Short-term flexural stiffness prediction of CFRP bars reinforced coral concrete beams

FRP (Fiber Reinforced Polymer) Bar reinforced coral concrete beam is a new type of structural member that has been used more and more widely in marine engineering in recent years. In order to study and predict the flexural performance of CFRP reinforced coral concrete beams, the flexural rigidity, crack morphology and failure mode of concrete were studied in detail. The results show that under the condition of similar reinforcement ratio, the flexural rigidity of CFRP reinforced coral concrete beam is significantly lower than that of ordinary reinforced concrete beam. Increasing the cross-section reinforcement ratio within a certain range can increase the bending stiffness of the test beam or reduce the deflection, but the strength utilization rate of CFRP reinforcement is greatly reduced. The short-term bending stiffness of the CFRP reinforced coral concrete beam calculated by the existing standard formula is obviously higher. This paper proposes a modified formula for introducing the strain inhomogeneity coefficient (Ψ) of CFRP bars and considers the relative slip between CFRP bars and coral concrete to predict the short-term flexural stiffness of coral concrete beams reinforced by CFRP bars. The formula was verified with the test results, and it was proved that the formula has a good consistency with the test results

Sustainable Concrete Using Seawater, Recycled Aggregates, and Non Corrosive Reinforcement

Using seawater and recycled concrete aggregate (RCA) in a concrete mix is potentially advantageous from a sustainability perspective. However, the high chloride levels expected in such a concrete mix demands the use of non-corrosive reinforcement in lieu of normal black steel to avoid corrosion problems. Glass fiber reinforced polymer (GFRP) is considered promising as an alternative reinforcement owing to its corrosion resistance and acceptable mechanical properties that minimize maintenance and repairs and extend service life. Yet, the relatively high initial cost of GFRP bars may mitigate its potential use. In view of that, the current thesis is aimed at verifying the safe and economic utilization of seawater, recycled concrete aggregate, and GFRP reinforcement to produce sustainable and efficient concrete structures. The main body of the thesis consists of five key studies. In the first study, an extensive experimental program was conducted to compare the fresh and hardened properties of freshwater- and seawater-mixed concretes. In the second study, the performance of concrete mixed with seawater and recycled coarse aggregates (at 100% replacement level) was experimentally investigated. The third study was carried out to experimentally examine the flexural performance of seawater-mixed recycled aggregate GFRP-reinforced concrete beams. In the fourth study, a life cycle cost analysis (LCCA) was performed (considering 100-year analysis period) to verify the cost performance of structural concrete combining seawater, RCA, and GFRP reinforcement for high-rise buildings as compared to the traditional reinforced concrete (i.e., with freshwater, natural aggregates, and black steel reinforcement). The fifth study evaluates the cost effectiveness of different reinforcement alternatives in a concrete water chlorination tank using LCCA: a comparison was established between four concrete reinforcing materials, namely, black steel, epoxy-coated steel, stainless steel, and GFRP through a 100-year analysis period. The results of these five studies suggest the potential use of the proposed combination (seawater + RCA + GFRP reinforcement) to produce safe and economic concrete structures

A Systematic Literature Review on the Effect of Seawater as A Promising Material on the Physical and Mechanical Performance of Concrete

