Ultra-high Performance Concrete Members Research Articles

Predicting corrosion in reinforced UHPC members through time-dependent multi-physics numerical simulation

Ultra-high-performance concrete (UHPC) has superior durability characteristics over traditional concrete. Improved durability behavior of UHPC has been attributed to the dense material property, which effectively constrains harmful material ingress and oxygen supply. However, the corrosion performance of reinforced UHPC under sustained mechanical loading, which may induce cracking, in addition to environmental conditioning is still not well characterized. This study investigates the electrochemical-mechanical coupling effects on deterioration mechanisms of reinforced UHPC beams subjected to service loading conditions and chloride attack through multi-physics simulation techniques. Finite element models were simulated considering the cracking induced by service loads and deformations caused by rust expansion on the cementitious matrix. Material transport properties such as chloride and oxygen penetration parameters were updated in each step of the time-dependent process based on cracking conditions. The simulation results show that there is substantial steel cross section and yielding load capacity loss, initial stiffness reduction, and damage area increase in reinforced concrete members while UHPC members showed relatively small cross section loss, negligible increase in UHPC damage, no observable reduction in initial stiffness, and minimal loss in yield load capacity. The effect of oxygen supply level on the corrosion performance is also explored showing that the corrosion rate of reinforced UHPC specimens were limited due to depleted oxygen at the steel-UHPC surface. Numerical simulation results were verified against experimental trends on corrosion performance of reinforced UHPC specimens. Further, the numerical framework herein provides an alternative way in predicting deterioration processes and evaluating service life performance of ductile reinforced concrete infrastructures in a computationally efficient manner.

A Comparative Study on the Shear Behavior of UHPC Beams with Macro Hooked-End Steel Fibers and PVA Fibers.

Structural members made of ultra-high-performance concrete (UHPC) have been attractive to engineers and researchers due to their superior mechanical properties and durability. However, existing studies were focused on the behavior of UHPC members reinforced with micro straight steel fibers at a volume fraction between 1 and 3%. There is a lack of studies on the influence of different types and amounts of fibers on the shear behavior of UHPC structural members. The objective of the study was to experimentally investigate the shear behavior of UHPC beams with macro hooked-end steel (MHS) fibers and polyvinyl alcohol (PVA) fibers, which are two of the most used fibers for high-performance fiber-reinforced cementitious composites. The shear behavior of ten large-scale non-prestressed UHPC beams was studied. The experimental parameters included the shear span-to-effective depth ratio, the fiber volume fraction, and the type of fibers. It was found that both MHS fibers and PVA fibers were effective in enhancing the shear performance of the UHPC beams whether the shear transfer mechanism was governed by arch action or beam action. Moreover, the measurement results of the average crack spacing imply the distinct difference in the fiber bridging effects of the MHS fibers and PVA fibers in the UHPC beams.

Drop-Weight Impact Resistance of Ultrahigh-Performance Concrete and the Corresponding Statistical Analysis

An experimental and statistical study on the impact resistance of ultrahigh-performance concrete (UHPC) is presented. The impact resistance was evaluated by conducting the drop-weight impact test with a hammer of 10 kg following ACI Committee 544 (ACI 544.9R-17). Three mixture types, namely ordinary concrete, nonfibrous UHPC matrix, and UHPC were designed, and each type was prepared with 40 cylindrical specimens with dimensions of Φ150×63.5 mm for impact test. The commonly used distribution functions for material properties (normal distribution and Weibull distribution) were selected to examine the test data, and the goodness of fit of these two distributions was evaluated using a Anderson-Darling test. Results indicate that the designed UHPC endured an average of 623 drops of impact weight before the first crack, while the ordinary concrete and nonfibrous UHPC matrix showed the first crack only after 26 drops and 17 drops, respectively. The higher-strength nonfibrous UHPC matrix broke with a fewer number of drops under impact load than the ordinary concrete (with coarse aggregate) due to the greater brittleness of the UHPC matrix. Both the normal and Weibull distribution can describe the impact resistance of ordinary concrete, while the nonfibrous UHPC matrix and UHPC showed poor fitness to either the normal or Weibull distribution. Statistical analysis results indicate large scatters in the impact resistance of UHPC, and tests with small sample size may result in unreliable judgment. In this paper a baseline of UHPC drop-impact resistance to inspire proper qualification of UHPC members designed to withstand impact loading is provided.

