Hybrid Fiber Reinforced Cementitious Composites Research Articles

Fiber Synergy of Polyvinyl Alcohol and Steel Fibers on the Bond Behavior of a Hybrid Fiber-Reinforced Cementitious Composite.

Based on multi-scale characteristics inherent in the cracking process of cementitious composites, fibers with different geometric dimensions are simultaneously used to restrain the formation and development of cracks at different scales. Accordingly, hybrid fiber-reinforced cementitious composites (HyFRCCs) exhibit excellent bond behavior and deformation capacity in terms of tension and compression, accompanied by higher damage tolerance. Using these benefits of the mechanical properties of HyFRCCs, the structural performance of HyFRCC structures under complex loading conditions can be improved. To objectively evaluate the contributions of all fibers to the mechanical properties of HyFRCCs, steel macro-fibers, and polyvinyl alcohol (PVA) micro-fibers were used to design several reinforced cementitious composites. Four of the specimens were mono-fibrous cementitious composites, three specimens were cementitious composites reinforced with hybrid fibers, and one was a non-fibrous cementitious composite. The synergy effect of the steel and PVA fibers was analyzed using various fiber combinations. The results indicated a significant enhancement of the bonding properties of HyFRCCs through the incorporation of PVA and steel fibers. Specifically, the peak bond strength, peak slip displacement, and residual bond strength exhibited increments ranging from 31.0% to 41.7%, 60.6% to 118.4%, and 34.6% to 391.3%, respectively, in comparison to the reference test block. Notably, the combined presence of the PVA and steel fibers consistently demonstrated a positive confounding effect on the residual bond strength. However, negative confounding effects were observed in terms of the peak bond strength and peak slip displacement, particularly with 1.0% steel fiber content and 0.5% PVA fiber content.

Bond-slip constitutive model and numerical analysis for rebar embedded in steel-polyethylene hybrid fiber-reinforced cementitious composites

The synergetic effect between the deformed rebar and steel-polyethylene hybrid fiber-reinforced cementitious composites (HECC) plays a critical role in assuring the performance of reinforced HECC structures. In this paper, the bond behavior between the deformed rebar and HECC was studied under direct pullout tests. Based on the experimental results, a simplified bond-slip constitutive model for the rebar embedded in HECC was proposed by modifying the existing bond-slip constitutive model, which is shown to be able to accurately describe the bond-slip relationship between the rebar and HECC and serve as the basis for reinforced HECC structural design. According to the distribution of bond stresses along the anchorage length, an anchorage position function was developed; and then a refined bond-slip constitutive model considering the anchorage position function was established. Furthermore, a finite element analysis (FEA) model, considering the nonlinear bond behavior between the rebar and HECC was built through the use of nonlinear spring elements based on the bond stiffness obtained from the proposed refined bond-slip constitutive model. The accuracy of the FEA model in predicting the bond-slip behavior between the rebar and HECC was also verified.

Characterization of mechanical behavior and mechanism of hybrid fiber reinforced cementitious composites after exposure to high temperatures

In this paper, we developed a novel hybrid fiber reinforced cementitious composites (HFRCCs) using steel fibers, polyvinyl alcohol (PVA) fibers and calcium carbonate whisker (CW) with high temperature resistance and cost-effectiveness. Mechanical and physical responses of HFRCCs after exposure to high temperature and roles of different fibers were particularly studied. The results showed that partially replacing PVA fibers by CW could reduce the deterioration of strengths and flexural toughness of HFRCCs before 600 °C because of significant nucleation effect and restraining cracking of CW. PVA fibers would melt above 200 °C and thus deteriorated the flexural and splitting tensile strengths, but less effective to compressive strengths. Steel fiber was most effective to increase the residual mechanical properties among these fibers because of its higher thermostability and strong bond with matrix. Generally, high temperature deteriorated the matrix and adversely affected the quality of fibers, which was mainly related to the different thermostability between fibers.

The hybrid effects of PVA fiber and basalt fiber on mechanical performance of cost effective hybrid cementitious composites

Unlike conventional concrete materials, micromechanical design theory is used in the material design processes of Engineered Cementitious Composites (ECC). The design theory based on micromechanics paves the way for the use of hybrid fibers in order to improve mechanical properties and reduce production costs since the cost of fibers being one of the main components of ECC is high. The combination of fibers up to a certain ratio in the mixtures triggers high tensile ductility (approximately 3% axial tensile strain capacity) along with narrow crack openings. The aim of the study was to improve the basic mechanical properties of hybrid fiber-reinforced cementitious composites by using PVA fiber and basalt fiber as a hybrid in order to decrease production costs. The total fiber content of 2% was formed with three different proportions of basalt fiber and PVA fiber and the impacts on the mortar properties were examined within the scope of the study. First of all, the ECC control sample consisting of only PVA fiber was produced. Then hybrid fibers were added into the mortar in three different combinations as 75% PVA + 25% basalt fiber, 50% PVA + 50% basalt fiber and 25% PVA + 75% basalt fiber at a total fiber content of 2%. Compressive strength, flexural strength, tensile strength and microstructures analyses were made on the mortars and they were compared with the control sample. The optimum hybrid combination was obtained at 75% PVA + 25% basalt fiber. According to the results of the experimental study, approximate results were obtained with respect to the reference sample in flexural strength of mortars and tensile strength of mortars by increasing PVA fiber ratio in the mixtures. As a result, performance characteristics of hybrid fiber reinforced cementitious composites were affected at different levels due to the mechanical and geometrical properties of the fibers used.

