Flexural Durability Research Articles

Flexural durability of BFRP bars reinforced geopolymer-based coral aggregate concrete beams conditioned in marine environments

Geopolymer is an environmentally friendly material that utilizes industrial solid waste, boasting reduced greenhouse gas emissions and energy consumption. It exhibits superior performance in terms of corrosion resistance and thermal stability compared to ordinary Portland cement (OPC). These excellent properties are crucial for marine engineering construction, offering significant value and application potential in marine engineering materials. In this study, geopolymer was employed as the cementitious material, with marine resources like seawater and coral aggregates sourced from remote island areas effectively utilized, and basalt fiber-reinforced polymer (BFRP) bars were incorporated as reinforcements to develop BFRP bars reinforced geopolymer-based coral aggregate concrete (GPCAC) beams. Laboratory aging procedures were employed to investigate the deterioration patterns and damage mechanisms affecting the flexural behavior of GPCAC beams under seawater immersion and dry-wet cycling conditions, comparing them with cement-based coral aggregate concrete (CAC) beams. The experimental results indicated that both CAC and GPCAC beams under simulated marine environments experienced a reduction in the number of cracks upon damage, but their crack spacing and width increased. Moreover, the flexural stiffness of CAC and GPCAC beams after seawater attacks tended to increase, but this increased stiffness did not translate to a higher loading capacity. Conversely, as the corrosion age increased, the ultimate load and deflection values of both CAC and GPCAC beams decreased to varying extents, with the load-carrying capacity degradation more pronounced in seawater dry-wet cycling environments than in seawater immersion conditions. Compared to CAC beams, GPCAC beams exhibited superior resistance to seawater erosion. Following 12 months of seawater dry-wet cycling, the ultimate loading capacity of CAC beams decreased by 12.2%, while that of GPCAC beams only degraded by 9.5%. Predictions of the flexural capacity of GPCAC beams using equations from existing FRP-reinforced normal aggregate concrete (NAC) specifications indicated slightly higher values than the experimental values, with an error margin of less than 15%. Overall, the formulas for the flexural capacity of NAC beams in existing FRP-reinforced NAC codes remained applicable to CAC and GPCAC beams.

Influence of corn cob ash additive on the structure and properties of cement concrete

In accordance with the Sustainable Development Goals (SDGs) concept, there is a need to find technologies that would help make concrete production less energy intensive and more environmentally friendly. One technology involves substituting some mineral components in concrete with rapidly renewable plant-based alternatives. This study aims to establish the essential patterns among the concrete composition, micro-structure, and properties of cementitious composites modified with corn waste. Additionally, it seeks to explore the potential for producing high-quality composites using this waste material. To assess the effectiveness of this kind of waste, the strength of the cement-sand mortar, several characteristics like compressive strength, flexural durability and water absorption of hardened concrete were studied. It is established that introducing corn cob ash (CCA) to substitute a part of the cement up to 16% is justified and allows to obtain mortar and concrete with enhanced properties. CCA has a beneficial impact on the properties of Cement Sand Mortar (CSM) when replacing cement by no more than 15%. The maximum effect was achieved at 10% CCA, and the rise of compressive and flexural strength were 6.06% and 6.32%. In concrete with a CCA amount of 8%, the most impressive growth of compressive strength was 7.14%, and the lowest value of water absorption, which is 10.31% lower compared to the ordinary composition. Including CCA reduces the properties like workability, density of concrete mixtures, and the hardened composite density. The scientific results obtained prove the possibility of using CCA as an effective mineral pozzolanic additive that improves the properties of concrete.

Influence of Exposure Period and Angle Alteration on the Flexural Resilience and Mechanical Attributes of Photosensitive Resin.

Despite the large number of studies addressing the effect of acrylic resin polymerization concerning flexural properties, limited research has been conducted on the manufacturing impact on a polymer’s mechanical properties. Photosensitive resinous materials are used in various engineering applications where they may be exposed to multiple detrimental environments during their lifetime. Therefore, there is a need to understand the impact of an environment on the service life of resins. Thus, flexural tests were conducted to study the effects of exposure time and angle on the flexural strength of resins. Herein, the main objective was to explore the strength, stability, and flexural durability of photosensitive resin (EPIC-2000ST) fabricated at different exposure times (E) and angle deviation varying from 0° to 85° with a 5° increment. The samples in circular rings were manufactured and divided into five groups according to their exposure time (E): 10 s, 20 s, 30 s, 40 s, and 50 s. In each exposure time, we designed rings via SolidWorks software and experimentally fabricated at different oblique angles (OA) varying from 0° to 85° with a 5° increment during each fabrication, i.e., OA = 0°, 5°, 10°, 15°, 20°, 25°, 30°, 35°, 40°, 45°, 50°, 55°, 60°, 65°, 70°, 75°, 80°, and 85°. Flexural strength was evaluated using a three-point bending test. Optical electron microscopy was used to examines the samples’ exterior, interior, and ruptured surfaces. Our experimental analysis shows that flexural strength was significantly enhanced by increasing exposure time and at higher oblique angles. However, at lower angles and less exposure time, mechanical flexural resilience declines.