Concrete is made from freshwater, cement, and aggregate and the only material shared with mankind, flora, and fauna is freshwater. One of the most concerning problems the world has been facing over the last few decades is the rising demand for freshwater due to the increasing global population and depleting source of freshwater by 2050. In Malaysia, the population is expected to rise from 32 million people in 2020 to 40.50 million people in 2050, which would correspondingly increase the demand for domestic houses, industrial areas, and other building construction as well as increase the overall usage of freshwater. The utilisation of seawater has been applied in constructing buildings and infrastructures since the time of the Roman Empire and the structures still survive for more than 2000 years against chemical attacks and underwater wave force. Given that seawater is considered an alternative mixing agent in concrete production, research on seawater-based concrete has continued to gain interest from the scientific community and undergone swift development. Therefore, the aim of this study was to present a systematic literature review on the recent development of concrete with seawater as the mixing agent and its effect on the physical and mechanical performance of the concrete. A four-stage investigation criterion was conducted for the data collection from the Scopus database, which includes the search parameter, identification, screening, and writing. The screening of the literature retrieved 53 articles, which were then classified based on the physical and mechanical properties of the concrete. Based on the review, the use of seawater as a single mixing agent reduced the physical and mechanical performance of the concrete. However, the incorporation of seawater with special chemical admixture, mineral admixture, and reinforcement with certain treatment resulted in a higher performance of the concrete. Finally, the review highlighted the various potential studies that can be performed to investigate the utilisation of seawater in the construction industry while achieving a sustainable solution to preserve the environment

Time-Dependent Reliability Framework for Durability Design of FRP Composites

The life-cycle performance, durability, and aging characteristics of Fiber Reinforced Polymer (FRP or Structural Composites) have been of keen interest to the engineers engaged in the FRP design, construction, and manufacturing. Unlike conventional construction materials such as steel and concrete, the design guidelines to account for the aging of FRP are somewhat scattered or not available in an approved or consistent format. Loss of strength over time or aging of any structural material should be of concern to engineers as the in-service lifespan of many engineering structures is expected to exceed 100 years. Use of durability strength-reduction factors or factors of safety (aka knock-down factors) is a common way to account for the anticipated in-situ site conditions during the FRP design phase; however, the considerations for FRP service life is often ignored or smeared into knock-down or safety factors. The individual or combined effect of these factors can be arbitrary and can lead to the system’s premature failure (or overdesigns), rendering FRP commercial application unreliable (or cost-prohibitive). Reliability or risk-based approach to the development of strength reduction factors has been successfully applied in modern Load, and Resistance Factor Design codes (e.g., highway bridge design specifications), and an original design framework (i.e., a set of ideas, tools or techniques that forms the basis for filling in the final details) incorporating the time-dependent behavior of FRP composites (e.g., decrease of mechanical strengths with an increase of variability with aging) is proposed. The research presented herein utilizes available natural and accelerated aged test databases to develop a relationship between the probability of failures (using reliability index and confidence intervals to measure reliability) and the desired service life of FRP members. The proposed framework illustrates how to use time-dependent reliability techniques to account for environmental and physical effects. For environmental effects, developing a direct relationship of reliability index with time-dependent durability works better, and for physical effects, indirect inclusion of probability in projecting the time (or cycles) to failure is more effective. The techniques presented in this research, along with three real-life design examples and a case study (i.e., the basis of design), can be readily used by design professionals to ascertain an adequate life cycle performance of FRP while maintaining a consistent component or system-level reliability. The intent is to allow others to refine this knowledge bank and to further the professional FRP design practice in a consistent, rational manner leading to the adaptation of formal codes and specifications. Although the presented data and associated findings primarily refer to pultruded glass fiber reinforced polymers (GFRP) in Vinylester resin, the presented framework can be easily extended to other structural composites. The report entails thorough documentation of published analytical and experimental formulations for various modes of FRP failures due to the typical aging process (e.g., moisture, temperature, alkalinity, and sustained loading, and a combination thereof) along with an associated sampling of durability strength reduction factors. Critical reviews of deterministic and stochastic methods are conducted, and gaps in the current approach to determining durability factors for FRP systems have been identified. A Basis of Design (BOD) for vinylester/polyester-based GFRP in a submerged marine condition using an accelerated test database with illustrative design examples has also been included for a better understanding of the proposed time-dependent reliability-durability concept. Understanding how an FRP system’s reliability changes over its life-span, designers will be able to confidentially choose the most suitable durability strength reduction factors, or factors of safety, that will meet their design’s target service life-span without exceeding strength or service limit states. Since absolute safety is not possible, all FRP members must be designed for a specific acceptable risk of failure. The research illustrates a unique set of techniques for determining FRP composites\u27 durability strength reduction factors, or threshold design values, by integrating durability characteristics developed in the laboratory tests with desired service lives and commonly acceptable risks of failure. Due to the limited availability of complete durability datasets, vast applications, varieties of FRP composites, and the enormity of calibration efforts required, this research proposes additional work to determine the final durability recommendations for the general use of FRP composites. However, this unique research forms a rational tool for designing specific FRP composites that are consistent with other modern design codes, takes into account their target service lives (e.g., 10, 50, 100 years), and bridges the gap between traditional deterministic FRP design methods and state of the art risked-based design philosophies