Calibration of KCC model for UHPC under impact and blast loadings

Ultra-high performance concrete (UHPC) is a promising material for both civil and military protective structures against the potential impact and blast loadings. However, the existing numerical simulation studies related to the material model calibrations for precisely describing the dynamic behaviors of UHPC structural members under both impact and blast loadings are limited, and the calibration procedures are also not in consensus. This paper aims to propose a comprehensive Karagozian & Case Concrete (KCC) model parameter calibration procedure and reliable parameter generation method to well predict the dynamic behavior of UHPC members subjected to dynamic loadings. First, the failure surface, equation of state (EOS), damage evolution and strain rate effect parameters were comprehensively calibrated based on the existing experimental and analytical data of UHPC, and general guidelines on the determination of key KCC model parameters for UHPC are given. Then, the numerical simulations with both the autogenerated and the calibrated parameters were carried out to predict the dynamic response and damage evolution of UHPC members, i.e., reinforced UHPC beam and column, UHPC-FST beam, and reinforced UHPC panel, under drop hammer impact and field explosion. By comparing the test data, the validation of the proposed parameter generation approach is verified. The present work can provide helpful references for designing and evaluating the UHPC structural members under potential impact and blast loadings.

Confinement effectiveness of CFRP strengthened ultra-high performance concrete cylinders exposed to elevated temperatures

Abstract Fire-related damage is an alarming concern to reinforced concrete (RC) structures throughout their service lives. When exposed to extreme temperatures, concrete can endure severe damage. Given that a complete replacement and/or demolition of fire-damaged structures can be an economic waste, a more viable option for extending the service life of the damaged structures involves repairing or strengthening the damaged members. Due to its more efficient qualities over conventional concrete, the use of concrete, such as ultra-high-performance concrete (UHPC) in the building industry, has dramatically grown in recent years. However, limited information is available about the confinement behavior of the unheated and heated UHPC members, particularly when wrapped with fiber-reinforced polymers (FRP). This paper investigates the effect of carbon fiber reinforced polymer (CFRP) sheet strengthening on the compressive strength of both UHPC and ultra-high-performance fiber reinforced concrete (UHPFRC). In this study, strengthening has been considered for the UHPC cylinders before and after they were subject to an elevated temperature of 400°C, and they were left to cool by air cooling. Six UHPC mixes, which were made without the use of fibers, steel fibers (SF) alone, a hybrid system of SF and polyethylene alcohol (PVA), in addition to a hybrid system of steel, PVA, and polypropylene (PP) fibers were tested. Regarding the plain and various fiber-reinforced UHPC both at room temperature and after being exposed to 400°C, the ultimate compressive strength of CFRP-confined concrete has shown an increase by 25% to 33% and 52% to 61%, respectively compared with the unheated specimens.

Vehicular impact resistance of highway bridge with seismically-designed UHPC pier

This study strives to numerically explore the performance of highway bridge supported by seismically-designed ultra-high performance concrete (UHPC) piers in resisting heavy truck impact. Firstly, six types of bridge piers are designed with considering two different concrete types (i.e., normal strength concrete (NSC) and UHPC) and three various seismic hazard levels (i.e., earthquake intensities (EI) of 7, 8, and 9) according to Chinese seismic design specifications, and the corresponding refined finite element (FE) models are established and validated by reproducing the tests of drop hammer impacting on reinforced NSC and UHPC members. Based on the well-verified FE models of simply-supported double-pier bent highway bridge and heavy truck, total 54 collision scenarios are carefully designed by referring to the actual accidents, and the vehicle-pier collision analyses are numerically performed by using the nonlinear FE analysis program LS-DYNA. Then, the effects of seismic fortification level and concrete type of impacted pier on the vehicular impact force and dynamic responses of entire bridge structure, as well as the damage and failure modes of both impacted pier and entire bridge are studied. It demonstrates the effectiveness of seismically-designed UHPC pier on improving the vehicle-impact resistance of bridge structure. Besides, more attentions should be paid to the safety of NSC-EI7 and UHPC-EI7 piers and the brittle shear failure in NSC-EI8 piers. Finally, aiming to quantitatively compare the anti-collision performances of entire bridge structure supported by NSC and UHPC piers under the identical seismic fortification intensity, a performance evaluation method of entire bridge structure is proposed based on the residual lateral displacement of the impacted pier. The present work can provide helpful references for the practical applications of UHPC in bridge piers and the on-site feasible evaluation of the residual performance of the post-collision bridge structure.

