High-performance Fiber-reinforced Cementitious Composites Research Articles

Toughness evaluation of ultra-high toughness cementitious composite specimens with different depths

Ultra-high toughness cementitious composite (UHTCC), which is a kind of high-performance fibre-reinforced cementitious composite, is characterised by tensile strain hardening behaviour and remarkable toughness capacity. The current study presents a toughness estimation of UHTCC beams of different depths under four-point bending. An improved method, based on ASTM C 1609 and JCI-SF 4, is used to evaluate the toughness capacity. In this method, an equivalent deflection transformation relationship between different depths of samples is introduced to ensure that toughness comparison is conducted at similar deformation states. Two toughness evaluation indices at equivalent controlling deflection are adopted. One is the new proposed toughness index Tv, which represents the energy dissipation per unit volume in the plastic hinge region, and the other is the traditional flexural strength parameter. Theoretical analysis and experimental results both indicate that the proposed toughness index Tv is independent of depth for strain hardening cementitious composite, which can be considered as an intrinsic material property.

Feasibility Study of Developing Green ECC Using Iron Ore Tailings Powder as Cement Replacement

This paper reports the results of an initial attempt of using iron ore tailings (IOTs) to develop greener engineered cementitious composites (ECCs). ECC is a unique class of high-performance fiber-reinforced cementitious composites featuring high tensile ductility and durability. However, the high cement usage in ECC limits the material greenness and increases the material cost compared with normal concrete. In this paper, IOTs in powder form are used to partially replace cement to enhance the environmental sustainability of ECC. Mechanical properties and material greenness of ECC containing various proportions of IOTs are investigated. The newly developed versions of ECC in this paper, with a cement content of 117.2–350.2 kg/m3, exhibit a tensile ductility of 2.3–3.3%, tensile strength of 5.1–6.0 MPa, and compressive strength of 46–57 MPa at 28 days. The replacement of cement with IOTs results in 10–32% reduction in energy consumption and 29–63% reduction in carbon dioxide emissions in green ECC compared with typical ECC. Thus, the feasibility of producing greener ECC with significantly reduced environmental impact using IOTs, and maintaining the mechanical properties of typical ECC, is experimentally demonstrated in this paper.

A high performance fibre reinforced cement based plaster for retrofitting RC members

A high performance fibre-reinforced cementitious composite (HPFRCC) material is developed to be used for retrofitting reinforced concrete members. It can be applied to the face of a concrete member to the desired thickness as a wet mix or as an adhesively-bonded prefabricated slab or strip. The material is compatible with concrete and possesses favourable strength and ductility properties, desirable for seismic retrofit. It overcomes some of the problems associated with the current techniques based on externally bonded steel plates and fibre-reinforced polymer (FRP) laminates caused mainly by the mismatch of their tensile strength and stiffness with that of the concrete member being retrofitted. An extensive rheological analysis is undertaken to develop the appropriate mixes using different types and mix proportions of constituent materials including; fine steel fibres, fine quartz sand, silica fume, cement and superplasticizer. Much reduced amounts of steel fibres are used compared to the previous studies so that ordinary mixing procedures could be applied and a more cost-effective retrofitting material could be developed. Samples made of the optimum mixes are shown to posses very high compressive and tensile strengths and sufficient ductility for the composite plaster to be used externally for strengthening and seismic retrofitting of concrete members.

Mechanical performance of corroded RC member repaired by HPFRCC patching

This paper presents a patch repair method that uses high performance fiber reinforced cement composites (HPFRCCs) to repair reinforced concrete members damaged by chloride attack. The beam specimens were deteriorated under chloride attack and then repaired using HPFRCC shotcreting, before they were loaded to investigate their mechanical performance. The experimental results indicates that even after formation of multiple fine cracks under applied load, the HPFRCC remains impermeable due to its very small crack width. With the proposed repair method, the HPFRCC patch layer allowed only very fine cracks to be formed in service conditions. The strength of a beam deteriorated by rebar corrosion could be recovered using HPFRCC patching if the amount of corrosion was less than 10%. It was also clarified that a combined use of a fiber net with HPFRCC patching improves the dispersibility of fine cracks in the HPFRCC layer.

