Structures In Aggressive Environments Research Articles

Health assessment of road bridges with Gerber saddles: non-linear planar models

A correct assessment of the structural behavior and performance of deteriorated structures is crucial both for a proper planning of maintenance works and for a correct design of new structures in aggressive environments. The aim of this work is to investigate the response of Gerber saddles to the variation of the two main parameters representing typical damaged scenarios: the concrete cover and the diameter of the steel reinforcements. The analyses are conducted through Finite Element two-dimensional non-linear models based on the compatible stress field; the results are compared with the relevant ‘Strut and Tie’ models. At first, parametric analyses are carried out, in order to evaluate the sensitivity of load capacity to the position of steel rebars and to the dimension of concrete cover; this first part of the contribution aims to highlight the importance of an adequate level of knowledge. Then, the contribution focuses on the reduction of saddle capacity due to degradation conditions, referred to both the loss of concrete cover and the corrosion of reinforcing bars. The analyses closes with a comparison among the results provided by the two-dimensional investigations and the ones provided by the relevant ‘Strut and Tie’ models.

Bond Behavior of Recycled Tire Steel-Fiber-Reinforced Concrete and Basalt-Fiber-Reinforced Polymer Rebar after Prolonged Seawater Exposure

The integration of basalt-fiber-reinforced polymer (BFRP) rebars into concrete design standards still remains unrealized due to limited knowledge on the performance of the rebars in concrete, particularly in terms of bond durability in harsh conditions. In this work, we investigated the bond durability characteristics of BFRP rebars in fiber-reinforced self-compacting concrete (FRSCC) structures. To this aim, a number of 24 FRSCC pullout specimens reinforced with either BFRP rebar or glass-fiber-reinforced polymer, GFRP, rebar, which is a commonly used type of FRP, were fabricated. Half of these specimens were submerged in simulated seawater for a two-year span, while the other 12 similar specimens were maintained in standard laboratory conditions for comparative purposes. Subsequently, all 24 specimens underwent monotonic and fatigue pull-out tests. The exploration in this study focused on investigating the influence of the environmental condition, reinforcement type, and loading type on the bond stress versus slip relationship, maximum bond stress, and failure mode of the specimens. Based on the results obtained and by adopting the durability approach of industry standards for prediction of the bond retention of FRP-reinforced concrete, the bond strength retention between BFRP/GFRP and FRSCC after 50 years of exposure to seawater was estimated. The outcomes of the study are expected to enhance engineers’ confidence in the use of FRP, especially BFRP, for constructing durable and sustainable reinforced concrete structures in aggressive environments.

Hysteretic Performance of Hybrid GFRP-Steel Reinforced Concrete Shear Walls: An Experimental Investigation

The vulnerability of steel reinforcement to corrosion is a severe problem affecting the overall performance and durability of concrete structures in aggressive environments. The interest in using alternative Glass fibre-reinforced polymer (GFRP) bars lies in their corrosion resistance and higher tensile strength-to-weight ratio. Nevertheless, experimental results on the seismic behaviour of GFRP-reinforced walls are scarce. This paper investigates the hysteretic performance of hybrid steel-GFRP reinforced concrete shear walls to provide valuable experimental evidence for such walls under seismic loading. Six RC shear walls with steel and GFRP reinforcement were tested under pseudo-static reversed-cyclic lateral load. Three shear walls were reinforced by GFRP bars as longitudinal and transversal reinforcement, and two walls were reinforced with hybrid GFRP-steel bars with different ratios of web reinforcement. A reference specimen, ordinary steel-RC shear walls, was also introduced to certify the capability of GFRP as reinforcement bars. The results indicated that the GFRP-reinforced concrete slender walls had a stable hysteretic response and slight residual drift up to failure. Lower residual deformations, higher displacement capacity, and increased lateral strength could be observed with the GFRP web reinforcement ratio increase. Moreover, the fundamental period of GFRP and hybrid GFRP-steel reinforced walls can reach more than twice its original value prior to failure.

Durability of a reinforced concrete structure exposed to marine environment at the Málaga dock

The durability of structures in aggressive environments does not often reach the service life for which they were designed. This paper shows the methodology and results obtained in the evaluation of a 22-year-old breakwater’s crow wall. The results reveal that there are no degradation processes or expansive reactions in the concrete, nor carbonation. However, there is high chloride contamination, which has led to depassivation of the reinforcement of the entire structure, which in turn has led to bursting and delamination of the cover in some areas. Monte Carlo analysis shows that the chloride concentration exceeds the critical concentration given by the regulations up to a depth of 150 mm. It is advisable immediate repair and protection of the structure given the condition of the structure.