Anchorage performance of bolt connection embedded in thin UHPC members

Ultra-High-Performance Concrete (UHPC) has the remarkable durability and outstanding mechanical properties such as exceptionally high compressive strength and superior tensile strength. Therefore, the cross section of UHPC structure is generally optimized to make members light and thin. This paper investigated the behavior of single bolt embedded in thin HSC (high strength concrete) and UHPC members under tension loading. Fourteen tension tests were conducted to study the influences of concrete type, embedment depth and diameter of bolt on anchorage performance. The anchorage performance of these anchors embedded in UHPC were significantly improved compared with the bolts in HSC concrete, in both load capacities and displacement capacities. The superior strength and fiber bridging reduced the Angle of fracture, which is approximately 20° to 24°. As a result, the concrete breakout failure area was improved, resulting in an increase in breakout strength and displacement capacity. The test results were discussed in detail to emphasize the influence of concrete splitting on the anchorage performance of bolts embedded in UHPC members. Compared with HSC members, due to the fiber bridging, failure of UHPC members did not happen when splitting. However, the concrete splitting resulted in the decrease of breakout strength. Finally, a splitting modification factor is proposed to predict anchorage strength based on the test results obtained in this paper and others.

Theoretical Local Buckling Behavior of Thin-Walled UHPC Flanges Subjected to Pure Compressions.

To enhance structural performance of concrete and reduce its self-weight, ultra-high-performance concrete (UHPC) with superior structural performance has been developed. As UHPC members with 180 MPa or above of the compressive strength can be designed, a rational assessment of thin-walled UHPC structural member may be required to prevent unexpected buckling failure that has not been considered while designing conventional concrete members. In this study, theoretical local buckling behavior of the thin-walled UHPC flanges was investigated using geometrical and material nonlinear analysis with imperfections (GMNIA). For the failure criteria of UHPC, a concrete damaged plasticity (CDP) model was applied to the analysis. Additionally, an elastic-perfectly plastic material model for steel materials was considered as a reference to establish differences in local buckling behavior between the UHPC and steel flanges. Finite element approaches were compared and verified based on test data in the literature. Finally, this study offers several important findings on theoretical local buckling and local bending behavior of UHPC flanges. The inelastic local buckling behavior of UHPC flanges was mainly affected by crack propagation due to its low tensile strength. Based on this study, possibility of the local buckling of UHPC flanges was discussed.

Dynamic responses of reinforced ultra-high performance concrete members under low-velocity lateral impact

This paper presents a combined experimental and numerical study on the low-velocity lateral impact behavior of reinforced ultra-high performance concrete (UHPC) members. Firstly, a total of eleven steel bar reinforced UHPC and two reinforced normal strength concrete (NSC) control specimens with the identical dimensions (300 mm × 300 mm × 2200 mm) were prepared and tested under drop hammer impact. By examining the influences of impact energy (16.66–33.32 kJ) and the axial force (140–1400 kN) on the dynamic damage and responses of specimens, the outstanding impact resistance of UHPC members is validated and assessed quantitatively. Besides, the presence of axial force can effectively improve the lateral impact resistance of the UHPC members, particularly the recovery of deformation. Secondly, based on the commercial finite element (FE) program LS-DYNA, a FE model was established to predict the impact behavior of UHPC members. The Continuous Surface Cap (CSC) model for NSC was adopted, and the corresponding model parameters for UHPC were calibrated based on a series of test data, i.e., static compressive and direct tensile tests, dynamic compressive and tensile tests, triaxial compressive tests, and hydrostatic tests. Furthermore, the generation method of CSC model parameters for UHPC was proposed, which was fully validated by comparing with the present and existing low-velocity impact test data on reinforced UHPC and UHPC filled steel tube (UHPC-FST) members.

