Environmental Reduction Factor Research Articles

An evaluation of mechanical properties and estimation of environmental reduction factors in welded API X70 steel pipeline in natural seawater

Due to the detrimental effect of damage induced by seawater in pipeline structures, there is a need to investigate the effects of natural seawater and air environments on mechanical properties of representative pipeline materials, to obtain useful data for estimation of their service lives. Hence, in this work, a X70 steel pipeline plate was welded using submerged arc welding technique; and subjected to air and natural seawater environments. Test specimens were soaked in seawater for twelve months at 28 °C. The parent plates, weld regions and the heat affected zones were investigated by evaluating their mechanical properties and fracture surfaces. The experimental findings revealed that the tensile strengths of parent and weld were 634.00 MPa and 674.00 MPa respectively, while the compressive stresses were 750.10 MPa and 750.40 MPa respectively with highest hardness value of 239HV. The findings also revealed that weld area and heat affected zone depend on material thickness, heat input and possible effect of residual stresses in the weldment. The fracture surfaces of test specimens showed combination of brittle and ductile failure mechanisms. Comparison of the test results revealed that seawater had significant effect on the mechanical properties and surface morphology of the API X70 steel pipeline with respect to immersion time.

Prediction of the Long-Term Tensile Strength of GFRP Bars in Concrete

The durability of two types of widely used glass fiber reinforced polymer (GFRP) bars, one without coating (G1) and one with slightly surface sand-coating (G2), were studied through accelerated aging. Concrete cylinders reinforced with GFRP bars were immersed in tap water in temperature-controlled tanks. The influence of different exposure temperatures, 20, 40, and 60 °C, and also different exposure times, 30, 60, 90, 120, and 180 days, on the degradation of the two types of GFRP bars was investigated. The tensile strengths of GFRP bars after different exposure times were evaluated with tensile tests, and the variation of the microstructure and elemental compositions of conditioned specimens was evaluated with scanning electron microscopy (SEM) images and energy dispersive X-ray spectroscopy (EDS), respectively. The degradation rate of the tensile strength retentions of two types of GFRP bars decreased with an increase in the exposure time at all exposure temperatures. The tensile strength retentions of the GFRP bars were studied by three commonly used prediction models. Based on the degradation mechanism of fiber-matrix debonding, a new model was proposed. These four models were evaluated with the test results and a new model proposed was suggested as the best model to predict the residual tensile strength of the GFRP bars. The durability parameters of the GFRP bars were discussed. The tensile strength retention tended to converge to a constant value (52%) with the increase of exposure time, which contributes to the determination of the environmental reduction factor in relevant design guides, and the fiber-matrix debonding was found to be the main degradation mechanism due to the surrounding concrete environment. The sand-coating had some effect on the activation energy of the GFRP bars.

Durability of FRP bars and FRP bar reinforced seawater sea sand concrete structures in marine environments

• Combination of the alkaline and marine environments aggravates the degradation of mechanical properties of FRP bars. • The variability of mechanical properties of FRP bars shows an increasing trend. • Bearing capacities of FRP bar reinforced SSC components decrease and the failure mode changes. • Environmental reduction factors in current codes are conservative. Fiber reinforced polymer (FRP) is one of the alternatives to steel, and can be directly used in seawater sea sand concrete (SSC). But FRP material still has durability problems in corrosive environments, which is one of the hot and difficult issues of current research. Based on the existing literature, this paper combs the degradation of the long-term property of FRP bars and the durability of FRP bar reinforced SSC (FRP-SSC) structures in the marine environment. The combination of the alkaline environment of concrete and the salt ions in sea sand and seawater aggravates the dissolution of the resin and debonding of the fiber-resin interface of FRP bars (particularly for BFRP bars). Therefore, the mechanical properties of FRP bars degrade with high variability which leads to the reduction of bonding between SSC and FRP bars. Additionally, the bearing capacity of FRP bar/steel-FRP composite bar (SFCB) reinforced SSC components in marine environments decreases, and the failure mode of components changes. The current codes use environmental reduction factors in the durability design of FRP bar reinforced concrete structures. But the values of reduction factors are conservative. Finally, it is pointed out that the quantification of variability for the mechanical property of FRP bars after long-term service, and the time-dependent reliability-based design methods of components are needed for further studies.