Surface modification of acrylic coating with anti‐corrosion and anti‐UV materials

AbstractThe use of organic coatings is the most common method of corrosion protection of metal structures in aggressive environments which act as a barrier between the corrosive environment and the metal structure. In this work, to increase the corrosion resistance and UV resistance of steel structures, an acrylic coating containing titanium oxide (TiO2), zinc phosphate (ZP), and benzophenone was used and the coating was characterized by open circuit potential (OCP) techniques, electrochemical impedance spectroscopy (EIS), dynamic polarization, Adhesive strength, salt spray, and UV weathering. The results showed that in the case of the acrylic sample, it has poor corrosion resistance and requires the presence of nanofillers. With the presence of TiO2 nanofillers, microporous and other defects were effectively blocked and the penetration of corrosive components into the interface of the metal coating and substrate was prevented. In the presence of ZP along with TiO2, all anodic and cathodic sites were coated with a film consisting of inhibitors released from zinc phosphate nanoparticles and thus acted as a barrier against electrolyte penetration into active metal sites. With the presence of an anti‐UV agent, benzophenone partially blocked surface defects and along with corrosion products prevented a sharp drop in resistance over longer periods.

A Simplified Approach for the Corrosion Fatigue Assessment of Steel Structures in Aggressive Environments.

Fatigue performance is often a key aspect when dealing with existing steel structures such as steel bridges or offshore constructions. This issue proves to be more critical as these structures are usually located in aggressive environments and are thus exposed to progressive degradation. Indeed, disruptive phenomena such as corrosion can severely worsen the fatigue performance of the steel components. Currently, the normative standards do not provide a codified procedure for the fatigue checks of steel structures subjected to ongoing corrosion. Within this framework, in this paper a simplified approach for the life-cycle assessment of corroded steel structures is proposed. For this purpose, the concept of “critical corrosion degree” is introduced, allowing the expression of corrosion fatigue checks in a more direct “demand vs. capacity” form with respect to the currently available methods. A first validation of such methodology is reported for the corrosion fatigue tests drawn from the literature. The predicted levels of critical corrosion are in good agreement with the values of artificially induced corrosion (i.e., 4, 8, and 12% of mass loss, respectively), with a maximum relative error of ≈9.3% for the most corroded specimen. Finally, parametrical analyses are performed, highlighting the influence of the model parameters on the corrosion fatigue performance of the steel elements.

Imperfection sensitivity study of hot‐rolled and laser‐welded stainless steel angle columns

AbstractStainless steel sections are used for structures in aggressive environments where the greater material cost can often be justified in return for longer maintenance‐free periods, for example in the water treatment, nuclear, petrochemical and food and beverage sectors. This paper presents a comparative imperfection sensitivity study of hot‐rolled and laser‐welded pin‐ended equal angle columns made of austenitic stainless steel grade 1.4301. Although the initial geometric imperfections in these structural elements are similar, there is a difference in the initial stress state due to the different manufacturing processes. The study includes three‐dimensional geometric imperfection measurements conducted by a laser scanner, and, in parallel residual stress measurements performed by the sectioning method using water jet cutting. The overall bow, camber, and twist imperfections are determined from the scanned specimens. In addition, the shapes of the residual stress patterns through the thickness of the angle leg are shown. Based on the findings related to imperfection distributions and amplitudes, a FE analysis is performed both on hot‐rolled and laser‐welded angles to study the influence of the variability of initial imperfections on compression resistance. The separate and combined effects of the measured residual stresses and initial out‐of‐straightness are considered and the reduction in the buckling resistances of initially straight angle columns is determined. The structural responses of hot‐rolled and laser‐welded columns are compared and discussed.

Selection of the optimal value of compressive stress in concrete under adverse external impacts

This article reviews the effect of static and dynamic compressive stresses on the durability of reinforced concrete structures in aggressive environments. Based on the analysis of previous work and research on this issue, the author describes the main activities to be implemented in the course of works to ensure the durability of concrete and safety of reinforcement. He outlines the necessary measures to reduce the magnitude of dynamic stresses in pile driving and to ensure the healing of microdamage incurred therein. It is proved in the article that the implementation of the proposed set of measures will allow using reinforced concrete piles as supporting structures of quays in harsh climatic conditions.

