Performance Fiber Reinforced Cement Composites Research Articles

Tailoring Engineered Cementitious Composites with local ingredients

Engineered Cementitious Composites (ECC) is a kind of High Performance Fiber Reinforced Cementitious Composites (HPFRCC) with a low fiber volume content of 2%. The unique properties of tensile strain hardening behavior and tight multiple cracks ensure that ECC can meet the stringent requirements of resiliency and durability of concrete infrastructures. While there are strong initiatives for the adoption of ECC in China, wider applications will require localization of material ingredients. In this paper, ECCs with local ingredients, including domestic PVA fibers, fly ash and crumb rubber, were developed under the guidance of micromechanics model for ECC. The fiber/matrix interface parameters and matrix parameters from single fiber pullout test and fracture toughness test respectively, were obtained for the tailoring of domestic ECC. The experimental results indicated that cost-effective ductile ECCs can be designed successfully using local material ingredients. These composites show an ultimate tensile strength of 4–5MPa and tensile strain capacity of 3–6%.

The influence of curing age and mix proportion on the uniaxial compressive properties of green high-performance fibre-reinforced cementitious composites

The influences of curing age and mix proportions on the uniaxial compressive properties of green high performance fibre-reinforced cementitious composites (GHPFRCC) in terms of the compressive strength and elastic modulus were examined, with constitutive relationships thus presented based upon the static compressive elastic modulus test. Sixteen groups of GHPFRCC specimens were prepared according to the orthogonal experiment method, with two curing periods employed (7 days, 28 days). Experimental results indicate that curing age has a significant influence on uniaxial compressive strength and elastic modulus; with the majority of early compressive strength and elastic modulus values reaching more than 50% of the final measured rates. Water–binder ratio was found to have the greatest influence on compressive strength and elastic modulus, with the mean compressive strength of GHPFRCC almost equal to that of concrete, whereas the elastic modulus of GHPFRCC is typically lower than that of concrete.

Elevated temperature resistance of ultra-high-performance fibre-reinforced cementitious composites

Elevated temperatures, specifically in the event of fire, are likely to cause extreme deterioration in fibre-reinforced polymer (FRP) strengthened reinforced concrete (RC) structures. Various types of high-performance cementitious composites (HPCC) have been explored for the protection of RC structural members against elevated temperature, but there is inadequate information in this regard for ultra-high performance fibre-reinforced cementitious composites (UHPFRCC) containing high-alumina cement (HAC) and ground granulated blast furnace slag (GGBS) in conjunction with hybrid fibres – a prospective fire-resistant UHPFRCC for structural members. In this study, the change in mechanical strength of UHPFRCC was examined before and after heat treatment, followed by thermal and microstructural analysis. Besides the control sample, three other samples containing up to 1·5% of basalt fibres, and 1 kg/m3 of polypropylene fibres, were prepared and tested. Another mix was also prepared with only 1 kg/m3 of polypropylene fibres. Each sample was heated to 400, 700 and 1000°C. Results showed that the use of hybrid fibres significantly improved the room temperature mechanical strengths of UHPFRCC, which were found to be 80 MPa and 14·3 MPa, respectively. However, the optimum residual compressive and flexural strength was attained by UHPFRCC with only PP fibres and hybrid fibres, respectively.

Development of a new Ultra High Performance Fibre Reinforced Cementitious Composite (UHPFRCC) for impact and blast protection of structures

Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs) represent a class of cement composites which have superior characteristics in terms of material properties. Their mechanical and fracture behaviour is substantially enhanced compared to other types of concrete. The aim of the specific paper is to present the results of an extended work focused on the development of the first UHPFRCC with the use of constituent materials available in Cyprus. The paper presents results on a broad variety of mechanical properties and the effect of several parameters on the strength development and the rheological characteristics of the produced material. Furthermore, the developed material should have certain properties and specifications, so as to have a sufficient response against blast and impact loading conditions. The optimum mixture has a water–binder ratio equal to 0.16 and volume fraction of steel fibres equal to 6%. The average compressive strength and specific fracture energy obtained for this mixture were around 175MPa and 26000N/m, respectively.