Behavior of High Performance PVA Fiber Reinforced Cement Composites under Uniaxial Compressive Load

Abstract. Based on an extensive experimental program, the paper studies the behavior of High Performance Fiber Reinforced Cement Composite (HPFRCC) under Uniaxial compression. The experimental parameters are: PVA fiber content by volume, fly ash and silica fume content. The compressive strength, peak strain as well as compressive stress-strain curves are obtained. The test results reveal that PVA fibers can greatly improve plastic deformation ability of HPFRCC, especially have significant impact on ductility after the peak stress, though fiber content has small influence on compressive strength. With the increase of fly ash content, peak stress of HPFRCC decreases, but toughness increases. 10% silica fume content has not obvious effect on compressive strength for HPFRCC with large quantities of fly ash , but leads to less ductile behavior.

Study on the Seismic Behavior of Green High-Performance Fiber-Reinforced Cementitious Composites Column

“Strong column and weak beam” failure rarely occurred in the Wenchuan earthquake, and the reasons were analyzed in this paper. A new type of frame column is presented, i.e. green high-performance fiber-reinforced cementitious composites (GHPFRCC) column, and the seismic behaviors are discussed. And this new type of structural member is vital to improve the seismic capacity of the frame structure.

Strain Energy Frame Impact Machine (SEFIM)

This paper proposes an innovative strain energy frame impact machine (SEFIM) designed to explore direct tensile behavior of high performance fiber reinforced cementitious composites (HPFRCC) at high strain rates. The proposed system utilizes an energy frame to store a large amount of elastic strain energy as well as to suddenly generate high rate tensile impact pulse. The prototype of SEFIM demonstrated that the proposed energy frame could store enough elastic strain energy to fail a large-sized tensile specimen at high strain rates in direct tension. The tensile stress versus strain curve of HPFRCC under high rate impact was obtained by using the prototype with the aid of a high speed camera system and dynamic strain gauges attached on the surfaces of the transmitter bar.

Effect of grain size on the mechanical properties and crack formation of HPFRCC containing deformed steel fibers

This research investigated the influence of sand grain size on the behavior of high-performance fiber-reinforced cementitious composites (HPFRCC). Four types of sand with different grain sizes were investigated using the same matrix composition containing 2.0% hooked and twisted fibers by volume. The compressive strength was significantly greater for the finer sand grains, despite little difference in the packing density. The better compressive strength was mainly due to the denser calcium silicate hydrate (CSH) resulting from an intensive pozzolanic reaction with the finer silica sand, rather than to an improvement in packing density. The interfacial bond strength of those fibers was notably improved, having favorable effects on the mechanical properties and multiple crack formation of HPFRCCs. Although both fibers showed superior properties in mortars with a finer sand grain, twisted fiber produced more sensitive behavior according to the sand grain size.

Cyclic responses of reinforced concrete composite columns strengthened in the plastic hinge region by HPFRC mortar

The brittleness of concrete raises several concerns due to the lack of strength and ductility in the plastic hinge region of reinforced concrete columns. In this study, in order to improve the seismic strength and performance of reinforced concrete columns, a new method of seismic strengthened reinforced concrete composite columns was attempted by applying High Performance Fiber Reinforced Cementitious composites (HPFRCs) instead of concrete locally in the plastic hinge region of the column. HPFRC has high-ductile tensile strains about 2–5% with sustaining the tensile stress after cracking and develops multiple micro-cracking behaviors. A series of column tests under cyclic lateral load combined with a constant axial load was carried out. Three specimens of reinforced concrete composite cantilever columns by applying the HPFRC instead of concrete locally in the column plastic hinge zone and one of a conventional reinforced concrete column were designed and manufactured. From the experiments, it was known that the developed HPFRC applied reinforced concrete columns not only improved cyclic lateral load and deformation capacities but also minimized bending and shear cracks in the flexural critical region of the reinforced concrete columns.