Reinforcement corrosion in coastal and marine concrete: A review

Concrete is used as a structural material for construction of buildings, jetties, harbors, etc. in many coastal and marine locations. The reinforcement used in concrete is susceptible to corrosion, resulting in loss of steel area, loss of bond, expansion of the reinforcement volume leading to cracking or spalling of concrete. Marine environment induces higher corrosion of reinforcement, compared to in-land locations. Concrete exposed to tidal fluctuations, or to the action of waves and currents are among the most severely affected. Corrosion of reinforcement in concrete is of major concern in coastal and marine environment. Control and monitoring of corrosion is a big challenge to engineers. In the recent years, different investigators reported their studies in this area. Depending on the severity of the exposure conditions, different corrosion inhibitors and protection methods have been attempted with varying degrees of success. The present article presents a generic review of the corrosion issues in marine concrete. Drawing from the experiences of the various researchers, the corrosion measurements, and corrosion control schemes, including use of coated reinforcements and corrosion inhibitors are discussed. The durability performance based design of concrete in the probabilistic framework and the life cycle cost analysis for durability design decisions have been identified as the future direction of corrosion protection of coastal and marine structures

Using basalt fiber reinforced polymer as steel reinforcement - Review

The production of affordable, lightweight polymers using sustainable composites reinforced with natural, eco-friendly fibers has recently attracted a lot of attention from both the research and manufacturing realms. Future construction of buildings must have the least negative impact on the environment while also being long-lasting. Basalt is the best material to utilize as reinforcement among natural fibers (animal, vegetable, or mineral) because of its advantageous qualities. The superior features of basalt rebar, such as its high tensile strength, low young's modulus, and corrosion-inhibiting properties, contribute to its operational excellence. This article summarizes the previous studies to investigate the use of basalt fiber-reinforced polymer (BFRP) bars as a substitute for steel reinforcement, emphasizing flexural strength, serviceability, and durability. That fits with the objective of this study, which is to analyse the most updated available data, compile the findings, and then identify any knowledge gaps that warrant future investigation. Moreover, the authors concluded following the review that basalt rebar might be used in construction as a more environmentally friendly and sustainable substitute for steel reinforcement

Évaluation de la durabilité des pieux en béton armé de barres et de spirales de PRFV en milieu marin