A review on seismic behavior of ultra-high performance concrete members

Ultra-high performance concrete (UHPC) is a type of cementitious composite, and demonstrates very high compressive strength and good ductility. The favorable ductility and energy dissipation capacity of UHPC material make it possible to achieve excellent seismic performance in all kinds of structural members. The paper reviewed the recent progress on the seismic behavior of UHPC members, including flexural members (beams and plates), compressive members (columns and shear walls), joints (beam-column joints and plate-column joints), strengthening (strengthening for columns, shear walls and joints) and connections (bar lap splice and grout). A series of potential future researches on the seismic behavior of UHPC members were finally suggested for promotion of the application of UHPC in civil engineering.

Calibration of KCC concrete model for UHPC against low-velocity impact

As an innovative material, UHPC (ultra-high performance concrete) is regarded as a promising material to improve dynamic resistant performance of civil engineering structures suffered from extreme loadings such as blast, shock and impact loading. The mechanical properties of UHPC members suffered from static/dynamic loading have been systematically investigated through many physical experiments. However, the rationality of the constitutive model utilized in numerical simulations (especially the finite element simulations) to precisely describe behaviors of UHPC has been little emphasized. The objective of this study, therefore, is to calibrate the KCC (Karagozian & Case Concrete) model to effectively predict behaviors of UHPC suffered from low-velocity impact loading. At the beginning, the properties of UHPC under triaxial compression were experimentally investigated by a series of triaxial compression tests to obtain the parameters of three strength surfaces by experimental data fitting. Meanwhile, EoS (equation of state) was derived by the combination of hydro-static compression test, “p-alpha equation” and Mie–Grueneisen equation of state. Moreover, suitable damage parameters were given by repeated trials, and the suitable model of strain-rate effect for UHPC was also suggested. The single element analysis results indicate that the calibrated KCC model can reasonably reflect the behaviors of UHPC under the uniaxial and triaxial stress state. Eventually, numerical results of low-velocity impact tests of UHPC columns and beams based on the calibrated KCC model agree very well with the tests results, which indicates the rationality of the calibrated KCC model for numerical simulations on low-velocity impact.

Effect of reinforcement ratio, fiber orientation, and fiber chemical treatment on the direct tension behavior of rebar-reinforced UHPC

The direct tension performance of rebar-reinforced ultra-high performance concrete (UHPC) was investigated in this paper. Nine series of dog-bone specimens were tested under the direct tension load at both material and component levels. The experimental variables include the reinforcement ratio, fiber orientation, and fiber chemical treatment. The experiments showed that the rebar-reinforced UHPC members exhibited the tensile failure with the rupture of steel rebars. Meanwhile, a single and localized main crack was observed, accompanied by closely spaced short and small micro-cracks. It is concluded that the addition of longitudinal reinforcement can effectively improve the post-cracking stiffness, the ability to restrain the crack width and the peak load of UHPC members under direct tension load, whereas indicated little influence on the elastic linear behavior and their first cracking load. Moreover, increasing the reinforcement ratio not only has these effects but also can significantly enhance the yield load and ultimate load. Nevertheless, increasing the reinforcement ratio has little effect on the pre-cracking stiffness and the first cracking load. In addition, the employment of parallel fiber orientation can significantly increase the post-cracking stiffness, first cracking load, yield load and peak load, and can significantly restrain the propagation of the crack width, as well as improve the tension stiffening response of UHPC. However, this method has little effect on the pre-cracking stiffness and the ultimate load. Besides, the fiber chemical treatment with ZnPh had no noticeable effect on the direct tension behavior of rebar-reinforced UHPC specimens. Finally, a formula was set up to calculate the tensile loading capacity of UHPC members and the prediction agreed well with the test results in the present and previous studies.