Tensile behaviour of high performance fibre-reinforced cementitious composites at high strain rates

The promise of fibre-reinforced cementitious composites for dynamic loading application stems from their observed good response under static loading. An experimental research aimed at contributing to the understanding of the behaviour of advanced fibre-reinforced cementitious composites subjected to low and high strain rates was carried out. The material behaviour was investigated at four strain rates (0.1, 1, 150 and 300 s−1) and the tests results were compared with their static behaviour. Tests at intermediate strain rates (0.1–1 s−1) were carried out by means of a hydro-pneumatic machine (HPM). High strain rates (150–300 s−1) were investigated by exploiting a Modified Hopkinson bar (MHB). Comparison between static and dynamic tests highlighted several relevant aspects. First, with the change in the strain rate, the Dynamic Increase Factor (DIF) of the material appears well predicted by some models proposed in the literature up to a value of 0.1 s−1, while at higher strain rates it increases less than expected from models. Moreover, the post-peak behaviour showed a stress plateau influenced by the fibres and dependent on the strain rate.

Space-Averaged Constitutive Model for HPFRCCs with Multi-Directional Cracking

This paper focuses on numerical modeling of high-performance fiber-reinforced cementitious composites (HPFRCCs), specifically polyvinyl alcohol engineered cement composites (PVA-ECCs) in the context of a space-averaged, fixed-crack approach. Compression, tension, and shear models are proposed. The compression and tension models include internal unloading and reloading paths. The shear model considers the shear stress transfer contributed by surface friction and fiber bridging in a phenomenological manner. The applicability of the models is verified against recent experiments on precracked PVA-ECC plates subjected to principal stress rotation, demonstrating that the proposed models replicate various responses of the plates. The degradation of initial stiffness and overall strength of plates with precracks at different angles is represented well. Lastly, this paper demonstrates the ability of the models to replicate the average strains spanning bidirectional multiple cracks occurring at the bottom surface of the precracked plates.

철근 보강 고성능 섬유보강 콘크리트의 인장 강성

콘크리트의 취성적인 인장 거동을 보완하기 위해 섬유를 혼입한 섬유보강 콘크리트에 대한 연구가 진행되어 왔으며, 그 중 인장균열 이후 변형 경화 거동(strain hardening behavior)을 보이는 고인성 섬유보강 콘크리트(HPFRCC)에 대하여 활발히 연구되고 있다. 하지만, 철근이 없는 HPFRCC의 인장 및 휨거동에 대해 주로 연구가 계속되어온 반면 철근이 배근된 HPFRCC 부재의 인장 거동에 대한 자료는 미흡한 실정이다. 따라서 이 연구에서는 HPFRCC의 인장거동에 대한 철근의 효과를 분석하기 위해 철근이 배근된 HPFRCC 부재를 제작하여 인장 강성(tension stiffening)에 대한 실험을 수행하였고, 인장 강성 실험 결과에서 HPFRCC의 인장 응력-변형률 관계를 도출하였다. HPFRCC는 균열발생 이후에서 항복에 이르기까지 인장 성능을 균일하게 유지하는 것으로 나타났다. 철근이 배근된 HPFRCC의 인장 강도는 철근이 없는 부재에서 측정된 인장강도에 비해 낮아지는 것으로 나타났으며, 이는 HPFRCC의 높은 건조수축량과 철근의 구속효과에 의한 것으로 사료된다. 이 연구에서 확인된 인장강성 실험 결과 및 분석 자료는 HPFRCC를 철근과 함께 적용할 경우 유용하게 활용될 것으로 기대된다.

Using Acoustic Emission to Quantify Damage in High-Performance Fiber-Reinforced Cement Composites under Cyclically Compressive Loading

High performance fiber-reinforced cement composites (HPFRCCs) show multiple cracks and a limited damage tolerance capability due to the debonding of the fibers of the cement matrix. For practical applications, it is necessary to investigate the fractural behavior of HPFRCCs to understand the mechanism of the microbehavior of a cement matrix containing reinforcing fibers. We have investigated the acoustic emission (AE) signals in HPFRCCs under monotonic and cyclic uniaxial compressive loads. Four types of specimen were tested. The experimental parameters studied were: the type of fiber (polyethylene or polyvinyl alcohol), the hybrid type (with steel cord), and the loading pattern. The data shows that the progress of the damage in HPFRCCs in the compressive mode is characteristic of the type of hybrid fiber and its volume fraction. From the AE data, the second and third compressive load cycles resulted in a successive decrease in the amplitude compared to the first compressive load cycle. In addition, an AE Kaiser effect was observed in HPFRCCs specimens up to 80% of their ultimate strength. These observations suggest that the AE Kaiser effect has potential for use as a new tool to monitor the loading history of HPFRCCs.