Experimental field investigation of impact and blast load resistance of Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs)

Ultra High Performance Fibre Reinforced Cementitious Composites (UHPFRCCs) represent a class of cement composites which have superior characteristics in terms of material properties. These materials have, however, a significant increase in cost compared to conventional and even High Performance Concrete and it is therefore appropriate to identify applications which will fully utilise their mechanical properties and performance characteristics. A new class of UHPFRCC material has been developed through the experimental work of a research project entitled “Mix Design, Mechanical Properties and Impact Resistance of UHPFRCCs”, designated UHP-CY. The material is characterised by high compressive strength, high tensile/flexural strength and high-energy absorption capacity. The research work presented in this paper focused on the experimental investigation of the quality and the behaviour of this material in a highly demanding application, such as the impact and blast resistance of structures. The impact resistance of UHP-CY slabs was experimentally verified in a range of real firing shots, using several weapons and projectile types. A purpose-built experimental setup was developed for this work. It was observed that relatively thin slabs made of this material can be an outstanding protective overlay of existing structures, since they can prevent the penetration of strong projectiles without shaped charges. Moreover, these panels can also minimise the damage of retrofitted Reinforced Concrete structures, hit by projectiles with shaped charges. The presence of a high volume fraction (i.e. 6%) of steel fibres in UHP-CY overlays contributes substantially to the control of the back face spalling and fragmentation of the RC walls.

Influence of Specimen Shape and Mix Proportion on Tensile Property of Green High Performance Fiber Reinforced Cementitious Composites (GHPFRCC)

Li, X.; Luo, M., and Yan, Q., 2015. Influence of specimen shape and mix proportion on tensile property of green high performance fiber reinforced cementitious composites (GHPFRCC).This paper investigates the tensile property of green high performance fiber reinforced cementitious composites (GHPFRCC) with focus on the influence of sample shape and mix proportion. Direct tensile tests are performed on the rectangle shaped plate coupons and dumbbell shaped ones, followed by sixteen kinds of mix proportions based on the orthogonal experiment method, considering such influencing factors as fly ash replacement by weight (60%, 65%, 70%, and 75%), water-binder ratio (0.24, 0.28, 0.32, and 0.36), sand-binder ratio(0.36, 0.46, 0.56, and 0.66), polyvinyl alcohol (PVA) fiber by volume (1.5%, 1.7%, 2.0%, and 2.2%) and water reducing agent by weight (0.10%, 0.15%, 0.20%, and 0.25%). And then, the tensile strength and ductility of GHPFRCC are highlighted and discussed. Experimental results show that the limit tensile deformation capacity of GHPFRCC is far better than that of the normal concrete. Water-binder ratio has a greater influence on the tensile strength and the optimal value is 0.24. GHPFRCC can obtain higher tensile strength when sand-binder ratio is 0.46. The limit tensile strength and deformation of the dumbbell shaped GHPFRCC specimens are usually better than those of the rectangle shaped plate coupons.

Development of high performance fiber reinforced cement composites (HPFRCC) for application as a transition layer of reinforced beams

This study presents the development and behavior analysis of high performance fiber reinforced cement composites (HPFRCC). The describedmaterials were specifically developed for application as a transition layer: a repair layer that constitutes the stressed chord of reinforcedconcrete beams strengthened in flexure with carbon fiber reinforced polymers (CFRP). Nineteen different composites were produced by thehybridization process, varying the conventional short steel fiber and steel microfiber (manufactured exclusively for this research) contentsto modify the microstructure of the material, thus enhancing the stress transfer process from the cement matrix to the fibers. To analyze theresponse to flexural loading, the composites underwent three point bending tests in notched prism specimens. The response of the materialwas obtained considering strength and tenacity parameters (flexural and fracture). There was evidence of high performance by the composites with a pseudo-hardening behavior.