Hybrid ANN models for durability of GFRP rebars in alkaline concrete environment using three swarm-based optimization algorithms

• Hybrid ANN models for estimating the durability of GFRP rebars in alkaline environment. • ANN-GWO was selected for calculating environmental reduction factor based on higher accuracy. • The rate of degradation in GFRP rebars changes with change in temperature. • Guidelines regarding environmental reduction factor to reflect long-term durability of GFRP rebars. This study investigates the non-linearity of GFRP degradation in terms of tensile strength retention (TSR) encompassing five input variables (i.e., diameter of GFRP rebar, volume fraction of fibers, pH of surrounding solution, temperature of surrounding solution, and duration of conditioning). Additionally, the degradation models were extrapolated to calculate environmental reduction factor (C E ). Based on high non-linear capabilities of artificial neural network (ANN) models, hybrid ANN models were created by deploying particle swarm optimization (PSO), grey wolf optimization (GWO) and marine predators algorithm (MPA) to predict the TSR of GFRP rebars conditioned at variable temperatures and durations. Trial and error procedure was adopted to select the optimal hyperparameter of the hybrid models. The developed models were subjected to statistical, accuracy, sensitivity and uncertainty analyses. ANN-GWO model yielded the highest correlation (R ≈ 0.89 and 0.88, MAE = 0.0558 % and 0.0914 %, and RMSE = 7.86 % and 11.67 %) for the training and testing datasets, respectively. Furthermore, Taylor diagram and accuracy matrix revealed that the performance of the models followed the order; ANN-GWO (R overall = 0.885) > ANN-PSO (R overall = 0.806) > ANN-MPA (R overall = 0.821). For GFRP rebars, made of E-glass fibers (volume fraction = 0.62) impregnated in vinyl ester resin conditioned at 28 °C with surrounding pH of 13, the values of C E for bar sizes 9.5 mm, 12.7 mm and 15.9 mm were recorded as 0.75, 0.87 and 0.95, respectively. It is highly recommended to consider the effect of bar size as an important variable in the design of GFRP reinforced concrete structures and keep C E ≈ 0.75 at 28 °C in alkaline environment.

Probabilistic calibration of environmental reduction and partial safety factors for the design of reinforced concrete beams strengthened by flax fibre reinforced polymers based on two-factor accelerated degradation tests

The main topic of this article is the probabilistic-based calibration of environmental reduction and safety coefficients for the design of reinforced concrete civil engineering structures repaired or strengthened by externally bonded flax fibre reinforced polymers (FRP). In view of the poor feedback on the durability of flax fibre composite materials used in civil engineering and the impossibility of conducting performance tests over several years, a two-factor accelerated test campaign based on the stimulation of composite degradation by increasing both temperature and humidity conditions was conducted. Flax-FRP (with a bio-based epoxy matrix) laminates and Flax-FRP-strengthened concrete slabs have been exposed over a period of two years to various couplings of temperature (from 20 °C to 60 °C) and humidity (from 50 % of relative humidity to water immersion), according to an asymmetrical Hoke design of experiments. Similar specimens were also exposed to outdoor natural ageing (climate of Lyon, FR) over a period of three years. Series of tests (more than 320 tests) aimed at monitoring the evolution of the degradation of mechanical characteristics (tensile capacity, tensile stiffness, shear strength, pull-off strength) directly associated with the possible modes of failure of structural elements repaired by composites, were carried out on control and aged specimens. A degradation model of these mechanical characteristics considering the competition of two mechanisms - inducing non-monotonic degradation-, and the influence of the temperature and the humidity - through the Eyring model -, was then developed and finally extended to consider the variability of the degradation under different climatic zones. On this basis, a reliability-based approach was adopted to propose environmental reduction and safety coefficients calibrated for Flax-FRP found within four international design guides (Fib bulletin 40, ACI-440, AFGC and TR55 guides). Finally, we showed the necessity to provide adaptable coefficients according to the climatic conditions in which the Flax-FRP elements will be installed.

