PVA Fibers Research Articles

Enhanced Ductility and Toughness of Desert Sand Engineered Cementitious Composites

Economical desert sand engineered cementitious composites (DS-ECCs) using a mixture of cement, fly ash, local desert sand, water, low-cost PVA fibers, and chemical additives were developed, aiming for a further enhancement in ductility and toughness. The mechanical behavior of DS-ECCs for two sand samples (from Mu Us and Tengger deserts, China) was determined using uniaxial tension/compression tests and three-/four-point bending tests. The results showed that desert sand-based ECCs with the designed mix ratios had better mechanical properties than the river sand-based ones. Compared with the river sand-based ECCs at 28 and 56 day, the DS-ECCs presented superior ultimate tensile and comparable compression strengths. The excellent ductility was characterized by ultimate tensile and compression strains of 3–7% and over 1%, respectively. Meanwhile, the DS-ECCs showed improved flexural properties with outstanding fracture and bending strengths (4–9 kN and 21–30 kN) and toughness. The findings of this study will further strengthen the mechanical performance of DS-ECCs and broaden their engineering applicability.

Toughening Mechanism of Directional Fabric Woven Net and/or Non-Directional Short-Cut Fiber-Reinforced Sprayed Cement Mortar Thin-Plates.

In this paper, a non-directional short-cut polyvinyl alcohol fiber (PVA), directional carbon-glass fabric woven net, and a combination of these fibers were used to reinforce sprayed cement mortar (named FRCM-SP, FRCM-CN, and FRCM-PN accordingly), and the direct tensile and four-point bending tests of these three types of thin plates were conducted. It was shown that the direct tensile strength of FRCM-PN reached 7.22 MPa under the same cement mortar matrix, which was 175.6% and 198.3% higher than that of FRCM-SP and FRCM-CN, respectively; the ultimate tensile strain of FRCM-PN was 3.34%, which was 65.3% and 1291.7% higher than that of FRCM-SP and FRCM-CN, respectively. Similarly, the ultimate flexural strength of FRCM-PN reached 33.67 MPa, which was 182.5% and 519.6% higher than that of FRCM-SP and FRCM-CN, respectively. In addition, the tensile, bending toughness index, and residual strength factor of FRCM-PN were much higher than those of FRCM-SP and FRCM-CN, indicating that the incorporation of non-directional short-cut PVA fibers improved the interfacial bonding properties between the cement mortar matrix and the fiber yarn and significantly enhanced the toughness and energy dissipation capacity of the sprayed cement mortar. Therefore, the use of a certain amount of non-directional short-cut PVA fibers can improve the interfacial bonding properties between the cement mortar and the fabric woven net while ensuring the spraying performance and significantly improving the reinforcing and toughening effect on the cement mortar to meet the demand for large-area rapid construction and structural seismic reinforcement.

Compression behavior of GFRP reinforced hybrid fibre reinforced concrete short columns subjected to eccentric loading

This paper presents the results of an experimental study carried out on the GFRP reinforced hybrid fibre concrete short columns subjected to eccentric compression. In this study, hybrid fiber-reinforced concrete was prepared in different volume ratios of hybrid fibers and the cooperative effect of the GFRP reinforcement and the steel-PVA hybrid fibre concrete with different fibre ratios under eccentric loading was explored. 10 GFRP reinforced hybrid fibre concrete short columns and 2 plain reinforced concrete short columns were tested to investigated their eccentric compressive properties. The tests results are presented in terms of failure modes, longitudinal reinforcement strain, concrete compressive strain and compressive load capacity of GFRP reinforced hybrid fibre concrete eccentrically compressed short columns. The results show that the concrete on the compressed side was crushed when the specimen under both the initial eccentricity of 50 mm and 100 mm the reinforcement were pulled on the tension side of specimen under a larger initial eccentricity of 100 mm. The addition of fibres can effectively prevent the crack generation and development and improve the bonding property between reinforcement and concrete. Besides, the addition of steel fibre contributes a better performance on the ultimate compressive capacity of specimen under a lager initial eccentricity with an optimal ratio of steel fibre at 1.4 %. PVA fibre effectively improve the ductility of the concrete, so that the hybrid fibre concrete elements remain relatively its integrity after failure. Finally, considering the effect of GFRP reinforcement and different ratios of steel fibre and PVA fibre on the compressive capacity of short concrete columns, the equation for the calculation of the ultimate compressive capacity of partial sections of eccentric columns is proposed, and a good agreement was observed between the tested and calculated value.