MECHANICAL PROPERTIES OF A PVA FIBER REINFORCED ENGINEERED CEMENTITIOUS COMPOSITE

High Performance Fiber Reinforced Cementitious Composites (HPFRCCs) are promising construction materials characterized by tensile strain hardening behavior. Engineered Cementitious Composite (ECC) is a special type of HPFRCC developed with enhanced ductility and durability. Coarse aggregates are usually excluded from the ECC matrix, and the reported ECCs are typically produced with microsilica sand having a maximum grain size of 200 µm. In this paper, a PVA-ECC mixture containing local dune sand with a maximum grain size of 300 µm was developed, and its compressive and tensile properties were experimentally investigated. A dog-bone-shaped specimen and a rectangular-coupon-shaped specimen were both used in the tensile test, and it was found after extensive research that the dog-bone specimen was more suitable than the rectangular coupon specimen. The experimental results from the dog-bone specimens indicated that the newly-developed composite possessed good tensile strain-hardening behavior, with a high ultimate tensile strength, and the compressive strength was comparable to that of existing PVA-ECCs.

Mechanical properties of high performance fiber reinforced cementitious composites

Extensive experimental studies on High Performance Fiber Reinforced Cement Composites (HPFRCC) owing to their remarkable properties have been carried out. Statistical studies have been mainly focused on Fiber Reinforced Concrete (FRC). An extensive study, including an experimental/statistical approach addressing key mechanical properties (compressive and flexural strength) and impact resistance of such high performance composites with inclusion of different volume of fibers has been carried out on two-hundred and forty specimens in this research.Results from this study revealed that compressive and flexural strength as well as impact resistance of HPFRCC follow the normal distribution. Furthermore, statistical data analyses (both parametric and nonparametric) showed higher percentage of fibers led in greater values for mechanical properties and impact resistance of HPFRCC. Moreover, based on acquired test results, equations were developed between mechanical properties and impact resistance of HPFRCC materials.

Chloride Ion Diffusion Coefficient of HPFRCC after Loading

Various methods have been used to reinforce cementitious material such as mortar and concrete that have weak tensile strength. Fiber Reinforced Concrete is one of the reinforcing methods that mixes a matrix with fibers that have strong tensile strength. Recently, High Performance Fiber Reinforced Cementitious Composites (HPFRCC) have been developed. HPFRCC provides a possible solution to this inherent problem of cracking by smearing one or several dominant cracks into many distributed microcracks. The present study explores the ductility characteristics of HPFRCC by measuring chloride diffusion coefficients after load is applied.

The Study of Steel Fiber Reinforced Concrete Durability Based on Damage Mechanics

In order to substitute steel reinforcement with steel fiber reinforced concrete, this paper studied steel fiber reinforced concrete durability based on damage mechanics. During recent years, steel fiber reinforced concrete has gradually advanced from a new, rather unproven material to one which has now attained acknowledgment in numerous engineering applications. The use of randomly distributed short fibers to improve the physical properties of a brittle or quasi-brittle matrix is an old concept. Most of the steel fiber reinforced concrete durability research just to solve a specific problem and no system of the structure performance degradation in certain circumstances. A formulation to model the mechanical behavior of high performance fiber reinforced cement composites with arbitrarily oriented short fibers. The formulation can be considered as a two scale approach, in which the macroscopic model, at the structural level, takes into account the micro-structural phenomenon associated with the fiber-matrix interface bond/slip process.