Flexural behavior of reinforced concrete beams with high performance fiber reinforced cementitious composites

This article presents an experimental study on the flexural performance of reinforced concrete (RC) beams with fiber reinforced cementitious composites (FRCC) and hybrid fiber reinforced cementitious composites (HFRCC) in the hinge portion. Beam specimens with moderate confinement were used in the study and tested under monotonic loading. Seven diverse types of FRCC including hybrid composites using fibers in different profiles and in different volumes are employed in this study. Companion specimens such as cylindrical specimens and prism specimens are also used to study the physical properties of composites employed. The moment-curvature, stiffness behavior, ductility, crack pattern and modified flexural damage ratio are the main factors considered in this study to observe the efficacy of the employed hybrid composites. The experimental outputs demonstrate the improved post yield behavior with less rate of stiffness degradation and better damage tolerance capacity than conventional technique.

Experimental Investigation on Compressive Toughness of the PVA-Steel Hybrid Fiber Reinforced Cementitious Composites

In order to achieve the whole process control of crack formation of engineered cementitious composites (ECC) under loading and improve the mechanical properties of ECC, PVA-steel hybrid fiber reinforced cementitious composites (HyFRCC) was proposed by mixing steel fibers with traditional ECC. And the key parameters to affect the HyFRCC performance are PVA fiber content, steel fiber content and aspect ratio of steel fiber. In order to investigate the mechanical properties of PVA-steel HyFRCC such as the compressive toughness, 15 PVA-steel HyFRCC specimens with different volume fraction of steel fiber and PVA fiber, together with 1 non-fibrous cementitious composites specimen and 3 ECC specimens with PVA fiber only for comparison were designed and uniaxial compression tests were conducted. Furthermore, the effect of fiber content, fiber type and fiber geometrical characteristic on the compressive toughness of HyFRCC were analyzed. The results show that PVA fiber content, steel fiber content and aspect ratio of steel fiber have little impact on the uniaxial compressive strength of the PVA-steel HyFRCC, while the peak strain, compressive toughness and the post-peak ductility of PVA-steel HyFRCC are improved significantly due to fiber hybridization. The formation of large scale cracks of ECC specimens after post-peak loading is restrained effectively with the addition of steel fiber. The mixture of PVA and steel fiber has a remarkable effect on the improvement of ECC compression toughness and crack control. It indicates that the energy dissipation and damage control capacity of the structural component with PVA-steel HyFRCC under seismic loading will be enhanced.

Effects of CaCO3 whisker, hybrid fiber content and size on uniaxial compressive behavior of cementitious composites

Introduction of hybrid fiber and calcium carbonate (CaCO3) whisker could improve the properties of cementitious composites. Nevertheless, little attention has been paid to influences of steel‐polyvinyl alcohol (PVA) hybrid fiber and whisker on stress–strain behavior of hybrid fiber reinforced cementitious composites (HFRCC). In this research, 19 groups of mixtures have been used to explore this topic. The results present that CaCO3 whisker can improve the compressive strength, peak strain and prepeak strain energy of steel‐PVA HFRCC. Generally, HFRCCs reach better compressive behavior when the fibers size are grading. For example, 13 mm steel fiber+ 6 mm PVA fiber+ whisker and 35 mm steel fiber+ 12 mm PVA fiber+ whisker are better than 13 mm steel fiber+ 12 mm PVA fiber+ whisker and 35 mm steel fiber+ 6 mm PVA fiber+ whisker. The results are employed to develop formulas for calculating the strength, deformation, and toughness of HFRCC. Two models were developed to evaluate the stress–strain response of HFRCC. The prediction results of prepeak stress–strain curves using Model 2 (piecewise function involves a cubic parabola and a rational fraction) are closer to the experimental curves and lower than those using Model 1 (continuous rational power function). Therefore, Model 2 is recommended if more accurate prediction of the prepeak stress–strain curve is required. Otherwise, the simpler Model 1 can be used.