Investigation of Workability and Mechanical Properties of PVA Fiber-Reinforced Phosphogypsum-Based Composite Materials.

To address the poor characteristics of low strength and poor toughness in phosphogypsum-based construction material, this study investigates the influence of different diameters, lengths, and dosages of polyvinyl alcohol (abbreviated as PVA) fibers on the workability and mechanical properties of phosphogypsum-based construction material. The results show that as the length and dosage of PVA fibers increase, the flowability of the slurry gradually decreases, and the setting time also shortens. With an increase in the diameter of PVA fibers, the rate of decrease in flowability slows down, and the rate of shortening of setting time also gradually slows down. Moreover, the inclusion of PVA fibers significantly improves the mechanical strength of the specimens. When PVA fibers with a diameter of 15 μm, length of 12 mm, and dosage of 1.6% are used, the phosphogypsum-based construction material reinforced with PVA fibers exhibits optimal performance. Under this mixing ratio, the strength values of the specimens for flexural strength, bending strength, compressive strength, and tensile strength are 10.07 MPa, 10.73 MPa, 13.25 MPa, and 2.89 MPa, respectively. Compared to the control group, the strength enhancements are 273.00%, 164.29%, 15.32%, and 99.31%, respectively. SEM scanning of the microstructure provides a preliminary explanation for the mechanism of how PVA fibers affect the workability and mechanical properties of phosphogypsum-based construction material. The findings of this study can provide a reference for the research and application of fiber-reinforced phosphogypsum-based construction material.

Anodic Aluminum Oxide Membrane Assisted Extrusion of Polymer Solutions for Hydrogel Formation

AbstractThe potential of polymeric nanostructures obtained by extruding polymer solutions through reusable anodic aluminum oxide (AAO) nanopores for the fabrication of nanostructures is investigated systematically to be able to unveil the potential impact of structure on cell culturing. Thus, nanostructured Na‐alginate and poly(vinyl alcohol) (PVA) polymers as well as blended alginate/PVA hydrogels are fabricated. Na‐alginate and PVA fibers with different dimensions can be obtained. By extruding Na‐alginate solutions into a non‐solvent also networks of uniform nanofibers (diameter <20 nm) are generated. PVA forms agglomerations of nanofibers and nanoparticles with diameter >100 nm. In addition, cell line‐dependent behavior of the cross‐linked PVA/alginate nanofibers is observed, which is characterized by reduced cell adhesion and cluster formation of PaTu 8988t cells on these blend nanofibers compared to normal cell adhesive behavior of NIH 3T3 cells.

Dressings produced from PVA nanofibers containing chloramphenicol

In this study, electrospun PVA membranes crosslinked with citric acid or glutaraldehyde and containing the antibiotic chloramphenicol (CLF) were obtained for the production of dressings. This material was characterized by SEM, FTIR, DSC, TGA NMR, degree of swelling, and solubility. The SEM images showed the possibility of obtaining nanofibers with a diameter between 600 and 700 nm. Crosslinking with citric acid (3% m/m) was the only one able to give stability to PVA fibers in water and preserve their morphology. The stability of PVA fibers in water was associated with a decrease in OH groups in PVA and an increase in crystallinity, both effects promoted by crosslinking. The increase in crystallinity due to crosslinking was observed by DSC, DRX, and FTIR analyses. A linear correlation was found between the increase in enthalpy of fusion and the increase in crystallinity. The FTIR analysis confirmed the incorporation of the drug into the fibers. The results of TGA analysis suggested that the presence of basic groups in the CLF molecule may act as proton receptors delaying the first stage of thermal degradation of the polymer. The absence of CLF-related peaks in the X-ray diffractograms and DSC curves suggests that the drug may be in an amorphous state, which improves the solubility of CLF and facilitates its immediate release, making the drug more bioavailable. The mechanism of CLF release indicated that the kinetics follows the typical Weibull model for matrix systems, showing an immediate release in the first 30 min. The membranes exhibited hemotoxicity below the limit established by ASTM F756–08. In addition, the disk diffusion tests showed antimicrobial activity against S. aureus, S. epidermidis, and P. aeruginosa strains, indicating that these membranes are promising for use in wound dressings with anti-infective biological activity.

