Fiber-reinforced Cement Research Articles

Numerical Modelling of Mechanical Behaviour of Fibre Reinforced Cementitious Composites

In this paper, a new numerical model is developed to model the tensile behavior of the cementitious composites reinforced with hybrid bagasse fibres and steel fibres based on the extended finite element method. The numerical model considers random fibre distribution, which is generated automatically, and the cohesive behavior, which represents the bonding between fibres and the matrix. The cementitious matrix is modeled using extended finite element method. The developed numerical model is implemented in commercial software ABAQUS and the computed results are compared with the corresponding experimental results for numerical validation. It is found that the tensile behavior of the composites predicted from the new numerical model is consistent with that obtained from experimental study, and that the developed numerical model can accurately predict the uniaxial tensile behavior, including the post-cracking behavior of fibre reinforced cementitious composites.

Direct-tensile and flexural strength and toughness of high-strength fiber-reinforced cement composites with different steel fibers

The main purpose of this study is to investigate effects of the type and volume fraction of steel fibers on the mechanical behaviors of fiber-reinforced cement composites (FRCCs) with high strengths. Various FRCC mix cases were designed and tested in two steps. At the 1st step, two types of steel fibers (straight and hooked) were examined with two different fiber volumes (1.0 and 1.5%). The test variables of the 1 st step included the type and volume fraction of steel fibers, and the inclusion of coarse aggregate. At the 2 nd step, ultrahigh strength FRCC mix cases using hooked steel fibers only were tested with two different fiber volumes (1.0 and 1.5%). Various mechanical tests were performed to evaluate the stress-strain behaviors of the FRCCs subjected to uniaxial compression, direct tension, and third-point bending. The test results reveal that the use of hooked steel fibers improved the tensile and flexural capacities of FRCCs more effectively than did the straight steel fibers. Also, the FRCCs generally demonstrated greater direct-tensile and flexural toughness compared with ordinary fiber reinforced concretes (FRCs).

Cyclic behavior of shear walls with HPFRCCs in the inelastic deformation critical region

This study presents a structural application of high-performance fiber-reinforced cement composites in the inelastic deformation critical region of the shear wall to improve the performance and reduce the disadvantages of conventional reinforced concrete members. Six small-scale wall specimens with the same aspect ratio and various configurations were tested under reversed cyclic loading, and their cyclic behaviors were evaluated and compared. The fiber cementitious material examined in this study exhibited excellent pseudo strain-hardening behavior in tension and high tensile ductility. The results of the quasi-static cyclic tests revealed that the deformation compatibility between the steel reinforcements and high-performance fiber-reinforced cement composite (HPFRCC) matrix could maintain composite integrity. Accordingly, the damage tolerance of the wall specimens for high inelastic deformation could be improved. Furthermore, the ultimate deformation and energy dissipation capacities of the wall specimens were dominated by the ductility and stability of the longitudinal reinforcements. Consequently, the combination of highly ductile mixture material and buckling-restrained measures of steel reinforcement, such as the steel sleeve presented in this paper, was proposed for use in shear walls under moderate or even higher axial loads. Copyright © 2016 John Wiley & Sons, Ltd.

Resistance of high-performance fiber-reinforced cement composites against high-velocity projectile impact

This paper presents experimental and numerical studies on the performance of seven high-performance fiber-reinforced cement-based composites against high velocity projectile impact (HVPI). The materials investigated involved four fiber-reinforced high-strength concretes (FRHSCs) with 28-day compressive strengths ranging from about 60 to 140 MPa, two strain hardening cement-based composites (SHCCs), and a fiber-reinforced high-strength mortar (FRHSM). Of the two SHCCs, one was reinforced with 0.5% steel fibers plus 1.5% polyethylene (PE) fibers by volume of the composites, whereas the other was reinforced with 2% of polyvinyl alcohol (PVA) fibers. The other composites were reinforced with 0.5% of steel fibers. Ogive-nose shaped projectiles, with a diameter of 28 mm and weight of about 250 g, were used for the HVPI tests at projectile velocities of ~400 and ~600 m/s. The localized damage, particularly the penetration depth, was examined and discussed. Results indicate that the higher compressive strength and greater toughness of cement-based composites, as well as the presence of strong coarse aggregate and fibers, contribute positively to the impact resistance of composites. In addition, it was found that the penetration depth of the composites subjected to HVPI is reduced with an increase in the elastic modulus, as well as with the “effective hardness index” calculated based on the hardness and proportion of the coarse aggregate and mortar matrix. Numerical studies were conducted to simulate the localized damage of the FRHSCs and SHCCs due to the HVPI using the finite element software LS-DYNA. The numerical models adapted predict the penetration depth well. The numerical simulation results indicate that it takes a longer time to stop the projectile traveling at the same initial velocity in the SHCC specimen than in the FRHSC specimen due to the absence of hard and strong coarse aggregate in the former.

