Transverse Shear Strength Research Articles

Effects of temperature and stress evolution on microstructural change and mechanical properties during friction element welding

Dissimilar material joining is essential for improving the strength-to-weight ratio of materials for various applications. Friction element welding (FEW) is a promising solution for joining highly dissimilar materials that vary in strength and thickness. However, the influence of the process parameters on the material’s resultant microstructure and mechanical properties remains unclear. In this study, the relationship between microstructure and microhardness distribution of the welded specimen is experimentally studied, and the effects of temperature and stress evolution are revealed by a thermal–mechanical finite element model. It is found that the microhardness can be improved by over 50% in the central region due to microstructural change and grain refinement. The beneficial microstructural change can be achieved by inducing either a high peak temperature (over the austenitization temperature) or a high peak stress (over the hardening factor) during the FEW process, which can be obtained by controlling the endload and rotational speed of the friction element. The size of the region with improved hardness is observed to vary with the depth of deformation in the steel layer. For the transverse shear strength (TSS), it is observed that irrespective of the temperature levels reached, TSS increases with increasing stress in the steel layer. Temperature plays a crucial role when the steel layer’s temperature is higher than the austenitization start temperature wherein TSS increases with the temperature.

Test methods for determination of shear properties of sandwich panels

This paper presents analysis and comparison of test methods for determining transverse shear strength and shear modulus of steel-faced sandwich panels commonly used in construction. The test methods are taken from the governing European standard EN 14509:2013. Two-point loading and four-point loading test methods as well as a full-scale test method are examined. Based on extensive experimental work on sandwich panels with varying core thickness, comprising mineral wool (MW) and polyisocyanurate (PIR) and encompassing both roof and wall panels, this study provides details of the test setup for the four-point loading and vacuum box methods with which a pure shear failure is obtained. Such details are missing from EN 14509. This paper highlights that the two-point loading method fails to consistently produce shear failure, especially in thicker panels, indicating it does not accurately measure transverse shear strength. The results of the experiments conducted in this study indicate that the four-point loading and full-scale test methods provide consistent shear failure for thicker panels while yielding greater transverse shear strength than the two-point loading test in general.

Durability of concrete-embedded GFRP bars after 20 years of tidal zone exposure: Correlation with accelerated aging tests

The application of non-metallic glass fiber-reinforced polymer (GFRP) bars as embedded reinforcement in reinforced concrete (RC) has been of great interest among researchers and practicing engineers alike, owing to its properties such as high strength-to-weight ratio and corrosion resistance. This study investigated the long-term performance of ribbed (RB) and sand-coated (SC) GFRP bars embedded in concrete columns exposed to harsh seawater conditions for approximately 20 years. The bars extracted from the concrete elements were tested to evaluate strength retention based on ASTM standard transverse and interlaminar shear strength tests. After the long-term field exposure, the ribbed and sand-coated GFRP bars exhibited 82.5 % and 79.4 % transverse shear strength retention, and 84.4 % and 78.1 % interlaminar shear strength retention, respectively, which corresponds to approximately 5 months of exposure in the accelerated solution specified by ACI 440.3R-12 guide. Scanning electron microscopy analyses revealed the extent of damage in the fibers, the matrix, and their interface, which validated the degradation in the mechanical strength of the exposed GFRP bars. Finally, correlations between long-term and accelerated exposure test conditions were developed to predict transverse and interlaminar shear strength in the field based on laboratory conditioning investigations.

