High-performance Fiber-reinforced Cementitious Composites Research Articles

Cyclic behaviour of steel ring filled with compressive plastic or concrete, installed in the concentric bracing system

The present study intended to evaluate the dynamic behaviour of steel ring filled with compressive plastic (SRP) or high-performance fibre-reinforced cementitious composites (SRC) situated at the intersection of the braces. High-performance fibre-reinforced cementitious composites and plastic materials, associated with steel ring connection, seem to be helpful to dissipate the energy through braces better. Therefore, in this paper, the behaviour of SRC and SRP connections was analyzed under cyclic loading. Results showed a steady and relatively wide hysteresis curve for both connections, where the tensile ductility factors of SRP and SRC connections were found to be equal to 2.77 and 13.66, respectively. However, in general, the plastic ring, being operated efficiently to delay appearing the inelastic zone in the SRP connection, was proved to outperform the HPFRCC material in the SRC connection. In addition, numerical results revealed that maximum tensile and compressive loads of SRP connection made with ST52 steel ring were found to be 14% and 10.7%, respectively, higher than those of SRP connection made with ST37 steel ring.

Tension and Cyclic Behavior of High-Performance Fiber-Reinforced Cementitious Composites

AbstractIn this research the constitutive behavior of high-performance fiber-reinforced cementitious composites (HPFRCCs) was evaluated experimentally under uniaxial monotonic tension and cyclic lo...

INFLUENCE OF HPFRCC COMPRESSIVE STRENGTH AND CONFINEMENT ON CONCRETE

The article analyses behavior of compressed concrete cylinders which were strengthened with external high performance fiber reinforced cementitious composite (HPFRCC) layer. Two different HPFRCC materials were used for the strengthening, which differed in fiber type. Two different types of loading were applied as well. The load was transferred through the whole cross section of the strengthened element and through the core – internal concrete. Loading through the whole cross section allows to validate the mixture law. Loading through the internal concrete allows to investigate the confinement effect. Comparison of theoretically calculated and experimental strength shows that mixture law and confinement effect is valid. Confinement by HPFRCC allowed to increase the strength of concrete about 4 times, but the ultimate strain remains similar. The strength of elements loaded through the whole surface has increased much more and additionally the ultimate strain has increased too.

Material properties and structural characteristics influencing deformation capacity and plasticity in reinforced ductile cement-based composite structural components

Composite structural components using high-performance fiber-reinforced cementitious composites (HPFRCCs) reinforced with mild steel have been observed to fail due to reinforcement fracture instead of crushing of the concrete material. Unlike traditional reinforced concrete members, experimental findings have shown that HPFRCC component ductility increases with reinforcement ratio; however, variation in deformation capacity for a given reinforcement ratio is still not well understood. This study investigates the influence of composite material properties and structural characteristics on deformation capacity of reinforced HPFRCC members using numerical simulation. Finite element models were simulated under monotonic loading to understand the variability in deformation capacity through HPFRCC damage patterns, bond-slip between HPFRCC matrix and longitudinal reinforcement, and spread of plasticity in the longitudinal reinforcement. Simulation results show that there is a substantial decrease in component deformation capacity with high strength HPFRCC materials due to the formation and propagation of flexural cracks. The effects of boundary conditions and shear span-depth ratio are also explored. Discussion is provided to assess the relative influence of HPFRCC material and structural characteristics on component-level performance in terms of cracking, strain distribution, and deformation capacity to better inform future development of materials and structural applications.

Behaviors of New RC Bridge Columns Made of Highly Flowable Strain-Hardening Fiber-Reinforced Concrete (HF-SHFRC) under Cyclic Loads

Abstract Remarkable development of high-strength concrete and reinforcement has been achieved nowadays. The purpose of the New Reinforced Concrete (New RC) project is aimed to reduce member section size by using high-strength concrete (f′c > 70 MPa) and high-strength rebars (fy > 685 MPa). Material consumption can be further reduced owing to the upgrade of strength. However, the brittle nature of high-strength concrete may also cause early cover spalling and other ductility issues. The addition of steel fibers is an alternative transverse reinforcement in New RC infrastructure systems. Highly flowable strain-hardening fiber-reinforced concrete (HF-SHFRC) has excellent workability in the fresh state and exhibits the strain-hardening and multiple-cracking characteristics of high-performance fiber-reinforced cementitious composites (HPFRCC) in their hardened state. This study aims to investigate the cyclic behavior of New RC bridge columns made of HF-SHFRC. Five large-scale bridge columns are subjected to cyclic lateral loading to verify their responses and deformation capacity. The test results show that by adding 1.5 % of high-strength hooked steel fibers, great deformation capacity is developed, in which either the stirrups spacing is increased to two times that of the control specimen or all tires are eliminated in New RC bridge columns. In addition, the accuracy of the proposed concept of equivalent lateral reinforcement is verified by the test results. Implementation of HF-SHFRC in New RC infrastructure offers opportunities to significantly simplify the design and construction of members for sustainable urbanization while ensuring adequate ductility and damage tolerance.