Macro-meso experiment of fiber-reinforced cement paste filling material

Macro-meso experiment of fiber-reinforced cement paste filling material

The variation in elastic modulus throughout the compression of foam materials

We present a comprehensive experimental study of the variation in apparent unloading elastic modulus of polymer (largely elastic), aluminium (largely plastic) and fibre-reinforced cement (quasi-brittle) closed-cell foams throughout uniaxial compression. The results show a characteristic “zero-yield-stress” response and thereafter a rapid increase in unloading modulus during the supposedly “elastic” regime of the compressive stress–strain curve. The unloading modulus then falls with strain due to the localised cell-wall yielding or failure in the pre-collapse stage and the progressive cell crushing in the plateau stage, before rising sharply during the densification stage which is associated with global cell crushing and foam compaction. A finite element model based on the actual 3D cell structure of the aluminium foam imaged by X-ray computed tomography (CT) predicts an approximately linear fall of elastic modulus from zero strain until a band of collapsed cells forms. It shows that the subsequent gradual decrease in modulus is caused by the progressive collapse of cells. The elastic modulus rises sharply after the densification initiation strain has been reached. However, the elastic modulus is still well below that of the constituent material even when the “fully” dense state is approached. This work highlights the fact that the unloading elastic modulus varies throughout compression and challenges the idea that a constant elastic modulus can be applied in a homogenised foam model. It is suggested that the most representative value of elastic modulus may be obtained by extrapolating the measured unloading modulus to zero strain.

Influence of Oxygen Plasma Surface Treatment of PET Micro Fibers on Flexural Strength of Reinforced Cement Pastes

Presented work deals with PET (polyethylene terephthalate) fiber-reinforced cement pastes and cool oxygen plasma fiber surface treatment used to attain the better adhesion between fibers surface and the cement matrix. Three sets of cement paste samples were made with the same matrix (CEM I 42.5R with water to cement ratio equal to 0.4). The two sample sets contained micro fiber reinforcement varying in surface properties. One set was reinforced with unmodified fibers, while in to the other set plasma treated fibers were used. As a comparative indicator to bending response of the composite materials, four-point destructive tests were carried out. The samples reinforced with unmodified fibers exhibited deflection-softening behavior during the post-cracking phase, while samples with plasma treated fibers exhibited deflection-hardening behavior.

A cohesive interface crack model for the matrix–textile debonding in FRCM composites

Existing masonry structures often need to be strengthened or repaired. Among non-traditional retrofitting techniques, Fibre Reinforced Cementitious Matrix (FRCM) materials are becoming more and more interesting, especially for the reinforcement of historical buildings. The bond strength of the FRCM reinforcement is one of the key factors affecting the behaviour of the reinforced member and failure mode mostly involves the failure of the textile/mortar interface. Based on experimental results on single lap pull–push shear tests on FRCM materials bonded to masonry blocks, a tri-linear bond–displacement behaviour at the textile–mortar interface is proposed. The last phase of the bond–slip law is characterized by a constant shear stress in order to model the friction phenomena between the matrix and the textile observed in the experimental tests. Analytical expressions for the load–displacement response and interfacial shear stress distribution at different loading stages are derived taking into account the effects of the friction phenomena. The model is discussed in detail and the analytical results are compared to experimental outcomes. Finally, a parametric analysis is performed to highlight the effect of bond length, cohesive bond–slip law parameters and friction on the load–displacement response.