The Influence of the Interface on the Micromechanical Behavior of Unidirectional Fiber-Reinforced Ceramic Matrix Composites: An Analysis Based on the Periodic Symmetric Boundary Conditions

The long-term periodicity and uncontrollable interface properties during the preparation process for silicon carbide fiber reinforced silicon carbide-based composites (SiCf/SiC CMC) make it difficult to thoroughly investigate their mechanical damage behavior under complex loading conditions. To delve deeper into the influence of the interface strength and toughness on the mechanical response of microscopic representative volume element (RVE) models under complex loading conditions, in this work, based on numerical simulation methods, a microscale representative volume element (RVE) with periodic symmetric boundary conditions for the material is constructed. The phase-field fracture theory and cohesive zone model are coupled to capture the brittle cracking of the matrix and the debonding behavior at the fiber/matrix interface. Simulation analysis is conducted for tensile, compressive, and shear loading as well as combined loading, and the validity of the model is verified based on the Chamis theory. Further investigation is conducted into the mechanical response behavior of the microscale RVE model under complex loading conditions in relation to the interface strength and interface toughness. The results indicate that under uniaxial loading, increasing the interface strength leads to a tighter bond between the fiber and matrix, suppressing crack initiation and propagation, and significantly increasing the material’s fracture strength. However, compared to the transverse compressive strength, increasing the interface strength does not continuously enhance the strength under other loading conditions. Meanwhile, under the condition of strong interface strength of 400 MPa, an increase in the interface toughness significantly increases the transverse compressive strength of the material. When it increases from 2 J/m2 to 20 J/m2, the transverse compressive strength increases by 28.49%. Under biaxial combined loading, increasing the interface strength significantly widens the failure envelope space under σ2-τ23 combined loading; with the transition from transverse compressive stress to tensile stress, the transverse shear strength shows a trend of first increasing and then decreasing, and when the ratio of transverse shear displacement to transverse tensile/compressive displacement is −1, it reaches the maximum. This study provides strong numerical support for the investigation of the interface properties and mechanical behavior of SiCf/SiC composites under complex loading conditions, offering important references for engineering design and material performance optimization.

Failure analysis of unidirectional FRP with fiber clusters under transverse pure shear

In nearly all the failure criteria for the FRP (fiber reinforced plastic), the fundamental strength of the FRP under uniaxial tensile, compressive and pure shear stress were utilized to construct appropriate mathematical function relationship with the multiaxial stress. Among them, the strength of the FRP under transverse pure shear stress was influenced by various factors and could not be directly obtained from tests. In this paper, transverse pure shear failure behavior of FRP was studied using finite element analysis based on RVE models, the RSE and HC algorithm were utilized to generate the FRP with different fiber distribution, mainly refers the different fiber clusters which was commonly experimentally observed. The bilinear cohesive model and extended linear Drucker Prager model were used to characterize the mechanical behavior of the interface and matrix respectively. Then, constraint of periodic boundary condition was applied for the RVE models. Difference on failure fracture behavior of FRP with different fiber distribution were identified and assessed under transverse pure shear stress, while the connection between stress triaxiality and initial damage equivalent plastic strain of the matrix was also altered. On this basis, the distinction of the maximum transverse pure shear stress, the crack resistance strength and the transverse shear strength was thoroughly discussed and identified, which provided a theoretic reference for the failure analysis of the FRP.

Finite element model analysis of long-term performance of composite anchorage based on double-material parameters

Carbon fibre-reinforced polymer (CFRP) tendons demonstrate the advantages of light weight, high strength, and superior corrosion resistance and have broad application prospects for long-span cable structures. However, given the low transverse shear strength of CFRP tendons, how to achieve long-term and reliable anchorage for CFRP tendons is a critical issue. The long-term performance (LTP) of a novel composite anchorage for CFRP tendon was assessed in this study. Then, a finite element model (FEM) with double-material creep parameters was established to reliably model the LTP experiment according to the creep parameters of the bonding medium and CFRP tendon. Finally, the effects of the free section tendon length, pre-tightening force, over-tensioning force, and elastic modulus of the bonding medium were analysed using the established FEM with double-material creep parameters. Results revealed no visible damage to the CFRP tendon and anchorage after the LTP experiment. The maximum tendon slippage was 0.054 mm, and the residual load ratio was 0.826. These phenomena indicate that the novel composite anchorage has excellent LTP. The FEM modelling results based on double-material creep parameters were in good agreement with the experiment results. The residual load ratio calculated by the FEM was 1% lower than the experimental value. Through the parameter analysis, the residual load ratio of the specimen was effectively improved under longer free section tendon condition, but tendon slippage increased to a certain extent. In addition, the LTP of the composite anchorage can be effectively improved by appropriately decreasing pre-tightening force and over-tensioning force. When the over-tensioning force was 1.4 times the test load, the tendon slippage was reduced by 34.2%, and the residual load ratio increased by 4.8%. The greater elastic modulus of the bonding medium in the range of 2.1 GPa–3.1 GPa, the worse the LTP of the composite anchorage.