Flexural capacity prediction of composite RC members strengthened with UHPC based on existing design models

Ultra-high-performance concrete (UHPC), a new generation of cementitious materials with very high strength, ductility, and durability, has been used for enhancing reinforced concrete (RC) structures as a strengthening material. The structural performance of RC members strengthened by UHPC or UHPC-concrete composite members is significantly improved. However, there are few methods for predicting the capacity of UHPC-concrete composite members. The present study proposes a simple method based on existing design models for the prediction of the flexural strength of composite RC members strengthened with UHPC at the tension zone. Rectangular stress block diagrams are used for the compression and tension zones of the conventional concrete and UHPC layers, respectively, in a composite section. The prediction results show good agreement with experimental results. The failure modes are predicted and compared with those observed in an actual test. Furthermore, a parametric study is carried out by varying some parameters, including the thickness of the UHPC layer and the compressive strength of UHPC. The results show that the proposed method can predict the flexural strength of UHPC-concrete composite members.

NUMERICAL SIMULATION OF THE BLAST-RESISTANT RESPONSE OF ULTRAHIGH-PERFORMANCE CONCRETE STRUCTURAL MEMBERS

This paper presents the blast responses of ultrahigh-performance concrete (UHPC) structural members obtained using finite element (FE) modelling. The FE model was developed using LS-DYNA with an explicit solver. In the FE simulation, the concrete damage model, which is a plasticity-based constitutive material model, was employed for the concrete material. The simulation results were verified against previous experimental results available in the literature and were shown to be in good agreement with the experimental results. In addition, the developed FE model was implemented in a parametric study by varying the blast weight charges. The numerical results for UHPC members were compared with those for conventional reinforced concrete (RC) members. The numerical responses, such as the maximum deflections, deflected shapes, and damage patterns, of the UHPC members subjected to blast loading were significantly better performance than those of the RC members as a result of the high strength and ductile capacity of UHPC.

Finite element modelling to predict the flexural behaviour of ultra-high performance concrete members

This paper presents a finite element (FE) modelling to predict the behaviour of ultra-high performance concrete (UHPC) members under static flexural loading. A plasticity-based constitutive model for concrete and an implicit solver in LS-DYNA were adopted in the numerical simulation. Experimental data for 21 UHPC specimens tested in the present study and in previous works were used to calibrate and validate the proposed FE model and modelling technique. The simulation was able to accurately predict the experimentally obtained ultimate strength, stiffness, and hardening and softening behaviours of the specimens. This demonstrates the effectiveness and adequacy of the developed FE model and modelling technique.

Design and behavior of super-long span cable-stayed bridge with CFRP cables and UHPC members

This paper proposes a cable-stayed bridge with carbon fiber-reinforced polymer (CFRP) cables and ultra-high performance concrete (UHPC) members and presents its design and structural behavior to analyze its feasibility with a super-long span. Based on the geometrical dimensions of a real cable-stayed bridge with a steel girder and cables in addition to a normal concrete (NC) pylon and main-span of 1088 m, a new counterpart cable-stayed bridge using CFRP cables and a UHPC girder and pylon was designed. The dimensions of the UHPC girder were quantified by the section stiffness, punching resistance, local stability, and shearing resistance. The cross-section sizes of the CFRP cables were determined by the principle of equivalent strength. The geometric and physical conditions of the UHPC pylon satisfied the principle of similarity theory. Using the finite element method, a comparative analysis of the mechanical behavior of two cable-stayed bridge schemes was conducted, specifically regarding the static behavior, global stability, aerostatic stability, dynamic mode, and seismic performance. The results indicated that the detailed design and superior performance of the CFRP and UHPC made it practical to form a highly efficient and durable concrete cable-stayed bridge system with CFRP cables and UHPC members. Moreover, these properties could enlarge the main-span of a concrete cable-stayed bridge to approximately 1000 m.