Correlation between hydration of cement and durability of natural fiber-reinforced cement composites

The influence of cement hydration on the durability of natural fiber-reinforced cementcomposites and the deterioration of the embedded natural fibers were investigated by incorporating four supplementary cementitious materials (SCMs). Cement hydration was presented to be a crucial factor in understanding natural fiber degradation behavior. The results indicated that the incorporation of SCMs slowed down both mineralization and alkaline hydrolysis of fiber cell walls by promoting the hydration of cement. This is attributed to the reduced alkalinity of pore solution and calcium hydroxide content. Degradation of natural fiber was significantly mitigated and the durability of cement composites was improved consequently.

Utilization of rice husk ash in green natural fiber-reinforced cement composites: Mitigating degradation of sisal fiber

This study aims to explore a novel approach to improve the durability of sisal fiber in cement composites by using by-products of biomass power plant: rice husk ash (RHA). The effects of two RHAs on the fiber's degradation were investigated indirectly by testing flexural behavior of sisal fiber-cement composite beams and directly by means of uniaxial tensile properties, thermal decomposition, crystallinity indices and microstructures of embedded fibers, after exploring up to 30 wetting and drying cycles. Allowing the distinction between pozzolanic activities, the efficiency of RHA was compared with two fly ashes and combinations of two clay minerals (metakaolin and nanoclay) with a cement substitution level of 30wt.%. The durability of composites was improved considerably by incorporating RHA owing to the mitigation of fiber's degradation: the ultimate tensile strength and cellulose fraction of embedded fibers were improved by 384% and 45%, respectively. Fine RHA and the combination of metakaolin and nanoclay yield similar efficiency in mitigating degradation of sisal fiber, and are better than the coarse RHA and fly ashes. The correlations between cement hydration and sisal fiber degradation were analyzed. The results indicate that degree of hydration, calcium hydroxide content and alkalinity of the cement matrix play decisive roles in alkali attacks and mineralization of fiber's cell walls.

The Influence of Additions in the Use of Glass Fibre Reinforced Cement as a Construction Material

Although in recent years glass fibre reinforced cement (GRC) has been used in buildings and infrastructure, its application in structural elements has been somewhat restricted due to the worsening of its mechanical properties with ageing and the limited data available related with its fracture energy. With the aim of developing existing knowledge of GRC, the fracture energy in an in-plane and out-of-plane direction of the panel has been obtained. Three types of GRC with different formulations have been tested. The results showed that the fracture energy of a GRC with a 25% addition of a pozzolanic admixture is 40% and 8% higher than a standard GRC in, respectively, in-plane and out-of-plane directions. Similarly, an addition of 25% of thermal-treated kaolin to a standard GRC increases its fracture energy up to 490% and 400%, to the corresponding orientation. The use of digital image correlation (DIC) in the fracture test analysis has permitted a description of the damaging patterns and explanation of the behaviours identified in the fracture tests performed. The multi-cracking process that appears explains the higher fracture energy found in the GRC with an addition of 25% of the aforementioned thermal-treated kaolin. The analysis performed by means of DIC and the results obtained showed GRC with an addition of 25% of thermal-treated kaolin to be the most suitable formulation for possible future structural applications with a short life span in horizontal and vertical elements.

Predicting the Behaviour of Fibre Reinforced Cement Treated Clay

Treating soft clay with cement and fibre has become an effective ground improvement technique for transport infrastructure. Application of recycled fibres in deep soil mixing columns in soft soil sections of road and rail projects is being considered by designers and clients as an efficient technique. However, the combined effect of cement and fibre at failure requires further investigation. As the effective stresses increase to a sufficiently high stress, the effect of cementation is diminished due to the degradation of cementation bonds and the fibre exhibits failure due to either complete pull-out or breakage from the soil matrix. Thus, the failure envelope of the reinforced soil gradually merges with that of un-reinforced soil at higher stresses. In this paper, a constitutive model is proposed to simulate the behaviour of the cement treated-fibre reinforced soil based on the Critical State Soil Mechanic and the Modified Cam Clay model. In particular, the proposed model captures the beneficial effects of cementation and fibre reinforcement such as the improvement in strength and ductility while the cementation degradation and the failure mechanism of the fibre are also considered. In addition, a series of un-drained triaxial tests were conducted to verify the performance of the proposed model. This paper concludes that adding fibre into the cement treated soil clearly improves its residual strength, thus, a significant increase in ductility is observed and well simulated. In this study, by modifying the mean effective stress to include the cementation degradation and the fibre failure mechanism, the proposed model results in realistic prediction for the behaviour of soil treated with cement and fibre.