Long‐term residual properties and durability of glass fiber reinforced polymer composite exposed to alkaline solution and natural weather for a decade

AbstractThis paper presents a comprehensive analysis of the residual thermal and mechanical properties of pultruded glass fiber reinforced polymer composite bars following a decade of conditioning in an alkaline solution and exposure to natural weather conditions. The study focuses on evaluating the changes in the glass transition temperature (Tg) of the polymer matrix and its impact on the bar's mechanical performance. The results indicate that the Tg retained approximately 94.7% of its initial value, with the decrease attributed to the plasticizing effect of absorbed water. The flexural modulus, flexural strength, and transverse shear strength were found to retain 91.8%, 77.2%, and 97.3% of their original values, respectively. The reductions in strength and stiffness were primarily attributed to a weakening in the bonding between the fibers and the polymer matrix. Fractographic analysis revealed that the failure of the plasticized and softened polymer matrix contributed to the observed reductions in strength. Interestingly, the short beam shear strength remained relatively unchanged, as the diffusion of water into the core of the bars at ambient temperatures had a minimal effect. This slower water diffusion in the core led to insignificant degradation of the short beam shear strength.Highlights GFRP bars were exposed to alkaline solution and natural weather for a decade. The water diffusion was a key factor in determining the residual properties of the GFRP bars. The absorbed water plasticises the polymer matrix in GFRP bars. The mechanical property losses in GFRP bars were associated with changes in the matrix property.

Study on durability of transverse shear properties for novel carbon/glass hybrid fiber‐reinforced polymer bars in simulated concrete environments

AbstractDurability on the transverse shear properties of hybrid fiber‐reinforced polymer (HFRP) bar may control the cross‐sectional load‐bearing capacity and failure mode of the HFRP bar reinforced concrete members due to its strength degradation with time. Herein, the degradation of novel carbon/glass (C/G)‐HFRP bars were accelerated in simulated concrete environments at 60°C to investigate the effects of fiber volume fraction and distribution pattern, matrix resin volume fraction, exposure environment, and period on their transverse shear properties. The results displayed that the transverse shear strength of the samples reduced by 15%, 20%, and 8% after exposure to the simulated ordinary concrete, seawater sea‐sand concrete environments, and tap water for 6 months, respectively. The inward diffusion of water molecules and free hydroxyl ions caused the hydrolysis of matrix resin, etching of glass fiber and debonding of fiber/matrix interface, which were the incentives of the degradation of C/G‐HFRP bars. The increase of matrix resin volume fraction and the application of a waterproof coating were recommended to alleviate the degradation of fibrous composites in concrete environments. Finally, two prediction models were proposed to determine the transverse shear strength of HFRP bar before and after exposure to different harsh environments, respectively. The comparisons indicated that the predicted values were coincided with the experimental results.