Impact of Nano-CaCO3 and PVA Fiber on Properties of Fresh and Hardened Geopolymer Mortar

Geopolymer is a green substitute for Portland cement but has low tensile strength, high brittleness and easy cracking. Therefore, fibers and nanomaterials are used to strengthen and toughen geopolymer composites. The influence of nano-calcium carbonate and PVA fiber on the properties of fresh and hardened geopolymer mortar were studied herein. The hybrid of long and short fibers with small content (0.8 vol.%) is conducive to flowability, while the hybrid with large content (1.6 vol.%) and nano-calcium carbonate is conducive to flowability. The slump flow and flow rate of geopolymer mortars with low fiber factor (product of fiber volume fraction and length-diameter ratio) decrease with the growth in nano-calcium carbonate content. As the PVA fiber factor reaches 464.8%, the slump flow and flow rate values of mortars with 0, 1 wt.% and 2 wt.% nano-calcium carbonate are close to each other. About 450% is the density packing threshold of PVA fiber in geopolymer composites. The combination of 0.8 vol.% 12 mm + 0.4 vol.% 6 mm fiber + 1 wt.% nano-calcium carbonate presents the highest flexural strength and flexural to compressive strength ratio, with a compressive strength of about 36 MPa. The optimal fiber factor range of PVA fiber in cement and geopolymer mortar is about 400% and higher than 600%, respectively. PVA fibers show more effective enhancement of flexural strength and toughness in geopolymer than cement mortar. The ultrasonic wave velocity and apparent density of geopolymer mortar show a downward trend as a whole with the increase in fiber factor. The intensity rise of the hump between 17° and 38° (2 θ) in the XRD pattern is observed. The SEM indicates that the surface of PVA fiber in geopolymer mortar with nano-calcium carbonate is heavily scratched, and the fiber filaments are rolled up, demonstrating improved bonding between PVA fiber and geopolymer mortar.

Doping nanocellulose crystal with poly(vinyl alcohol) for water‐resistant composite fibers with enhanced mechanical and dyeing performances

AbstractAcetalization has been commonly adopted to realize the improvement on the water resistance and mechanical properties of poly(vinyl alcohol) (PVA) composite fibers. However, acetalized PVA fibers only have a very low concentration of hydroxyl groups on the surface and thus have poor dyeing performance. In this case, hydroxyl‐rich nanocellulose (NC) offers a fascinating solution for improving the dyeing properties of PVA fibers. Herein, we developed NC/PVA composite fibers by wet spinning the aqueous mixture of NC and PVA followed with acetalization treatment. Compared with pure PVA fibers, NC/PVA composite fibers had a significant improvement of 36% and 53% in terms of tensile strength and elongation at break when the NC content was 10 wt%, respectively. More importantly, when the NC content reached 20 wt%, the K/S value of the composite fiber was approximately threefold greater in comparison to that of the PVA fiber, indicating that the dyeing performance of NC‐modified composite fibers was greatly improved. This work provides a simple and easy method to possess PVA fibers with excellent dyeing properties and mechanical properties, demonstrating the potential to realize the application of PVA fibers in more practical scenarios.

Mechanical Properties and Microstructure of Rice Husk Ash-Rubber-Fiber Concrete under Hygrothermal Environment.