Numerical Verification of the Use of GFRP Reinforcement in the Ceiling Slab of a Garage House

One of the major advantages of fibre reinforced polymers (FRPs) is their high tensile strength and low weight to strength ratio. Compared to steel reinforcement, this is one of the main and decisive features that could determine the choice of materials used in the design. Since there is no corrosion for this type of reinforcement, it is very suitable for concrete structures in aggressive environments. This point, along with others, gives concrete structures reinforced with FRPs significant advantages over conventional concrete structures with steel reinforcement. Different material properties and behaviour of FRP when compared to steel reinforcement result in the need of the modification of established design procedures, especially in the area of the ultimate strain, because FRP reinforcement has a different σ-ε diagram than the steel reinforcement. The experimental verification of the new design procedures is necessarily needed. This paper summarizes the results of practical design and calculations of the resistance of alternatively steel and GFRP reinforced concrete ceiling slab of a garage house and experimental results on the beam specimens reinforced with GFRP reinforcement tested under four-points test. It was necessary to adjust the conventional procedures in calculating the required area of GFRP reinforcement in order to avoid brittle failure of the cross-section (rupture of reinforcement). This is ensured by abiding the balance reinforcement level. Another fact to be considered is the creep rupture phenomenon causing immediate rupture of GFRP reinforcement under a high level of sustained loading. The reduction of GFRP strength according to the long-term loading results in rising required area of reinforcement. Finally, the serviceability limit state is checked. According to the low modulus of elasticity of GFRP reinforcement, the deflection should be the limiting factor for the amount of reinforcement designed.

Interfacial adhesion mechanism between organic polymer coating and hydrating cement paste

Surface coatings have proved to be one of the most effective methods to protect the concrete structures in aggressive environments. However, coating the structures with polymer after 28 days of curing/hydration to get the best interfacial performance has little scientific backing. The measured surface free energy of the hydrating cement paste showed that the surface energy is high for a 2-day hydrated paste compared to cement paste cured for 7, 28 days. This opens up the possibility for exploration into coating an acrylic based polymer on a concrete surface before it reaches 28 days of hydration, which has been investigated in this study. The practical work of adhesion between the hydrating cement paste and polymer as measured from macro mechanical tests showed to have a dependency on the surface evolution of the cement paste. However, it was also observed that it depends equally on the polymer functional groups. Poly (methyl methacrylate) (PMMA), when coated on a 2-day hydrated cement paste, showed higher interfacial strength than when coated on later days (7, 14, 28 days). In the case of epoxy, irrespective of when the polymer was coated, it had the same interfacial strength. The influence of the evolving cement paste and the polymer functional group (PMMA in particular) on the interfacial strength at the micro- and molecular-length scales are discussed. It is found that the free/adsorbed calcium form a metal-complex with the ester functional group of the polymer in addition to the physical interactions, resulting in higher interfacial strength. The observations shed light on the importance of interfacial science and act as a guideline for the design of effective polymer-cement coatings.

Development of Weather-Resistant 3D Printed Structures by Multi-Material Additive Manufacturing

Additive manufacturing, or 3D printing, has had a big impact on the manufacturing world through its low cost, material recyclability, and fabrication of intricate geometries with a high resolution. Three-dimensionally printed polymer structures in aerospace, marine, construction, and automotive industries are usually intended for service in outdoor environments. During long-term exposures to harsh environmental conditions, the mechanical properties of these structures can be degraded significantly. Developing coating systems for 3D printed parts that protect the structural surface against environmental effects and provide desired surface properties is crucial for the long-term integrity of these structures. In this study, a novel method was presented to create 3D printed structures coated with a weather-resistant material in a single manufacturing operation using multi-material additive manufacturing. One group of specimens was 3D printed from acrylonitrile-butadiene-styrene (ABS) material and the other group was printed from ABS and acrylic-styrene-acrylonitrile (ASA) as a substrate and coating material, respectively. The uncoated ABS specimens suffered significant degradation in the mechanical properties, particularly in the failure strain and toughness, during exposure to UV radiation, moisture, and high temperature. However, the ASA coating preserved the mechanical properties and structural integrity of ABS 3D printed structures in aggressive environments.

