Shear Strength Degradation Research Articles

Mechanical behavior of en-echelon joints under cyclic shear loading conditions: Roles of joint persistence and loading conditions

Studying the mechanical response of en-echelon joints under cyclic shear loading conditions can provide novel insights into the instability of jointed rock masses under seismic conditions. To investigate the effects of joint persistence, normal stress, cyclic distance, and shear velocity on the cyclic shear behavior of en-echelon joints, a series of cyclic shear tests in the laboratory was performed. Findings revealed that the failure morphography of en-echelon joints manifested through brecciated shear zones and abraded rupture surfaces, resulting in notable reductions in shear strength and significant compressibility. The degradation factor of shear strength ranged from 0.363 to 0.708 after ten cycles. The shear strength degradation factor showed an inverse relationship with joint persistence and normal stress while exhibiting a direct correlation with cyclic distance over ten cycles. En-echelon joints characterized by moderate joint persistence, high normal stress, small cyclic distance, and low shear velocity demonstrated increased cyclic friction strength. Moreover, normal stress and joint persistence exerted a more significant influence on shear strength compared to cyclic distance and shear velocity. For en-echelon joints, shear stiffness increased during small shear displacements with cycle number while decreased during large shear displacements; shear stiffness was inversely proportional to the cyclic distance and joint persistence, and directly proportional to the normal stress. Compressibility of en-echelon joints correlated directly with joint persistence, normal stress, cyclic distance, and shear velocity. Compared to normal stress and cyclic distance, joint persistence and shear velocity exhibited less influence on compressibility

ENHANCING MECHANICAL RELIABILITY OF SILVER SINTERED JOINTS WITH COPPER NANOWIRES IN HIGH-POWER ELECTRONIC DEVICES

Abstract This study investigated the mechanical reliability of silver-sintered die attachment under harsh operating conditions, and explored the advantages of adding copper nanowires to improve the bond's mechanical properties. Samples were prepared using a template-assisted electrochemical deposition process to coat the substrate surface with copper nanowires, and were subjected to thermal aging at various temperatures to assess their mechanical reliability. Results showed that the incorporation of copper nanowires in the substrate interface significantly reduced degradation in shear strength as a result of thermal aging, acting as mechanical reinforcement and improving the interfacial resilience against mechanical shear stress. The addition of copper nanowires also reduced the void formation in the thermal aging, resulting in a more robust and reliable bond. The study demonstrates the potential of using copper nanowires as a reinforcing agent to enhance the mechanical properties of silver-sintered die attachment, particularly for high-temperature applications.

Impact of Shear Strength Degradation on Raft Foundation Performance in Clay Shale

Impact of Shear Strength Degradation on Raft Foundation Performance in Clay Shale

Experimental investigation on the frost resistance of RCC layers with various interface treatments

This research investigates the influence of various interface treatment methods on the frost resistance performance of Roller Compacted Concrete (RCC) layers. Freeze-thaw cycle tests were conducted on RCC with interfaces treated using cement mortar, expansion agent mortar, and nano-SiO2 mortar. The study evaluated shear failure modes, shear strength, crack expansion, pore structure, and liquid uptake of the RCC interface after freeze-thaw cycles under different treatment methods. Results reveal that expansion agent mortar and nano-SiO2 mortar improve the shear strength of RCC after freeze-thaw cycles more effectively than cement mortar. The freeze-thaw cycles increase the width and expansion rate of cracks at the RCC interface during the shear process, while mortar treatments help delay crack development. Additionally, the pore volume at the RCC interface gradually increases, and the uniformity of pore distribution decreases under freeze-thaw cycles. During liquid uptake, mortar treatments slow down the upward migration of liquids by improving the pore structure at the interface. The liquid uptake of RCC exhibits a distinct linear relationship with its shear strength and pore structure. As liquid uptake time increases, water first fills larger pores before gradually entering smaller ones. Freeze-thaw cycles cause an increase in pore volume and enlargement, which leads to greater liquid uptake. Based on the damage mechanism of the RCC interface under freeze-thaw conditions, a model of shear strength degradation due to freeze-thaw cycles was established, aligning well with experimental results. Mechanism analysis indicates that nano-SiO2 and expansion agents enhance frost resistance by filling interface pores and cracks through reactions with certain compounds, thereby improving the microstructure.