In order to study the mechanical properties of rice husk ash-rubber-fiber concrete (RRFC) under hygrothermal environment, the optimal group was selected by orthogonal test. The mass loss, relative dynamic elastic modulus analysis, strength analysis, degradation degree analysis after cyclic loading and internal microstructure analysis of the optimal group of RRFC samples after dry-wet cycles under different environments and temperatures were compared and analyzed. The results show that the large specific surface area of rice husk ash optimizes the particle size distribution of RRFC specimens, reacts to form C-S-H gel, enhances the compactness of concrete, and forms a dense structure as a whole. The presence of rubber particles and PVA fibers effectively improves the mechanical properties and fatigue resistance of RRFC. The comprehensive mechanical properties of RRFC with rubber particle size of 1-3 mm, PVA fiber content of 1.2 kg·m-3 and rice husk ash content of 15% are the best. The compressive strength of the specimens after dry-wet cycles in different environments generally increased first and then decreased, reaching a peak at the seventh dry-wet cycle, and the compressive strength of the specimens under chloride salt solution decreased more than that under clear water solution. Thes provided new concrete materials for the construction of highways and tunnels in coastal areas. Under the premise of ensuring the strength and durability of concrete, it is of great practical significance to explore new roads for energy conservation and emission reduction.

Analysis of the Effect of Protective Properties of Concretes with Similar Composition on the Corrosion Rate of Reinforcing Steel Induced by Chloride Ions.

This study presents a comparison of the protective properties of three concretes of similar composition on the effect of chloride ions. To determine these properties, the values of the diffusion and migration coefficients of chloride ions in concrete were determined using both standard methods and the thermodynamic ion migration model. We tested a comprehensive method for checking the protective properties of concrete against chlorides. This method can not only be used in various concretes, even those with only small differences in composition, but also in concretes with various types of admixtures and additives, such as PVA fibers. The research was carried out to address the needs of a manufacturer of prefabricated concrete foundations. The aim was to find a cheap and effective method of sealing the concrete produced by the manufacturer in order to carry out projects in coastal areas. Earlier diffusion studies showed good performance when replacing ordinary CEM I cement with metallurgical cement. The corrosion rates of the reinforcing steel in these concretes were also compared using the following electrochemical methods: linear polarization and impedance spectroscopy. The porosities of these concretes, determined using X-ray computed tomography for pore-related characterization, were also compared. Changes in the phase composition of corrosion products occurring in the steel-concrete contact zone were compared using scanning electron microscopy with a micro-area chemical analysis capability, in addition to X-ray microdiffraction, to study the microstructure changes. Concrete with CEM III cement was the most resistant to chloride ingress and therefore provided the longest period of protection against chloride-initiated corrosion. The least resistant was concrete with CEM I, for which, after two 7-day cycles of chloride migration in the electric field, steel corrosion started. The additional use of a sealing admixture can cause a local increase in the volume of pores in the concrete, and at the same time, a local weakening of the concrete structure. Concrete with CEM I was characterized as having the highest porosity at 140.537 pores, whereas concrete with CEM III (characterized by lower porosity) had 123.015 pores. Concrete with sealing admixture, with the same open porosity, had the highest number of pores, at 174.880. According to the findings of this study, and using a computed tomography method, concrete with CEM III showed the most uniform distribution of pores of different volumes, and had the lowest total number of pores.

Enhanced Thermal Conductivity of Nanodiamond Nanosheets/Polymer Nanofiber Composite Films by Uniaxial and Coaxial Electrospinning: Implications for Thermal Management of Nanodevices

Nanotechnology is gradually applied to the preparation of heat dissipation materials with the miniaturization of electronic devices. Electrospinning technology has received extensive attention due to its unique advantages in constructing continuous nanofibers. In this work, uniaxial-polyvinyl alcohol/nanodiamond (U-PVA/ND) and coaxial-polyvinyl alcohol/nanodiamond (C-PVA/ND) composite fiber films with different microscopic morphologies were constructed by uniaxial and coaxial electrospinning. The results show that the thermal conductivities of U-PVA/ND and C-PVA/ND composite fibers with 60 wt % ND content are 71.3 and 85.3 W m–1 K–1, respectively, which are 171.2 and 205.1 times greater than that of the pure PVA fiber film. In addition, the maximum thermal decomposition temperature (Tmax) and volume resistivity of the C-PVA/ND composite fiber film were 364.3 °C and 2.29 × 1015 Ω·cm, respectively, demonstrating the excellent thermal stability and electrical insulation of the composite fiber film. This experiment results provide strong evidences of electrospinning technology for the preparation of highly thermally conductive composites. So, thermally conductive films can be used as the outer layer of electronic components to accelerate their heat dissipation and extend their service life.

