Polyvinyl Alcohol Fiber-Reinforced Cementitious Composite Research Articles

Durability and Mechanical Properties of Nano-SiO2 and Polyvinyl Alcohol Fiber-Reinforced Cementitious Composites Subjected to Saline Freeze-Thaw Cycles.

To investigate the effects of nano-SiO2 (NS) and polyvinyl alcohol (PVA) fibers on the durability and mechanical properties of cementitious composites subjected to saline freeze-thaw cycling, a series of PVA fiber-reinforced cementitious composite (PFRCC) specimens were prepared using various fiber contents, and a series of NS and PVA fiber-reinforced cementitious composite (NPFRCC) specimens were prepared using various combinations of NS and fiber contents. Durability and fracture toughness tests were subsequently conducted on the specimens after different numbers of saline freeze-thaw cycles. The results indicate that the degradation of material properties can be divided into slow and accelerated damage stages before/after 50 freeze-thaw cycles. The durability and fracture toughness of the specimen series tended to increase, then decrease with increasing NS and PVA contents, suggesting optimum levels. When the PVA fiber content was 0.5%, PFRCC specimens had the best durability after saline freeze-thaw cycles; when the NS and PVA fiber contents were 1.0% and 0.5%, respectively, NPFRCC specimens had the best durability and fracture properties, and the initiation toughness, destabilization toughness, and fracture energy after 100 saline freeze-thaw cycles were 120.69%, 160.02%, and 451.31%, respectively. The results of this study may guide future exploration of the durability and mechanical properties of concrete subjected to freeze-thaw action.

Interaction Mechanism of Cementitious Composites Containing Different Twisted PVA Fiber Bundles

Fiber-reinforced cementitious composites (FRCCs) have made significant progress in improving the tensile and flexural properties of concrete members. Studies have shown that polyvinyl alcohol (PVA) fibers can effectively enhance the toughness of FRCCs, but the haphazard distribution of short-cut fibers makes it difficult to give full play to the high tensile strength of the fibers, and it is difficult for bundled fibers to effectively bond with the concrete substrate, which has become a challenge in the study of changing materials. Twisting the fibers by a physical process to improve the bonding performance of PVA fibers with FRCC substrate is a safe and feasible solution. However, research on silicate cementitious composites reinforced with twisted PVA fibers is limited. In this study, the interaction mechanism of through-length twisted PVA FRCCs with different twist factors and fiber bundle numbers was investigated. A concrete matrix material configured from silicate cement, fly ash, silica fume, and medium sand, in which PVA fibers with different twist factors were pre-incorporated, was used for the tests. Three-point bending tests were carried out on specimens with different twist factors (0, 50, 100, and 150 twists per meter) and fiber bundle numbers 1, 2, and 3. Compared to the untwisted PVA fiber specimens, the twist factor of 100 and the single fiber bundle specimens showed significant improvements in the bending properties, including a 36% increase in deflection, a 68% increase in the equivalent bending stress, and a 119% increase in energy consumption. Micro-X-ray computed tomography scans showed improved bending properties and energy consumption capabilities due to enhanced bonding properties as a result of the increased fiber–matrix interaction area and surface toughness.

Durability and microstructure of cementitious composites under the complex environment: Synergistic effects of nano-SiO2 and polyvinyl alcohol fiber

