Fiber In Mortar Research Articles

Physically simulating the dispersion of chopped carbon fibres in mortar

Carbon fibre dispersion exerts a critical influence on the characteristics of carbon fibre-reinforced cement mortars (CFRCMs). This study accordingly investigated the dispersion of chopped carbon fibres (CCFs) in mortar using physical experiments with a transparent simulated mortar system comprising colloidal silica and silica sand as replacements for cement and aggregate, respectively, and evaluated the microstructures and conductive performances of corresponding CFRCM specimens. In the simulated solutions, bundled CCFs in order were more prone to disperse into single fibres than clustered ones in disorder due to no physical fixation, colloidal silica prevented the formation of CCF clusters during stirring, and the shear force of moving sand dispersed but also broke CCFs. In the CFRCMs, sand aggregates reaggregated dispersed CCFs while larger sand particles increased CCF dispersion and improved specimen conductivity. Thus, decreasing the amount of CCFs clusters before dispersion, and a short stirring time in a single direction should be provided to prepare CFRCMs with well-dispersed CCFs. Meanwhile, a more dispersible aggregate and less formation of void should be also essential.

Machine learning application to predict the mechanical properties of glass fiber mortar

In this study, the mechanical properties of glass fiber mortars have been predicted using machine learning tools, Response Surface Methodology (RSM), and Artificial Neural Network (ANN) approach. This study focused on mortar, in which cement has been partially replaced by 20% fly ash and 20% hydrated lime. In the experiments, the compressive strength of mortars has been determined after curing the mixes for 7 and 28 days. Glass fiber was added to the proportions of 0%, 0.2%, 0.4%, 0.6%, 0.8%, and 1% by weight of cement. The compressive strength of mortar incorporated with glass fiber increases according to an increase in the proportion of glass fiber. Results indicate that the optimal proportion of glass fiber in mortar had been observed to be 0.6%. The predicted compressive strength on day 28 has been modeled using RSM and ANN. The RSM model has been used to predict mechanical properties (R2 ≥ 0.7534) accurately. Furthermore, the appropriate R threshold (R > 0.999) for training, testing, and validation demonstrates that the ANN model has successfully captured the variability in the data. The results show that with the high correlation between the experimental and prediction results, more accuracy has been observed in the ANN model than in the RSM model.

Tensile Behavior of Basalt-Fiber-Grid-Reinforced Mortar before and after Exposure to Elevated Temperature

This paper presents an experimental study on the tensile behavior of basalt-fiber-grid-reinforced mortar (BGRM) before and after exposure to an elevated temperature of 300 °C considering the effect of fiber grid type, short polyvinyl alcohol fiber (PVA), and high-temperature exposure time. The experimental results show that the mortar plates reinforced with woven textile T25 and fiber-reinforced polymer (FRP) grid G50 exhibited more pronounced strain-hardening behavior. The highest peak stress was obtained for the T25-reinforced plate, which was 85% and 32% higher than that of the T5- and G50-reinforced plates, respectively. Meanwhile, the bridging effect of PVA fibers in mortar can improve the tensile properties. As the high-temperature exposure time increased, the cracking and peak stress of BGRM decreased significantly. Especially for the T5-reinforced plate after exposure to elevated temperature for 2 h, the cracking and peak stress decreased by 60.5% and 38%, respectively. The positive effect of short PVA fibers on the tensile properties of the BGRM became obsolete owing to the melting of short fibers at high temperature. Furthermore, an exponential strength degradation model related to high-temperature exposure time was proposed.