Effects of joint persistence and testing conditions on cyclic shear behavior of en-echelon joints under CNS conditions

Cyclic shear tests on rock joints serve as a practical strategy for understanding the shear behavior of jointed rock masses under seismic conditions. We explored the cyclic shear behavior of en-echelon and how joint persistence and test conditions (initial normal stress, normal stiffness, shear velocity, and cyclic distance) influence it through cyclic shear tests under CNS conditions. The results revealed a through-going shear zone induced by cyclic loads, characterized by abrasive rupture surfaces and brecciated material. Key findings included that increased joint persistence enlarged and smoothened the shear zone, while increased initial normal stress and cyclic distance, and decreased normal stiffness and shear velocity, diminished and roughened the brecciated material. Shear strength decreased across shear cycles, with the most significant reduction in the initial shear cycle. After ten cycles, the shear strength damage factor D varied from 0.785 to 0.909. Shear strength degradation was particularly sensitive to normal stiffness and cyclic distance. Low joint persistence, high initial normal stress, high normal stiffness, slow shear velocity, and large cyclic distance were the most destabilizing combinations. Cyclic loads significantly compressed en-echelon joints, with compressibility highly dependent on normal stress and stiffness. The frictional coefficient initially declined and then increased under a rising cycle number. This work provides crucial insights for understanding and predicting the mechanical response of en-echelon joints under seismic conditions.

Numerical investigation of plastic hinge length and lateral displacement capacity in precast concrete columns reinforced with SFCBs

Basalt fiber-reinforced polymer (BFRP) presents several advantages, including a moderate elastic modulus, cost-effectiveness, and a substantial fracture strain. A steel-FRP composite bar (SFCB) is a composite bar consisting of an inner steel bar and outer longitudinal BFRP, and it offers favorable initial modulus, high durability, and controllable post-yield stiffness. This study aims to address the issue associated with poor corrosion resistance, connection defects, and low integrity in traditional precast concrete columns with grouted sleeves (PCC-GSs) by employing bond- and post-yield-controlled precast concrete columns reinforced with SFCBs (PCC-SFs). The 3D finite element analysis (FEA) modeling was validated by comparing the results with those of six PCC-SFs and three precast reinforced concrete (RC) columns obtained from the experiment. The results encompass failure modes, load-displacement responses, strain distributions of SFCBs, and section curvature along the columns. The predicted errors for the peak load of S10B85–1P, S10B85–2P, and S10B85–3P are 6.4%, 0.1%, and 1.9%, with a mean error of 2.8%. The predicted errors for the ultimate deformation of S10B85-3PL and ST10B85–3P are within 20%, with a value of 6.0% and 18.7%. Subsequently, a series of FEA models were developed to analyze the effects of various on the development mechanism of plastic hinge length (PHL) for the PCC-SFs under lateral loading. The parameters included the post-yield stiffness ratio, equal-stiffness reinforcement ratio, axial force ratio, concrete strength, and bond strength. The longest plastic hinge length can reach 1.91D (D is the width of the column). An adjusted prediction model for the equivalent PHL in PCC-SFs was proposed and evaluated following a discussion of existing empirical models. Finally, the study explored the effects of these parameters on the load-displacement response, and the rationality of Priestley's shear-strength degradation model in PCC-SFs was validated. Based on the CEN model, an improved prediction model of the total chord rotation capacity was proposed.