Axial Behavior of Noncircular High-Performance Fiber-Reinforced Cementitious Composite Members Externally Jacketed by CFRP Sheets

AbstractAs the first study reported in the literature on the axial behavior of noncircular high-performance fiber-reinforced cementitious composite (HPFRCC) members externally jacketed by fiber-rei...

Experimental study on seismic performance of precast LSECC/RC composite joints with U-shaped LSECC beam shells

Precast beam-column joints are key components of precast reinforced concrete (RC) frame structures. The complex reinforcement details in the joint zone due to high seismic demand have made the prefabrication and construction process in regions with high earthquake intensity difficult to perform. As a type of high-performance fiber-reinforced cementitious composites (HPFRCCs), low-shrinkage engineered cementitious composite (LSECC) exhibits stable strain hardening and multiple cracking properties with a dry shrinkage even lower than that of normal concrete. A partial substitution of concrete with LSECC can significantly improve the seismic performance and damage tolerance of beam-column joints and help simplify the reinforcement details in the joint zone. This paper proposes a novel precast LSECC/RC composite beam-column joint using U-shaped precast LSECC beam shells. Five interior beam-column sub-assemblages were tested under cyclic loading, including one monolithic and four precast specimens. Parameters including lap splice length, transverse and longitudinal reinforcement ratios were studied. The proposed construction process was proven to be both easy and fast. The performance of the precast joints were evaluated in terms of the ultimate capacity, deformation, energy dissipation, shear distortion and strength of the joint core. The test results showed that the proposed joints could effectively simplify the joint reinforcement details while maintaining the required seismic performance. The diagonal cracks in the joint zone without transverse reinforcement were well controlled. A few stirrups in the joint zone could reduce the shear deformation and improve the energy dissipation capacity. The shear strength of the LSECC joints without any transverse reinforcement were found to be similar to the nominal shear strength of well-confined normal concrete joints suggested by ACI 318-14.

Nonlinear seismic assessment of irregular coupled wall systems using high‐performance fiber‐reinforced cement composites

SummaryReinforced concrete coupled wall systems that consist of multiple shear walls linked by coupling beams are known to be very effective for resisting lateral loads in high‐rise buildings. As to improving the seismic capacity of coupled wall systems, high‐performance fiber‐reinforced cement composites (HPFRCCs) have been recently considered. These materials are characterized by tension strain‐hardening behavior that can improve the ductility and toughness of structures subjected to reversed cyclic loading. In this study, nonlinear finite element analyses were conducted to investigate the effects of HPFRCCs on the seismic behavior of irregular tall buildings with coupled wall systems. The coupling beams were modeled using moment hinge elements, and the structural walls were modeled using fiber elements. Comparisons between analysis and test results of coupled wall specimens with and without HPFRCCs indicate that the modeling methods used well predict both the overall and local behaviors. The responses of a 56‐story irregular tall building with coupled walls are discussed with focus on the effects of HPFRCCs. It is noted that the use of HPFRCCs in coupling beams and structural walls of one‐fourth height from the base greatly affects the failure mode. For irregular tall buildings, nonlinear response history analysis indicates higher mode effects are critical.

Seismic Behavior of High-Performance Fiber-Reinforced Cement Composites Beam-Column Connection with High Damage Tolerance

The purpose of this study is to investigate and evaluate the feasibility of using high-performance fiber-reinforced cement composites (HPFRCC) to satisfy the requirement of transverse reinforcement in beam-column joint under seismic loads. The basic mechanical properties of the HPFRCCs are determined by compression, uniaxial tension, and direct shear tests. Four half-scale exterior beam-column connections are cast and tested under cyclic loads. The cracking patterns, hysteresis behavior, ductility, energy dissipation with damping characteristics and joint shear capacity of the HPFRCC beam-column connections are analyzed, investigated, and compared to the cyclic responses of normal concrete connections designed with/without seismic criteria of ACI. The test results revealed that HPFRCC connections considerably enhances shear and flexural capacity and also improved the deformation and damage tolerance behavior in post-cracking stage comparing to normal concrete connections in ultimate stages. Also, the failure mode of HPFRCC specimens changed from shear mode to flexural mode comparing to the connections without seismic details. Severe damages are observed in normal concrete connection designed without considering seismic criteria. Wide diagonal cracking and damage are observed on the designed NC connections under large cyclic displacement at drift 6%. However, in HPFRCC connections, joint remained intact without any cracks and damage until the test end. This implies that the shear stress requirement can be satisfied without any need to the transverse reinforcement in the HPFRCC joint.