Durability and Long-Term Performance Prediction of Carbon Fiber Reinforced Polymer Laminates.

The feasibility of strengthening deteriorated or under-capacity concrete structures with external carbon-fiber-reinforced polymer (CFRP) laminates has been widely validated in the literature. However, there is a lack of knowledge on the in situ long-term performance and age-related environmental degradation of the mechanical properties of the laminates. The current study involved the immersion of coupons from a common new CFRP laminate in heated water at 23, 45, and 60 °C for 224 days. The coupons were then tested for residual tensile properties, such as tensile capacity and elastic modulus, using ASTM D3039 (2017) specifications. The CFRP tensile capacity and elastic modulus decreased by a maximum of 33% and 26%, respectively, for 224 days of exposure. Based on the test data, an age-based long-term prediction model with excellent reliability for CFRP laminate tensile capacity was developed. The model was then calibrated with test results from old CFRP coupons collected from an existing CFRP laminate retrofitted concrete bridge. The calibrated model output was then compared with the environmental reduction factor from ACI 440.2R-17 and a few other common sources. It was found that the ACI specified a reduction factor of 0.75, which does not consider the CFRP age and overestimates the design tensile strength of the CFRP laminate by approximately 13%, which may compromise the structural safety of retrofitted bridges. The reduction factors from the other guidelines varied between 0.51 and 0.85.

Uniaxial Compression Behavior of Short Square and Circular RC Piles Constructed with GFRP Bars and Spirals Preconditioned in Simulated Marine Environments

The current experimental investigation assessed the durability of reinforced concrete (RC) piles with glass fiber-reinforced polymer (GFRP) bars and spirals exposed to simulated marine environments. A total of 18 specimens—9 square (300 mm in cross section) and 9 circular (304 mm in diameter)—and short RC piles were prepared and tested under uniaxial compression. For each pile geometry, three specimens were reinforced with pristine GFRP bars as reference piles. The other six piles were reinforced with GFRP bars that had been exposed to marine environments at subtropical regions (22°C) or accelerated aging temperature (60°C) for 12 months, three specimens for each environment. Mechanical property and microstructural analysis tests were carried out to characterize the conditioned/aged GFRP bars. The GFRP-RC piles conditioned at 60°C exhibited similar behavior to their reference counterparts. The current environmental reduction factors for GFRP reinforcing bars stipulated in design codes and guidelines are conservative. A more accurate design equation to calculate the axial capacity of piles should consider the contribution of longitudinal GFRP bars even when exposed to marine environments.

Prediction of residual tensile strength of glass fiber reinforced polymer bars in harsh alkaline concrete environment using fuzzy metaheuristic models

The long-term durability of glass fiber reinforced polymer (GFRP) bars in harsh alkaline environments is of great importance in engineering, which is reflected by the environmental reduction factor in various structural codes. The calculation of this factor requires robust models to predict the residual tensile strength of GFRP bars. Therefore, three robust metaheuristic algorithms, namely particle swarm optimization (PSO), genetic algorithm (GA), and support vector machine (SVM), were deployed in this study for achieving the best hyperparameters in the adaptive neuro-fuzzy inference system (ANFIS) in order to obtain more accurate prediction model. Various optimized models were developed to predict the tensile strength retention (TSR) of degraded GFRP rebars in typical alkaline environments (e.g., seawater sea sand concrete (SWSSC) environment in this study). The study also proposed more reliable model to predict the TSR of GFRP bars exposed to alkaline environmental conditions under accelerating laboratory aging. A total number of 715 experimental laboratory samples were collected in a form of extensive database to be trained. K-fold cross-validation was used to assess the reliability of the developed models by dividing the dataset into five equal folds. In order to analyze the efficiency of the metaheuristic algorithms, multiple statistical tests were performed. It was concluded that the ANFIS-SVM-based model is robust and accurate in predicting the TSR of conditioned GFRP bars. In the meantime, the ANFIS-PSO model also yielded reasonable results concerning the prediction of the tensile strength of GFRP bars in alkaline concrete environment. The sensitivity analysis revealed GFRP bar size, volume fraction of fibers, and pH of solution were the most influential parameters of TSR.