Shear performance and durability of adhesively bonded spruce wood-concrete composite joints: Effects of indoor and outdoor environmental conditions, mechanical load, and their coupled effect

A long-term study was conducted on double-lap spruce wood-concrete joints to investigate their shear strength and stiffness over a 12-month period. These joints were manufactured using both wet and dry processes, each incorporating two adhesive types for bonding the wood to the concrete: a brittle epoxy and a ductile polyurethane (PUR). The experimental design exposed the joints to three specific long-term environments: (1) outdoor exposure, (2) indoor conditions with applied load, and (3) outdoor conditions with applied load. The wood-concrete joints exposed to outdoor conditions were subjected to destructive shear testing at intervals of 0 (serving as the reference sample), 2, 4, 6, and 12 months, respectively. For joints subjected to both indoor and outdoor conditions with shear loading, the shear deformation of joints was monitored continuously over the 12 months before performing the destructive tests. A gradual reduction in the shear stiffness and strength of dry joints (produced using the dry bond method) exposed to outdoor conditions was observed over a 12-month period, primarily due to bond failure at the concrete-adhesive interface. The wet joints exhibited no degradation in shear stiffness and strength across long-term conditions over the same period. The bond failure observed in dry joints was predominantly associated with stresses arising from dimensional changes in the wood. No degradation was found in the cross-linking density of the adhesive or in the concrete's compressive stiffness and strength.

Fatigue life prediction method for reinforced concrete deck slabs subjected to repeated moving wheel loads and failing in shear

AbstractAs bridge deck slabs experience the direct impact of repeated concentrated wheel loads, they are more susceptible to fatigue‐related damage than other bridge components. In this context, a fatigue life prediction method for reinforced concrete (RC) bridge decks has been developed based on failure mechanisms of RC slabs tested under moving wheel loads. Initially, the formulas encompassed shear strength and S–N equations, accommodating variations in environmental and support conditions, are proposed to facilitate the fatigue life prediction of slabs exposed to constant moving wheel load. Subsequently, a model for shear strength degradation formulated using experimental findings on beam‐like elements is utilized in predicting the fatigue life of slabs subjected to stepwise moving wheel loads. The validity of the proposed method was established by comparing its results with previous experimental data. Notably, compared with the existing prediction equation, the proposed method exhibited more accurate fatigue life prediction results.

The effect of combined use of plybamboo sheathings and self-tapping screws in enhancing wood-frame shear wall performance

ABSTRACT Plybamboo panels are renewable and eco-friendly structural panels with high strength, good dimensional stability, and affordability, making them highly suitable for wood-frame construction. This study presents an experimental investigation of the wood-frame shear wall constructed with plybamboo-sheathing panels with self-tapping screws (STSs) subjected to monotonic and cyclic loadings. Performance parameters including shear strength, elastic shear modulus, ductility ratio, stiffness degradation, and energy dissipation were evaluated. Results indicate that the combined use of plybamboo sheathings and STSs can substantially reduce failures due to the tearing of sheathing, fastener head pull-through, and fastener withdrawal. The plybamboo-sheathed wood-frame shear walls with STSs had over 1.8 times shear strength and 1.4 times ultimate displacement than those of comparable wood-frame shear walls with nails, respectively, maintaining over 80% of their maximum lateral load capacity at a drift level over 4%. Moreover, the influence of aspect ratio and screw spacing on the elastic shear modulus, shear strength, and stiffness degradation of the plybamboo-sheathed wood-frame shear walls with STSs are consistent with those for common wood-frame shear walls.