Post-fire seismic behavior of two-bay two-story frames with high-performance fiber-reinforced cementitious composite joints

High-performance fiber-reinforced cementitious composite (HPFRCC) has potential to greatly improve the fire resistance and seismic behavior of concrete structures. This paper reports an experimental investigation on post-fire seismic behavior of two-bay two-story frames with HPFRCC joints. Four reinforced concrete frames were fabricated; three of them were tested in compartment fire for 60 min. The fire was regulated following ISO-834 temperature curve. Two different fire scenarios (one- and two-bay fire) were investigated. Two frames were made of monotonic conventional concrete; the other two frames had HPFRCC joints. Each frame was tested under a constant vertical load and a pseudo-static cyclic horizontal load with increased magnitude until the frame failed. The effects of the HPFRCC and fire scenarios on the failure mechanism, hysteretic loops, envelope curve, stiffness degradation, and energy dissipation of the frames were evaluated. The experimental results revealed that the fire exposure reduced the load capacity and deformability of the frames. In the two-bay fire scenario, the use of HPFRCC joints increased the post-fire load capacity by 11%, ultimate deformation by 6%, initial stiffness by 30%, and energy dissipation by 21%. The cyclic behavior of the frame in one-bay fire was better than that in two-bay fire. The frames with HPFRCC joints demonstrated better cyclic behaviors than the virgin reinforced concrete frame.

Investigation of the usability of high-performance fiber-reinforced cement composites containing high-volume fly ash and nanomaterials as repair mortar

High-performance fiber-reinforced cement composite (HPFRCC) mixtures containing high-volume fly ash and nanomaterials are investigated in this study. In order to determine high early strength and high connection performance between repair mortar produced with HPFRCC containing nanomaterials, high volume fly ash, and concrete which will be repaired, compressive strength, elasticity, and slant shear test were conducted on the samples. The experimental results showed that HPFRCC mixtures containing nanomaterials increased the strength on 1, 3, 7, 28, and 90 days in comparison to control mortars for compressive strength test. Also, the samples containing nanosilica gave the highest compressive strength in all mixtures. In addition, the samples containing nanosilica gave the best result for elasticity modulus, showing similarity to compressive strength test. For the bond strength, deformations were observed on the old concrete in the samples formed from HPFRCC mixtures and old concrete. Expected sloping surface sliding was not occurred.

Static and fatigue push-out tests of short headed shear studs embedded in Engineered Cementitious Composites (ECC)

Engineered Cementitious Composites (ECC) is a family of high-performance fiber-reinforced cementitious composites with high tensile ductility and emerging in steel-concrete composite structures. In the composite structures, shear force transfer through shear connectors plays a critical role to integrate the steel and concrete. This study experimentally investigates the static and fatigue behaviors of short studs embedded in ECC through push-out tests of nine specimens. The test results of the shear strength, slip capacity, and fatigue resistance are compared with current design codes. The shear strength agrees well with that obtained from AASHTO LRFD, while the Eurocode 4 and Chinese code underestimate the shear strength. The slip capacity satisfies the ductility requirement in Eurocode 4. Based on the fatigue tests results, an S-N curve related to a survival probability of 95% is proposed. Empirical formulas are derived as a tool to help predict the load-slip behavior of the specimen under fatigue loading.

Tri-axial compressive properties of high-performance fiber-reinforced cementitious composites after exposure to high temperatures

This study experimentally investigates tri-axial compressive properties of high-performance fiber-reinforced cementitious composites after exposure to high temperatures up to 800 °C. First, 16 mixtures were designed and tested to evaluate the effect of mixture proportioning variables on the tri-axial compressive properties. The investigated mixture proportioning variables included the water-to-binder ratio (0.24–0.36), sand-to-binder ratio (0.36–0.66), fly ash content (60–75%), fiber content (1.5–2.2%), and superplasticizer content (0.10–0.25%). Based on the test results, an optimum mixture was presented and tested at five confining pressure levels up to 25 MPa and three loading rates up to 60 με/s before and after exposure to high temperature. The cylinders were exposed to the targeted temperatures and then loaded under combined constant lateral confining pressure and an increasing longitudinal compressive load until failure. The tri-axial compressive strength degraded as the heating temperature increased from 200 °C to 800 °C; the strain limit increased with the heating temperature from 600 °C to 800 °C. As the confining pressure increased from 5 MPa to 25 MPa, the tri-axial compressive strength increased by about 50% at 25 °C and 80% at 800 °C.

