Fiber Reinforced Cement Composites Research Articles

Bond behavior simulation of deformed rebar in fiber-reinforced cementitious composites using three-dimensional meso-scale model

Fiber-reinforced cementitious composites (FRCC) can effectively develop the bond ductility of deformed rebar due to the high tensile resistance and strain capacity. This study presents a numerical method to evaluate the bond behavior of deformed rebar in FRCC based on 3D rigid body spring model (3D RBSM). Beam elements are used to model the rebar and the link elements are used to connect beam elements with RBSM elements as matrix. The same local bond-slip relationship for rebar is assigned at the link elements for both the simulation cases of plain mortar and FRCC. The model could properly simulate the single fiber to mechanical behavior of FRCC and the bond performance of rebar in FRCC. The results revealed that discrete fibers are the principal factors that preventing the splitting bond crack propagation and the stress propagation suggests the presence of high local bond stress around the rebar, improving bond ductility.

Anomalous matrix and interlayer pore structure of 3D-printed fiber-reinforced cementitious composites

Ordinary 3D-printed neat cement paste generally possesses a porous interface between two neighbored filaments. Our work demonstrates that the addition of glass microfibers into cementitious slurries may lead to an anomalous pore structure, i.e., the increased porosity of the inner and outer matrices in filaments and the densified interlayer between filaments in fiber-reinforced cementitious composites (FRCC). Limited glass microfiber addition (0.6%) has no benefits to the bending strength of FRCC beams, the compressive strength of filament matrix, and the bonding behaviors between filaments. The coupled mechanisms of lubrication layer and pressurized bleeding on the surface of filaments, and air-void entrapments in the matrix of filaments were proposed to account for the formation of the anomalous pore structure and strengths. Our findings would deepen the understanding of matrix-interlayer structures in 3D-printed FRCC towards better tuning and design of 3D printing-based additive manufacturing.

Influence of Matrix Strength on Bridging Performance of Fiber-Reinforced Cementitious Composite with Bundled Aramid Fiber

The bundled aramid fiber has good bond properties in the cementitious matrix, and is expected to have high bridging performance in the fiber-reinforced cementitious composite (FRCC). To investigate the influence of matrix strength on the bridging performance of FRCC with the bundled aramid fiber, the uniaxial tension test of FRCC, the pullout test for an individual fiber, and the calculation of bridging law are conducted with the main parameters of matrix strength and fiber volume fraction. From the test results, the maximum tensile load of FRCC and the maximum pullout load of an individual fiber increase as the matrix strength also increases. The calculation result of the bridging law considering the effect of matrix strength expresses the bridging performance of the bundled aramid fiber well. The calculation result also shows that the bridging strength has a linear relationship up to a compressive strength of around 50 MPa.

Eco-Friendly, High-Ductility Slag/Fly-Ash-Based Engineered Cementitious Composite (ECC) Reinforced with PE Fibers

Engineered cementitious composites (ECCs) are a special class of ultra-ductile fiber-reinforced cementitious composites containing a significant amount of short discontinuous fibers. The distinctive tensile strain-hardening behavior of ECCs is the result of a systematic design based on the micromechanics of the fiber, matrix, and fiber–matrix interface. However, ECCs require extensive cement content, which is inconsistent with the goal of sustainable and green building materials. Consequently, the objective of this study is to investigate the mechanical performance of slag/fly-ash-based engineered cementitious composites (ECCs) reinforced with polyethylene (PE) fiber under axial compressive loading, as well as direct tensile and flexural strength tests. The composites’ microstructure and mineralogical composition were analyzed using images obtained from scanning electron microscopy (SEM), X-ray energy diffraction spectroscopy (EDS), X-ray powder diffraction (XRD), and X-ray fluorescence (XRF). The experimental results reveal that a slag-containing composite mixture shows strain-hardening behavior and comparable ductility properties to those of fly-ash-based composite mixtures. A ternary system of binder materials with 5% and 15% slag can increase the compressive strength of ECC by 3.5% and 34.9%, respectively, compared to slag-free ECC composite. Moreover, the microstructural results show that the slag-based cementitious matrix has a more closely cross-linked and dense microstructure at the matrix–aggregate interface. In addition, the concentration of particles on the surface of the fibers was higher in the slag-based cementitious composites than in the fly ash-based composite. This supports the concept that there is a stronger bonding between the fibers and matrix in the slag-based cementitious matrix than in fly-ash-based matrix.