Flexural behaviour of rebar-reinforced ultra-high-performance concrete beams

A detailed experimental programme was conducted to investigate the structural behaviour of rebar-reinforced ultra-high-performance concrete (UHPC) beams subjected to pure bending and combined bending and shear. Four flexural bending tests and four bending–shear tests were conducted and four different reinforcement ratios (1·09%, 2·75%, 3·60% and 4·99%) were used. The bending characteristics of the rebar-reinforced UHPC beams under static loading were assessed, including cracking, failure patterns, deflection, ductility and flexural capacity. The influence of the reinforcement ratio on the flexural performance of the rebar-reinforced UHPC beams was observed and analysed. A model was developed for predicting the ultimate flexural capacity of rebar-reinforced UHPC beams. The adequacy of the prediction model was assessed using experimental data from the current study and the published literature, and the results showed that the model can be used to estimate the ultimate flexural capacity of rebar-reinforced UHPC members accurately. The results of this study provide valuable information for a comprehensive understanding of the structural behaviour of rebar-reinforced UHPC members.

Tension-stiffening effect in steel-reinforced UHPC composites: Constitutive model and effects of steel fibers, loading patterns, and rebar sizes

The tensile performance of steel-reinforced concrete members is closely associated with the bond interaction between concrete and the embedded rebar. Ultra-high performance concrete (UHPC) is a rapidly emerging concrete material that has an ultra-high compressive strength and bond strength. When it is reinforced with short, discontinuous fibers, it features a tensile strain-hardening behavior and a damage pattern of closely spaced narrow cracks. The present study investigated the tensile behavior of steel-reinforced UHPC members. Sixteen samples were tested, with the experimental variables including embedded rebar sizes, loading patterns, and steel fibers. The tensile responses of the steel-reinforced UHPC samples were evaluated using multiple performance measures, including the damage pattern, stiffness, load-deformation relationship, rebar strain, and the tension-stiffening behavior of UHPC. The test results showed that the enhanced bond strength due to the inclusion of steel fibers transformed the failure pattern of the steel-reinforced UHPC from multiple localized cracks into a single localized crack, which intensified the strain concentration in the embedded rebar. Although the addition of fibers substantially strengthened the tension-stiffening response of the UHPC, it also raised critical concerns about premature failure, especially when UHPC members were reinforced with small steel bars and subjected to monotonic loading. In addition to the experimental study, a tetra-linear constitutive model that was able to reasonably represent the tension-stiffening behavior of fiber-reinforced UHPC up to failure was suggested in this study.

An Experiment on the Bond-Slip Behaviors of Pre-Tensioned Prestressed UHPC Members

An Ultra High Performance Concrete (UHPC) exhibits very high compressive and tensile strength and excellent durability comparing to those of the conventional concrete. The applications of UHPC to precast and/or prestressed concrete result the optimum utilization of high strength characteristics. This paper experimentally investigates the bond-slip behaviors between prestressing strands and UHPC in pretnesioned members. The diameters of strands, 12.7mm and 15.2mm, the cover depths and tensioning forces are chosen as variables, which are known to affect the bond behaviors. The bond-slip curves for various specimens are obtained and the equations for bond strengths of UHPC are derived based on experiments.

Design of UHPC Structural Members: Lessons Learned and ASTM Test Requirements

Abstract Over the past decade, ultra-high performance concrete (UHPC) has been used in several pilot projects, which included designing of different bridge components. In each case, it became clear that the design efficiency and cost effectiveness of the UHPC structural member was not possible when the conventional approaches developed for normal concrete members were followed. More efficient structural design solutions were realized when alternative geometries and/or unique properties of the UHPC were taken advantage of in the design process. Structural testing of these members and/or field testing of bridges designed with UHPC structural members showed that their performance was extremely satisfactory in spite of adopting new design concepts and alternative geometries. Drawing design experience from bridge girders to bridge decks to UHPC piles to wind turbine towers, this paper summarized the important lessons learned and established ASTM test requirements that could facilitate designing of cost-effective UHPC members and connections with satisfactory performance. In this process, ultimate strength for flexure, shear and torsion, fatigue resistance, serviceability issues and long-term behavior of different UHPC members were given consideration.