Effect of geopolymer concrete cover on improving tensile and transverse shear behaviors of BFRP bars after exposure to high temperature

The integration of high-temperature resistant geopolymer concrete, reinforced with basalt fiber reinforced polymer (BFRP), addresses several challenges encountered by conventional reinforced concrete structures, such as elevated energy consumption, substantial carbon emissions, and susceptibility to steel corrosion. To investigate the impact of geopolymer concrete cover on the mechanical performance of BFRP bars after high temperature treatment, this study conducted mechanical tests on a total 406 tensile specimens and 406 transverse shear specimens, spanning a temperature range from ambient temperature to 700 °C. The BFRP bars with diameters of 6 mm, 12 mm, and 16 mm underwent heat treatment durations of 0 h, 1 h, 2 h, and 3 h. Subsequently, they were examined for mass loss rat, residual tensile properties, and residual shear strength following natural cooling. Notably, this study also compared the impact of different geopolymer concrete cover thickness (30 mm, 40 mm, and 50 mm) on these performance parameters. The test results revealed that with an increase in heating temperature, the resin of BFRP experienced decomposition, leading to alterations in surface morphology, as well as changes in tensile and shear failure modes. In the temperature range of 400 °C to 700 °C, bare BFRP bars exhibited a significant decrease in both tensile and transverse shear strengths, with strength loss rates ranging from 50% to 90%. Moreover, the degradation in shear strength was comparatively slower than that in tensile strength. The presence of geopolymer concrete cover effectively mitigated the strength degradation of BFRP bars following high temperature treatment, and this protective effect improved with an increase in the concrete cover thickness. Additionally, scanning electron microscope (SEM) analysis was employed to elucidate the damage mechanisms for both bare and geopolymer concrete-covered BFRP bars. SEM results indicated that the deterioration induced by high temperature treatment gradually propagated radially from the edge to the core area of the bar. Finally, a simplified calculation model was adopted to evaluate the residual tensile strengths of BFRP bars wrapped in geopolymer concrete after high temperature treatment.

Fracture behaviour of Sn-58Bi alloy reinforced by activated bamboo charcoal

Sn-Bi solders are considered by PV manufacturers as acceptable Pb-free alternative due to its low operating temperature and cost, despite being prone to brittleness caused by coarse Bi phases. Bamboo charcoal (BC) is a sustainable and environment-friendly resource with high surface area and its addition to Sn-Bi solder meets the requirement of a green solder, in line with environmental regulations. This study aims to improve the shear strength and reduce brittleness of the Sn-Bi solder alloy by using a sustainable reinforcement, the activated bamboo charcoal. Sn-58Bi solder paste was reinforced with 0.25, 0.50, 0.75 and 1.00 wt.% of activated BC, respectively and reflowed to create a single lap shear joint. Aging response was determined through accelerated aging at 120 °C for 7 days and 14 days. Shear strength of the joints increased as the activated BC content increased in the as-reflowed condition and there was lower degradation in shear strength for heat-aging specimens compared to pure Sn-Bi solder. No failures occurred via Mode 3 when the as-reflowed samples contained 0.50 wt.% or more of activated BC, and the 7- and 14-day heat-aged samples were free from Mode 3 failures when the activated BC composition was at 0.75 wt.% and above. Fracture surfaces showed transitions from flat and smooth surface to elongated-dimple structures even with just 0.25 wt.% of activated BC addition. While prolonged heat-aging increased cleavage presence, increasing amounts of activated BC reduced facet numbers and dimple sizes, indicating successful suppression of Bi phase segregation.

Asphalt pavement pothole repair with recycled material and preheating: Laboratory and field evaluation

Asphalt pavement pothole repair with hot-mix asphalt (HMA) is one of common maintenance activities for transportation agencies, which requires considerable energy use and generates greenhouse gas emission (GHG) for production of HMA. This study investigated mechanical performance and environmental impact of an innovative pothole repair method using recycled asphalt pavement (RAP) and preheating. According to the common failure modes of asphalt patch, comprehensive laboratory tests were conducted on the lab-made and field-cored specimens, including indirect (IDT) strength, interface bonding strength, and abrasion resistance at dry, freeze-thaw, and pore pressure conditions. Based on laboratory testing results of the HMA with 0%–50% RAP contents, HMA with 30% RAP was selected for pothole repair in the field test section because it can lead to satisfactory moisture resistance and comparable interface bonding and abrasion resistance with traditional HMA. After repair, field cores were collected for additional laboratory analysis. The results show that moisture resistance of the patching materials decreased with the increase of RAP content. The freezing thaw (FT) effect was found to cause more degradation in IDT and interface shear strength than dynamic pore water pressure simulated in moisture induced stress tester (MIST), while the pore water pressure caused more abrasion loss of patching material. On the other hand, preheating the pothole before repair was found to be effective in enhancing mechanical performance and durability of asphalt patch under various environmental conditions. With the application of preheating, asphalt patching repaired by HMA with 30% RAP can achieve comparable or better performance than that made with traditional HMA, while reducing energy consumption and carbon emission.