Transverse Shear Capacity Predictions of GFRP Bars Subjected to Accelerated Aging Using Artificial Neural Networks

This paper presents the results of three different types of glass fiber-reinforced polymer (GFRP) bars subjected to different harsh environmental conditions. Three types of pultruded GFRP bars, namely, Bar A (13.04 mm dia.), Bar B1 (13.02 mm dia.), Bar B2 (10.19 mm dia.), and Bar C (13.22 mm dia.) were subjected to accelerated aging. GFRP specimens were exposed to four conditionings (alkaline, alkaline with salt, acidic, and water), two temperature regimes (20°C and 60°C), and three time regimes (3, 6, and 12 months). The mechanical strength retention of the bars investigated based on the transverse shear strength (TSS) test, conforming to ASTM D7617M-11 revealed a decline in the shear strength characteristics of specimens proportionally with the exposure time. In general, Bar A, Bar B1, and Bar B2 performed well, but Bar C performed the worst since Bar C exhibited the least mechanical strength retention at elevated temperatures. Scanning electron microscopy (SEM) of the cross section of the conditioned specimens revealed the nature of the evolution of deterioration and the state of glass fibers, polymeric resin matrix, and fiber-matrix interface, validating the decrease in transverse shear capacity of the bars. SEM micrographs showed fiber damage, with debonding occurring at the fiber-matrix interface and cracking of the polymeric resin. Leaching out of glass fibers into the matrix of varying degrees upon conditioning was observed through the X-ray mapping of silicon. Furthermore, strength prediction models developed using multiple linear regression and artificial neural network (ANN) techniques were compared. Coefficients of correlation (R2) of 0.94 and 0.76 and root mean square errors (RMSE) of 7.43 and 12.00 were obtained with models developed using ANN and multiple linear regression, respectively, showing that ANN can be used as a robust tool for GFRP shear strength prediction.

Thermomechanical performance of continuous carbon fibre composite materials produced by a modified 3D printer

First of all, this article aimed to evidence the role of a modified printer developed for continuous carbon fibre reinforced PolyAmide (cCF/PA6-I) together with the use of a fully open slicing step on the printing quality and the longitudinal/transverse tensile and in-plane shear properties. A comprehensive assessment of the microstructure and properties with a similar material (cCF/PA6-I), but produced with a commercial printer (i.e., Markforged® MarkTwo) has been achieved. Our customised printer and the open slicer used have made possible to better control the print conditions (i.e., layer height and distance between filaments), to reduce the porosity from more than 10% to about 2% and improve the mechanical properties.Moreover, the understanding of the behaviour of these 3D printed composites with wide-ranging external temperatures is mandatory for future use in a severe environment and/or development of new thermally active 4D printed composites.The 3D printed cCF/PA6-I composites have been then thermomechanically characterised along different printing directions (0, 90 and ± 45°) from −55 to +100 °C. Unlike the longitudinal properties that hardly change with temperature, the transverse and in-plane shear stiffness and strength of these 3D printed composites were particularly sensitive to temperature variations, with decreases of 25–30% and 30–55%, respectively. This was due to the high sensitivity of the polymer matrix, the fibre/matrix and interfilament interfaces when the composites were loaded along those directions, because damages induced by internal thermal stresses. Fractography has also been carried out to reveal damage mechanisms.

A study of impact induced stress due low velocity impact on laminated composite skewed hypar shell roof

The doubly ruled hypar shell, being one of the most feasible shell roof configurations, enjoys industrial preference for covering large column free areas. This class of shells is unique as the only curvature here is the cross curvature and these do not admit easy closed form solution particularly when the boundary conditions are complicated. Laminated composite, an innate choice to different industrial sectors for its huge specific strength and stiffness, good weathering resistance, is now being extensively employed in civil engineering. However the low transverse shear strength of the composite shell impelled the researchers to study the response of the same under the action of impact loads. In the present study, a finite element code is functioned to investigate the impact induced stress history generated in simply supported laminated composite hypar shell for different impact velocities of a spherical solid striker. Contact behavior is described by modified Hertzian contact law where as time dependent equations are solved using Newmark’s time integration algorithm in present analysis. A practicing engineer often has to select a particular shell option consisting stacking sequence among a number of possibilities. The present paper discusses the behaviour of composite hypars under low velocity impact and different stresses induced due to the same from engineering standpoint to propose a selection guide line among the available options and to proposes values of practical parameters like the equivalent static loads and dynamic magnification factors for designing such shells through static simplification of the problems.