Influence of calcium carbonate whisker and polyvinyl alcohol- steel hybrid fiber on ultrasonic velocity and resonant frequency of cementitious composites

Inclusion of hybrid fiber in cementitious composites could restrict the growth of cracks at different stages and improve the mechanical properties of concrete, and adding calcium carbonate (CaCO3) whisker would further improve the mechanical properties of cementitious composites. Nevertheless, no attention has been paid to the effects of steel- polyvinyl alcohol (PVA) hybrid fiber and whisker on ultrasonic pulse velocity (UPV) and resonant frequency (RF) of hybrid fiber reinforced cementitious composites (HyFRCC), although they have been used widely in quality assessment of concrete. In this research, 114 specimens have been used to explore the influences of steel-PVA hybrid fiber and whisker on the UPV, RF parameters and the mechanical properties. The results of this research present that there may exists “fiber gradation” in HyFRCC, because there is always a best fiber combination to reach the greatest compactness and highest non-destructive testing results. In addition, the partial substitution of PVA fiber by whisker decreased UPV and RF and increased density loss rate and compressive strength except for one mixture. Therefore, UPV, RF can reflect the effect of whisker on the inner structure and detect the variation, and have potential use to evaluate HyFRCC in engineering applications.

New models for predicting workability and toughness of hybrid fiber reinforced cement-based composites

The new models using reinforcing index to predict workability and toughness of hybrid fiber reinforced cementitious composites (HyFRCC) were systematically studied in this paper. The existing models are discussed and new quadratic function models are proposed. A RIV considering elastic modulus of fibers is employed to calculate the workability parameter of fresh HyFRCC, and the analysis indicates that the slump cone, V funnel, J-Ring and L-Box test results can all be predicted by this workability model.In addition, a RIV considering tensile strength of fibers is employed to calculate the toughness of harden HyFRCC. The analysis indicates that this toughness model can be used to predict the compressive toughness, flexural toughness, equivalent flexural strength (according to JCI-SF4), I5, I10 and I20 (according to ASTM C1018) of HyFRCC, without considering the matrix (mortar or concrete) and fiber combination (e.g., steel-polyvinyl alcohol fiber-whisker, steel-cellulose fiber, steel-polypropylene fiber and so on).The new models have extensive applicability and good correlation with experimental results, which can help offering good behaviors to HyFRCC fresh mixtures, even hardened states, in design and construction practice via fiber mix optimization.

Study on the Mechanical Properties of High Performance Hybrid Fiber Reinforced Cementitious Composite (HFRCC) under Impact Loading

The dynamic material properties of high performance hybrid fiber reinforced cementitious composites (HFRCC) with various volumetric fractions of steel and polyvinyl alcohol (PVA) fibers were studied by the Split Hopkinson Press Bar (SHPB) test. The results show that HFRCC with higher volumetric fraction of steel fibers are more sensitive to stain rate and the dynamic compressive strength increase more prominently with the strain rate increasing, but peak strain shows the opposite trend. The PVA fibers increase the ductility of HFRCC more effectively than steel fibers. Compared to PVA fiber reinforced cementitious composites (FRCC), HFRCC present better dynamic material properties under impact loading.

Crack modeling of steel–carbon hybrid FRCCs

An experimental study to investigate nonlinear material behavior in tension of steel–carbon hybrid fiber reinforced cementitious composites (FRCC) was performed. In the tests, tensile strength, toughness index, and fracture properties, including fracture energy and crack opening or elongation, were measured. Based on the test results, a fictitious crack model for steel–carbon hybrid FRCC was developed. The proposed crack model was verified by comparing its predictions with the test results. Acceptable accuracy in simulating the tensile behavior of steel–carbon hybrid FRCC was obtained. For convenience in design and structure analysis, simplified equations to predict tensile strength and fracture energy in hybrid FRCC were developed.

Corrosion of Reinforcing Steel in Fiber Reinforced Cementitious Composites

For the purpose of global sustainability the long life of structures is essential and the durability performance of reinforced concrete structures is one of the key issues to be resolved. This paper reports the results of a series of long term corrosion tests on fiber reinforced cementitious composites containing polyethylene (PE) alone and hybrid steel cord (SC) and PE fibers. The results are also compared with ordinary mortar. The specimens are subjected to accelerated corrosion for one year by applying external potential to the steel bar anode and a cathode made out of a steel wire mesh placed outside the concrete. Durability performances of the specimens are examined through regular monitoring of the time to initiate corrosion, the corrosion area ratio, corrosion depth, and the amount of steel loss. Results show that the hybrid fiber reinforced cementitious composites (HFRCC) containing hybrid SC and PE fibers exhibited excellent performance compared to mortar and fiber reinforced cementitious composites (FRCC) containing PE fiber. The order of the durability performance is HFRCC, FRCC, and Mortar. It is observed that the sacrificial corrosion of some of the SC fibers in the HFRCC specimen played an important role in the significant reduction of steel bar corrosion in the specimen.

