Fiber-reinforced Cement Research Articles

Chloride Permeability of Damaged High-Performance Fiber-Reinforced Cement Composite by Repeated Compressive Loads.

The development of cracking in concrete structures leads to significant permeability and to durability problems as a result. Approaches to controlling crack development and crack width in concrete structures have been widely debated. Recently, it was recognized that a high-performance fiber-reinforced cement composite (HPFRCC) provides a possible solution to this inherent problem of cracking by smearing one or several dominant cracks into many distributed microcracks under tensile loading conditions. However, the chloride permeability of HPFRCC under compressive loading conditions is not yet fully understood. Therefore, the goal of the present study is to explore the chloride diffusion characteristics of HPFRCC damaged by compressive loads. The chloride diffusivity of HPFRCC is measured after being subjected to various repeated loads. The results show that the residual axial strain, lateral strain and specific crack area of HPFRCC specimens increase with an increase in the damage induced by repeated loads. However, the chloride diffusion coefficient increases only up to 1.5-times, whereas the specific crack area increases up to 3-times with an increase in damage. Although HPFRCC shows smeared distributed cracks in tensile loads, a significant reduction in the diffusion coefficient of HPFRCC is not obtained compared to plain concrete when the cyclic compressive load is applied below 85% of the strength.

Flexural behavior of precast reinforced concrete composite members reinforced with structural nano-synthetic and steel fibers

In this study, structural nano-synthetic and steel fibers were used to reduce the amount of steel rebar distributed in precast reinforced concrete composite members. The flexural performance of the members was evaluated using longitudinal steel ratios of 1.65 and 1.20 and a transverse steel ratio of 0.20. Hybrid fiber mixtures consisting of various amounts of structural nano-synthetic and hooked-end steel fibers were used as reinforcing materials along with the steel rebar. The nano-synthetic fiber volume fractions were 0.4, 0.5, and 0.6vol.%, and the steel fiber contents were 5, 10, and 20kg/m3. Flexural performance tests were carried out for the resulting hybrid fiber-reinforced cement composites. The test results demonstrated that the hybrid fiber-reinforced cement composites satisfied the necessary conditions to replace the general reinforcing bars according to the RILEM standard when the mixture contained 0.4vol.% of nano-synthetic fiber and 20kg/m3 of steel fiber. The flexural behavior of a 350×180×1500-mm precast composite member reinforced by such a hybrid fiber mixture and steel rebar was evaluated; its maximum load was 30% greater than the designed ultimate load and 3.5% greater than that of a steel fiber-reinforced composite member.

Stress analysis of a crack in a fiber-reinforced layered composite

Brittle matrix composites such as fiber-reinforced cements and ceramics are often bonded to dissimilar materials such as metals or other ceramics. The mismatch in elastic properties can affect the growth of matrix cracks located near the bonded interface. In this paper, a bonded system comprising of an elastic layer sandwiched between two identical elastic half-spaces is considered. A mathematical model is developed based on the distributed dislocation technique, for the analysis of a bridged straight crack embedded in the elastic layer. The bridging tractions are considered to be dependent on the crack opening displacement. The stress field is assumed to be plane stress or plane strain and all three-dimensional effects are disregarded.The numerical results include the critical stress required to initiate failure of the matrix and the failure of fibers bridging the crack. The dependencies of these critical values upon the thickness of the composite layer as well as the mismatch in elastic properties are presented in dimensionless form. The results can be used to estimate the residual strength of bonded composites with a flaw near the material interface.

Sisal fiber-reinforced cement composite with Portland cement substitution by a combination of metakaolin and nanoclay

This paper reports the partial replacement of Portland cement (PC) by combination of metakaolin (MK) and nanoclay (NC) in sisal fiber-reinforced cement composites by studying the microstructure, mechanical behavior, and the interfacial properties between fiber and cement matrices. The mechanical properties of cement matrix and natural fiber-reinforced composites are studied using compressive strength development and flexural behavior, respectively. The tensile behavior of the natural fiber was also investigated and analyzed by Weibull distribution model. The characteristics of hydration products were analyzed by scanning electron microscope, X-ray diffraction, and thermogravimetry analysis. Our results show that the combination of MK and NC can improve the hydration of cement more effectively, with better microstructure and enhanced mechanical properties, than mixes without them. The calcium hydroxide (CH) contents of matrixes with 50 wt% combined substitutions, containing 1, 3, and 5 wt% of nanoclay, were 58.12, 60.16, and 64.25 % less than that of PC, respectively. The ettringite phase is also effectively removed due to the substitution of MK and NC, which improve both Al/Ca and Si/Ca ratios of calcium silicate hydrates (C–S–H) due to the high content of SiO2 and Al2O3. The interfacial bond between fiber and cement matrix and flexural properties of sisal fiber-reinforced cement composites are also significantly improved. The optimum interface adhesion between sisal fiber and matrix was achieved by replacing cement by 27 % MK and 3 % NC, which increased the bond strength and pull-out energy by 131.46 and 196.35 %, respectively.