Flexural Durability of Seawater Coral Aggregate Concrete Beams Reinforced with Basalt FRP Bars

Flexural Durability of Seawater Coral Aggregate Concrete Beams Reinforced with Basalt FRP Bars

Evaluation of Flexural Durability of High Strength Textile for Robotic Applications

Evaluation of Flexural Durability of High Strength Textile for Robotic Applications

Tests to estimate the heat rate effect on the flexural durability of transport vehicle gear wheels

The article presents the test results concerning the effect of thermal loads on the flexural durability of gear wheels of transport vehicle high-loaded transmissions. The tests were performed using a universal hydraulic pulsation machine and a thermal loader at five fixed temperature levels from twenty to two hundred degrees Celsius. As a result of the performed tests, a significant dependence of the flexural durability of gear wheels on their thermal state was established. In the expected maximum temperature area, corresponding to the temperature of the low tempering of the gear wheel material, it decreased sharply more than ten times.

Evaluation of Flexural Durability of High-Strength Textile for Robotic Applications

Evaluation of Flexural Durability of High-Strength Textile for Robotic Applications

Flexural Durability and Chloride Diffusion Equation of TRC-Strengthened Beams under a Chloride Environment

In this study, the chloride ion diffusion and structural performance of beams reinforced with textile-reinforced concrete (TRC) were evaluated. The parameters investigated were chloride concentration, sustained load and number of textile layers. The results demonstrate that the content and diffusion coefficient of chloride increased with increasing chloride concentration. Higher chloride concentrations accelerated the crack propagation and deflection changes and caused the reduction of the load-carrying capacity of the beams. The sustained load promoted the chloride transport of the TRC, increasing the chloride ion content and diffusion coefficient and causing substantial damage to the microstructure of the TRC. In addition, the performance (such as cracking resistance, deflection and flexural capacity) of beams with a large sustained load ratio decreased to a less extent than did the performance of the unloaded beams. The content and diffusion coefficient of chloride in the unstrengthened beams were obviously larger than those in the strengthened beams, but increasing the textile layers number had little influence on these factors. In addition, for the unstrengthened beams, the cracks and deflections developed rapidly, and the load decreased greatly, especially the cracking load. Finally, in accordance with Fick's second law of diffusion, a chloride diffusion equation in TRC layers under new boundary conditions was proposed.

Research on chloride diffusion and flexural behavior of beams strengthened with TRC subjected to dry-wet cycles

This paper presents an experimental study on the flexural durability of beams strengthened with TRC subjected to dry-wet cycles. The effects of dry-wet cycles (180, 210, 240, 270 and 330) and the short-cut fiber contents (0, 0.2%, 0.5% and 1%) on chloride transport and flexural behavior were investigated. The results showed that with the increase of dry-wet cycles, the chloride ion content in the TRC increased, while the diffusion coefficient decreased, the micro-structure of the TRC matrix was obviously damaged after 330 cycles. A certain amount of short-cut fibers was beneficial to improve the chloride transport resistance of the TRC matrix. The effect of increasing dry-wet cycles on the overall mechanical properties of the strengthened beams fluctuated when there were few dry-wet cycles. However, the mechanical properties of the strengthened beams significantly diminished after 330 cycles. The mechanical properties of the strengthened beams were enhanced with the increase of short-cut fiber content, and the promotion effect was obvious as it reached 1%. Finally, the ultimate bearing capacity formula of TRC-strengthened beams subjected to dry-wet cycles was modified based on the test results.

The durability of seawater sea-sand concrete beams reinforced with metal bars or non-metal bars in the ocean environment

In this article, the flexural durability of three types of seawater sea-sand concrete beams that were fully reinforced with steel bars, 304 stainless steel bars, or fiber-reinforced polymer bars were comparatively tested. Beam specimens were conditioned in a 40°C seawater wet–dry cycling environment and a 50°C seawater immersion environment for up to 9 months with an interval of 3 months. The test results showed that in the absence of an additional current (even if the temperature is elevated), the flexural properties of the seawater sea-sand concrete beams reinforced with steel bars and stainless steel bars after 9 months of conditioning did not show any degradation trends. However, for the carbon fiber–reinforced polymer bar–reinforced beams (top bars and stirrups are both basalt fiber–reinforced polymer bars) conditioned in the high-temperature and high-humidity environment considered, the failure modes changed from concrete crushing in the pure bending section to concrete crushing at loading points in the shear span with a maximum reduction of 30% in the ultimate load-carrying capacity. In addition, the crack distribution of conditioned carbon fiber–reinforced polymer bar–reinforced beams became sparse, and the crack width increased significantly, with a maximum of 2.2 times. In addition, obvious sudden load drops were observed in the tested load–displacement curves.