An exponential strength degradation model for clay: From mathematical model to numerical application

Investigation in strain-softening behavior of clay is of great significance for offshore geotechnical engineering. Although several models could be used to characterize the degradation of undrained shear strength of clay with cumulative shear strain, it is necessary to improve accuracy of them. In this study, based on full-flow cyclic penetration test, an exponential strength degradation model with one parameter α is proposed, where α is the function of the fully remolded resistance factor and the ratio of initial extraction to initial penetration resistance. The reliability of the proposed model is verified by comparing indices (strength and sensitivity) calculated by it and by other existing strain-softening models. In addition, a large deformation finite element (LDFE) analysis based on the proposed model is conducted for pipe-clay interaction, and efficiency of the model is verified by comparing numerical results with centrifuge test results. The influence of α on the normalized penetration resistance were discussed, and demonstrate the necessity of accurately evaluating degradation of undrained shear strength of clay.

Macroscopic and Microscopic Characteristics of Strength Degradation of Silty Soil Improved by Regenerated Polyester Fibers under Dry-Wet Cycling.

The structural stability of silt foundations, particularly sensitive to moisture content, can be severely compromised by recurring wetting and drying processes. This not only threatens the foundational integrity but also raises grave concerns about the long-term safety of major civil engineering endeavors. Addressing this critical issue, our study delves into the transformative effects of reclaimed polyester fiber on subgrade silt exposed to such environmental stressors. Through rigorous wet-dry cycle tests on this enhanced soil, we evaluate shifts in shear strength across varying confining pressures. We also dissect the interplay between average pore diameter, particle distribution, and morphology in influencing the soil's microstructural responses to these cycles. A detailed analysis traces the structural damage timeline in the treated soil, elucidating the intertwined micro-macro dynamics driving strength reduction. Key discoveries indicate a notably non-linear trajectory of shear strength degradation, marked by distinct phases of rapid, subdued, and stabilized strength attrition. Alterations within the micropores induce a rise in both their count and size, ultimately diminishing the total volume proportion of the reinforced soil. Intriguingly, particle distribution is directly tied to the wet-dry cycle frequency, while the fractal dimension of soil particles consistently wanes. This research identifies cement hydrolysis and pore expansion as the dominant culprits behind the observed macroscopic strength degradation due to incessant wet-dry cycles. These revelations hold profound implications for risk management and infrastructural strategizing in areas dominated by silt foundations.

Shear strength degradation of gas hydrate-bearing sediment due to partial hydrate dissociation

Extraction of methane hydrate from subseafloor reservoir may potentially trigger seabed slides and induce subsidence. To address the problems, it is crucial to properly characterize the phase equilibrium condition of pore hydrate and the shear strength of the soil. As one of the key constitutive components, the phase equilibrium condition enforces a constraint over pore gas pressure, temperature and unhydrated water content. Such a constraint, however, has been traditionally ignored in analyzing the mechanical behavior of hydrate-bearing soil. In this paper, a series of stepwise hydrate dissociation tests was performed, and the phase equilibrium condition of pore hydrate was determined, providing an effective way to evaluate the unhydrated water content during hydrate dissociation. Meanwhile, a series of direct shear tests was also conducted to explore the shear strength characteristics of the soil. It is shown that the shear strength of the hydrate-bearing soil can be significantly influenced by pore gas pressure, unhydrated water content, hydrate saturation and several other factors. In particular, the measured shear strength depends upon the initial water content of the sample, pointing to a potential problem that the shear strength could be wrongly determined if not properly interpreted. A shear strength criterion, which enforces the equilibrium condition of pore hydrate, is developed for hydrate-bearing soil, establishing a link between the equilibrium condition and the shear strength. The proposed equation describes well the shear strength characteristics of hydrate-bearing soils, remarkably unifying the effects of pore pressure, temperature, water content and hydrate saturation.