As the most commonly used construction material for marine buildings, cementitious composites are exposed to a complex environment of coupled action of relative humidity, temperature, and chloride salts erosion, which severely impacts the safety and longevity of marine buildings. The effect of nano-SiO2 dosage on the durability of polyvinyl alcohol fiber-reinforced cementitious composites (PVAF-RCC) for the preparation of marine buildings under the complex environment was investigated in this work. The complex environment with the temperature of 50 °C, relative humidity of 100%, and chloride salt concentration of 5% was simulated by the environment chamber. The cementitious composites exposed to the complex environment for 30 d were tested for anti-permeability, anti-chloride ion penetration, frost resistance, and chloride salt erosion resistance. Furthermore, the pore characteristics of the cementitious composites and the micromorphology of nano-SiO2, matrix, and fibers were characterized and analyzed by the combination of scanning electron microscope and mercury intrusion porosimetry tests. Results revealed that the durability of cementitious composites improved initially and subsequently decreased with rising the dose of nano-SiO2 under the complex environment. PVAF-RCC consisting of 1.5% nano-SiO2 obtained the best durability. As the nano-SiO2 dosage increased, the total porosity and cumulative porosity of PVAF-RCC decreased first and subsequently increased. Nano-SiO2 refined and improved the pore structure of PVAF-RCC and the interface between matrix and PVA fibers through its filling effect and participation in the hydration reaction to generate C-S-H gels with filling effect to convert more harmful and harmful pores into less harmful or harmless pores, thus enhancing the compactness and durability of cementitious composites under the complex environment.

Mechanical Properties of Polyvinyl Alcohol Fiber-Reinforced Cementitious Composites after High-Temperature Exposure.

The mechanical properties of cementitious composites before and after exposure to high temperature are affected by calcium–silicate–hydrate (C–S–H) gels. To evaluate the effects of high temperature, plyvinyl alcohol (PVA) fiber content, and the cooling method on properties of cementitious composites, physical, mechanical, and microscopic tests were performed in this study. The target temperatures were 25, 100, 200, 300, 400, 600, and 800 °C. The PVA fiber contents were 0.0, 0.3, 0.6, 0.9, 1.2, and 1.5 vol%. The high-temperature resistance of PVA fiber-reinforced cementitious composite (PVA-FRCC) specimens was investigated through changes in their appearance, mass loss, compressive strength, splitting tensile strength, flexural strength, and microstructure. The results showed that PVA fibers reduced the probability of explosion spalling in the PVA-FRCC specimens exposed to high temperatures. The mass loss rate of samples exposed to temperatures below 200 °C was small and lower than 5%, whereas a significant mass loss was observed at 200 °C to 800 °C. A small rise in the cubic compressive and splitting tensile strengths of samples was found at 400 °C and 300 °C, respectively. Below 400 °C, the fibers were beneficial to the mechanical strength of the PVA-FRCC specimens. Nevertheless, when the temperature was heated above 400 °C, melted fibers created many pores and channels, which caused a decrease in the strength of the specimens. The method of cooling with water could aggravate the damage to the cementitious composites exposed to temperatures above 200 °C. High temperature could lead to the decomposition of the C–S–H gels of the PVA-FRCC samples, which makes C–S–H gels lose their bonding ability. From the perspective of the microstructure, the structure of PVA-FRCC samples exposed to 600 °C and 800 °C became loose and the number of microcracks increased, which confirmed the reduction in macro-mechanical properties.

Effect of polymer coatings on the freezing–thawing and carbonation resistances of nano-SiO2 and polyvinyl alcohol fiber-reinforced cementitious composites

The inclusion of nano-SiO2 and polyvinyl alcohol (PVA) fibers can improve the strength and toughness of cementitious composites, and the durability can be further enhanced by protecting the surface of the composite with a polymer coating. Herein, three types of nano-SiO2 and PVA fiber-reinforced cementitious composites were prepared with water–binder ratios of 0.35, 0.40, and 0.45. Furthermore, the following three types of polymer coatings were applied to the surfaces of the protective objects: single-layer and double-layer chlorinated rubber coatings, polyurethane coatings, and permeable silane impregnation agents. The effects of the types and number of layers of polymer coatings on water absorption, freezing–thawing resistance, and carbonation resistance of the nano-SiO2 and PVA fiber-reinforced cementitious composites, as well as the effects of the water–binder ratio of the cementitious composites on the protective efficiency of the polymer coatings, were investigated. The results revealed that the three types of polymer coatings could decrease the capillary water absorption of cementitious composites and improve the freezing–thawing resistance and carbonation resistance of the composites. The carbonation depth and mass loss after freezing–thawing cycles of the material coated with a single polymer coating were reduced by 12–66% and 30.2–60.4%, respectively, compared with the corresponding values for the cementitious composites without coatings. Moreover, the effect of the double-layer polymer coatings was superior to that of the single-layer coatings. As the water–binder ratio decreased, the influence of the polymer coating on the durability of the cementitious composites became increasingly apparent.