Bonding Characteristics of Macrosynthetic Fiber in Latex-Modified Fiber-Reinforced Cement Composites as a Function of Carbon Nanotube Content

The effect of carbon nanotube content (0, 0.5, 1.0, 1.5, and 2.0% of the cement weight) on the bonding properties of macrosynthetic fiber in latex-modified hybrid fiber cement-based composites (LMHFRCCs) was evaluated. The slump value, compressive strength, and bonding strength were measured for each LMHFRCC. As the carbon nanotube content increased to 1.5%, the bonding properties of the macrosynthetic fiber improved. However, the bonding performance deteriorated at a carbon nanotube content of 2.0%. A decrease in the fluidity of the mix negatively affected the dispersion of the nanotubes in the LMHFRCCs. The addition of carbon nanotubes also affected the relative bonding strength independently of the improvement in compressive strength. Microscopic analysis of the macrosynthetic fiber surfaces was used to understand changes in the bonding behavior.

Behavior of high-performance fiber-reinforced cement composite columns subjected to horizontal biaxial and axial loads

Current design in the ACI building code for reinforced concrete columns under seismic load combinations requires reinforced detailing which causes reinforcement congestion and construction difficulties. As an alternative solution, the use of high-performance fiber-reinforced cement composites (HPFRCC) with an economical type of Poly Vinyl Alcohol (PVA) fibers in column elements was investigated in this paper. Six column specimens with 2/3 scale including three standard reinforced columns and three columns using PVA fibers were tested. In the research work herein presented, biaxial cyclic lateral loads were applied to specimens subjected to either 10% or 30% constant axial loads. The experimental results are presented and the global behaviors of the tested columns are discussed, particularly focusing on stiffness and strength degradations due to increasing cyclic demand. Test results indicated superior damage tolerance and stable inelastic load–displacement responses up to 5% or 9% drift for the HPFRCC columns, even though they suffered severe shear cracks. Specimens without PVA all showed very limited ductility and low strengths.

Behaviour of fibre-reinforced beams with diagonal reinforcement

Diagonal reinforced coupling (DRC) beams can provide excellent strength, stiffness and energy dissipation capacities. However, fabricating DRC beams at construction sites is difficult due to reinforcement congestion and interference among the reinforcements due to the complex arrangement required by current design provisions. The objective of this study is to simplify the reinforcement details of DRC beams by reducing the transverse reinforcement around the beam perimeter that is required for the confinement of DRC beams. This is achieved by using high-performance fiber-reinforced cement composites (HPFRCC) for DRC beams. Experiments are conducted using six specimens under reversed cyclic loads to evaluate the hysteretic behaviours of the HPFRCC DRC beams. The test results show that the use of HPFRCC in DRC beams is very effective, providing a confinement effect with transverse reinforcement. HPFRCC DRC beams with half the transverse reinforcement required by ACI 318-11 provide almost identical energy dissipation capacities as concrete DRC beams detailed according to ACI 318-11.

Composite properties of high-strength polyethylene fiber-reinforced cement and cementless composites

This paper presents an experimental study of the composite properties of cement based- and alkali-activated ground-granulated blast furnace slag (GGBS) based composites reinforced by high-strength polyethylene fibers and a discussion of the different behaviors of the two types of binder-based composites. A series of experiments, including those to test the density, compression, and uniaxial tension, was performed to characterize the mechanical properties of the composite. The test results indicated that an alkali-activated GGBS composite shows a higher tensile strain capacity with smaller crack widths and crack spacings than a cement-based composite, although the alkali-activated GGBS composite showed lower compressive and lower tensile strength than the cement-based composite with the same water-to-binder ratio. It was also observed that the alkali-activated GGBS-based composite has higher ratio of the tensile strength to the compressive strength than the cement-based composite.

