UHPC) for thin bonded overlays. However, UHPC can exhibit high autogenous shrinkage leading to cracking under restrained conditions. This study investigated the synergistic effect of using pre-saturated lightweight sand (LWS) and a CaO-based expansive agent (EA) to mitigate shrinkage of UHPC. Five non-proprietary UHPC mixtures, a latex-modified concrete (LMC), and a conventional concrete (CC) were tested for material properties, including pore-size distribution, hydration kinetics, and bond strength. The mixtures were used to cast 16 bonded overlay slab specimens measuring 1 × 2 m with overlay thicknesses of 25, 38, and 50 mm. In-situ variations of strain, temperature, and relative humidity of overlay materials as well as cracking and overlay-substrate bond strength were monitored for 27 months. Test results indicated that the optimum UHPC made with 5% EA and 35% LWS had a relatively low autogenous and drying shrinkage of 190 and -310 με, respectively, at 28 d and the highest bond strength (3.1 MPa at 28 d). Such values were −520 and −520 με and 2.35 MPa, respectively, for UHPC made without any EA and LWS, and 20 and -475 με and 2.75 MPa, respectively, for the mixture prepared with 35% LWS. No cracking was observed in UHPC overlay slab specimens, whereas the CC and LMC overlays started cracking after approximately half a year. The increase in overlay thickness reduced crack density of the CC and LMC slabs. The optimum UHPC mixture made with 35% LWS and 5% EA had positive in-situ strain of 45 and 200 με over the 27-month testing period, indicating that the overlay was in compression. Direct pull-off strength of the UHPC was higher that of the LMC and CC mixtures and failure occurred in the CC substrate compared to the interface for the CC and LMC overlays.

Experimental behavior of poly methyl methacrylate polymer concrete for bridge deck bulb tee girders longitudinal field joints

As an emerging practice of accelerated bridge construction (ABC), top flanges of precast deck bulb tee girders (DBTs) can be longitudinally connected on-site using ultra-high performance concrete (UHPC) field joints. Robust UHPC mixes can be proprietary, expensive and might need special expertise to work with it. Thus, exploring viability of alternative materials for such field joints could be beneficial. Poly Methyl Methacrylate Polymer concrete (PMMA-PC) is another construction material with superior mechanical properties that have been used for overlays and can provide a potential alternative to UHPC for field joints. The objective of this study is to investigate the structural performance of PMMA-PC for DBTs longitudinal field joints and compare it to UHPC. An experimental investigation was conducted to test two full-scale specimens, with representative DBTs flanges/slabs, under vertical loading at the University of Nevada, Reno. The two specimens were identical except for field joint material (UHPC versus PMMA-PC). The structural response was evaluated for connection performance under the AASHTO service and ultimate loads, peak strength, damage progression and mode of failure, and local steel reinforcement strains. The results demonstrated that PMMA-PC can be successfully used for longitudinal field joints of the DBTs with comparable performance to UHPC field joints.

A novel approach using sustainable structures in preventing coastal erosion and forming sandy beach in Vietnam

A new solution using ultra-high performance concrete (UHPC) sheet piles was a hard wall structure combined with gabion groyne dams for the purpose of shore protection, sand accretion, and tourist beach creation was proposed in this study. The proposed approach was then applied to meet the both shore protection and sandy beach generation requirements of private Rung Duong resort project in Ba Ria-Vung Tau, Vietnam. The UHPC sheet piles reinforced by fiber reinforcement polymer (FRP) installed in form of a vertical wall were designed and constructed for the shore protection purpose. Together with the later built gabion groyne dam system, the combined structure brought a very good coastal protection effect. As a result observed from Rung Duong resort, the shoreline was pushed back out very far from the resort, while sandy beaches in front of the resort were formed and expanded widely.