Investigation of mechanical properties of PVA fiber-reinforced cementitious composites under the coupling effect of wet-thermal and chloride salt environment

In this study, the mechanical properties of polyvinyl alcohol fiber-reinforced cementitious composites (PVA-FRCC) under the coupling effect of wet thermal and chloride salt environment were investigated through a series of experiments, including compressive strength, flexural performance, elastic modulus, three-point bending fracture, and scanning electron microscope (SEM) tests. An environmental simulation test chamber was used to simulate the wet-thermal and chloride salt environment, in which the parameters of temperature, relative humidity (RH), mass fraction of the NaCl solution, and action time were determined to be 50 °C, 100%, 5%, and 30 d, respectively. The volume contents of the PVA fibers incorporated in the cementitious composites were 0, 0.3%, 0.6%, 0.9%, 1.2%, and 1.5%. The results indicated that the mechanical properties of the cementitious composites decreased after being subjected to the coupling effect of the wet-thermal and chloride salt environment. The incorporation of the PVA fibers improved the mechanical properties of the cementitious composites under the coupling effect of the wet-thermal and chloride salt environment. When the addition content of PVA fiber was approximately 0.6–0.9%, the mechanical performance of PVA-FRCC was the best. Compared with the cementitious composite without fibers, the maximum growth rates of the cube, axial and residual compressive strength, elastic modulus, and flexural strength of the PVA-FRCC under the coupling effect of the wet-thermal and chloride salt environment owing to the addition of PVA fiber reached 29.96%, 46.92%, 29.71%, 46.15%, and 67.06%, respectively. In particular, the 1.5% PVA fiber dosage increased the initiation and unstable fracture toughness, and fracture energy by 145.57%, 333.01%, and 2656.38%, respectively.

Fracture performance prediction of polyvinyl alcohol fiber-reinforced cementitious composites containing nano-SiO2 using least-squares support vector machine optimized with quantum-behaved particle swarm optimization algorithm

Based on least-squares support vector machine optimized using a quantum particle swarm optimization algorithm (QPSO-LSSVM), a prediction model was established to predict the fracture properties of polyvinyl alcohol fiber-reinforced cementitious composites (CCs) containing nano-SiO2 (PVA-CCNS) and improve its accuracy and effectiveness. Nineteen groups of measured data obtained from fracture performance tests on a three-point bending notched PVA-CCNS beam were selected for analysis and prediction. The prediction results of the QPSO-LSSVM model were compared with those of the least-squares support vector machine optimized with the particle swarm optimization algorithm, least-squares support vector machine and back-propagation neural network models. The simulation analysis results indicated that the goodness of fit (R2) values of the fracture energy, initial fracture toughness and unstable fracture toughness were 0.790, 0.940 and 0.950, respectively, for the QPSO-LSSVM prediction model. In addition, the fitting degree between the measured and predicted values of the QPSO-LSSVM prediction model was better than those of the other three models. The higher accuracy, better convergence, and robustness of the QPSO-LSSVM model than the other three models proves that the QPSO-LSSVM model is an optimal method for predicting the fracture performance of CCs. The proposed model can guide the mix proportion design of CC mixtures.

Behavior Deterioration and Microstructure Change of Polyvinyl Alcohol Fiber-Reinforced Cementitious Composite (PVA-ECC) after Exposure to Elevated Temperatures.