The effect of thickness on the transverse shear strength of nomex honeycomb cores

Honeycomb materials are commonly used as cores for sandwich panels. While empirical evidence exists showing that the transverse shear strength of a honeycomb core is affected by its thickness, the accuracy of empirical guidelines and the reasons for the changes in strength are not well understood. Four-point flexural testing of sandwich beams and a detailed cellular finite element model are used to investigate transverse shear failure of Nomex™ honeycomb core material. Transverse shear strengths at varying core thicknesses were compared to manufacturer specifications and used to determine normalised strength correction factors for thickness. These factors correlated well with trends shown in previous literature, where core shear strength decreases with increasing core thickness. The failure mode investigation showed a transition between modes as core thickness increased. The thinner cores experience shear fracturing of individual cell walls followed by local cell wall buckling, intermediate thickness cores initially failed by cell wall local buckling, then fractured and larger thickness cores appeared to fail by overall cell column buckling.

Mechanical and failure analysis of thick composites under hygrothermal conditions by a novel coupled hygro-thermo-mechanical multiscale algorithm

A novel coupled hygro-thermo-mechanical multiscale-APFEA (HTM-multiscale-APFEA) algorithm is developed to precisely predict the mechanical and failure behavior of thick fiber-reinforced laminated composites under hygrothermal conditions. The Fourier and Fick's equations are simultaneously solved by the proposed fully-coupled temperature-moisture concentration (FCTM) algorithm to account for their mutual effects on each other. Two subroutines, one responsible for the homogenization, failure analysis, and also linking the macro and micro models of the composite material, and another for establishing the constitutive equations and failure analysis of the cohesive/adhesive material, are integrated into a user-defined material code extended for also defining the materials failure behavior. The effects of temperature and moisture conditions on the stiffness, strength, coefficients of hygrothermal expansions (CHEs), and fracture toughness of matrix and cohesive/adhesive materials are considered. The results of the HTM-multiscale-APFEA algorithm are verified against the results of experimental data, analytical high-order theories, and reliable numerical analysis. Furthermore, the failure analysis of composite laminate under hygrothermal conditions coupled with mechanical loading (bending) is carried out by the HTM-multiscale-APFEA algorithm, and compared with experimental data. The results have shown that the transverse tensile strength, shear strength, and transverse Young's modulus of the composite material degrade respectively about 72%, 13%, and 40% in the most severe hygrothermal conditions at the material boundaries; while the normal stiffness and normal strength of the cohesive/adhesive material decline by about 73% and 47%, respectively, at outer layers. In addition, the mixed-mode fracture toughness of the adhesive material elevates from 0.55 ×103N/m at inner layers to 2.14 ×103N/m at outer layers of adhesive material. The proposed algorithm is highly flexible and can easily be adapted to model different types of laminated composites.

Stress invariant-based failure criteria for predicting matrix failure of transversely isotropic composites: Theoretical assessment and rationalized improvement

Stress invariant-based failure criteria, which are acknowledged for their simple expression but elegant description, still remain irrational considerations in its original formulation with regard to matrix failure in FRP composite materials. This study firstly re-examines the debatable hypothesis of infinite strength under equi-biaxial transverse compression. Afterwards, further attention is paid to the intrinsic relationship of transverse strengths when employing the assumption of transverse isotropy. During the formulation of the improved failure criteria from invariant theory, one notable feature is that deductions of strength coefficients, rather than direct use of measured strengths, are preferred to satisfy the mathematical and physical logic underlying the predefined assumptions and conditions. The analytical expressions for transverse shear strength and biaxial tensile strengths are deduced with Mohr’s fracture hypothesis, while biaxial compressive strength is estimated according to the theory of ductile/brittle transition. The predictions are validated based on computational micromechanics. The proposed criteria can be totally defined in terms of conventionally uniaxial strengths, thereby eliminating the need of biaxial strength parameters that are difficult to be measured experimentally. Combined practically and virtually experimental evaluations show that more reasonable and more accurate predictions under various stress conditions can be achieved by the developed stress invariant-based criteria, especially for the combined transverse normal stress case.