Seismic retrofit of unreinforced masonry walls using precast panels of fiber-reinforced cementitious composite

In this study, a practical seismic retrofit technique was developed for unreinforced masonry (URM) walls using precast panels of fiber-reinforced cementitious composites (FRCC). A hybrid fiber-type comprising steel and nylon fibers with a total volume fraction of 1% was adopted for fabricating the FRCC panels. A total of five URM walls were fabricated and tested under cyclic loading. The primary test parameters are the shear key types between precast panels and steel reinforcement details for the precast panels. From the test results, the URM walls retrofitted by precast panels with the proposed shear keys and reinforcement details showed a great improvement in terms of load-carrying and deformation capacity, stiffness degradation, and energy dissipation capacity compared to the control URM specimen. In addition, test specimens using additional reinforcement such as steel re-bars in the grooves of the panels and turnbuckles exhibited an increase of load-carrying capacity in both loading directions, in comparison with the counterparts without additional reinforcement. Eventually, a strength model was proposed to estimate the lateral strength of URM walls retrofitted by precast panels, and overall, its prediction indicates a good correlation in comparison with the experiment results.

Assessment of Bond Strength of GFRP Bars Embedded in Fiber-Reinforced Cementitious Composites

Assessment of Bond Strength of GFRP Bars Embedded in Fiber-Reinforced Cementitious Composites

Effects of Wetting and Drying Cycles on Microstructure Change and Mechanical Properties of Coconut Fibre-Reinforced Mortar

Natural fibre-reinforced cementitious composites are commonly used as outer construction materials. They usually suffer weather as a result of being expose to various types of climates. In this study, a series of experimental tests were carried out to investigate the deterioration mechanism and mechanical properties of mortars incorporating coconut fibres due to repeated wetting and drying. The results indicated that although the compressive strength was found to increase after the first cycle, both compressive and flexural strengths underwent a significant decrease in the fifth cycle. In addition, at high temperatures, mortar matrixes retain their stable structure, according to the results of TGA analysis. When wetting and drying curing was applied, there was a significant degradation of fibres in the mortar.

Properties of 3D-Printed Polymer Fiber-Reinforced Mortars: A Review.

The engineering applications and related research of fiber-reinforced cement and geopolymer mortar composites are becoming more and more extensive. These reinforced fibers include not only traditional steel fibers and carbon fibers, but also synthetic polymer fibers and natural polymer fibers. Polymer fiber has good mechanical properties, good bonding performance with cement and geopolymer mortars, and excellent performance of cracking resistance and reinforcement. In this paper, representative organic synthetic polymer fibers, such as polypropylene, polyethylene and polyvinyl alcohol, are selected to explore their effects on the flow properties, thixotropic properties and printing time interval of fresh 3D-printed cement and geopolymer mortars. At the same time, the influence of mechanical properties, such as the compressive strength, flexural strength and interlaminar bonding strength of 3D-printed cement and geopolymer mortars after hardening, is also analyzed. Finally, the effect of polymer fiber on the anisotropy of 3D-printed mortars is summarized briefly. The existing problems of 3D-printed cement and polymer mortars are summarized, and the development trend of polymer fiber reinforced 3D-printed mortars is prospected.

Influence of Glazed Hollow Bead on the Performance of Polyvinyl Alcohol Fiber Reinforced Cement Composites

To improve the thermal insulation properties and toughness of concrete, the glazed hollow bead (GHB) and polyvinyl alcohol (PVA) fiber reinforced cementitious composites (GPCC) were investigated by orthogonal test, which includes six GHB mass percentage (20%, 40%, 60%, 80%,100%, 120%), three PVA volume fraction (1%, 1.5%, 2%) and water binder ratio (0.26, 0.30, 0.34). Compressive, split tensile strengths and thermal conductivity of GHB-PVA reinforced cementitious composites (GPCC) were tested, and the mechanism of fibers was analyzed from a microscopic perspective. The results revealed that the thermal insulation will be significantly improved with the increased content of GHB, but the compressive and split tensile strength will be decreased simultaneously. No obvious effect was found by the PVA fiber addition on its strength indexes, and the presence of GHB will affect the bridging action of PVA fibers. The water binder ratio has more effect on strengths than thermal conductivity. Based on the mechanical performance rather than the thermal insulation analysis test, the optimal mix proportions were proposed: mass percentage of 40% GHB, a volume fraction of 1.5% PVA fiber, and 0.26 water-binder ratio. Moreover, the anchoring and bridging effect of PVA fibers will effectively balance the stress generated by the shrinkage of cement paste, and inhibits or even prevents the development of cracks. However, a certain number of tiny cracks will be formed near the GHB, and between GHB and PVA fibers, which will cause local stretching and peeling of PVA, and shattering inside the GHB with the increase of external force. The findings of this study can provide a useful reference for the application of an insulated-bearing material with GHB and PVA fiber.