Effectiveness of high performance fiber-reinforced cement composites in slender coupling beams

This study aims at exploring the use of high performance fiber-reinforced cement composites (HPFRCCs) as an innovative method of improving the seismic performance of slender coupling beams. Also, the effect of diagonal reinforcement in slender coupling beams is evaluated in comparison to conventional reinforcement. Three 1/2-scale coupling beams having the length-to-depth ratio of 3.5 were tested under cyclic lateral loading up to about 10% drift. The key test variables were material type and reinforcement layout. For the material type, normal concrete and HPFRCC using PVA discrete fibers of 2% volumetric ratio were compared. The mix proportions of the HPFRCC were determined through detailed material tests. Two types of reinforcement layout were tested: conventional and diagonal layout. Furthermore, the strength and stiffness characteristics of reinforced concrete or HPFRCC coupling beams are examined by assembling a database of almost all coupling beam tests available in literature.

The effect of pre-setting pressure on the flexural strength and fracture toughness of SIFCON during the setting phase

Slurry Infiltrated Fibre Concrete (SIFCON) is a special type of steel fibre-reinforced cement composite with superior mechanical properties, including compressive, tensile, shear and flexural strengths with extraordinary toughness values. In this study, the effects of pre-setting the pressures of SIFCON were examined. The fresh (plastic) SIFCON samples were put into a specified beam mould. Six different (Control (without pressure), 3, 6, 9, 12 and 15MPa) pre-setting pressures were applied. In this study, the maximum flexure strength was observed to be 67.54MPa under 15MPa pre-setting pressure. According to the without-pressure control, the flexure strength was improved by 43.5% at a 15MPa pre-setting pressure. In addition, the fracture toughness was increased by approximately 46% with a 6MPa pre-setting pressure. With the pre-setting pressure, the application can decrease the element thickness or the fibre proportion use, which is the most costly item.

Investigation of Glass Fibre Reinforced Cement (GFRC) Material Exposed to High Temperatures

In this paper we present the tests of high temperatures resistances of glass fibre cement plates. The aim of the research was to determine the values of tensile strength in bending for samples subjected to annealing at temperatures 200, 300, 400 and 500 °C in endurance at the highest temperature level for 24 hours. The bending strength was performed according to the norm EN 1170-4. The thermal dilatometric analysis was performed in the temperatures till 540 °C.

Effect of eccentric compression loading on the strains of FRCM confined concrete columns

The paper describes the effect of eccentric compression on the strains of RC columns, reinforced with FRCM (Fibre Reinforced Cementitious Matrix) composites. Over the span of a dozen or so years, many research studies have been dedicated to the learning of the behaviour of FRP confined concrete elements. The comprehensive test results of axially and eccentrically compressed elements as well as numerous theoretical analyses provide an opinion on the effectiveness of FRPs (Fibre Reinforced Polymers). Under the FRP system, the bonding of a composite material with concrete is made using epoxy resin, on the other hand, under the FRCM system, a composite material is bonded with concrete using a mineral mortar. The FRCM strengthening is relatively poorly recognised, and the research studies presented aim at the widening of the knowledge acquired to date. The testing was performed on 15 slender reinforced concrete columns that were strengthened longitudinally and/or transversally with a composite mesh under the FRCM system. The elements were subjected to axial compression and on the eccentrics: h/6 and h/12. The paper presents the testing preparation and performance method. The description of the strengthening effectiveness was made basing on the values of the energy of destruction. On the grounds of the analysis of the Poisson’s ratio value, the impact of the strengthening method and of the eccentric on the state of stress of the material being tested was reviewed.