Abstract : Conventional concrete reinforced (RC) with black steel in marine environment suffers damage due to corrosion. Most field examination studies found heavy corrosion before achieving 75-100 years of the service life desired by the Federal Highway Administration (FHWA). Lately, glass fiber-reinforced polymers (GFRP) as internal reinforcement in concrete have proved outstanding structural and long-term durability performance in corrosive environments. The last three decades witnessed a significant revolution in the usage of GFRP in civil engineering projects to raise the service lives and reduce maintenance costs of RC structures. Over three-thousands bridges over Canada and U.S. included GFRP bars as reinforcement for constructing the most elements vulnerable to corrosion due to de-icing salts and annual thermal changes (i.e., deck slabs) as well as the usage in reinforcing the culvert bridges in the U.S. The field examination for the bridge’s barrier walls, deck slabs, and culvert built with GFRP bars after 10-20 years in service indicates good long-term durability. The usage of GFRP bars and spirals in the RC columns, piers, and piling system is widely accepted and recommended in most conclusions of previous studies. Most investigations in the past have focused mainly on the behavior of RC piles/columns under concentric, eccentric, and cyclic loading, disregarding the relationship between the structural and durability behavior. This thesis presents the results of the axial compression test for forty-eight RC square and circular piles exposed to the marine environment and two conditioning temperatures for 12-months. All specimens have laboratory-scale dimensions measuring 300 mm for square pile's width, 304 mm for circular pile's diameter, and 1000 mm general height. The durability conditioning regime is comprised of two environments; (i) simulation for the marine environment in sub-tropical regions (22°C), (ii) simulated marine environment at accelerated temperature (60°C). Phase (I) contains 18-concrete square piles and Phase (II) includes 18-concrete circular piles. The thirty-six concrete piles were: six specimens were without internal reinforcement, 6-specimens were reinforced with hybrid reinforcement (steel bars and GFRP spirals), and the remaining twentyfour specimens were fabricated with pristine GFRP bars and spirals. For each phase, twelve pile specimens were subjected to the conditioning regime for 12-months, six specimens for each conditioning temperature. Whereas phase (III) includes 6- square and 6-circular RC piles, which were made of GFRP reinforcement directly immersed in the simulated marine environment at 22 and 60°C for 12-months before integrating into concrete, three GFRP-cages for each aging temperature. Several structural variables were investigated through the three phases such as longitudinal reinforcement (ratio and diameter) and transverse reinforcement (pitch and configurations). In addition, a microstructural analysis program (SEM, DSC, and FTIR) was carried out on GFRP material extracted from the aged piles and those directly exposed to the conditioning regime. Concrete cores taken from the aged piles were examined by optical microscopy (OM) to assess the bond between concrete and bars/spirals. This thesis also introduces a characterization for GFRP bars exposed directly to the marine environment based on tensile, bond, and horizontal shear tests. The experimental axial compression capacities of GFRP-RC piles were compared with the values predicted using the available design equations in the current design codes. The results obtained from microstructural analyses showed that GFRP reinforcement used in this study possesses good long-term durability in concrete saturated with the marine environment or in solutions simulated seawater environments at 60°C after 12-months. OM images for the concrete/bar contact circumference revealed that bars/spirals firmly bond to concrete. A 0.85 is the lowest retention in the tensile and bond strengths of GFRP bars, while the retention in horizontal shear strength reaches 0.95 after direct exposure to the marine environment at 60°C for 12-months. Based on the compressive tests, the axial compression behavior of GFRP-RC square and circular pile did not adversely affect by immersion in the simulated marine environment at 22 or 60°C for 12-months or using pre/conditioned GFRP material. The axial compression capacity of ten GFRP-RC pile specimens submerged in the simulated marine environment at 60°C was enhanced by 116-125% compared to their unconditioned counterparts as a result of an increase in the concrete compressive strength. Specimens fabricated with GFRP material aged at 60°C exhibited similar ductile behavior and axial compression capacities of their counterparts constructed with pristine GFRP material. Despite the tensile strength reduction after exposure to aggressive environments, GFRP reinforcing materials effectively perform their structural function as internal reinforcement of RC piles. All investigated structural variables effectively affect the compressive behavior of GFRP-RC piles in the marine environment. The reduction factors for GFRP-RC structures specified in CSA (2019a) and AASHTO (2018a), and CSA (2017) yielded lower axial compression capacities than those obtained experimentally. A more accurate design equation to calculate the axial load capacity of the GFRP RC piles should consider the contribution of longitudinal GFRP bars even when exposed to severe marine environments.Le béton conventionnel armé (RC) avec de l'acier noir dans un environnement marin subit des dommages dus à la corrosion. La plupart des études d'examen sur le terrain ont révélé une forte corrosion avant d'atteindre les 75-100 ans de la durée de vie souhaitée par la Federal Highway Administration (FHWA). Récemment, les polymères renforcés de fibres de verre (PRFV) utilisés comme armature interne dans le béton ont prouvé qu'ils présentaient des performances