Discussion on HRBF500 Grain Reinforcement and C100 High-Performance Fiber Reinforced Cementitious Composites (HPFRCC) in the Civil Air Defense Work

The clearance requirement of civil air defense work is a critical question; existing design will lead higher cost and the inconvenience in construction. Through introduction the material properties of HRBF500 reinforced and high-performance fiber reinforced cementitious composites (HPFRCC), calculated the design value of strength and the coefficient of strength for the two materials, provided theoretical for civil air defense work design for the future use HRB500 and the C100 HPFRCC. Based on the practical projects, contrast the frame beam using the HRB335 and C40 with HRBF500 and C100 HPFRCC for reinforcement and cross-section, the results showed that: with the same beam width and same reinforcement, the new material can effectively reduce the high of beams. The combination of these two new materials has a long-term significance in the civil air defense work.

Strain rate dependence of HPFRCC cylinders in monotonic tension

High-Performance Fiber-Reinforced Cementitious Composite (HPFRCC) materials exhibit strain hardening in uniaxial, monotonic tension accompanied by multiple cracking. The durability of HPFRCC materials under repeated loading makes them potentially suitable for seismic design applications. In this paper, the strain rate dependence of tensile properties of two HPFRCC materials in cylindrical specimens is reported from a larger study on strain rate effects in tension, compression and cyclic tension–compression loading. The cylindrical specimens were loaded in monotonic tension at strain rates ranging from quasi-static to 0.2 s−1. To evaluate the impact of specimen geometry on tensile response, coupon specimens loaded in monotonic tension under a quasi-static strain rate were compared to corresponding cylindrical specimens made from the same batch of material. Tensile strength and ductility of the HPFRCC materials were significantly reduced with increasing strain rate. Multiple cracking, strain hardening, strain capacity, and the shape of the stress–strain response were found to be dependent on specimen geometry. SEM images taken of the fracture plane of several specimens indicated that pullout and fracture of the fibers occurred for both HPFRCC materials studied here.

Evaluation of toughness of textile concrete

High Performance Fibre Reinforced Cementitious Composites (HPFRCC) are characterized by a stress–strain response in tension that exhibits strain-hardening behaviour accompanied by propagation of multiple cracks. This process is often referred to as pseudo-ductility due to multiple cracking with relatively large energy absorption capacity. The cracking characteristics are dependent on matrix strength, fibre/matrix bond, fibre volume fraction and the aspect ratio of the fibre used in the composite. The matrix cracking strength and interfacial bond vary with the degree of hydration of cement in the matrix, which is time and environment dependent. This study analyses the multiple cracking patterns formed in weathered Textile Concrete (TC) samples due to direct tensile testing, and links the cracking patterns to the tensile behaviour. The specimens used for the study were thin laminates which were produced by casting six layers of specially made polypropylene (PP) textile in fine-grained mortar. The samples were cured under controlled laboratory conditions for 28 days, and thereafter exposed to different weathering regimes for different periods. The weathered samples were tested in direct tension in a Universal Testing Machine (UTM) over a range of stresses. For all the samples tested, it was observed that the tensile behaviour was characterised by strain hardening and multiple cracking, which gave high tensile strains in excess of 20% at final failure. It was further found that the cracking patterns varied mainly with age, weathering history and stress levels. Other factors that contributed to the cracking characteristics were moisture state of the specimen and the fibre/matrix bonding strength. A strong bond and dense matrix resulted in wide crack spacings compared with samples with a weaker bond which developed closely spaced cracks. A general trend of increasing crack widths and crack spacings with ageing was observed which was accredited to increased hydration accompanied by an increase in fibre/matrix bond strength.