Numerical studies on steel-UHPC-steel sandwich beams with novel enhanced C-channels

Firstly, this study developed a new type of sandwich composite beam using ultra-high performance concrete (UHPC) and novel enhanced C-channels (ECs). Then, this study developed a nonlinear finite element model (NFEM) for steel-UHPC-steel sandwich beams with ECs (SUSSB-ECs) using general software package ABAQUS. The developed NFEM detailed simulated the novel sandwich composite beams including the complex geometry of ECs, the complex interactions between the ECs and UHPC core, and nonlinearmechanical properties of UHPC and steel. The comparisons of NFEM simulation results with eight four-point bending tests indicated that the NFEM simulated well the ultimate strength behaviour of SUSSB-ECs in terms of load versus strain/deflection curves, deformations and cracks in UHPC, and stiffness/strength indexes. Parametric studies were then performed with the developed NFEM to study the key parameters influencing the ultimate strength behaviour of SUSSB-ECs. The parametric studies showed that increasing the thickness of tension and compression steel faceplates had significant influences, but the spacing of ECs had marginal influences on ultimate strength behaviours of SUSSB-ECs. Reducing the shear span ratio did not change the flexural failure, but reduced the flexural bending resistance of SUSSB-ECs. Increasing the grades of steel faceplates had ignorable influences on the stiffness, but significantly increased the bending resistance of SUSSB-ECs.

Experimental investigation and seismic vulnerability assessment of low flexural strength rectangular bridge piers retrofitted with ultrahigh-performance concrete jackets

Effectiveness of an innovative retrofitting technique using ultrahigh-performance concrete (UHPC) jackets was investigated, for “as-built” bridge piers with low flexural strength. Cyclic loading test was performed on the pier specimens, two of which were retrofitted with a mono-wide-strip UHPC (W-UHPC) jacket, and the other two were with a multi-narrow-strip UHPC (N-UHPC) jacket. Their seismic responses were compared, regarding damage evolution, hysteretic behavior, skeleton curve, ductility and energy dissipation. The piers with the W-UHPC jacket exhibited a higher lateral strength, but were prone to plastic hinge relocation. Comparatively, N-UHPC jacket improved the piers’ ductility and smeared concrete damage. Nevertheless, guaranteeing the tight contact between the N-UHPC jacket and the shaft was crucial. Both W- and N- UHPC jackets mitigated residual drift and concrete damage, and thereby enhancing the piers’ seismic resilience. Four enhancing mechanisms from the UHPC jackets are discussed, namely passive confinement effect, cross-section enlargement effect, gap-opening effect, and interface-opening effect. Alongside, 3D solid and 1D fiber-based finite element (FE) models are constructed to represent the piers’ nonlinear static push-over (SPO) and cyclic responses, respectively. Finally, seismic vulnerability of the retrofitted piers was evaluated by generating structure-specific fragility curves.

Flexural responses of steel-UHPC composite beams under hogging moment

Using ultra-high performance concrete (UHPC) in the hogging moment regions of composite beams might significantly enhance their cracking and flexural performance. In the present paper, the flexural test was performed on steel-UHPC composite beams with stud connectors (SU-S) and bolt connectors (SU-B) at the interface. Crack resistance, ultimate flexural capacity, failure modes, and deformation characteristics of SU-S and SU-B under hogging moment were investigated. The test results showed that steel-UHPC composite beams exhibited excellent cracking and flexural performance under the hogging moment. As compared to the steel-normal strength concrete (NSC) composite beam (SC-S), cracking load and ultimate flexural capacity of steel-UHPC composite beams increased by around 340% and 26%, respectively. Moreover, the length and width of cracks in the UHPC flange plate developed slowly with load. Many short and small cracks were observed, having a close spacing in the UHPC flange plate. However, ductility and rotation capacity of both SU-S and SU-B under the hogging moment were smaller than those of SC-S. Due to the bolts’ slip in SU-B, the tensile stress in the UHPC flange plate was reduced, resulting in higher crack resistance and rotation capacity than SU-S, while its flexural stiffness and ultimate flexural capacity were slightly smaller than those of SU-S. Finally, theoretical formulas were proposed for calculation of the slip moment, moment at crack width of 0.05 mm and ultimate moment of the steel-UHPC composite beams under the hogging moment. The test results verify the applicability of these formulas to predict flexural capacity of the steel-UHPC composite beams.