Direct tensile behavior of shape-memory-alloy fiber-reinforced cement composites

We demonstrated the pre-stressing capability of short shape-memory-alloy (SMA) fiber-reinforced cementitious composites (SMA-FRCC) by performing direct tensile tests after heat treatment. Two types of SMA fibers were added by 1.5% volume content in a mortar matrix with 55MPa compressive strength. After 10min of heat treatment on the tensile specimens of SMA-FRCCs, the length of specimen was noticeably shortened due to shape-memory effects, which consequently generated pre-stressing effects. Furthermore, heat treatment noticeably increased the Young’s modulus of SMA-FRCCs in tension due to shape-memory effects.

ANALYSIS OF MECHANICAL PROPERTIES OF HYDROTHERMALLY CURED HIGH STRENGTH CEMENT MATRIX FOR TEXTILE REINFORCED CONCRETE

The main objective of this article is to describe the influence of hydrothermal curing conditions in an autoclave device (different pressure and temperature), which took place at various ages of a fresh mixture (cement matrix – CM, and fibre-reinforced cement matrix – FRCM), on textile reinforced concrete production. The positive influence of autoclaving has been evaluated through the results of physical and mechanical testing – compressive strength, flexural strength, bulk density and dynamic modulus of elasticity, which have been measured on specimens with the following dimensions: 40×40×160mm<sup>3</sup>. In addition, it has been found that increasing the pressure and temperature resulted in higher values of measured characteristics. The results indicate that the most suitable surrounding conditions are 0.6MPa, and 165 °C at the age of 21 hours; the final compressive strength of cement matrix is 134.3MPa and its flexural strength is 25.9MPa (standard cured samples achieve 114.6MPa and 15.7MPa). Hydrothermal curing is even more effective for cement matrix reinforced by steel fibres (for example, the compressive strength can reach 177.5MPa, while laboratory-cured samples achieve a compressive strength of 108.5MPa).

Laboratory evaluation on the effectiveness of polypropylene fibers on the strength of fiber-reinforced and cement-stabilized Shanghai soft clay

This paper presents a laboratory evaluation on the strength behavior of cement–clay admixture improved by polypropylene fiber. Waste polymer textile bags are harmful to the environment and sustainable means to reuse them are urgently being sought. A novel method to recycle these waste polymer textile bags is applying them in soft soil improvement projects, such as compacted-pavement base/subbases. In order to verify the effectiveness of fiber bundles used in soil mixing, a series of laboratory investigation are conducted on fiber-reinforced cement-improved soft Shanghai clay. In the tests, two types of polymer fibers were employed; the first one is monofilament polypropylene fiber and the other is fiber bundles split from polymer textile bags. The tests were conducted using unconfined compressive strength (UCS) test after the specimen of fiber–soil–cement admixture were cured for some period. The results show that fiber additive can significantly improve the strength and ductility of the cement treated Shanghai clay. The UCS of fiber–soil–cement admixture is related to both content and length of fiber. Both two kinds of fiber-reinforced cement clay reached their peak strength at fiber content of 0.5%. UCS will slowly reverse if the fiber content continues to increase. Even though the polypropylene fiber works better than the fiber bundles, the difference is less than 5%. These results indicate that the fiber bundles split from polymer bags can be used as the reinforcement in soil mixing, thus providing a novel approach to treat waste polymer textile bags.

Case Study on Early Age Shrinkage of Cement-based Composites

The aim of this paper was to study the behaviour of new high-performance fibre-reinforced cement composite materials (FRCC) that are reinforced with polyvinyl alcohol (PVA) fibres. The shrinkage deformations at early age, the compressive strength and modulus of elasticity of the new compositions had been determined. Test results shows that the addition of PVA fiber 1.10% and 0.55% by weight of the cement has negligible influence on concrete drying shrinkage, however, it is affect the concrete plastic and autogenous shrinkage. The results of the experiments permitted the prediction of long-term deformations of the concrete. Wider use of this material permit the construction of sustainable next generation structures with thin walls and large spans that cannot be built using the traditional concrete.