Carbonic Anhydrase-Embedded ZIF-8 Electrospun PVA Fibers as an Excellent Biocatalyst Candidate.

There is a growing concern that the increasing concentration of CO2 in the atmosphere contributes to a potential negative impact on global climate change. To deal with this problem, developing a set of innovative, practical technologies is essential. In the present study, maximizing the CO2 utilization and precipitation as CaCO3 was evaluated. In this manner, bovine carbonic anhydrase (BCA) was embedded into the microporous zeolite imidazolate framework, ZIF-8, via physical absorption and encapsulation. Running as crystal seeds, these nanocomposites (enzyme-embedded MOFs) were in situ grown on the cross-linked electrospun polyvinyl alcohol (CPVA). The prepared composites displayed much higher stability against denaturants, high temperatures, and acidic media than free BCA, and BCA immobilized into or on ZIF-8. During 37 days of storage period study, BCA@ZIF-8/CPVA and BCA/ZIF-8/CPVA maintained more than 99 and 75% of their initial activity, respectively. The composition of BCA@ZIF-8 and BCA/ZIF-8 with CPVA improved stability for consecutive usage in recovery reactions, recycling easiness, and greater control over the catalytic process. The amounts of calcium carbonate obtained by one mg each of fresh BCA@ZIF-8/CPVA and BCA/ZIF-8/CPVA were 55.45 and 49.15 mg, respectively. The precipitated calcium carbonate by BCA@ZIF-8/CPVA reached 64.8% of the initial run, while this amount was 43.6% for BCA/ZIF-8/CPVA after eight cycles. These results indicated that the BCA@ZIF-8/CPVA and BCA/ZIF-8/CPVA fibers could be efficiently applied to CO2 sequestration.

Boron carbide reinforced electrospun nanocomposite fiber mats for radiation shielding

AbstractIn this study, 1 wt% boron carbide (B4C) reinforced PVA nanofibers were fabricated by the electrospinning technique as a new generation of ultra‐thin, lightweight, and flexible neutron shielding nanocomposites. The influence of B4C particles' size and morphology on the fiber formation and radiation shielding performance of fiber mats was investigated. The results indicate that the particle characteristics have a dramatic influence on the formation and properties of nanocomposites. The thicknesses of individual fibers reinforced with sol–gel synthesized nano‐sized boron carbide particles were in the range of 50–250 nm, while those containing commercial B4C powder were produced in the thickness range of 1–2 μm. In contrast to the commercial particles, the sol–gel synthesized nano B4C particles enhanced the fiber mat's density and the roundness of individual fibers. Both theoretical and experimental radiation shielding studies showed that B4C reinforcement successfully improved the neutron and gamma attenuation of the neat PVA matrix. Furthermore, it was found that a 6.5 mm thick PVA nanofiber mat, reinforced with only 1 wt% B4C nanoparticles shielded up to about 7.4% of the initial neutron flux. Compared to the neat PVA fiber mat, reinforcement of PVA fibers with 1 wt% sol–gel synthesized nano‐sized boron carbide particles enhanced the neutron shielding by 50.31%. Moreover, even though B4C is not an effective gamma shielding reinforcement, the amplified density of nanocomposite fiber mats also enhanced gamma attenuation.

Water‐driven shape memory nanocomposite fibers for actuators

AbstractShape memory polymer (SMP) can store entropic energy during programming and release the energy as recovery. The released energy is determined by the recovery strain and the recovery stress. The low recovery stress of SMP limits its application. In this paper, shape memory nanocomposite fibers (SMNFs) prepared by wet spinning through a two‐step orientating process show thermo‐active and water‐driven shape memory effect. Carbon nanotubes (CNTs) are uniformly dispersed in SMNF and aligned along the SMNF axis. SMNF with 13 wt% CNT has an average maximum recovery stress of ~160 MPa at 100°C, which is almost five times higher than that of a pure PVA fiber. The uniform distribution of the orientational CNTs in the SMNFs and the confinement effect of the CNTs confirmed by the increased relaxation time contribute to the increment of the recovery stress. Aligned CNTs impede the mobility of amorphous chains and increase the Tg of SMNFs. The twisted SMNF can drive an object up to 25 times its own weight in water to rotate and lift. The rotational velocity of the twisted SMNF is sensitive to temperature. Water molecules acting as plasticizers greatly enhance the mobility of the PVA chains, and the SMNF in water releases the stored entropic energy at room temperature. The SMNF with high recovery stress demonstrates its potential for applications in the field of actuators and artificial muscles.