Determination of shear stresses in the measurement area of a modified wood sample

Abstract The purpose of the experiment was to determine the distribution of shear stresses in the measurement area of a natural and modified wood sample. Previous wood shear tests conducted on a typical Iosipescu specimen have shown that a complex stress state exists at the bottom of the notch. With transverse loading of the samples, flexure occurs and normal stresses arise from the bending moment and thus fibers are deformed. For the investigations oriented on shear, shear with stretching, and shear with compression, a special specimen was prepared which differed by notch geometry from a typical Iosipescu specimen. A new test machine is described in the article, which is equipped with special specimen holders to perform investigations in complex stress conditions. Crack patterns recorded for natural and modified wood are presented. For all tests, numerical finite element model simulations were performed to obtain stress distributions inside the specimens. The calculated stress distributions were visualized as contour line projections for natural and modified wood. Transverse shear strength values for the modified Iosipescu sample were found to exceed the magnitude of previously published ASTM D1037-87 test results. The test results proved that the strength properties of anisotropic materials in a complex state of stress can be assessed with great accuracy. This is very important in engineering applications.

Durability assessment of GFRP rebars in marine environments

Technologies developed over the last two decades have facilitated the use of glass fiber reinforced polymer (GFRP) bars as internal reinforcement for concrete structures, specially in coastal environments, mainly due to their corrosion resistance. To-date, most durability studies have focused on a single mechanical parameter (tensile strength) and a single aging environment (exposure to high alkalinity). However, knowledge gaps exists in understanding how other mechanical parameters and relevant conditioning environments may affect the durability of GFRP bars. To this end, this study assesses the durability for different physio-mechanical properties of GFRP rebars, post exposure to accelerated conditioning in seawater.Six different GFRP rebar types were submerged in seawater tanks, at various temperatures (23°C, 40°C and 60°C) for different time periods (60, 120, 210 and 365 days). In total six different physio-mechanical properties were assessed, including: tensile strength, E-modulus, transverse and horizontal shear strength, micro-structural composition and lastly, bond strength. It was inferred that rebars with high moisture absorption resulted in poor durability, in that it affected mainly the tensile strength. Based on the Arrhenius model, at 23°C all the rebars that met the acceptance criteria by ASTM D7957 are expected to retain 85% of the tensile strength capacity.

Durability of GFRP bars embedded in seawater sea-sand concrete: A coupling effect of prestress and immersion in seawater

Using prestressed glass fibre-reinforced polymer (GFRP) bars for seawater sea-sand concrete (SSC) structures in offshore engineering is of particular interest for improving the utilisation of GFRP and natural resources. However, limited information is available on the effects of prestressing on the durability of GFRP. Therefore, the durability of SSC-coated GFRP bars was investigated under the coupling effect of prestressing and immersion in seawater at room temperature, 40 °C, and 60 °C, with prestress levels set at 20% and 40% of the ultimate tensile strength (%fu) of GFRP. The tensile properties, interlaminar shear strength, transverse shear strength degradation after 0 d, 30 d, 60 d and 120 d, and the prestress loss of GFRP within 70 d were studied. The results showed that SSC wrapping was not conducive to the long-term performance of GFRP bars due to the alkaline environment, and the prestress further accelerated the tensile strength degradation, with the tensile strength decreasing almost to zero for the specimens (with 40% fu prestress level) immersed in seawater after 120 days at 40 °C and 60 °C. However, the interlaminar shear strength and transverse shear strength retention were 37.1% and 52.2% for 60 °C immersion under the same conditions, respectively. These findings suggest that the shear properties degenerated more slowly than the tensile properties of the prestressed GFRP bars embedded in SCC under seawater environment, which also evidences that the glass fibres were damaged more heavily than the epoxy vinyl resin under the prestressing.