Experimental Study and Theoretical Models on Compressive Properties of Ultrahigh Toughness Cementitious Composites

Ultrahigh toughness cementitious composite (UHTCC) is a new class of high performance fiber-reinforced cementitious composites which exhibits pseudostrain hardening and multiple cracking phenomena. The main objectives of this paper are to investigate the compressive properties of UHTCC and to develop the constitutive models to describe it. The complete study includes an experimental phase and an analytical phase. In the experimental phase, the stress-strain curves were directly obtained, and the compressive parameters, i.e., strength, average strain at maximum stress, elastic modulus, and Poisson’s ratio, were calculated. The relationships of compressive parameters as a function of compressive strength were proposed according to the test results. The comparisons between UHTCC and matrix were carried out to understand the fiber effect on the compressive parameters. In the theoretical phase, comparisons were conducted between experimental results and existing models. As a result, two analytical relationships were proposed for design purpose under ultimate limit state conditions and nonlinear analysis of UHTCC structures. The research should lead to better understand the compressive properties of UHTCC and the mechanisms of fiber reinforcement for UHTCC and to provide analysis models for design or analysis of UHTCC structural members.

Corrosion protection performance of High Performance Fiber Reinforced Cement Composites as a repair material

Abstract This paper regards the corrosion protection performance of High Performance Fiber Reinforced Cement Composites (HPFRCC) as a repair material. For the purpose of improving workability, the volumetric fiber content in HPFRCC was decreased from its usual rate of 1.5% to as low as 0.75%. The applicability of HPFRCC as a repair material for preventing steel corrosion was investigated using specimens that simulated either surface coating repair or patch repair. The results can be summarized as follows: Patch repair with HPFRCC to depths beyond the backside of the reinforcement effectively suppressed chloride penetration and prevented reinforcement corrosion, whereas surface coating with HPFRCC could not prevent corrosion of the steel in the RC substrate. As long as the fiber content is set so that only fine cracks are formed under service conditions, differences in fiber content did not affect the corrosion preventing performance of HPFRCC as a repair material.

Hybrid Rotating/Fixed-Crack Model for High-Performance Fiber-Reinforced Cementitious Composites

High performance fiber-reinforced cementitious composite (HPFRCC) materials are distinguished from conventional concrete materials by their unique strain-hardening behavior in tension, which translates into enhanced shear and bending resistance at the structural level. The favorable properties of HPFRCC have motivated researchers to explore using the material to replace traditional concrete in critical elements of a structure. To predict the behavior of HPFRCC components under various loading conditions, a material model based on a plane stress, orthogonal, hybrid rotating/fixed crack approach was developed in this study. The developed material model addresses the material's pronounced strain hardening behavior and takes into account its loading/ unloading/reloading characteristics. The validity of the developed material model is shown through extensive comparisons between experimental data and numerical results for test specimens exhibiting varied structural responses. The comparison results indicate that the developed HPFRCC material model is capable of simulating the behavior of HPFRCC structures with reasonable accuracy.

Bidirectional Multiple Cracking Tests on High-Performance Fiber-Reinforced Cementitious Composite Plates

This article describes how an experimental program was conducted to investigate the effects of simultaneous opening-sliding of multiple cracks on the behavior of high-performance fiber-reinforced cementitious composites (HPFRCCs). For this purpose, 12 HPFRCC plates were tested in bending and under two constitutive principal stress directions. To facilitate reorientation of the stress fields, the plates were precracked and then sawed with certain orientations. Finally, the plates were retested in bending to failure. The results showed that the change in principal stress direction had a substantial effect on macroscopic plate behavior, as marked by reductions in strength and initial stiffness. The effect of stress field reorientation on the cracking pattern was, however, minimal. Regardless of the orientation of the new principal stress direction to that of precracking, a somewhat orthogonal crack pattern always appeared. To characterize the mechanisms involved, the relationship within the constant moment span of each plate is presented and discussed.