structurelles et de durabilité à long terme exceptionnelles dans des environnements corrosifs. Les trois dernières décennies ont vu une révolution significative dans l'utilisation des PRFV dans les projets de génie civil pour augmenter la durée de vie et réduire les coûts de maintenance des structures en béton armé. Plus de trois mille ponts au Canada et aux États-Unis ont inclus des barres GFRP comme renforcement pour la construction des éléments les plus vulnérables à la corrosion due aux sels de déglaçage et aux changements thermiques annuels (c'est-à-dire les dalles de pont), ainsi que pour le renforcement des ponceaux aux États-Unis. L'examen sur le terrain des murs de protection, des dalles de pont et des ponceaux construits avec des barres GFRP après 10 à 20 ans de service indique une bonne durabilité à long terme. L'utilisation de barres et de spirales en GFRP dans les colonnes, les piliers et les systèmes de pilotis en béton armé est largement acceptée et recommandée dans la plupart des conclusions des études précédentes. La plupart des recherches dans le passé se sont concentrées principalement sur le comportement des pieux/colonnes en béton armé sous des charges concentriques, excentriques et cycliques, sans tenir compte de la relation entre le comportement structurel et la durabilité. Cette thèse présente les résultats de l'essai de compression axiale pour quarante-huit pieux RC carrés et circulaires exposés à l'environnement marin et à deux températures de conditionnement pendant 12 mois. Tous les spécimens ont des dimensions à l'échelle du laboratoire mesurant 300 mm pour la largeur du pieu carré, 304 mm pour le diamètre du pieu circulaire, et 1000 mm de hauteur générale. Le régime de conditionnement de durabilité est composé de deux environnements ; (i) simulation pour l'environnement marin dans les régions subtropicales (22°C), (ii) environnement marin simulé à température accélérée (60°C). La phase (I) comprend 18 pieux carrés en béton et la phase (II) comprend 18 pieux circulaires en béton. Les trente-six pieux en béton étaient les suivants : six spécimens n'avaient pas d'armature interne, six spécimens étaient renforcés par une armature hybride (barres d'acier et spirales GFRP), et les vingt-quatre spécimens restants étaient fabriqués avec des barres et des spirales GFRP vierges. Pour chaque phase, douze spécimens de pieux ont été soumis au régime de conditionnement pendant 12 mois, six spécimens pour chaque température de conditionnement. Tandis que la phase (III) comprend 6 pieux RC carrés et 6 circulaires, qui ont été réalisés avec des armatures GFRP directement immergées dans l'environnement marin simulé à 22 et 60°C pendant 12 mois avant d'être intégrées dans le béton, trois cages GFRP pour chaque température de vieillissement. Plusieurs variables structurelles ont été étudiées au cours des trois phases, telles que les armatures longitudinales (ratio et diamètre) et les armatures transversales (pas et configurations). De plus, un programme d'analyse microstructurelle (SEM, DSC, et FTIR) a été réalisé sur le matériau GFRP extrait des pieux vieillis et ceux directement exposés au régime de conditionnement. Des carottes de béton prélevées sur les pieux vieillis ont été examinées par microscopie optique (OM) pour évaluer la liaison entre le béton et les barres/spirales. Cette thèse présente également une caractérisation des barres GFRP exposées directement à l'environnement marin, basée sur des essais de traction, de liaison et de cisaillement horizontal. Les capacités expérimentales de compression axiale des pieux en GFRP-RC ont été comparées aux valeurs prédites en utilisant les équations de conception disponibles dans les codes de conception actuels. Les résultats obtenus à partir des analyses microstructurales ont montré que le renforcement GFRP utilisé dans cette étude possède une bonne durabilité à long terme dans du béton saturé de l'environnement marin ou dans des solutions simulant des environnements d'eau de mer à 60°C après 12 mois. Les images OM de la circonférence de contact béton/barre ont révélé que les barres/spirales adhèrent fermement au béton. Une rétention de 0,85 est la plus faible dans les résistances à la traction et à l'adhérence des barres GFRP, tandis que la rétention de la résistance au cisaillement horizontal atteint 0,95 après une exposition directe à l'environnement marin à 60°C pendant 12 mois. D'après les essais de compression, le comportement en compression axiale des pieux carrés et circulaires en GFRP-RC n'a pas été affecté par l'immersion dans l'environnement marin simulé à 22 ou 60°C pendant 12 mois ou par l'utilisation de matériau GFRP pré-conditionné. La capacité de compression axiale de dix spécimens de pieux RC en GFRP immergés dans un environnement marin simulé à 60°C a été augmentée de 116-125% par rapport à leurs homologues non conditionnés en raison d'une augmentation de la résistance à la compression du béton. Les spécimens fabriqués avec un matériau GFRP vieilli à 60°C ont présenté un comportement ductile et des capacités de compression axiale similaires à ceux de leurs homologues construits avec un matériau GFRP vierge. Malgré la réduction de la résistance à la traction après exposition à des environnements agressifs, les matériaux de renforcement GFRP remplissent efficacement leur fonction structurelle en tant que renforcement interne des pieux RC. Toutes les variables structurelles étudiées affectent efficacement le comportement en compression des pieux GFRP-RC dans l'environnement marin. Les facteurs de réduction pour les structures en GFRP-RC spécifiés dans CSA (2019a) et AASHTO (2018a), et CSA (2017) ont donné des capacités de compression axiale inférieures à celles obtenues expérimentalement. Une équation de conception plus précise pour calculer la capacité de charge axiale des pieux RC en GFRP devrait tenir compte de la contribution des barres longitudinales en GFRP, même lorsqu'elles sont exposées à des environnements marins sévères

