Prediction Of Long-term Durability Research Articles

Characteristics and Models of Moisture Uptake in Fiber-Reinforced Composites: A Topical Review.

Fiber-reinforced composites are commonly exposed to environments associated with moisture and solution, resulting in uptake, which causes changes in the bulk resin, the fiber-matrix interface, and even the fiber itself. Knowledge about uptake behavior and diffusion mechanisms and characteristics are critical to better understanding the response of these materials to environmental exposure faced through service to developing better materials through selection of constituents and to the prediction of long-term durability. This paper reviews aspects of uptake mechanisms and subsequent response, as well as models that describe the sorption process, with the aim of providing a comprehensive understanding of moisture-uptake-related phenomena and characteristics such as uptake rate, diffusion and relaxation/deterioration constants, transitions in regimes, and overall response.

Long-Term Durability Prediction of Slag–Fly Ash-Blended Engineered Cementitious Composite Subjected to Chloride and Sulfate Salt

Long-Term Durability Prediction of Slag–Fly Ash-Blended Engineered Cementitious Composite Subjected to Chloride and Sulfate Salt

Prediction of long-term durability of unidirectional/multidirectional basalt fiber- and hybrid fiber-reinforced polymer profiles under concrete environment

Recently, concrete composite structures based on a fiber-reinforced polymer (FRP) profile, which serves in the corresponding alkaline concrete environment have been widely used. Unlike FRP bars, the long-term durability of FRP profiles in concrete remains unclear, particularly for those with multidirectional (MD) or hybrid fibers, whose internal structure differs from that of FRP bars. This study focused on the tensile strength degradation of FRP profiles exposed to an artificial concrete environment solution at various ambient temperatures. Three types of FRP specimens were considered, including unidirectional (UD) basalt FRP (BFRP), MD BFRP and MD basalt-carbon hybrid FRP profiles. The results show that the alkaline environment of the concrete caused a decrease in the tensile strength of the FRP profiles, and the rate of degradation in strength significantly accelerated as the ambient temperature increased; however, the environment had no apparent effect on the elastic modulus. In addition, the strength degradation of MD FRP profiles was more significant than that of UD FRP profiles after corrosion due to insufficient impregnation of the fibers by the resin, which results in initial defects as well as increased intrusion of external moisture and corrosive media. Scanning electron microscopy (SEM) was employed to analyze the morphology and degradation mechanism of FRP profiles in a concrete environment. Moreover, a long-term prediction method for tensile strength retention of three types of FRP profile in arbitrary ambient temperatures is proposed based on the Arrhenius equation.

Comprehensive analysis and prediction of long-term durability of factor IX activity following etranacogene dezaparvovec gene therapy in the treatment of hemophilia B

Objective Congenital hemophilia B is a rare bleeding disorder caused by defects in the gene encoding factor IX (FIX) leading to coagulation deficiency. Recurrent bleeds may cause chronic pain, disability, and reduced quality of life. Phase 2 b and 3 single-arm, open-label, single-dose trials assessing etranacogene dezaparvovec gene therapy for hemophilia B have demonstrated sustained FIX activity levels over observed periods, but long-term durability of the treatment effect has not been established. Using statistical modeling, we estimate long-term durability of FIX activity levels after receiving etranacogene dezaparvovec. Methods Participants from Phase 2 b (N = 3; NCT03489291) and 3 studies (N = 52; NCT03569891) were included. Two participants who did not respond to treatment were excluded. FIX activity was assessed by one-stage activated partial thromboplastin time assay. FIX activity levels at Month 6 post-treatment were considered baseline. Bayesian and Frequentist linear mixed models predicted FIX activity levels up to 25.5 years at an individual and population level with pre-treatment adeno-associated virus 5 (AAV5) neutralizing antibody (NAb) status as primary covariate. Results Bayesian and Frequentist linear mixed models predicted no more than 6/55 (10.91%) observed participants would have FIX activity levels <2% up to 25.5 years post-infusion. Bayesian model-based predictions of future participants suggest >80% would be free from prophylactic FIX replacement products 25.5 years post-infusion. Both models predicted FIX activity levels were not significantly influenced by pre-treatment AAV5 NAb status. Conclusions People with hemophilia B receiving etranacogene dezaparvovec would likely achieve durable FIX activity levels and remain free of prophylactic FIX replacement products for up to 25.5 years following single administration. The long-term factor IX durability predictions are based on statistical methods and results in vivo may differ.