Evaluation of resonance acoustic mixing technology using ultra high performance concrete

This study presents an investigation on the mixing efficiency of Resonance Acoustic Mixing (RAM) Technology® using ultra-high performance concrete (UHPC). In the first part, RAM is optimized through acceleration curve profiles, specific mixing energy, and workability spread flow tests. In the second part, RAM is compared with a regular table top paddle mixer with regards to its effects on workability and flow, as well as, compressive and flexural strength properties. For the UHPC used in this study results showed that: 1) RAM was a viable mixing technology for UHPC, and 2) RAM produced samples of reduced rheological properties, but increased mechanical properties compared to a table top paddle mixer.

Electro-mechanical self-sensing response of ultra-high-performance fiber-reinforced concrete in tension

Abstract The electro-mechanical self-sensing response of ultra-high-performance fiber-reinforced concretes (UHPFRCs), a type of strain-hardening steel-fiber-reinforced concretes (SH-SFRCs), in tension was investigated. The self-sensing capacity of SH-SFRCs was significantly enhanced by using ultra-high-performance concrete (UHPC) as the matrix. The high electrical resistance of UHPC noticeably increased the magnitude of the resistivity reduction of UHPFRCs in tension to 437.7 kΩ-cm, compared to the lower values (149.1 kΩ-cm) of SH-SFRCs. UHPFRCs showed the highest gauge factor (433) until the first cracking point, whereas the SH-SFRCs with a 152 MPa compressive mortar matrix showed the highest gauge factor (73.7) within the strain-hardening region. An embedded copper wire mesh type electrode efficiently reduced the electrical polarization.

State of the Art: Mechanical Properties of Ultra-High Performance Concrete

During the past decades, there has been an extensive attention in using Ultra-High Performance Concrete (UHPC) in the buildings and infrastructures construction. Due to that, defining comprehensive mechanical properties of UHPC required to design structural members is worthwhile. The main difference of UHPC with the conventional concrete is the very high strength of UHPC, resulting designing elements with less weight and smaller sizes. However, there have been no globally accepted UHPC properties to be implemented in the designing process. Therefore, in the current study, the UHPC mechanical properties such as compressive and tensile strength, modulus of elasticity and development length for designing purposes are provided based on the reviewed literature. According to that, the best-recommended properties of UHPC that can be used in designing of UHPC members are summarized. Finally, different topics for future works and researches on UHPC’s mechanical properties are suggested.

Fatigue Life Assessment of Orthotropic Steel Deck with UHPC Pavement

In recent years, a number of large-span bridges with orthotropic steel decks were constructed in China. With increasing traffic volumes and higher wheel loads, many fatigue cracks developed at the welds and the edge of cut-out holes. This paper aims at presenting the numerical analysis on the fatigue performance of the orthotropic steel deck using ultrahigh performance concrete (UHPC) overlay as the deck pavement instead of the conventional asphalt concrete pavement. By using finite element method (FEM) model, stress distribution at fatigue sensitive locations under the action of wheel loads is characterized and the obtained stress ranges indicate that the UHPC pavement significantly reduces the magnitude of the stress peak valued. A suggested truck stream model based on the weigh-in-motion (WIM) data of four bridges in China is employed to calculate the stress variation at specific fatigue details. Furthermore, the fatigue damage accumulation at fatigue details under the UHPC and conventional asphalt concrete pavement is studied based on Miner’s linear cumulative damage rule and the rain-flow method. The results indicate that the UHPC pavement on the orthotropic steel deck can extend the service lives of the concerned regions over 100 years, but the fatigue lives will reduce significantly when the elastic modulus of UHPC decreases to 50% of the original value.