Modulating impact resistance of flax epoxy composites with thermoplastic interfacial toughening

The application of natural flax fibre/epoxy composites is growing in the automotive sector due to their good stiffness and damping properties. However, the impact damage resistance of flax/epoxy composites is limited due to the brittle nature of both epoxy and flax fibres and strong fibre/matrix adhesion. Here, biobased thermoplastic cellulose acetate (CA) is deployed as a fibre treatment to alter the damage development of flax/epoxy composites subjected to low-velocity impact. The perforation threshold energy and the perforation energy of unmodified cross-ply composites increased respectively by 66% and 42% with CA-treated flax fibres. The CA-modification modestly decreased the transverse tensile strength and in-plane tensile shear strength of the composites. However, it altered the brittle nature of flax/epoxy laminates in quasi-static tests into ductile failure with clearly increased fibre–matrix debonding.

Effect of alkalinity on the shear performance degradation of basalt fiber-reinforced polymer bars in simulated seawater sea sand concrete environment

The durability of the basalt fiber-reinforced polymer (BFRP) bar in an alkaline environment is a major problem that prohibits its use as reinforcement in a marine concrete structure. One potential remedy is to reduce the alkalinity of the concrete. For evaluating the feasibility of this technique, the mechanical durability of BFRP bars was investigated in a simulated seawater sea sand concrete environment using accelerated degradation tests. The interlaminar and transverse shear strengths after various exposure times were measured to determine the degree of degradation. The moisture uptake test was also conducted to show the moisture content of the conditioned BFRP bar. Furthermore, the deterioration of matrix and basalt fiber was analyzed by Fourier transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, and inductively-coupled plasma mass spectrometry. The findings showed that reducing alkalinity effectively mitigates moisture uptake, the loss in interlaminar shear strength, and transverse shear strength of BFRP bars. The moisture absorption of BFRP bars is reduced from 5.47% to 0.14% by lowering the pH from 13.2 to 10.1. BFRP bars exposed to the solution with a pH of 13.2 lose the maximum interlaminar and transverse shear strengths, which are 47.08% and 6.17% greater than those with the pH of 10.1. The intensity of alkaline disintegration reactions is considerably declined at the pH of 12.3, whereas the alkalinity-related degradation is marginal at the pH of 10.1. The outcomes of this study indicate that applying this approach can lower epoxy resin degradation while also mitigating basalt fiber etching. This study can also provide insight into the use of low-alkalinity concrete to enhance the long-term performance of FRP bars in concrete structures.

Experimental Investigation of Long Term Seawater Durability and Shear Properties of Pultruded GFRP Composite

The effect of long term immersion in seawater at different temperatures on the properties of pultruded glass fibre reinforced polymer (GFRP) composite rebar was investigated. Samples were conditioned in seawater and in dry at 23, 55 and 75 °C for 0, 8, 20, 30 and 36 months to analyse the changes in shear properties such as transverse shear strength (TSS) and short beam shear strength (SBSS). Both TSS and SBSS increased after conditioning in dry at 55 and 75 °C; on the other hand, TSS decreased gradually due to conditioning in seawater at 23, 55 and 75 °C, whereas SBSS decreased due to conditioning in seawater only at 75 °C. Microscopic analysis specified that the shear strength decreased due to fibre/matrix interfacial failure as a result of de-bonding and fibre pull-out. Compared to the short beam shear test, the transverse shear test was found to be a sensitive technique to measure the durability of pultruded GFRP rebar. FT-IR analysis indicated superficial hydrolysis reaction of polymer matrix occurred when the sample was conditioned at 75 °C. A reversible change in glass transition temperature (Tg) and in viscoelastic property of the polymer matrix was observed due to conditioning in seawater at 23 and 55 °C.