Mechanical Behaviour of Sisal Fibre Reinforced Cement Composites

Mechanical Behaviour of Sisal Fibre Reinforced Cement Composites

Debonding of composites on a curved masonry substrate: Experimental results and analytical formulation

Externally bonded mortar based composites have become a popular technique for strengthening masonry arches and vaults. The effect of the curved substrate on the bond properties is one of the key factors affecting their structural behaviour. This paper presents the results of an experimental campaign of debonding tests on straight and curved substrates made of bricks assembled with mortar and strengthened either with Carbon Fibre Reinforced Cementitious Matrix (CFRCM) or Steel Reinforced Grout (SRG). The experimental results get insight into the failure mechanisms that take place in mortar based composites and disclose the effect of the substrate curvature on the interfacial strain distribution and on the load–displacement response. The experimental results are compared with the outcomes of a predictive model, proposed in this work, which provides a closed-form analytical solution to the debonding process of a thin plate on a rigid substrate with constant curvature. The model, which is based on an interface cohesive law, coupled in the tangential and normal directions, as a consequence of the curvature, is able to predict the decrease in bond stiffness and strength for increasing curvature, as shown by experimental results.

Modeling of fiber-reinforced cement composites: Discrete representation of fiber pullout

The discrete modeling of individual fibers in cement-based materials provides several advantages, including the ability to simulate the effects of fiber dispersion on pre- and post-cracking composite performance. Recent efforts in this direction have sought a balance between accurate representation of fiber behavior and computational expense. This paper describes a computationally efficient approach to representing individual fibers, and their composite behavior, within lattice models of cement-based materials. Distinguishing features of this semi-discrete approach include: (1) fibers can be positioned freely in the computational domain, irrespective of the background lattice representing the matrix phase; (2) the pre- and post-cracking actions of the fibers are simulated with little computational expense, since the number of system degrees of freedom is independent of fiber count. Simulated pullouts of single fibers are compared with theory and test results for the cases of perfectly-plastic and slip-hardening behavior of the fiber–matrix interface. To achieve objective results with respect to discretization of the matrix, pullout forces are distributed along the embedded lengths of fibers that bridge a developing crack. This is in contrast to models that lump the pullout force at the crack surfaces, which can lead to spurious break-off of matrix particles as the discretization of the matrix is refined. With respect to fracture in multi-fiber composites, the proposed model matches theoretical predictions of post-cracking strength and pullout displacement corresponding to the load-free condition. The work presented herein is a significant step toward the modeling of strain-hardening composites that exhibit multiple cracking.

Optimizing the formulation of flax fiber-reinforced cement composites

Because of their hydrophilic nature, flax fibers absorb water during the mixing stage and release it gradually during the curing step. Thus, the rheological properties and the setting of the cement paste are deeply disturbed. In addition, the diametrical shrinkage of the fiber in the desorption stage can lead to a weakening of the fiber–matrix bond. It is therefore necessary to carry out treatment of the fiber and/or cement mixture to prevent the fiber/matrix debonding. The results obtained from these formulations show an improvement in the rheology and the mechanical performances of the composites.

Failure Mechanism Investigation of Continuous Fibre Reinforced Cementitious Composites by Pull-out Behaviour Analysis

Pull-out test is a reliable tool to investigate the failure mechanism of continuous fibre reinforced composites. In this work, we develop an analytical model to study the pull-out behaviour of a continuous fibre reinforced cementitious composite. This work is presented by two parts: the first part is the development of an analytical model to analyze a yarn/matrix system. This model is based on the analysis of the stress and displacement of the yarn combining continuity conditions. The second part is concerned with the verification of the developed model by experimentation. The comparison between the analytical results and experimental results has shown that the experimental results are in good agreement with those obtained according to the analytical model developed in this work.

대각철근을 갖는 고성능 섬유보강 시멘트 복합체 연결보의 이력거동 평가

병렬전단벽시스템은 경제적이고 효율적인 구조시스템이지만, 연결보의 복잡한 철근상세가 요구된다. 이를 보완하고자 ACI-318에서는 개선된 철근상세를 제안하고 있지만 과도한 횡보강근으로 현장 적용에 어려움이 따른다. 이 연구에서는 횡보강철근량을 감소시킨 대각철근을 갖는 HPFRCC 연결보 상세를 제안하고, 형상비 2.0 실험체를 통해 현행 기준에 만족하는 대각철근을 갖는 철근콘크리트 연결보와 이력거동을 비교 평가하였다. 그 결과, HPFRCC의 횡구속 효과를 확인하였고, 횡구속 철근을 기준의 1/2로 배근하고 HPFRCC로 보강한 연결보는 현행기준에 따른 연결보와 유사한 내진성능을 보였다. HPFRCC 보강을 통해 대각보강된 철근콘크리트 연결보의 횡구속 철근량을 감소시킴으로써 철근상세의 단순화가 가능할 것으로 판단된다.