Effect of self-healing on fatigue of engineered cementitious composites (ECCs)

This paper presents a pioneer study on the effects of self-healing on the flexural fatigue performance of engineered cementitious composites (ECCs), a unique class of high-performance fiber-reinforced cementitious composites (HPFRCC) exhibiting tensile strain-hardening behavior with tensile strain capacity in excess of 3% with only 2% or less fiber content by volume. Results show that self-healing greatly extends the fatigue life of ECC because water/dry conditioning not only heals the matrix cracks but also recovers the fiber/matrix interfacial bonds which leads to increased fiber-bridging strength. ECC fatigue life increases with increasing fatigue pre-damage level because higher fatigue pre-loading cycles together with water/dry conditioning troubleshoots more potential failure planes. Repeated healing at lower pre-damage level is feasible and significantly extends fatigue life of ECC.

Cyclic behavior of diagonally reinforced slender HPFRCC coupling beams with reduced diagonal and transverse reinforcement

Slender diagonally reinforced coupling beams (DRCBs) have been increasingly used for coupled shear wall systems in high-rise buildings, which can reduce the height of buildings and associated construction costs. However, in practice, it is difficult to make slender DRCBs according to current design provisions due to heavy reinforcement congestion. To alleviate the reinforcement congestion problem and improve the cyclic behavior of the coupling beams, High Performance Fiber-Reinforced Cementitious Composite (HPFRCC) DRCBs with new reinforcement arrangements or a reduced amount of reinforcement have been developed. The objective of this study is to explore the cyclic behavior of slender DRCBs made of HPFRCC with polyvinyl alcohol (PVA) fibers. Experimental tests were conducted with six DRCB specimens with a length-to-height (ln/h) of 3.5 to investigate the effect of the HPFRCC and the amount of diagonal and transverse reinforcement on the cyclic behavior of slender DRCBs. In this study, an empirical equation for predicting the shear strength of slender HPFRCC DRCBs was also proposed, considering the contributions of the HPFRCC and the amounts of diagonal and transverse reinforcements. The proposed equation was verified by using HPFRCC DRCB specimens with ln/h ranging from 2.0 to 3.5.

Investigation of the Flexural Behavior of RC Frames Strengthened with HPFRCC Subjected to Lateral Loads

The strengthening of damaged concrete structures using new cementitious composites such as high-performance fiber-reinforced cementitious composites (HPFRCC) with proper strain hardening behavior under cyclic loads is a suitable solution for economic utilization of RC structures. In this paper, the technique and results of strengthening the damaged and undamaged frames with HPFRCC composite thin layer subjected to lateral and gravity loads are presented. Experimental program includes four frames, one unstrengthened and undamaged frame as reference, one strengthened undamaged frame, and two strengthened partially damaged (with initial 55 and 75 percentage of ultimate load), and they were tested under both vertical and lateral loads. The results indicated that the ductility of two strengthened frames with initial 55, 75% damage of the maximum load and the undamaged strengthened frame was up to 110, 60, and 121% more than that of reference frame, respectively. The yielding loads of the tension bars at the strengthened damaged and undamaged specimens had been significantly increased up to 42%, and ultimate loads of the undamaged and two damaged frames (55, 75%) were increased up to 38 and 35, 16% compared to the reference frame; energy absorption in three same frames was 2.37, 2.75, 1.83 times of that of unstrengthened reference frame.

Simulation of Deformation Capacity in Reinforced High-Performance Fiber-Reinforced Cementitious Composite Flexural Members

Strategies used to simulate the response of ductile cementitious materials, such as high-performance fiber-reinforced cementitious composites (HPFRCCs), have primarily focused on simulating the ductile cementitious composite material-level response in tension, compression, and shear. However, recent experimental research has shown that the interaction between steel reinforcement and HPFRCCs is critical to the structural performance and deformation capacity of reinforced HPFRCC members. In this paper, an emphasis is placed on predicting reinforced HPFRCC component deformation capacity by studying the reinforcement strain causing fracture in monotonic and cyclic simulations with different reinforcement ratios. All simulations are compared with experimental results from testing of reinforced engineered cementitious composite (ECC) flexural members. A cyclic bond-slip interface material model for reinforced ECC components is developed from experimental data and implemented in a finite-element framework. Numerical simulations of reinforced ECC structural components modeled with perfect bond were compared with the proposed interface bond-slip material model. The results show that including bond-slip behavior in simulations improves predictions of component strength, stiffness, and deformation capacity when the simulations are compared to perfect bond models and experimental results. The sensitivity of simulations to tensile strength and fracture energy is explored, and recommendations for using a damaged fracture energy parameter based on cyclic uniaxial material experiments are discussed. Considerations for understanding factors influencing predicted fracture in reinforced HPFRCC structural components is presented by analyzing reinforcement strain, including bond-slip interface elements, and by using a cyclic fracture energy material parameter.