Durability evaluation of GFRP rebars in harsh alkaline environment using optimized tree-based random forest model

GFRP bars reinforced in submerged or moist seawater and ocean concrete is subjected to highly alkaline conditions. While investigating the durability of GFRP bars in alkaline environment, the effect of surrounding temperature and conditioning duration on tensile strength retention (TSR) of GFRP bars is well investigated with laboratory aging of GFRP bars. However, the role of variable bar size and volume fraction of fiber have been poorly investigated. Additionally, various structural codes recommend the use of an additional environmental reduction factor to accurately reflect the long-term performance of GFRP bars in harsh environments. This study presents the development of Random Forest (RF) regression model to predict the TSR of laboratory conditioned bars in alkaline environment based on a reliable database comprising 772 tested specimens. RF model was optimized, trained, and validated using variety of statistical checks available in the literature. The developed RF model was used for the sensitivity and parametric analysis. Moreover, the formulated RF model was used for studying the long-term performance of GFRP rebars in the alkaline concrete environment. The sensitivity analysis exhibited that temperature and pH are among the most influential attributes in TSR, followed by volume fraction of fibers, duration of conditioning, and diameter of the bars, respectively. The bars with larger diameter and high-volume fraction of fibers are less susceptible to degradation in contrast to the small diameter bars and relatively low fiber's volume fraction. Also, the long-term performance revealed that the existing recommendations by various codes regarding environmental reduction factors are conservative and therefore needs revision accordingly.

Environmental reduction factors of BFRP bars in coral aggregate concrete in high temperature and high humidity environments

Fiber Reinforced Polymer (FRP) bar-reinforced coral aggregate concrete (CAC) structures are a new solution to help alleviate the shortage of construction materials on islands far from the mainland and the insufficient durability of steel-reinforced concrete components. The long-term tensile strength of FRP bar embedded in CAC in high temperature and humidity marine environments is still uncertain due to the differences between environmental factors and results in laboratories and the field. In this paper, a new approach that considers the effects of relative humidity, external environment temperature, and design life was proposed to obtain environmental reduction factors for FRP bars. In this approach, laboratory results and field environmental parameters were combined to predict the service life of FRP bars in a real environment. The residual tensile strength of BRFP bars in CAC at high temperatures and high humidity in a marine environment was evaluated by accelerated testing. The environmental reduction factors of the BRFP bars were predicted using temperature and humidity data that were collected over one year. The CE values of the BFRP bars in CAC were predicted to be 0.77, 0.75, and 0.73 for 50, 100, and 200 years of service, respectively, in high temperature and high humidity environments.

Bond assessment of two types of SRP strengthening systems subjected to severe conditions

Using composite materials to retrofit structures has expanded quickly the last few years due to its applicability and economic feasibility. For most of these systems including the new ones, their mechanical properties have been investigated extensively, but their durability bond performance still has not. Therefore, due to the lack of data regarding the long term performance, it is has been hard on the construction industry to implement these systems. Thus, to enrich the construction and design standards with bond durability information, an investigation was carried out at Missouri University of Science and Technology, Rolla, Missouri, USA to study the bond durability of Steel Reinforced Polymer (SRP) strengthening system. Two types of SRP systems were applied including: micro-fine galvanized (RG) and micro-fine brass coating (RNG) steel fibers where both of them were exposed to several harsh conditions. The conditions used in this study included tap water submersion for 3000 h, hot water submersion for 4000 h at 50 °C (122° F), and salt water submersion for 1500 and 4000 h. Additionally, other specimens were made and placed outside for real-time weather exposure. The real-time weather exposure included subjecting the specimens to temperature and humidity fluctuations, freeze–thaw cycles, and ultraviolet (UV) radiation from the sun. Upon completion the desired exposure duration, all the specimens were tested for bending using a three-point load fixture to evaluate the bond performance of the strengthening system. All the results were then compared with control specimens to obtain a better evaluation of their bond performance. Furthermore, tensile coupon tests were made as well to enhance the mechanical evaluation. The results showed that there was a substantial decrease in bond strength resulted from the water immersion. In addition to the water influence, temperature also negatively affected the durability of bond strength. On the other hand, salt presence did not affect the bond strength. Based on the performance of the strengthening system, an environmental reduction factor, CE, of 0.75 was proposed for wet environment and 0.65 for harsh environment.