Mechanical and long-term durability prediction of GFRP rebars with the adoption of low-pH CSA concrete

• The low-pH CSA concrete is utilized for enhancing durability of GFRP rebar. • Tensile strength retention of GFRP rebar is much higher in low-pH CSA concrete. • The corrosion of glass fibers and VE matrix are observed from microscopic level. • The long-term tensile performance of GFRP rebar is proposed by empirical expression. Glass fiber-reinforced-polymer (GFRP) composites have been considered a good alternative to conventional steel rebars in structures. However, the high-pH value (∼13) of normal concrete would lead to severe degradation of GFRP rebars. Yet limited research seems to have investigated the durability of GFRP rebars embodied in low-pH concrete. In this study, the physical and mechanical properties of GFRP rebar embedded in low-pH concrete (∼11) are evaluated by replacing ordinary Portland cement (OPC) with calcium sulfoaluminate (CSA) cement. The tensile strength retention of GFRP rebars inside the CSA concrete (pH = 11) is observed to be around 17% higher than that inside the OPC concrete (pH = 13) at 40 °C after 12 months. Additionally, the tensile strength retention of GFRP rebars in CSA concrete at 23 °C after 100 years is greatly increased from 52.7% to 79.1% in comparison to GFRP rebars in OPC concrete based on the prediction equation. Even though the glass transition temperature of vinyl ester and its hydrolysis reaction are insensitive to the concrete alkalinity, the improved durability can be explained by fewer glass fiber fractures, vinyl ester matrix cracking and interfacial debonding for GFRP rebars embedded in the CSA concrete. The results of this study provide engineers with a new approach to improving the durability performance of GFRP rebars.

Effect of Cross-Linking Density on Horizontal and Vertical Shift Factors in Linear Viscoelastic Functions of Epoxy Resins

Epoxy resins are an important class of thermosetting resins, and their network structure, obtained by the curing reaction of epoxy and amine compounds, plays an important role in the material properties. We here revisited a time–temperature superposition (TTS) principle applied to the dynamic viscoelastic functions of epoxy resins, in which the network was well defined and systematically varied on the basis of the length of n-alkyl diamine. The superimposition of isothermal curves in the frequency domain required not only a horizontal shift but also a vertical shift, regardless of the length of n-alkyl diamine. The temperature dependence of the horizontal shift factor, aT, could be well expressed by the Williams–Landel–Ferry equation. The fitting parameter, called C2, increased with decreasing alkyl chain length of the diamine, meaning that the thermal expansion of the free volume was suppressed due to greater cross-linking density. This was qualitatively confirmed by a full-atomistic molecular dynamics (MD) simulation. Meanwhile, the vertical shift factor, bT, increased with increasing temperature, and the extent was smaller with increasing cross-linking density. This can be explained in terms of the entropic contribution to the modulus in the temperature region above the glass transition temperature. The entropy change estimated using the isobaric molar heat capacity from the MD simulation strongly supported this hypothesis. The knowledge here obtained should be useful for a better design of thermosetting polymers as well as for the prediction of long-term durability.

3D acid diffusion model for FRP-strengthened reinforced concrete structures: Long-term durability prediction

Fibre-reinforced polymer (FRP) composites have been utilised as promising and popular solutions to strengthen existing reinforced concrete (RC) structures. Due to the increasing industrial activities, growing population and climate change, corrosive environments (e.g. acid rains) that diminish the durability of FRP-strengthened RC structures are becoming more common. The long-term durability of structures in these corrosive environments is central to the success of any strengthening technique. Despite this urgency, very limited research data is available regarding the degradation of RC structures strengthened with the FRP in acidic environments. This paper evaluates the impact of sulphuric acid on the performance of externally bonded FRP-strengthened RC structures and investigates the long-term behaviour of concrete, FRP composite, and the FRP-concrete interface. The acid diffusion mechanism within the FRP-concrete bond system is studied with the establishment of both one-dimensional (1D) and three-dimensional (3D) models. Moreover, a reduction factor (βα) accounting for the degrading effect of acid, is proposed to predict the retained bond strength at the FRP-concrete interface. The proposed models provide a theoretical basis for the durability design and the service life prediction of FRP-strengthened RC structures when subjected to acid attack.

A parametric study to improve suitability of micro-deval test to assess unbound base course aggregates

Micro-deval test provides a measure of resistance and durability of aggregates submerged in water through the actions of aggregate particles and abrasion from steel balls. The presence of water in the test chamber provides a more realistic assessment of field conditions when compared with Los Angeles (LA) abrasion test. Currently there is only one testing procedure in the United States (U.S.) to evaluate the coarse aggregates using micro-deval tests. Previous studies indicate that there has been significant interest in utilizing micro-deval test to assess the suitability coarse aggregates to be used in asphalt concrete and their field performance. However the studies related to evaluating coarse aggregates with micro-deval test for base course applications are very limited. This study attempts to address how the micro-deval testing procedure may be revised to better assess the performance of aggregates considered for the base course. Aggregates with seven different geological compositions were used in the study. Total of 250 micro-deval tests were performed and the results confirmed the repeatability and the suitability of the proposed method to all of the tested aggregates. As part of this study, a threshold is determined for the optimum amount of abrasive charge that should be used in the tests to obtain maximum material loss regardless of the geological make-up of the aggregate. If this approach is followed, a strong relationship between the number of revolutions and percent material loss is achieved. This relationship provides an opportunity to shorten the micro-deval tests and also an approach to assess durability of aggregates at number of revolutions significantly larger than what is prescribed in the existing micro-deval testing procedure. This ability may be used in the future to more realistically relate the long-term durability prediction of aggregates as it relates to field performance of base course.