Experimental Research on the Flexural Failure Properties of Green High Performance Fiber Reinforced Cementitious Composites (GHPFRCC)

Green high performance fiber reinforced cementitious composites (GHPFRCC) is a new class of Engineered Cementitious Composites (ECC) with high volume fly ash based on the orthogonal experimental method. Focus is placed on the flexural failure properties of GHPFRCC, considering the influences factors like fly ash content, water-binder ratio, sand-binder ratio, PVA (Polyvinyl Alcohol) fiber and water reducing agent, et al. The experimental results indicate that the failure process of GHPFRCC beam can be divided into three stages including elastic stage, yield stage and failure stage. The multiple fine cracks appeared in the specimen can effectively dissipate energy.

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.

A micromorphic model for steel fiber reinforced concrete

A new formulation to model the mechanical behavior of high performance fiber reinforced cement composites with arbitrarily oriented short fibers is presented.The formulation can be considered as a two scale approach, in which the macroscopic model, at the structural level, takes into account the mesostructural phenomenon associated with the fiber–matrix interface bond/slip process. This phenomenon is contemplated by including, in the macroscopic description, a micromorphic field representing the relative fiber–cement displacement. Then, the theoretical framework, from which the governing equations of the problem are derived, can be assimilated to a specific case of the material multifield theory.The balance equation derived for this model, connecting the micro stresses with the micromorphic forces, has a physical meaning related with the fiber–matrix bond slip mechanism. Differently to previous procedures in the literature, addressed to model fiber reinforced composites, where this equation has been added as an additional independent ingredient of the methodology, in the present approach it arises as a natural result derived from the multifield theory.Every component of the composite is defined with a specific free energy and constitutive relation. The mixture theory is adopted to define the overall free energy of the composite, which is assumed to be homogeneously constituted, in the sense that every infinitesimal volume is occupied by all the components in a proportion given by the corresponding volume fraction.The numerical model is assessed by means of a selected set of experiments that prove the viability of the present approach.

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.

Dynamic behaviour of HPFRCC in tension

High Performance Fiber Reinforced Cementitious Composites belong to a new class of structural materials characterized by high strength and ductility. Thanks to the high energy absorbed during the fracture process, due to multiple cracking and pull-out phenomena, they are often suggested for dynamic loading applications. Current understanding of the dynamic response is very limited because of very few investigations have been actually carried out. An experimental research aimed at contributing to the understanding of the behaviour of advanced fiber-reinforced cementitious composites subjected to low and high strain rates was carried out. The material investigated is a High Performance Fiber Reinforced Cementitious Composites. Straight high carbon steel micro-fibers were used. The material behaviour was investigated at several strain rates and the tests results were compared with their static behaviour. Tests at intermediate strain rates were carried out by means of a hydro-pneumatic machine (HPM), while high strain rates were investigated by exploiting a Split Hopkinson Tensile Bar (SHTB). A comparison between static and dynamic tests highlighted several relevant aspects regarding the influence of fibers on the peak strength and post-peak behaviour at high strain rates. Finally, this material will be employed in the construction of an innovative tunnel segment designed for extreme conditions (high temperature and shock).

Seismic Performance of Steel Braces Jointed with High Performance Fiber Reinforced Cementitious Composites and Steel Bars

Steel-braced frames have been widely used for retrofitting due to their effectiveness in terms of their light weight and short construction period. The steel-braced frame retrofitting method is difficult to apply, however, to the inner frames of buildings. Consequently, there has been a demand for a braced frame retrofitting method that can be broadly and easily applied to both the inner and outer frames of buildings. In this study, a retrofitting method using steel-braced frames with HPFRCC and steel bars is proposed. The pre-fabricated upper and lower segments of the brace member are connected on-site with HPFRCC, meaning that the proposed method is applicable to the inner frames of buildings as a seismic retrofitting method that has the advantage of simple and rapid installation. The tension force is transmitted only through the steel bars, which transmit the compression force to the HPFRCC of the joint that connects the three brace units. The results of cyclic tests of four specimens clearly showed that steel braces using HPFRCC and steel bars ensure stable structural performances and improve construction efficiency.

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.