Current-induced solder evolution and mechanical property of Sn-3.0Ag-0.5Cu solder joints under thermal shock condition

Solder joint reliability suffers great challenges due to high current density and miniature solder bump diameter of electronic packages at cryogenic temperature. To tackle these issues, the solder microstructure evolution and the corresponding failure mechanism should be emphasized. In this study, the current-induced microstructure characteristics and mechanical behavior of Sn-3.0Ag-0.5Cu (SAC305) solder joints during thermal shock process was thoroughly addressed over cycles by combining diffusional, electrical, thermal and mechanical features. This result verified that the combining method of thermal shock and electromigration (EM) contributed to the atom diffusion and high thermal stress formation, further causing intermetallic compound (IMC) growth, the repaid dissolution of Cu pad and high thermal stress of the solder joints. High stress induced by either the thermal expansion mismatch of different component, large temperature change (ΔT =346 ℃) and severe lattice distortion became the direct reason for twins and cracks formation of SAC305 solder joints. The combination of crack propagated along the interface and the quick dissolution of Cu substrate at the corner accelerated the eventually failure of the solder joints. Moreover, as the thermal chock cycles was extended, the initiation and propagation of cracks at the cathode side weaken the cathodic shear strength. High stress-induced twin formation at the interface effectively moderated the shear strength degradation due to anode IMC growth after 9 cycles. This study contributed to thoroughly grasp the failure mechanism of the solder joints and design the twin-strengthened Sn-based solder joints under the coupling effects of extreme temperature variation and current stressing.

Highly reliable micro-scale Cu sintered joint by oxidation-reduction bonding process under thermal cycling

Thermal cycling reliability of micro-scale Cu sintered joint by oxidation-reduction bonding (ORB) process for power module die attach was investigated. A robust bonding strength of Cu ORB joint over 40 MPa with the bonding temperature of 300 °C and applied pressure of 0.5 MPa was successfully achieved. After thermal cycling, there is no evidence of significant crack propagation or delamination at the Cu sintered layer, resulting in no shear strength degradation up to 1000 cycles. The highly reliable Cu sintered joint by ORB can be achieved, as a result, Cu ORB process can be promising technique for power module die attach process.

Shear Strength of Loess in the Yili Region and Corresponding Degradation Mechanisms under Different Cycling Modes

In the Yili region, China, complex environmental conditions induce repeated wet–dry (WD) and freeze–thaw (FT) cycles, deteriorating soil shear strength and producing frequent loess landslides. In this study, we collected soil samples from the Alemale landslide, Yili Prefecture and performed their triaxial shear tests with different numbers of WD, FT, and WD-FT cycles. In addition, we summarized the change mechanisms of loess mechanical properties and its deterioration, in the Yili region, under different cyclic effects. Subsequently, the test results under the three cycling modes were compared and analyzed, the differences in the deterioration effects of different cyclic conditions on loess were discussed in depth, and finally, a multiple linear regression model was established and the weights of single factors under the action of coupled cycles were analyzed. The results show the following: (1) Regardless of the confining pressure values, the principal stress evolution trends in soil samples under different cycling modes were generally consistent, i.e., after an initial increase, peak values were reached, followed by a final decline. (2) Under unconsolidated undrained (UU) conditions, shear strength values of all soil samples tested under the three cycling modes dropped after the first twenty cycles, exhibiting different evolution patterns. (3) Coupled WD-FT cycling most significantly promoted soil shear strength degradation, with less WD cycling effect, and FT cycling had the least significant effect; in all three modes, the first cycle had the highest contribution to this effect. From the perspectives of cohesion, angle of internal friction, and decay of shear strength attenuation, the coupled WD-FT cycling effect on soil shear strength could not be reduced to a simple single-factor addition–subtraction relationship. (4) Weight analysis of soil samples after WD, FT, and WD-FT cycling revealed that WD cycles in the coupled WD-FT cycling mode had the most significant impact on the shear strength attenuation of soil samples (contributing 57%), FT cycles had a medium impact (contributing about 33%), while the effect of the total number of cycles was negligible (about 10%). The research results provide experimental and theoretical bases for subsequent control of loess landslides.