Prediction of long-term durability of FRP under seawater environment

Prediction of long-term durability of FRP under seawater environment

A Effective Solution Method Based on Bayesian Rule for Prediction of Long-Term Tensile Strength of GFRP Bars in Concrete Beams

It is necessary to research on the long term structural behavior of GFRP bars in concrete by limited samples. The two models, Arrhenius Equation and Fick’s Law were compared to form a long-term durability prediction thinking. Based on the work and ideas of the prior researchers, a detailed derivation of the iterative equation on the Bayesian prediction was conducted. Especially, a new likelihood function was set up to solve the long term behavior prediction of GFRP bars in concrete with less information. Then a new and effective solution method was developed. The residual strength behavior of GFRP bars in concrete beams after seven years’ environmental exposure was analyzed. The results showed that the theoretical predictions and experimental data were very close and theoretical prediction model was reasonable.

Molecular Dynamics Study for Sintering Characteristics of Solid Oxide Fuel Cell Anode

The prediction of long-term durability of SOFC anode is important to understand the sintering phenomena in the anode, which are affected by microstructure, materials, and impurities. To understand the sintering phenomena considering the effects of materials and chemical species, molecular dynamics (MD) simulation is one of the most effective computational methods. In this study, we developed a theoretical methodology based on the master sintering curve to analyze the sintering property. We performed MD simulation for the densification of both Ni and YSZ porous structures. The sintering activation energy obtained from our proposed method was in reasonable agreement with the experimental result.

Long-term durability prediction models for GFRP bars in concrete environment

This article presents a durability study of glass fiber reinforced polymer (GFRP) bars within concrete environment and provides recommendations for effective accelerated ageing methods, data reduction and validation, and formulation of master curves for long-term predictions. Concrete beams reinforced with GFRP bars were immersed in tap water inside temperature-controlled tanks. Sustained load was applied to beam samples, and elevated temperatures were used to accelerate the ageing of GFRP bars. After exposure, GFRP bars were tested for residual tensile strength, which was considered as a measure of the durability performance of the specimens. Scanning electron microscopy (SEM) images were used to evaluate the microstructural changes of conditioned specimens. Short-term (up to 270 days) results showed that compared to alkalinity and low sustained load, moisture and elevated temperature played much more important roles in accelerating environmental attack to GFRP bars. Based on the short-term test results, the dominant degradation mechanism for GFRP bars in concrete was found as the deterioration of fiber/matrix interface. A degradation model based on Arrhenius concept and prediction procedures are given, and correlations with other studies and field data are provided. The tensile strength retentions for GFRP bars in saturated concrete subjected to sustained load were predicted. It was found that degradation rates decreased rapidly, but tensile strength retentions at different exposure temperatures converge to a constant value with the increase of exposure time. Beyond fiber-matrix debonding, there is a possibility that other degradation mechanisms such as fiber corrosion may start to dominate the deterioration process of GFRP bars with time.

Prediction of long-term durability of unidirectional CFRP

This study examines the applicability of the SFF model (Koyanagi J, Kotani M, Hatta H and Kawada H. A comprehensive model for determining tensile strengths of various unidirectional composites. J Compos Mater 2009; 43: 1901–1914) to the time and temperature dependence of strength for two kinds of CFRP. The only difference in the materials is the reinforcing carbon fiber, which is not time or temperature-dependent; the time and temperature dependence of strength for the two materials differ. The SFF model, however, can follow their strengths well. Postulating the SFF applicability, the validity of the conventional accelerated testing methodology by elevated temperature and a simple method to predict long-term durability, including creep lifetime, are discussed.

A technical assessment cement bonded wood particleboard

The paper summarises test work on cement bonded particleboards carried out at the Princes Risborough Laboratory over the last fifteen years. Evaluation of short term mechanical properties has been complemented by information on the long term creep behaviour of these boards. Assessment of short term performance has embraced both mechanical testwork and the reaction of the material to water; evaluation of long term performance, which is of more importance, involved quantifying the extent of creep under long term loading, the prediction of long term durability using various methods of accelerated ageing, the measurement of actual loss in performance under 10 years natural exposure, and the evaluation of the resistance of the product to biodeterioration. The paper ends with a general appraisal of these products and concludes that their outstanding merit lies in extending the application of wood based panels into areas where there is either a high risk of fire or moisture.