Improving the tensile resistance at high strain rates of high-performance fiber-reinforced cementitious composite with twisted fibers by modification of twist ratio

This study aims to examine effects of twist ratio on the tensile resistance at high strain rates and strain rate sensitivity of high-performance fiber-reinforced cementitious composites (HPFRCCs) with a small amount of twisted fibers. Two types of twisted steel fibers with different twist ratios, T3-fibers (3 twists/30 mm) and T9-fibers (9 twists/30 mm), were incorporated at 1% by volume into two matrices with different matrix strengths, M1 (56 MPa) and M2 (84 MPa). The direct tensile test results indicated that HPFRCCs with 1% twisted fibers generated not only high tensile resistance at high strain rates but also great rate sensitivity by maintaining tensile strain hardening accumulated with multiple micro cracks at high strain rates. T9-fibers produced the highest tensile resistance at high strain rates in M1 whereas T3-fibers did in M2. In addition, T9-fibers exhibited lower rate sensitivity than T3-fibers in all matrices. Theoretical models have been used successfully to predict dynamic post cracking strength of HPFRCCs with twisted fibers considering number of twists and the predicted results showed good agreements compared to the experimental results.

Rheological and Mechanical Properties of High-Performance Fiber-Reinforced Cement Composites with a Low Water-Cement Ratio.

High-performance fiber-reinforced cement composites (HPFRCCs) have been widely used in structural engineering due to their excellent performance. With the trend of lightweight construction, these materials, which can be used in prefabricated components, are becoming more and more important. This study investigated the influence of the water–cement (w/c) ratio, within the 0.19–0.28 range, on the rheological and mechanical properties of HPFRCCs; the pore structure and microstructure were observed to evaluate its effect. An elastic modulus test showed that a smaller w/c ratio would result in a higher rigidity of the material. Both the yield shear stress and plastic viscosity decreased to significantly different degrees with an increasing w/c ratio; a decrease in the yield shear stress and plastic viscosity was conducive to air discharge from the composite and, hence, reduced the air content. Most of the internal pores had a diameter of 20–100 nm or larger than 200 nm, while the proportion of those with a diameter of 100–200 nm was relatively low. When the w/c ratio was below 0.22, the flexural and compressive strengths barely increased due to an increment in the number of larger pores (i.e., diameter >200 nm). The results showed that the yield shear stress, plastic viscosity, pore uniformity, and the number of pores with a diameter above 200 nm are the dominant factors affecting the HPFRCC performance at a low w/c ratio.

Viscoelasticity and energy dissipation as indicators of flexural fatigue behavior in a ductile carbon fiber-reinforced cementitious composite

In this manuscript, we present research on the fatigue behavior of a cementitious composite reinforced with chopped carbon fibers. The fatigue life is determined by dynamic mechanical analysis, offering information about viscoelasticity in addition to more traditional damage indicators such as strain development. X-ray computed tomography was used to visualize microcracks during the fatigue experiment. Reinforced composites were found to be considerably longer-lasting than the unreinforced matrix material, as the fibers lead to significant pseudoductility and microcracking. A rise of inelastic events in the material’s viscoelastic behavior was found to be an excellent early indicator of fatigue failure.

PVA fiber reinforced cement composites with calcined cutter soil mixing residue as a partial cement replacement

In this paper, a cutter soil mixing residue (CSMR), which is a soil–cement solid waste, was calcined and then used as a partial cement replacement in polyvinyl alcohol fiber reinforced cement composites (PVA-FRCCs). The binder chemistry was characterized using XRD, TGA and FTIR. The fiber–matrix interfacial properties were examined with SEM. The composite mechanical properties, including compressive strength, flexural properties and tensile behaviors and fiber bridging stress-crack opening relationships, were investigated. Results showed that the calcined CSMR can produce additional hydrates to aid the strength gain and densify the fiber–matrix interface. With a cement replacement level up to 40%, the tensile strength was not compromised, while the tensile strain capacity significantly increased to a maximum value of 3.2%. The micromechanical analysis revealed that the improved strain capacity is mainly attributed to the optimized fiber–matrix interface yielding enhanced pseudo strain-hardening indices. The results obtained in this study indicate that calcined CSMR is an attractive novel supplementary cementitious material for developing greener strain-hardening cementitious composites.

A Comparative Study on the Shear Behavior of UHPC Beams with Macro Hooked-End Steel Fibers and PVA Fibers.