In the case of fire, explosive spalling often occurs in cementitious composites due to dense microstructure and high pore-pressure. Polymer fibers were proved to be effective in mitigating such behavior. However, deterioration of these fiber-reinforced cementitious composites inevitably occurs, which is vital for the prediction of structural performance and prevention of catastrophic disaster. This paper concentrates on the behavior and mechanism of the deterioration of polyvinyl alcohol fiber-reinforced engineered cementitious composite (PVA-ECC) after exposure to elevated temperatures. Surface change, cracking, and spalling behavior of the cubic specimens were observed at room temperature, and after exposure to 200 °C, 400 °C, 600 °C, 800 °C, and 1200 °C. Losses in specimen weight and compressive strength were evaluated. Test results indicated that explosive spalling behavior was effectively prevented with 2.0 vol% polyvinyl alcohol fiber although the strength monotonically decreased with heating temperature. X-ray diffraction curves showed that the calcium hydroxide initially decomposed in the range of 400–600 °C, and finished beyond 600 °C, while calcium silicate hydrate began at around 400 °C and completely decomposed at approximately 800 °C. Micrographs implied a reduction in fiber diameter at 200 °C, exhibiting apparent needle-like channels beyond 400 °C. When the temperature was increased to 600 °C and above, the dents were gradually filled with newly produced substance due to the synergistic effect of thermal expansion, volume expansion of chemical reactions, and pore structure coarsening

"Relationship of Rheology, Fiber Dispersion, and Strengths of Polyvinyl Alcohol Fiber-Reinforced Cementitious Composites"

"Relationship of Rheology, Fiber Dispersion, and Strengths of Polyvinyl Alcohol Fiber-Reinforced Cementitious Composites"

Durability Assessment of PVA Fiber-Reinforced Cementitious Composite Containing Nano-SiO2 Using Adaptive Neuro-Fuzzy Inference System

In this study, the durability of polyvinyl alcohol fiber-reinforced cementitious composite containing nano-SiO2 was evaluated using the adaptive neuro-fuzzy inference system (ANFIS). According to the structural characteristics of the cementitious composite material and some related standards, the classification criteria for the evaluation indices of cementitious composite materials were clarified, and a corresponding structural framework of durability assessment was constructed. Based on the hypothesis testing principle, the required test data capacity was determined under a certain degree of accuracy, and durability experimental data and expert evaluation results were simulated according to statistical principles to ensure that there were sufficient datasets for ANFIS training. Using an environmental factor submodule as an example, 14 sets of actual test data were used to verify that the ANFIS can quickly and effectively mimic the expert evaluation reasoning process to evaluate the durability of cementitious composites. Compared with other studies related to the durability of cementitious composites, a systematic evaluation system for the durability of concrete was established. We used a polyvinyl alcohol fiber-reinforced cementitious composite containing nano-SiO2 to conduct a comprehensive evaluation of cementitious composites. Compared with the traditional expert evaluation method, the durability evaluation system based on the ANFIS learned expert experience, stored the expert experience in fuzzy rules, and eliminated the subjectivity of expert evaluation, thereby making the evaluation more objective and scientific.

Graphene oxide-coated Poly(vinyl alcohol) fibers for enhanced fiber-reinforced cementitious composites

The interface properties between fiber and matrix predominantly influence the mechanical performance of fiber reinforced cementitious composites (FRCCs). In this study, the interface between polyvinyl alcohol (PVA) fibers and mortar was modified by coating graphene oxide (GO) on the fiber surface. Experimental results showed the GO@ PVA fibers improved the tensile strength of FRCCs by 35.6% compared to that of pristine PVA FRCCs. Theoretical analysis indicated this significant improvement was attributed to the enhancement of the chemical bond energy (Gd) at fiber/matrix interface. With GO surface modification, the Gd was increased more than 80 times, changing the failure mode at the interface from adhesive failure to cohesive failure.