Durability of reinforced concrete beams strengthened by galvanized steel mesh-epoxy systems under harsh environmental conditions

Strengthening and rehabilitation of reinforced concrete (RC) structural elements are being efficiently carried out by fiber-reinforced polymer (FRP) composite materials. However, their long-term durability is still causing concerns for the repairing industry. Recently, the use of steel wire mesh-epoxy systems for strengthening is gaining the attention of researchers and engineers and their long-term durability warrants investigation. This paper presents the results of an extensive experimental study carried out on 60 RC beams strengthened in flexure by medium and high cord density galvanized steel mesh (MSM, HSM). In order to evaluate the durability of these strengthening systems, the RC beams were exposed to direct sunlight and immersed under saline water for 6, 12, and 24 months. The beams were tested under four-point bending till failure after each exposure period. The MSM and HSM strengthened beams showed up to 51 and 62% higher load-carrying capacity than that of the control beams at 28 days, respectively, and up to 82% after two years of sun and saline water exposure. Furthermore, the exposed beams showed significant delay in crack initiation, no pronounced degradation in strength or stiffness, and no delamination of epoxy. On the contrary, there was significant improvement in the strength of the exposed beams, especially that of the MSM. Based on ACI 440.2R-17 Guidelines, environmental reduction factors were proposed for the exposed beams. This study showed that galvanized MSM and HSM laminates could be promising and durable alternative materials for rehabilitation, retrofitting, and strengthening of RC members under harsh climatic conditions of elevated temperature, high salinity, and high humidity.

A performance-based characterisation of CFRP composite deterioration using active infrared thermography

This study explores the effect of sulphuric acid (H2SO4) on the physical and mechanical properties of carbon fibre-reinforced polymer (CFRP) and its constituent elements including epoxy resin and fibrous reinforcement. Specimens are exposed to decreasing pH levels through an accelerated aging regime and subsequently tested by mechanical and non-destructive methods. Active infrared thermography is applied to develop a quantitative framework for material degradation. The effect of acid exposure is subsequently assessed through a performance criterion based on thermal energy variation. Microscopic analyses through scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) reveal the material degradation and impact of acid at the fibre-epoxy interface. Tensile testing on FRP and epoxy resin coupons indicate up to 25% reduction in strength. An acid attack model is developed for the environmental reduction factor (CE) that is shown to compare well with experimental data. The performance-based environmental reduction factor presented expands our understanding of the FRP material response to aggressive environments and its effectiveness during the in-service life of structure.

Bond evaluation of SRP strengthening system exposed to several harsh environmental conditions