INFLUENCE OF COMPOSITE MATERIALS AND PROPORTION ON THEIR FRESH PROPERTIES AND MECHANICAL ONES OF HYBRID FIBER REINFORCED CEMENTITIOUS COMPOSITES

In this study, influence of composite materials and mix proportions on the fresh properties and the mechanical ones of Hybrid Fiber Reinforced Cementitious Composites ( HFRCC ) was experimentally investigated. Then, the influence was analyzed by applying the excess paste thickness theory proposed by Kennedy in 1940 and formulated as functions of dominant factors. Results of the experiment and the analysis revealed the following matters:1. The relative yield value and the relative plastic viscosity of HFRCC (yield value and plastic viscosity of HFRCC normalized by those of paste) decreased as the fiber volume content increased, and influenced by the geometry of contained steel fiber. Though it could not be quantified only by the excess paste thickness, the influence of sand-binder ratio, admixtures, volume content of each fiber and the geometry of the steel fiber on fresh properties and mechanical ones of HFRCC could be quantified by introducing modified excess paste thickness. However, it was not possible to apply it to express the influence of different water binder ratio.2. The value of ductility index obtained by three point bending test increased as the fiber volume content and the aspect ratio of the steel fiber increased. By introducing modified excess paste thickness, the influence of sand binder ratio, water binder ratio, fiber volume content and aspect ratio of the steel fiber on the value of ductility index of HFRCC could be quantified. However, it was not possible to apply it to express the influence of different admixtures.

Experimental Research on Mechanical Performance of Hybrid Fiber Reinforced Cementitious Composites with Polyvinyl Alcohol Short Fiber and Carbon Textile

Combining the advantages of both carbon textile reinforced concrete and strain-hardening cementitious composites, research on hybrid fiber reinforced cementitious composites with polyvinyl alcohol (PVA) short fiber and carbon textile has been carried out for developing a new kind of anticracking technique, which can disperse the cracks innocuously and improve durability, service life, and load-bearing capacity of concrete structures. Compared with textile reinforced mortar, influences of the surface treatment of carbon textile, water-binder ratio, volume content of PVA fiber on crack resisting, load-bearing capacity, and bond property of the tested composite have been investigated through four-point bending experiments and pull-out tests. The experimental results present excellent structural and material behaviors with high toughness and prominent cracking control ability. The proposed approach for surface treatment of carbon textile by spreading sand with different grain sizes on the surface of carbon roving impregnated with an epoxy resin obviously improves bond properties between the roving and the matrix. For the hybrid fiber reinforced cementitious composites, the integrated performance, particularly cracking response was evidently influenced by the volume content of PVA fiber; composites with 1.5% PVA fiber behaves much better than the one with 1.0% PVA fiber.

Observation of Multiple Cracking in Hybrid FRCC at Micro and Meso Levels

Development of high-performance construction materials is one of the key issues for the sustainability of structures, and this is one of the reasons for the development of ductile fiber reinforced cementitious composites (FRCC). The purpose of this study is to observe microcracking in high-performance FRCC at the micro and meso levels to clarify the detailed mechanisms causing ductile behavior. In the experiments, a specially designed system was used to observe the surface of specimens under tensile loading by means of an electron microscope. X-ray technique with a contrast medium was also applied to observe internal cracking around a deformed bar. A formation of a number of microcracks on the surface of the FRCC was observed even before loading. These microcracks subsequently grew and/or other cracks occurred to generate multiple cracking as the load increased. The accumulation of multiple cracks produced extended nonlinearity of FRCC. In the vicinity of the deformed bar in the FRCC, multiple cracks were formed from the lug of the bar and the crack width was much thinner than in plain mortar. Thus FRCC surely contributes to dispersal of bond cracks and resistance to the expansion of cracks.

Amnestic aphasia

Inclusion of hybrid fiber in cementitious composites could restrict the growth of cracks at different stages and improve the mechanical properties of concrete, and adding calcium carbonate (CaCO3) whisker would further improve the mechanical properties of cementitious composites. Nevertheless, no attention has been paid to the effects of steel- polyvinyl alcohol (PVA) hybrid fiber and whisker on ultrasonic pulse velocity (UPV) and resonant frequency (RF) of hybrid fiber reinforced cementitious composites (HyFRCC), although they have been used widely in quality assessment of concrete. In this research, 114 specimens have been used to explore the influences of steel-PVA hybrid fiber and whisker on the UPV, RF parameters and the mechanical properties. The results of this research present that there may exists “fiber gradation” in HyFRCC, because there is always a best fiber combination to reach the greatest compactness and highest non-destructive testing results. In addition, the partial substitution of PVA fiber by whisker decreased UPV and RF and increased density loss rate and compressive strength except for one mixture. Therefore, UPV, RF can reflect the effect of whisker on the inner structure and detect the variation, and have potential use to evaluate HyFRCC in engineering applications.