Structural members made of ultra-high-performance concrete (UHPC) have been attractive to engineers and researchers due to their superior mechanical properties and durability. However, existing studies were focused on the behavior of UHPC members reinforced with micro straight steel fibers at a volume fraction between 1 and 3%. There is a lack of studies on the influence of different types and amounts of fibers on the shear behavior of UHPC structural members. The objective of the study was to experimentally investigate the shear behavior of UHPC beams with macro hooked-end steel (MHS) fibers and polyvinyl alcohol (PVA) fibers, which are two of the most used fibers for high-performance fiber-reinforced cementitious composites. The shear behavior of ten large-scale non-prestressed UHPC beams was studied. The experimental parameters included the shear span-to-effective depth ratio, the fiber volume fraction, and the type of fibers. It was found that both MHS fibers and PVA fibers were effective in enhancing the shear performance of the UHPC beams whether the shear transfer mechanism was governed by arch action or beam action. Moreover, the measurement results of the average crack spacing imply the distinct difference in the fiber bridging effects of the MHS fibers and PVA fibers in the UHPC beams.

Fracture response of wollastonite fiber-reinforced cementitious composites: Evaluation using micro-indentation and finite element simulation

The paper presents indentation studies on wollastonite fiber incorporated cementitious systems. The acicular nature of the fibers is poised to delay the coalescence of micro-cracks in such systems thus leading to tougher building materials. Towards that end, load-penetration depth results from the indentation studies are employed to ascertain elastic and fracture properties of wollastonite-incorporated cementitious composites. While up to 10% mass-based cement-replacement by wollastonite results in comparable elastic moduli as compared to conventional binders, the fracture toughness increases by as much as 33%. In order to gain insights into the toughening mechanisms brought about by the fine fibers, a microstructure-guided numerical simulation strategy is adopted towards effective fracture performance prediction. The performance enhancement of the wollastonite systems is corroborated by the finite element-based simulations carried out on the virtual microstructures that accurately capture the heterogeneity of such systems. Besides fracture performance enhancement, the wollastonite-incorporated cementitious systems also contribute towards development of sustainable cement replacing compositions. Moreover, the micromechanical predictive tool developed in this study facilitate efficient means to tune the materials structure for desired performance.

Strengthening of the concrete face slabs of dams using sprayable strain-hardening fiber-reinforced cementitious composites

Strengthening of the concrete face slabs of dams using sprayable strain-hardening fiber-reinforced cementitious composites

Pullout behaviour of shape memory alloy fibres in self-compacting concrete and its relation to fibre surface microtopography in comparison to steel fibres

Superelastic nickel-titanium shape memory alloy (SMA) can recover large strains. Hence, SMA fibres (SMAFs) have been incorporated into concrete to provide re-centring and crack-closing ability to the concrete. Since the structural performance of fibre-reinforced cementitious composites is significantly influenced by the fibre pullout mechanism, this research was focused on the pullout behaviour of SMAFs and their associated parameters. Single fibre pullout tests were performed on straight and hooked-end SMA and steel fibres (SFs) embedded in self-compacting concrete. The experimental investigation considers three variables: the type of hooked-end, embedded length, and loading rate. The full range of pullout load-slip behaviour was obtained under two different loading rates. The results were analysed in the slip corresponding to maximum pullout load, maximum tensile stress induced in fibre, material use factor, pullout energy, average and equivalent bond strength. Straight SMA fibres showed a weaker interfacial bond with concrete than steel counterparts. SMA fibre with 45° hooked-end showed the highest bond strength among SMA fibres considered in this study. The increase in the embedded length of most of SMAFs and SFs caused a significant increase in the pullout load without changing the configuration of the pullout load-slip curve. The pullout behaviour of SMAFs was almost rate-insensitive, whereas SFs exhibited evident rate sensitivity in the pullout. The observed differences between SMA and steel fibres were clarified based on fibre surface micro-topography and roughness and matrix damage. This difference was explained based on the surface micro-topography of fibres and matrix damage.

Ultra-High Performance Hybrid Polyvinyl Alcohol-Polypropylene Fiber-Reinforced Cementitious Composites with Augmented Toughness and Strain-Hardening Behavior

Ultra-High Performance Hybrid Polyvinyl Alcohol-Polypropylene Fiber-Reinforced Cementitious Composites with Augmented Toughness and Strain-Hardening Behavior

Influence of Various Paraments on Properties of Basalt Fiber-Reinforced Cementitious Composites

Influence of Various Paraments on Properties of Basalt Fiber-Reinforced Cementitious Composites

Mechanical Characteristics of Self-Healing, Deflection-Hardening, High-Performance Fiber-Reinforced Cementitious Composites Using Coarse Aggregates

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