Bridge retrofitting is a billion-dollar industry. Thus, finding effective and economically feasible solutions to strengthen bridges that deteriorate to extend service life until replacement is feasible is a critical global need. There are several types of fiber reinforced polymers (FRP) based repair systems available now commercially to strengthen bridge members including systems that utilize carbon, glass, and now even steel fibers. The latter is a system most often referred to as steel reinforced polymer (SRP) and is considered fairly new to the bridge industry; yet a very promising system due to its close-to-carbon fiber strength, and close-to-glass fiber price. One current research gap for SRP has been the performance of this system relative to exposure to environmental conditioning and its overall durability resilience. In this work, the SRP strengthening system used both micro-fine galvanized and micro-fine brass coated steel fibers to externally reinforce concrete prisms using the recently published American Concrete Institute (ACI) 440.9R-15 approach to evaluate FRP bond behavior. Companion dog-bone style coupon specimens were also prepared using both SRP systems to examine tensile mechanical properties of the SRP system alone. Both types of specimens were exposed to several types of harsh environments including cycles of freeze-thaw, varying temperature, and cycles of humidity. The study investigated accelerated environmental exposure in an environmental chamber as well as direct real-time weather exposure. The environmental chamber involved subjecting the specimens to freeze-thaw cycles, cycles of varying temperature, and humidity cycles. For the real-time weather exposure, the specimens were exposed to daily weather for 12 months in Rolla, Missouri, USA where the city is moderately exposed to freeze-thaw, high-range of temperature fluctuation, and wide ranging humidity levels. The results of the flexural tests conducted indicated that the bond strength between the SRP and concrete interface was reduced by harsh environment. All conditioned specimens had a mode II or mode III bond failure, while the control specimens failed in mode I. Real-time weather specimens failed at lower deformation levels with less concrete-covered substrate than those conditioned in the environmental chamber. An ACI 440 style environmental reduction factor, CE, of 0.75 is suggested for wet-environment and 0.65 for highly aggressive environment based on the work undertaken in the overall study.

Influence of long-term outdoor exposure in a frigid zone on the CFRP-to-concrete bond behavior

The bond strength between a carbon-fiber-reinforced polymer (CFRP) plate or sheet and concrete is susceptible to harsh field environments and plays a key role in the strengthening function of CFRP in the externally bonded strengthening technology. In the present study, the influence of outdoor exposure in northeast China, a frigid zone, on the bond behavior between pultruded CFRP plate and concrete block was investigated using a single-lap shear test. The test results indicated that the exposure caused a change in the cohesive failure of concrete to debonding between the concrete and adhesive, similar to water immersion. The fracture energy, maximum shear bond stress and load capacity of the CFRP-concrete bond joint decreased with the exposure time. An environmental reduction factor was proposed to account for the degradation of the CFRP–concrete bond for the investigated exposure.

Theory-based approaches and microstructural analysis to evaluate the service life-retention of stressed carbon fiber composite strands for concrete bridge applications

Prestressed concrete girders and piles with steel strands are used in construction of bridges in North America, due to their economy of design, fabrication, and installation. However, they are often exposed to harsh environments, which results in rapid degradation. Therefore, carbon fiber reinforced polymer (CFRP) tendons have successfully been introduced as prestressing reinforcement for pile applications. This paper presents a study on the physical characterization, microstructural analysis, and durability performance of unstressed and stressed carbon-fiber composite cables (CFCCs) for prestressing applications. This is achieved through testing 120 CFCC specimens, subjected to stress levels of about 40% and 65% of their guaranteed strength, and 51 specimens without sustained load under tension. Moreover, prediction models were introduced to assess the long-term performance and retentions of CFCC strands. The models included Arrhenius model, Fick's law, Fib Bulletin (40) model, and a developed approach that incorporates the effects of temperature, design life, and relative humidity of exposure into the environmental reduction factor. Based on the predication model, the tensile strength retention (CE) for CFCC strands, is predicted to retain over 0.95 and 0.84 of ultimate tensile strength for a relative humidity (RH) < 90% and a moisture saturated environment (RH = 100%), respectively, after 100 years of service life with elevated temperature and sustained load.

Statistical analysis and theoretical predictions of the tensile-strength retention of glass fiber-reinforced polymer bars based on resin type