Electromechanical Response of High-Performance Fiber-Reinforced Cementitious Composites Containing Milled Glass Fibers under Tension.

The self-damage sensing capacity of high-performance fiber-reinforced cementitious composites (HPFRCCs) that blended long- (1 vol %) and medium-length (1 vol %) smooth steel fibers was considerably improved by adding milled glass fibers (MGFs) with a low electrical conductivity to a mortar matrix. The addition of MGFs (5 wt %) significantly increased the electrical resistivity of the mortar matrix from 45.9 to 110.3 kΩ·cm (140%) and consequently improved the self-damage sensing capacity (i.e., the reduction in the electrical resistivity during the tensile strain-hardening response) from 17.27 to 25.56 kΩ·cm (48%). Furthermore, the addition of MGFs improved the equivalent bond strength of the steel fibers on the basis of the higher pullout energy owing to the accumulated cementitious material particles attached to the surfaces of steel fibers.

Seismic behavior of 3-D ECC beam-column connections subjected to bidirectional bending and torsion

Special moment resisting frames (SMF) are commonly used in low- and medium-rise buildings located in regions of high seismicity. Although adequate performance of this seismic force resisting system was observed in prior earthquakes in terms of protecting buildings from collapse, the formation of plastic hinges in the beams and columns causes irreparable damage to the beam-column connections. Recently, interest in using fiber-reinforced concrete (FRC) has been growing to enhance energy absorption capacity and damage tolerance of beam-column connections and other components in reinforced concrete (RC) buildings. Prior research has mostly focused on the application of steel FRC (SFRC) in 2-D beam-column connections. However, little is known about the performance of exterior beam-column connections that are usually subjected to more complex loading during an earthquake, involving bi-directional bending and torsion of the column. In addition to the loading, the geometry of the connection requires a more involved test setup (i.e., with an out-of-plane beam and proper boundary conditions). In this research, the use of engineered cementitious composites (ECC) in 3-D exterior beam-column connections is investigated experimentally to improve building seismic performance. ECC is a special class of high-performance fiber-reinforced cementitious composites (HPFRCC) that, compared to conventional concrete, exhibits higher tensile ductility, energy absorption and shear resistance, in addition to improved bond performance with reinforcing steel (rebar). To understand the performance of exterior beam-column connections under complex loading conditions, scaled 3-D specimens were constructed and tested under simulated seismic loads. To improve the performance of the connections, conventional RC was replaced with reinforced ECC (RECC) that extends from the panel zone to the adjoining beams and columns to cover the potential plastic hinge regions. This paper discusses the loading protocols, the test setup for 3-D exterior beam-column connections, and the improvement in the joint behavior with the application of RECC as compared to conventional RC. The results suggest that the efficient use of ECC in the potential plastic hinge regions can improve the capacity and damage tolerance of beam-column connections under realistic seismic loading conditions.

Enhancement of seismic performance of beam-column joint connections using high performance fiber reinforced cementitious composites

In this paper, six half-scale exterior beam-column joint connections are casted and tested under cyclic loads to investigate and evaluate the possibility of using high performance fiber reinforced cementitious composites (HPFRCC) to remove the necessity of confining (transverse) reinforcements and solve the construction problems in beam-column joints under seismic loads. Fiber reinforced cementitious materials used in this study comprises 2% volume fraction of hybrid fiber, hooked end steel fiber and hybrid macro synthetic fibers. The basic mechanical properties of HPFRCC are determined by uniaxial tension and compression tests. The hysteretic behavior, ductility, stiffness, energy dissipation, damping characteristics and cracking patterns of HPFRCC beam-column joint connections are evaluated and compared with those of normal concrete with and without special seismic requirements in joints. The test results revealed that HPFRCC connections considerably enhanced shear and flexural capacity as well as deformation and damage tolerance behavior at post-cracking stage compared to those of normal concrete at ultimate stages. Moreover, the failure mode of HPFRCC specimens changed from shear mode to flexural mode compared to the failure mode of concretes without required seismic details.