An experimental and numerical study on the coupling effect of CLT wall-to-floor angle bracket connections

Cross-laminated timber (CLT) wall panels are commonly connected to the floor or foundation using metal connections, which play a critical role in determining the seismic performance and energy dissipation of the CLT shear walls. In this study, to comprehend the tension–shear coupling effect of the CLT wall-to-floor angle bracket connections under seismic loads, both monotonic and cyclic shear tests were conducted on the angle brackets that were also simultaneously applied with different levels of prescribed vertical axial tension. The influence of the co-existent axial tension on the horizontal shear performance of the angle brackets was analyzed. Furthermore, a numerical model of the angle brackets was developed and validated with the experimental results, which could predict the tension–shear coupling effect based on the monotonic loading scenario. Based on the numerical model, parametric analysis was conducted, and an analytical tension–shear interaction diagram representing the coupling effect of the angle brackets under seismic loads was established. It is found that with an increase of the axial tension from 0 to 30 kN, the shear resisting capacity of the angle brackets is diminished by 33.29%, and the pinching effect of their hysteretic load–displacement curves is mitigated. When the number of the connection-to-floor screws of the angle brackets was increased from 10 to 14, the shear resisting capacity of the angle brackets can be enhanced by 6.43%, and their shear strength degradation can be relieved by 12.85–56.25%. For the CLT wall-to-floor angle brackets, the analytical interaction diagram can be described using one bilinear function, which consists of the ratio between the shear to the shear resistance and the ratio between the tension to the pull-out resistance.

Shear performance degradation of basalt fiber‐reinforced polymer bars in seawater environments: Coupled effects of seawater sea‐sand geopolymer mortar coatings and sustained loading

AbstractGeopolymers, as a promising substitute for ordinary cement, exhibit different coating effects with regard to the durability of basalt fiber‐reinforced polymer (BFRP) bars. In this study, a comparative investigation was carried out on the shear performance of prestressed BFRP bars coated with seawater sea‐sand geopolymer mortar (SSGM). The alkaline content of the SSGM was 4% or 6%. The prestress level was 20% of the ultimate tensile strength at room temperature. The immersion temperatures were room temperature (RT), 40, or 60°C. Interlaminar shear tests and transverse shear tests were conducted at each period (30, 60, 120, and 240 days). The results showed that BFRP bar coated with 6% alkaline content exhibited a slightly higher degradation of shear strength. Furthermore, the prestress developed microcracks in the bars and weakened the interface between the fiber and resin matrix, particular at the elevated temperature. This led to further degradation of the BFRP bars. Additionally, a comparison was made between the shear strength results of BFRP bars coated with SSGM and those coated with ordinary portland concrete or seawater sea‐sand concrete, revealing that the long‐term shear performance of BFRP bars was less negatively impacted by the SSGM coating.Highlights Coupled effects of SSGM coatings and sustained loading on the degradation of BFRP bars are investigated. SSGM provides better protection for BFRP bars than cement‐base concrete. Alkaline content of activator in SSGM has insignificant impact on the BFRP degradation.