Concrete columns confined with fibre reinforced cementitious mortars: Experimentation and modelling

The structural behaviour of concrete columns strengthened with a system made up of fibre nets embedded in an inorganic stabilized cementitious matrix under an uniaxial load was investigated. Medium size specimens with circular and square cross-section were cast and subjected to monotonic uniaxial compression, to investigate the efficiency of a p-Phenylene BenzobisOxazole (PBO) Fibre Reinforced Cementitious Mortar (FRCM) system in increasing both strength and ductility. The experimental results show that the confinement system adopted produced a noticeable increment in strength and ductility, though the low mechanical ratios of fibre considered were not always able to ensure hardening behaviour up to rupture. Modelling of concrete confined with FRCM is presented as a rather straightforward procedure through the sum of stress contributions of the confined concrete and the mortar of the confinement system, separately.

Influence of Casting Direction on Fracture Energy of Fiber-Reinforced Cement Composites

This paper is focused on behavior of fiber reinforced cement composites (FRC) and ultrahigh-performance fiber reinforced cement composites (UHPFRC) in dependence on the direction of casting. Twelve prismatic samples of size of 400 x 100 x 100 mm were cast into moulds; six of these were FRC and the other six were UHPFRC. Three samples of both series were cast in the common horizontal direction and the other three in the vertical way. It was found that fracture energy of horizontally cast prisms was approximately three times higher in both cases than the vertically cast ones. The peak loads of FRC were very similar for both ways of casting. On the other hand the UHPFRC behaved differently, the peak load of horizontally cast prisms was approximately 2,5 times higher than the vertically cast ones. It was demonstrated that these differences are caused by the way of casting and vibration.

High-Performance Fiber-Reinforced Concrete: Development and Evaluation as a Repairing Material

This paper describes the development of high-performance fiber-reinforced concrete (HPFRC) with very high strength and the feasibility of using this concrete as a repairing material. Initially two HPFRC mixtures were developed and cured using four different curing conditions. Compressive strength and flexural strength were determined for those eight combinations. Compared to high-performance fiber-reinforced cement composites (HPFRCC), the increase in compressive strength was in the range of 25–105%. Flexural strength was found to be similar to that of HPFRCC. Based on these strength results, one mixture proportion and two curing conditions were further selected for three bond tests, i.e., direct shear, slant shear, and pull-off. The results showed comparable bond strength in case of direct shear, 20% increase in slant shear, and 40% increase in pull-off when compared with other similar studies.

Attempts to apply high performance fiber-reinforced cement composite (HPFRCC) to infrastructures in South Korea

High performance fiber-reinforced cement composite (HPFRCC) exhibits several desirable characteristics, such as strain-hardening, multiple fine cracks, energy dissipation and crack damage tolerance. These attractive properties have allowed the industry and researchers to apply HPFRCC mixtures successfully to various concrete structures. This paper presents the results of HPFRCC research efforts that range from the study of fundamental properties to practical applications for reinforced concrete structures in South Korea. The findings of this study indicate that HPRFCC can be used to retrofit reinforced concrete structures and to enhance their strength, ductility and seismic performance.

Effectiveness of low-cost fiber-reinforced cement composites in hollow columns under cyclic loading

This study is to investigate the effectiveness of low-cost fiber-reinforced cement composites (FRCCs) on improving the seismic performance of hollow bridge columns. FRCCs with an economical type of hooked steel fibers were used. Five 1/4-scale rectangular hollow columns were tested under quasi-static lateral cyclic loading. The main test variables included steel fiber volumetric ratio (0%, 1%, or 2%), the presence of coarse aggregates, and column length-to-depth ratio (2 or 3). In all specimens, no transverse reinforcement was provided to identify the sole contribution of concrete or FRCCs on the confinement as well as the shear strength. The specimens having FRCCs exhibited stable inelastic load–displacement responses up to 3% or 4% drift, even though they suffered severe shear cracks. In contrast, one specimen with normal concrete only showed very limited ductility. The specimen with the higher fiber ratio generally achieved the larger displacement ductility and the greater energy dissipation, and also better sustained intensive cracking damage.

The effect of high temperature on the performance of CFRP and FRCM confined concrete elements

This paper presents results of research into CFRPs (Carbon Fibre Reinforced Polymers) and FRCM (Fibre Reinforced Cementitious Matrix) confined concrete elements exposed to high temperatures. Concrete cylinder specimens were reinforced with CFRP sheets and FRCM mesh and exposed to the following temperatures: +40°C, +60°C, +80°C, over a period of 24h. Immediately after taking the specimens out of the climatic chamber they were tested until failure. Their temperature was monitored constantly prior, during and after testing by thermal imaging cameras. This paper discusses damage patterns and presents analysis of limit load capacity based on both laboratory experiments and analytical calculations. Also presented was the stress–strain relationship for elements exposed to high temperatures.