Bond Behaviors of Steel Fiber in Mortar Affected by Inclination Angle and Fiber Spacing

Considering the random orientation and distribution of steel fibers in concrete, the synergistic reinforcement of steel fibers on concrete is much complex than the bond of single fiber. It is meaningful to study the bond behavior of steel fiber during many actions. With the inclination angle of steel fiber to pullout direction and the fiber spacing as main factors, this paper carried out fifteen groups of pullout tests for hook-end steel fiber embedded in manufactured sand mortar. The inclination angle ranged from 0 to 60°, and the fiber spacing ranged from 3.5 mm to 21.2 mm. The characteristic pullout load-slip (PL-S) curve of steel fibers are given out after treating the original complete curves of each group test. The values of key points featured the debonding, peak and residual pullout loads and slips are determined from the characteristic PL-S curves. Based on a multi-index synthetical evaluation method, the nominal debonding strength, bond strength, residual bond strength and the debonding work, slipping work, and pullout work, as well as the debonding energy ratio, slipping energy ratio, and pullout energy ratio are analyzed. Results indicate that the bond performance represented by above indexes changes with the inclination angle and spacing of steel fibers. Except for the bond mechanism performing the same as aligned steel fibers by pullout test, the bond is dominated by the resistance of mortar to peeling off near pullout surface and scraping along pullout direction. When the inclination angle is over 15° or 30°, the bond performance is generally decreased, due to the peeling off of mortar on surface of transversal section with a certain depth. When the fiber spacing is over than 5 mm, the bond performance becomes worst due to the scraping out of mortar along with the slip of steel fibers.

Experimental and finite element analysis on flexural behavior of mortar beams with chemically modified kenaf fibers

In this study, raw kenaf fibers (RKF), alkaline treated kenaf fibers (AKF), and alkaline-hydrogen peroxide treated kenaf fibers (AHPKF) were prepared and then incorporated into mortar to evaluate their impact on the flexural behavior of mortar. In addition to the fiber type, the effect of fiber dosage (0.25%, 0.5%, and 0.75% by weight of cement) on flexural behavior was also studied. Finite element analysis (FEA) was conducted to assist in examining the stress and cracking strain within the mortar specimens. The results show that with the increase of fiber dosage, although the compressive strength and flexural strength of the mortar decrease, a huge improvement of flexural toughness can be achieved. By comparing these three types of kenaf fibers, AKF provides the best performance compared to the other two. With the addition of superplasticizer, the flexural behavior of mortar can be further improved. The microstructure analysis provides some insight into the flexural behavior of mortars with chemically modified kenaf fibers. Lastly, the finite element analysis indicates that the presence of fibers in mortar can increase the residual load, slow down crack propagation, and reduce the cracking strain.

Technological Perspective for Use the Natural Pineapple Fiber in Mortar to Repair Structures

The use of natural fiber in cementitious materials can contribute to the improvement of technological properties and environmental issues related to the reuse of agro-industrial waste. World pineapple production is approximately 12.8 million tons per year, generating large environmental impacts, because the disposal natural fibers in landfills. The objective of this research was to evaluate the potential of reusing the natural fiber from the pineapple crown as a reinforcement element in eco-friendly mortar for the purpose of recovering building structures committed to coastal environments, evaluating the influence of the fiber surface treatment process with NaOH and its durability in laboratory conditions, in addition to avoiding the disposal of this waste in landfills. The natural fibers were characterized physically, morphologically and chemically, in the treated and untreated (natural) condition, for further technological evaluation of mortars in the fresh state, such as consistency, specific mass, incorporated air and water retention. Comprehensive studies of the hardened state were also carried out to study mechanical strength (compressive, flexural and tensile), water absorption due to capillarity and immersion, as well as durability by evaluating mass loss and mechanical strength after exposure conditions. The results showed that the fiber treatment process improved its characteristics for application in mortar with addition of 2.5% fiber treated in cement mass, causing the better in the technological and durability properties, and a proposed new means of disposing of agro-industrial waste, contributing to a circular economy.

Effects of a Short Heat Treatment Period on the Pullout Resistance of Shape Memory Alloy Fibers in Mortar.