Eco-friendly PVA-LYS fibers for gold nanoparticle recovery from water and their catalytic performance.

In this work, we grafted lysine on PVA electrospun fibers, using a green preparation technique. The resulting fiber mats were proposed for gold nanoparticles (AuNPs) removal from water. The efficiency of three fibers with different lysine amounts (10, 20, and 30%) was investigated. The incorporation of amino groups in PVA fibers was firstly proved by FTIR, SEM, and elemental analysis, confirming the presence of lysine. Among the three different fibers, PVA-LYS 30% has shown the best removal efficiency, reaching 65%, at pH equal to 5. Adsorption isotherms were studied and showed that the Langmuir model is the best model fitting our experimental results, with a maximum adsorption capacity of 20.1mgg-1. Metal-ligand interactions and electrostatic attraction between protonated amino groups of lysine on the fibers and negatively charged, citrate capped, AuNPs are the main proposed mechanisms for AuNP adsorption on the fibers. Sustainability of AuNPs adsorbed on these fibers has been checked through their reuse as catalyst for the reduction of 4-nitrophenol to 4-aminophenol. The process was completed within 60min, and their reusability showed more than 99% efficiency after 5 reduction cycles. Our results prove that green PVA-LYS fibers can extract nanoparticles from water, as low cost-effective and eco-friendly adsorbent, and contribute to the promotion of a circular economy approach, through their reuse as catalyst in the reduction of pollutants.

Experimental study on the dynamic splitting tensile properties of polyvinyl-alcohol-fiber-reinforced cementitious composites

In this study, the dynamic splitting performance and energy absorption capacity of polyvinyl- alcohol-fiber-reinforced engineered cementitious composites were studied using a split Hopkinson pressure bar system. By using a high-speed camera, changes in the surface strain fields and crack expansion patterns of specimens under different striking pressures were observed and validated, and experimental results for four types of fiber-reinforced concrete and one type of plain concrete without PVA fibers were obtained. The strain-rate effect on the dynamic tensile strength of fiber-reinforced concrete and plain concrete was confirmed. Digital image correlation measurement results indicate that microcracks were present near the radial primary cracks in the fibrous concrete, where strain concentration zones were formed. Additionally, PVA fibers can effectively reduce the rate of decline following the peak in the localization factor, and the PVA fibers begin to play a bridging role following the generation of microcracks, which slows the damage development of specimens, allowing them to absorb more impact energy.

Multiscale analysis of silane coupling agent modified rubber-fiber concrete interfaces

This study employs PVA fibers to improve the performance of rubber concrete and silane coupling agent to change the incompatibility between rubber and cement in order to weaken the issue of a weak interfacial transition zone between rubber and cement foundation (KH570). The results showed that 1.5% content of KH570 modified 15% content of rubber-1.5% content of PVA fiber with the best effect. KH570 was identified using XRD, FTIR, and SEM characteristics. It was discovered that KH570 experienced a dehydration condensation reaction with free or adsorbed water in the cement, which helped to maintain the integrity between the cement matrix and the rubber. It strengthened the bond between the cement, the rubber, and the PVA fibers and enhanced the cement's capacity to encapsulate the rubber. Finally, molecular dynamics simulations reveal that cement and rubber are connected by Si-O-Si and molecules appear to be cross-distributed, increasing interfacial compatibility and reducing interfacial effects. It can be clearly observed in the interfacial bonding mechanism that KH570 is mainly a C-S-H matrix with parallel or perpendicular connections at the tail end.