(Invited) Development of Flexible Conductive Polymer Electrodes for Recording and Stimulation of Neural Tissue

We describe the development of thin, flexible conductive polymer electrodes for recording and stimulation of excitable tissue including brain, spinal cord, peripheral nerve, and muscle. The electrode material characteristics are intended to mitigate the foreign body response. Manufacturing is based on 3-D robotic deposition of alternating layers of insulating polymer, and polymer doped with electrically conductive particles forming the electrodes and interconnections. The robot can produce multilayer structures and supports synthesis of the electrode array with integrated electronics at low cost. We have performed in vivo and in vitro testing, including flexural tests which demonstrate electrical and mechanical reliability for over 100 million flexions. The capacitive nature of the electrodes provides reversible charge storage capacity that is comparable with other high charge capacity materials. Manufacturing Process: The robotic system first deposits an insulating substrate using a silicone co-polymer which is well established as a chronic implant material. After the substrate cures, a layer of conductive ink based on polymer doped with electrically conductive particles is deposited to form the electrodes and interconnections. Next, an overcoat of insulating polymer is deposited. This process may be repeated to form multilayer structures, similar to the process of printed circuit board manufacturing. Because the ink is mostly polymer by volume fraction, an entire structure has mechanical properties of a homogeneous polymer. This mechanical matching of insulating and conducting phases provides high flexibility and flexural durability. Composite structures with features as small as 100 µm trace width, 200 µm pitch and 30 µm thin insulating layers are achieved with high reproducibility including optional connection directly onto printed circuit boards. Electrode Testing : Mechanical and electrical performance of the devices has been verified through mechanical compression, stretch, and bend tests, and accelerated lifetime soak testing. These stress tests have verified the conductivity of the traces and electrodes and the insulation of the polymer for over 100 million bend cycles (tested per EN 45502-2) and lifetimes equivalent to over 400 days in vivo. The electrodes have also been successfully validated in chronic in vivo studies in rat, cat, rabbit and pig models. Electrical Characterization : DC resistances of the ECoG array vary with trace length and thickness, and are generally on the order of several hundred ohms over several inches of trace. Electrical impedance spectroscopy (EIS) was performed after soaking the arrays in saline solution for at least 12 h, and yielded trace-to-saline impedances below 10 kΩ for frequencies in the range of 0.2 Hz to 1 MHz. Cyclic voltammetry was performed with a Pt counter electrode and a fresh Ag/AgCl reference electrode with a scan rate of 20 mV/s. The reversible charge storage capacity (RCSC) increased with cycling as is common with other materials used for stimulation. After several cycles, the RCSC is on the order of 1 – 1.5 mC/cm2, comparable with other high charge storage capacity materials. This is consistent with the capacitive nature of the platinum embedded within dielectric polymer. Demonstration of Chronic Wireless ECoG Recording : We have developed a wireless recording system used in conjunction with the flexible electrode array. A four-electrode array was implanted subdurally over sensory cortex in swine for chronic ECoG monitoring. Leads from the array passed to a subcutaneous transmitter placed between the scapulae. The transmitter sent data to an external transceiver via infrared transmission. We demonstrated wireless transmission of evoked ECoG recordings over 63 days as the paw was electrically stimulated.

Long-term durability of tri-axial woven CFRP tube structure extended along the spin axis of spinning platforms for the SCOPE mission

This study investigates the strength and long-term durability of a spin-axis extensible rigid antenna element, made of tri-axial woven carbon fiber-reinforced polymer (CFRP), for a spinning spacecraft. Due to a slight deviation between the spin axis and antenna-extended axis with the spin, the antenna is subjected to centrifugal body force; the centrifugal force enhances the antenna deflection. A relationship between centrifugal force and antenna deflection is derived from beam theory. As the apparent material modulus decreases with time, the deflection increases simultaneously. The time dependence of mechanical properties of the tri-axial woven CFRP is hence examined by a creep test. The time-dependent failure criterion of the antenna is then examined using a flexural durability test. Based on the beam theory and experimental results, we examine the long-term reliability of applying the tri-axial woven CFRP to extensible rigid antenna for the spinning spacecraft, especially for SCOPE mission; it is verified that the current design tolerance for the mission assures certain durability for long-term usage.

Flexural durability of FRP bars embedded in fiber-reinforced-concrete

This paper presents the results of the long-term flexural behaviors of a hybrid system consisted of continuous fiber-reinforced-polymer (FRP) rebar and fiber-reinforced-concrete (FRC). Flexural durability for the FRP/plain concrete system that served as a reference is also reported. Test results indicated that the ultimate flexural strength and ductility experienced minor reduction when exposed to combined environmental conditioning, including freeze–thaw cycles, high temperature (60°C), and de-icing salt solution. The degradation of concrete may be the main reason for the flexural strength degradation. The addition of fibers with a volume fraction of 0.5% improved the flexural behavior by increasing the ductility level by more than 30%, when compared to the companion beam, for both unweathered and weathered beams. After being subjected to the environmental conditioning, ductility indices for all the tested beams were still above the minimum requirement of 4.