The feasibility of the crack closure of cementitious composites reinforced with shape memory alloy (SMA) fibers was investigated by performing single-fiber pullout tests. To demonstrate the fast crack closing ability, in this study, a heat treatment (300 °C) was applied for a short time (10 min). A short heat treatment was applied for 10 min, after the slip reached 0.5 mm, to activate the shape memory effects of cold-drawn SMA fibers. Two types of alloys were investigated, NiTi and NiTiNb, with two geometries, either smooth or dog-bone-shaped. During the heat treatment, the pullout stress of the SMA fibers initially decreased due to thermal extension, and then increased after heating for 1–3 min, resulting from the shape memory effects. However, their pullout stress recovery during and after the heat treatment was different for the different alloys and fiber geometries. The NiTi fibers generally produced a higher and faster recovery in terms of their pullout stress than the NiTiNb fibers, while the dog-bone-shaped fibers showed a faster pullout stress recovery than the smooth fibers.

Inductive method for the orientation of steel fibers in recycled mortars

Mortars elaborated with recycled aggregates raise two main difficulties: lower mechanical strengths and higher shrinkage compared to traditional mortars. For this reason, fibers were used to improve the properties. Steel fibers are the most employed for their ferromagnetic qualities, what helps to orient them influenced by magnetic field. This paper argues how recycled mortars with steel fiber oriented under the influence of 500 mT field reach flexural strengths 10% higher than those with non-oriented fibers. Thus, mechanical strengths are closer to traditional mortars. Inclusion of fibers in mortar is suitable for obtaining shrinkage values similar to those obtained in traditional mortars.

Rheological and mechanical properties of hybrid fiber reinforced cement mortar

A new hybrid fiber system containing steel fiber, polyvinyl alcohol fiber (PVA fiber) and calcium carbonate (CaCO3) whisker was employed to further improve hardened properties and reduce engineering cost of cement mortar. In this paper, the rheological properties, flow rate and flow spread were measured to evaluate the workability of hybrid fiber reinforced mortar in fresh state. Mechanical strength and flexural toughness of mortars were tested in hardened state. The results indicated that, flowability of fresh hybrid fiber reinforced mortar decreased after substituting PVA fiber for steel fiber and further CaCO3 whisker for PVA fiber in mortar. This is mainly due to the flexibility of PVA fiber and large specific surface area of CaCO3 whisker. The hybrid fiber reinforced mortar shows promising mechanical strength and flexural toughness due to the multi-scale crack resistance formed by micro- and macro-fibers. M5 specimen (1.5% steel fiber+0.4%PVA fiber+1.0% CaCO3 whisker) exerts the best flexural performance and relatively higher compressive strength, exhibiting an obviously positive hybrid effect of fibers.

Bond Resistance of L-Shaped Shape Memory Alloy Fibers in Mortar

Bond Resistance of L-Shaped Shape Memory Alloy Fibers in Mortar

Effect of nano and micro-silica on bond behaviour of steel and polypropylene fibres in high volume fly ash mortar

This paper presents the effects of nano silica (NS), micro silica (MS) and combined NS and MS on bond behaviour of steel and polypropylene (PP) fibres in high volume fly ash (HVFA) mortar. Three types of bend configuration of hook-end steel fibre commercially available are considered, while the PP fibre was crimped shape. Three different fly ash contents of 40%, 50% and 60% (by wt) as partial replacement of ordinary Portland cement (OPC) are considered in HVFA mortar, while a control mortar containing 100% OPC was also considered. The NS and the MS was added as 2% and 10% (by wt), respectively as partial replacement of OPC in HVFA mortar containing 40% fly ash. In the case of combined NS and MS, 2% NS and 10% MS was used as partial replacement of OPC in HVFA mortar. However, in the case of HVFA mortars containing 40% fly ash and different NS and MS, total OPC content of 60% was kept constant in all HVFA mixes containing NS, MS and NS+MS. This was considered to compare these mixes with HVFA mortar containing 40% fly ash. Results indicate that maximum pull-out force of both steel and PP fibres decreases with increase in fly ash contents in HVFA mortars at both 7 and 28days. The addition of 2% NS and 10% MS showed almost similar improvement in the maximum pull-out force of steel and PP fibres at both ages in HVFA mortar containing 40% fly ash. The combined use of 2%NS+10%MS also improved the maximum pull-out force and higher than 2% NS and 10% MS. The reduction in large capillary pores in HVFA mortars containing nano and micro silica observed in Mercury Intrusion Porosity test improved the bond of steel and PP fibres in those mortar due to formation of additional calcium silicate hydrate (C-S-H) gel is believed to be the reason behind this improvement. The maximum pull-out force also increased with increase in number of bends in the hook-end of steel fibre in all mortars in this study at both 7 and 28days. Extra energy absorbed by the higher number of bends is the reason of such improvement in maximum pull-out force. However, in the case of absorbed energy mixed results are observed in the case of different number of bends in steel fibre ends. Good correlations also exist between the maximum pull-out forces of all three types of steel fibres with compressive strength of mortars showing strong influence on the bond behaviour.