Influence of Fiber Orientation on Bridging Performance of Polyvinyl Alcohol Fiber-Reinforced Cementitious Composite

Crack bridging performance of fibers strongly affects the tensile characteristics of fiber-reinforced cementitious composites (FRCCs) after first cracking. The fiber orientation distribution is likely to be affected by factors that include fresh-state properties, casting method, formwork geometry, and others. The objective of this study is to investigate the influence of the fiber orientation on the bridging performance in polyvinyl alcohol (PVA) FRCCs through a visualization simulation using a water glass solution and a calculation of the bridging law. The main parameter of the investigations in the present study is the casting direction. To evaluate the fiber orientation distribution quantitatively, an approximation methodology using an elliptic function is newly introduced. The bridging stress versus crack width relationship is calculated considering the elliptic distribution, the snubbing effect, and the fiber strength degradation. The calculated stress-crack width curves can express the uniaxial tension test results after first cracking well.

Frost resistance of polyvinyl alcohol fiber and polypropylene fiber reinforced cementitious composites under freeze thaw cycling

This paper presents an experimental study that was conducted to clarify the effect of reinforcing short fiber characteristics such as the length, tensile strength, and adhesion on the frost resistance of fiber reinforced cementitious composites (FRCCs) by incorporating two types of polyvinyl alcohol (PVA) fibers and polypropylene (PP) fiber. FRCCs with a 1.5% volume ratio of fiber were investigated for frost resistance under freeze–thaw action of 300 cycles and were compared with non-fiber reinforced cementitious composite (Plan) specimens. The air void characteristics of mixtures were also investigated by mercury intrusion porosimetry (MIP), linear transverse method, and scanning electron microscope (SEM) images. The difference of the fiber type (PVA and PP) characteristics was affected by the dispersion of blended fibers in FRCCs and by the adhesion performance between the cementitious matrix and the fibers in the microstructure. Hence, the results of the compressive behavior indicated that the PVA FRCC specimens have superior resistance on the reduction of the compressive strength before and after freeze–thaw cycling compared to PP FRCC and Plain specimens. Additionally, the test results of the relative dynamic elastic modulus and mass loss indicated that the PVA FRCC specimens remain durability after freeze–thaw action of 300 cycles compared with virgin specimens. Therefore, the results of freeze–thaw tests revealed that the blending of PVA fibers to FRCC is considerably effective for frost resistance.

Effects of loading conditions and specimen thickness on the flexural behavior of fiber-reinforced cementitious composites

The flexural performance of polypropylene (PP) and polyvinyl alcohol (PVA) fiber reinforced cementitious composites (FRCC) have been investigated within the scope of this study. Thin plates and relatively thicker prismatic specimens have been prepared by using three fiber-matrix combinations. The center-point and two-point loading flexural performance of these specimens has been determined in terms of; first cracking strength, flexural strength and toughness. Test results showed that there is a significant difference in the flexural properties and toughness between thin specimens (mini-plates; thickness/span = 0.08) incorporating PP and PVA fibers. Despite their different shaped load-deflection curves, the flexural load carrying capacity of PP and PVA FRCCs was approximately same with the prismatic specimens (thickness/span = 0.31). According to center-point and two-point loading flexural test results, two-point loading condition seems more appropriate to visualize multiple cracking for PVA fiber reinforced thin members.

Prediction for Relative Dynamic Elastic Modulus of PVA-ECC under Freezing and Thawing Cycles

This study focuses on the relative dynamic elastic modulus of the polyvinyl alcohol fiber reinforced cementitious composite (PVA-ECC) after three hundred freeze-thaw cycles. The Artificial Neural Network of freeze-thaw cycles prediction was finally established through data analysis with the help of BP artificial neural network, calculation method optimization and sample training, many times’ trails of the hidden layer and every hidden unit, and the optimal selection of the training function. The results show that there is a small relative error between the predicted value and the actual one of the specimen of the relative dynamic elastic modulus of the PVA-ECC, and the established artificial neural network model bears a higher prediction precision.