Composites for hydraulic structures: a review

Composites for hydraulic structures: a review Composites have evolved over the years and are making major in-roads into the marine, aviation and other industries where corrosions and self-weight are the major impediments to advancing the state-of-the-art. Civil Works engineers have been reluctant to make use of these composite advantages, partially because of the absence of well documented success stories, accepted design and construction practices or specifications, and limited understanding of composites, higher initial costs and others. A few navigational structures using FRP composites have been designed, manufactured and installed in the United States of America and Netherlands, recently. US Army Corps of Engineers is embarking on higher volume applications of composites for navigational structures. This report is aimed at summarizing the state of the art of fiber reinforced polymer (FRP) composites for hydraulic structures including design, construction, evaluation and repair. After a brief review of history and introduction of fundamentals of composites, their manufacturing techniques, properties, and recent field applications are presented, including FRP rebar for bridge decks, other highway and railway structures, gratings, underground storage tank, pavement, sheet and pipe piling, FRP wraps, moveable bridges, utility poles, etc. Focus is placed on applications of composites in waterfront, marine, navigational structures including lock doors, gates, and protection systems. Design of hydraulic composite structures is presented for the cases available, such as design of FRP recess panel, Wicket Gates, Miter Gates, FRP slides and repair of corroded steel piles. This report also reviews engineering science issues such as fracture and fatigue, durability, creep and relaxation, UV degradation, impact resistance, and fire performance. The report concludes with summary remarks and recommendations after a discussion on operation and maintenance guidance including nondestructive evaluation inspection techniques. Intention is to provide up to date information on composite design, manufacturing and evaluation methodologies that are applicable for fabrication and maintenance of navigational structures. This report is a living document with advances taking place with time as waterborne transport infrastructure community makes progress with FRP systems. This report is expected to be useful for those decision-makers in government, consultants, designers, contractors, maintenance and rehab engineers whose focus is to minimize traffic interruptions while maximizing cost effectiveness