Experimental Research on Anti-Cracking Ability of Polyacrylonitrile Fiber Mortar

This paper adopts panel constraint method to research the influence of different mixing amount of polyacrylonitrile fiber on plastic cracking of mortar. The research result shows that polyacrylonitrile fiber can prevent cracking and refine the cracks, and the effect will become more obvious with increase of its mixed amount. When the mixed fiber in mortar is more than 1.0kg/m3, the crack can be reduced to more than 90%. The best mixed amount of polyacrylonitrile fiber in mortar is 1~1.5kg/m3. This experimental result can provide theoretical basis for improving anti-cracking performance of mortar or concrete.

Multiscale characterization of chemical–mechanical interactions between polymer fibers and cementitious matrix

Together with a series of mechanical tests, the interactions and potential bonding between polymeric fibers and cementitious materials were studied using scanning transmission X-ray microscopy (STXM) and microtomography (μCT). Experimental results showed that these techniques have great potential to characterize the polymer fiber-hydrated cement-paste matrix interface, as well as differentiating the chemistry of the two components of a bi-polymer (hybrid) fiber – the polypropylene core and the ethylene acrylic acid copolymer sheath. Similarly, chemical interactions between the hybrid fiber and the cement hydration products were observed, indicating the chemical bonding between the sheath and the hardened cement paste matrix. Microtomography allowed visualization of the performance of the samples, and the distribution and orientation of the two types of fiber in mortar. Beam flexure tests confirmed improved tensile strength of mixes containing hybrid fibers, and expansion bar tests showed similar reductions in expansion for the polypropylene and hybrid fiber mortar bars.

Acoustic Emission Hit Generation Behavior of Basalt Fiber High Strength Mortar under Compression

Acoustic emission (AE) has been applied to study the fracture mechanics of concrete and other cementitious materials. In this paper, the AE hit generation behaviour is employed to investigate the fracture of high strength mortar containing basalt fiber under compression. A variety of amount and length of basalt fiber were used in mortar mix. Result shows that there is no significant effect observed on behavior of AE hit generation due to the differences amount and length of basalt fiber in mortar. All indicates the similar behaviour that can be described into three stages. At the second stage when maximum load starts to occur, AE hits are generated significantly indicating nucleation of many cracks. Materials failure in ductile manner since AE activities still can be recorded at long after post peak behaviour.