This paper presents experimental investigation, statistical analysis, and theoretical predictions of tensile-strength retention of glass fiber-reinforced polymer bars, made with vinyl-ester, polyester, or epoxy resins. The durability of glass fiber-reinforced polymer bars was evaluated as a function of time of immersion in alkaline solution. The aging of the three glass fiber-reinforced polymer bar types consisted of immersion glass fiber-reinforced polymer bar samples in an alkaline solution (up to 5000 h) at different elevated exposure temperatures. Subsequently, the physical and tensile properties of the unconditioned bars were compared with that of the conditioned bars to assess the durability performance of the glass fiber-reinforced polymer bars. Microstructure of all of the glass fiber-reinforced polymer bar types was investigated with scanning electron microscopy, energy dispersive spectroscopy, and Fourier transform infrared spectroscopy for both the conditioned and unconditioned cases, to qualitatively explain the experimental results and to assess changes and/or degradation in the glass fiber-reinforced polymer bars. In addition, the long-term performance of glass fiber-reinforced polymer bars was assessed considering the effect of service years, environmental humidity, and seasonal temperature fluctuations. The test results showed that the tensile strength of the glass fiber-reinforced polymer bars was affected by increased immersion time at higher temperatures and the reduction in tensile strength was statistically significantly dependent on the type of resin system. The prediction approach of the glass fiber-reinforced polymer bars based on the environmental reduction factor ( CE) after 200 years indicated that the CEvalues for vinyl-ester, epoxy, and polyester glass fiber-reinforced polymer bars can be conservatively recommended to 0.81, 0.75, and 0.71, respectively, for a moisture-saturated environment (relative humidity = 100%) and at 30℃. The polyester glass fiber-reinforced polymer bars experienced greater debonding at the fiber–resin interface than the vinyl-ester and epoxy glass fiber-reinforced polymer bars.

Effect of the environment on the performance of GFRP reinforcing bars

Abstract Fiber reinforced Polymer (FRP) composites are currently employed in the civil engineering industry as externally bonded reinforcement (EBR) of existing reinforced concrete (RC) and masonry structures and as internal reinforcement of concrete elements as an alternative to steel reinforcing bars. Carbon FRP (CFRP) composites are mainly used for EBR applications whereas glass FRP (GFRP) bars are employed as internal reinforcement of concrete elements. This paper sheds light into the effect of different aggressive environments on the tensile behavior of reinforcing GFRP bars. 356 results of tensile tests of GFRP bars subjected to hot dry and humid air, different alkali environments, salt solutions with various concentrations, and plain and distillated water were collected from the literature. According to the “design by testing” procedure provided by EN 1990, a statistical analysis of the results was carried out to calibrate environmental reduction factors able to provide reliable estimations of the long-term behavior of GFRP bars subjected to different exposure conditions. For a given aggressive environment, a clear and unique degradation trend could not be identified, which points out the need of a standard testing procedure able to provide reliable and repeatable results.

Effects of hydrothermal aging on carbon fibre/epoxy composites with different interfacial bonding strength

This paper presents an investigation on the effects of hydrothermal aging on carbon fibre reinforced polymer (CFRP) composites with different interfacial bonding strength. The combination of electrochemical oxidation and sizing treatments effectively enhanced the long-term interlaminar shear strength (ILSS) retention from 0.24–0.38 to 0.74–0.86 for CFRP in hydrothermal environment, which basically met the specified environmental reduction factor CE (0.85) given in ACI 440.2R-08. The improved durability of fibre/epoxy interface was also evidenced by the moisture absorption and desorption tests and scanning electron microscopy (SEM). In addition, the dynamic mechanical thermal analysis (DMTA) was directly used to characterize the degradation of interface adhesion for CFRP, and the damping at fibre/epoxy interface (tan δin) was evaluated and finally linked with the ILSS results.

A refined prediction method for the long-term performance of BFRP bars serviced in field environments

A new kind of advanced composite reinforcement, basalt fiber reinforced polymer (BFRP) bars, has not yet been widely adopted by design codes/guidelines worldwide, likely due to the lack of reliable long-term performance data. This paper proposed a refined prediction method for the long-term performance of BFRP bars that considers the effects of service year, concrete-wrap, environmental humidity and seasonal temperature fluctuations. According to the available accelerated aging tests data in the literature, the environmental reduction factors (ERFs) for a BFRP bar used as a concrete internal reinforcement in a field environment are predicted. The results showed that the ERF for BFRP bars can be recommended to be 0.84 or 0.72 for an RH<90% and a moisture saturated environment (RH=100%), respectively.