Microstructural evolution and dynamic compressive properties of engineered cementitious composites at elevated temperatures

This paper presents a comprehensive study on the microstructural evolution and quasi-static and dynamic compressive properties of engineered cementitious composites (ECC) at elevated temperatures (20, 105, 250, 400, 600 and 800 °C). Split Hopkinson pressure bar (SHPB) was adopted to investigate the compressive behaviour of ECC at various strain rates after exposure to elevated temperatures, while the corresponding microstructural evolution was characterised using scanning electron microscopy (SEM), digital electron microscope and mercury intrusion porosimetry (MIP) along with fractal analysis. Results indicate that ECC exhibited strain rate effect and high temperature sensitivity simultaneously. The residual dynamic compressive strength of ECC increased by 33.0–50.4% with the rising strain rate from 79.8 to 127.1 s−1. It reached the maximum value at 105 °C but reduced to 14.3−25.8% at 800 °C compared to that at 20 °C. The change in dynamic increase factor of ECC for various temperatures and strain rates can be well predicted using the developed equation. The thermal decomposition of PVA fibres was the main detrimental affecting the dynamic performance of ECC at sub-high temperatures (below 400 °C), whereas the negative effects caused by the formation of pores and microcracks in the matrix dominated at higher temperatures (400−800 °C). Microscopic damage induced by elevated temperatures aggravated the deterioration degree under dynamic compressive load, whilst the larger the difference in the macro/micro pore structural fractal dimension of 2.50/2.67, the greater the temperature softening effect on impact resistance of ECC.

Mechanical characteristics of fiber-reinforced microcapsule self-healing cementitious composites by orthogonal tests

This study combined the microcapsule self-healing system with fiber reinforced concrete (FRC), and investigated the effects of microcapsule content, mineral admixture type, mineral admixture content, and fiber type on tensile and compressive strength, ductility, and self-healing properties of the fiber-reinforced microcapsule self-healing cementitious composites by the orthogonal test method. For the uniaxial tensile and cubic compression tests, the optimum tensile strength group consists of a 2.2 mass ratio of GGBS, PE fiber, and no microcapsules. The optimum compressive strength group consists of a 2.2 mass ratio of GGBS, hybrid fiber, and no microcapsules. Microcapsule content and fiber type are the main factors affecting tensile properties, and an increase in the microcapsule content will reduce the tensile strength and compressive strength of the matrix. The optimum tensile strain group consists of 10% microcapsule content and a 2.2 mass ratio of GGBS and PE fiber. The results of the energy-based steady-state crack propagation test show that the fiber type is the most critical factor affecting the ductility, and the tensile ductility of the PE fiber group is higher than that of the PVA fiber group. The scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) diagram proved the healing effect of the fiber-reinforced microcapsule self-healing cementitious composite.

Predicting the flexural behavior of steel-PVA hybrid fiber reinforced cementitious composite

In this paper, experimental and theoretical investigations were performed on the flexural response of steel-PVA hybrid fiber reinforced cementitious composite (SPHFRCC). For the experimental part, a series of slump flow tests, direct tensile tests, and four-point bending tests were performed to explore the effect of the sand/binder ratio (S/B) (1.08, 1.18, 1.28), fiber content (0, 1.5%, 1.6%, 1.75%, 1.9%), and fiber hybrid proportion (1:15, 1:6, 4:15, 2:5, 3:4). The main findings manifested that increasing PVA fiber content can seriously weaken the workability of SPHFRCC, while the impact of S/B was negligible. Maintaining a steel fiber content of 1.5% and adding PVA fiber from 0 to 0.4% resulted in a decrease in the slump by 12.3% and slump flow diameter by 43.0%. The post-cracking tensile response of SPHFRCC demonstrated strain hardening due to the presence of PVA fibers. Moreover, increasing PVA fiber proportion can tremendously raise the flexural strength and toughness, while the enhancement at an excessively high proportion of PVA fibers would be weakened. With a total fiber content of 1.75%, the addition of PVA fibers at 0.25%, 0.5%, and 0.75% to partially replace steel fibers resulted in an increase in the flexural strength by 9.3%, 34.3%, and 22.4%, and the flexural toughness corresponding to the deflection L/150 by 43.8%, 42.2%, and 47.2%, respectively. In the theoretical part, a novel tensile constitutive model was developed considering the probabilistic model and the effect of fiber pullout orientation. Also, a calculation method for the flexural response of SPHFRCC beams was presented in accordance with the sectional analysis. The validity of the developed models was evaluated by the comparisons between the test values and estimated curves.