Effect of pozzolans on the performance of fiber-reinforced mortars

Abstract Randomly oriented short fibers have been shown to increase tensile strength and retard crack propagation of cement based materials such as fiber-reinforced mortars for diverse applications, especially in aggressive environments. In the case of reinforced concrete, it is very important to produce a “high quality” cover in order to prevent corrosion of the rebars. In order to obtain a high performance material the use of a pozzolan is advisable because low permeability is achieved. The objective of this research was to determine the effect of pozzolans such as silica fume (SF), fly ash (FA), and metakaolin (MK) on the properties of fiber-reinforced mortars. Different types of natural and synthetic fibers were used. A superplasticizer was used to keep the same workability as that of the control mortar. Results of the mechanical and durability properties of the fiber-reinforced mortars are reported. The results show that a loss of resistance due to embedding fibers in mortar is compensated for by the increase in strength caused by silica fume or metakaolin additions to the mortar. The addition of 15% of SF or MK produces an improvement of up to 20% and 68%, respectively, when compared with those mortars without addition. There is a significant decrease in the coefficient of capillary absorption and chloride penetration when a highly pozzolanic material is incorporated into the matrix. In general, these materials, especially SF and MK, improve the mechanical performance and the durability of fiber-reinforced materials, especially those reinforced with steel, glass or sisal fibers. The fly ash addition had a different performance, which could be attributed to its low degree of pozzolanicity.

Ozone treatment of carbon fiber for reinforcing cement

Ozone treatment of isotropic-pitch-based carbon fiber was found to increase the surface oxygen concentration and change surface oxygen from C–O to CO, thereby causing the contact angle between fiber and water to be decreased to zero. Thus, the bond strength between fiber and cement paste was increased and the tensile strength, modulus and ductility of carbon fiber reinforced cement paste were increased. Moreover, the degree of dispersion of fibers in mortar was increased and the effectiveness of the fibers for reducing the drying shrinkage was improved. As a consequence, the strain sensing ability of carbon fiber reinforced mortar was improved in terms of increased gage factor and better repeatability. The ozone treatment did not affect the morphology, tensile strength or volume electrical resistivity of the fiber itself.

Performance of natural fibre reinforced mortar roofing tiles

Interest in natural fibres as reinforcement in developing countries arose (when the use of steel and glass fibres in the industrialized countries was being researched and developed in the late 1960s) mostly because of their lower cost and better availability in the developing world. The use of natural fibres as reinforcement for mortar to be used mainly for roofing has been debated for a long time. Initially, it was rightly thought that natural fibres will adversely affect the setting of Portland cement and as such they should not be used. Later on it was found that natural fibres are embrittled by the hydration products of Portland cement and made ineffective within a short time, especially in hot climates. While such discussions were going on, the initially adopted large corrugated roofing sheet (corrugated iron sheet size) was being found impractical (mainly because of handling and curing problems) and its size was being reduced gradually. The present paper discusses difficulties encountered in the production and use of natural fibre reinforced mortar roofing tiles and means of reducing the adverse effects of Portland cement hydration products on the performance of natural fibres in mortar.

Fibre mortar composites in fire conditions

AbstractA small‐scale test series was carried out using the heating system (radiant exposure) of a cone calorimeter to detect any differences in the way different fibres affect the thermal properties of a standard mortar. The fibres were different polypropylene, polyacrylonitrile, aramide, carbon or steel. Fibres affect the release of moisture from the fibre mortar material. Local pressures caused by water vaporization due to rapid heating can be decreased by incorporating fibres. Fibres have a weak insulating effect. However, use of polyacrylonitrile fibres in mortar may increase the risk to spalling under rapid thermal exposure such as fire. The moisture level in specimens is highly significant for their thermal properties and hence their fire behavior.

Effect of strain-rate on the pull-out behaviour of fibres in mortar

An experimental programme dealing with the pull-out response of fibres from a portland cement mortar matrix at various loading velocities is described. Three types of fibres, namely, steel, glass and polypropylene are used. A range of loading velocities from 4.2 × 10 −3cm/sec to 300 cm/sec is explored. A special experimental procedure is developed. It allows the pulling out of a group of fibres simultaneously hence reducing the scatter in the results. The effects of loading velocity (strain rate) on the load-time response of fibres, their equivalent bond strength and their energy absorption to failure or to complete pull-out are analysed. Also, the limitation of the testing procedure and its influence on the reliability of the results is addressed.