Experimental investigation into the flexural behaviour of basalt FRP reinforced concrete members

The durability of reinforced concrete structures is an ongoing challenge for engineers, particularly in harsh environments. In these conditions, concrete is susceptible to excessive cracking which allows water or other aggressive agents to penetrate the structure, thereby accelerating the deterioration, mainly through corrosion, of the steel reinforcement. The deteriorated concrete structures require frequent maintenance to achieve and extend their service life and may need expensive rehabilitation measures. The use of fibre-reinforced polymer (FRP) rebars, such as carbon and glass FRPs, can be an effective, sustainable and durable solution to enhance the durability of reinforced concrete structures in aggressive environments. Another type of FRP that has gained popularity in construction in the last two decades is basalt fibre-reinforced polymer (BFRP), which is the subject of the current paper. In order to investigate their behaviour, an experimental programme comprising five reinforced concrete beams and seven one-way spanning slabs has been conducted, and is described herein in detail. Three different types of reinforcement were included in the tests, namely sand-coated BFRP bars, ribbed BFRP bars as well as regular carbon steel reinforcement, for comparison. All of the members were tested up until failure. The test results are presented and analysed, with particular focus given to the cracking moment, ultimate moment capacity, deflections and also crack opening widths. The results are compared with the guidance currently available in several international design codes. In addition, based on the results and analysis presented herein, design recommendations for reinforced concrete with BFRP rebars are proposed.

Effects of Internal Force Redistribution on the Limit States of Continuous Beams with GFRP Reinforcement

Fiber-reinforced polymers (FRP) are commonly used as internal reinforcement in RC structures in aggressive environments. The design of concrete elements reinforced with FRP bars is usually ruled by serviceability criteria rather than the ultimate limit state. Six continuous concrete beams over two spans with longitudinal and transverse glass FRP (GFRP) reinforcement were investigated until failure to estimate the effects of different reinforcement arrangements on the limit states of continuous beams. The ratio of longitudinal reinforcement between the midspan and middle support sections (i.e., the design moment redistribution) and the type of GFRP reinforcement were the main parameters. The experimental results were compared to prediction models and other code formulations under serviceability and ultimate limit states. The bond-dependent coefficient kb was investigated to assess adhesion conditions for GFRP reinforcement and concrete. The results showed that moment redistribution in continuous beams with GFRP reinforcement happens with slippage between the reinforcement and concrete in the middle support without the load capacity being reduced. A modified model was suggested for better deflection prediction of continuous beams reinforced with GFRP bars. Based on deformability factors, the tested continuous beams, although containing GFRP reinforcement that has brittle behavior, showed a certain kind of ductile behavior.

Modified strip model for punching-shear strength of FRP-reinforced concrete edge–column slab connections

The use of fiber-reinforced polymer (FRP) bars as internal reinforcement for concrete structures in aggressive environments has emerged as an innovative solution to eliminate corrosion problems. Glass FRP (GFRP) reinforcing bars have recently gained wide acceptance as a viable construction material for sustainable new constructions due to their costing less than other FRP types. This paper reports the test results for full-sized edge–column slab connections (ECS –connections) reinforced with sand coated GFRP bars. These connections were cast using normal-strength concrete (NSC) and high strength concrete (HSC). The effect of concrete strength (NSC and HSC) and moment-to-shear force ratio (M/V) (300 mm, 600 mm) on the performance of the tested connections were examined. In addition, a new mechanical model, called Modified Strip Model, is presented for punching-shear strength predictions of FRP reinforced concrete (RC) ECS –connections. The test results reveal that the use of HSC directly augmented the punching-shear strength and improved the load–deflection response of the tested connections, However, Increasing the M/V ratio produced significant shear stresses, thus decreasing the punching-shear strength for the NSC and HSC connections, respectively. The mechanical model presented herein takes into account all possible mechanisms of loads transfer in FRP-RC ECS-connections. Hence, a complete shear–moment (V-M) interaction diagram can be plotted to predict the punching strength of such connections. Moreover, the model revealed higher accuracy and narrower scatter for punching-shear strength predictions compared to other available equations in FRP design codes and guides. The EN 1992–1-1–05 punching-shear equation was also examined for FRP-RC ECS–connections and adapted to consider the tensile properties of the FRP bars instead of steel.

СТРУКТУРА И СВОЙСТВА ЦЕМЕНТНОГО КАМНЯ С МОДИФИКАТОРАМИ

At present the durability of concrete is standardized by such indirect indicators as the quality of materials used, and the concrete and reinforced concrete technology. The regulatory documents determine concrete density indicators depending on the operating environment. The purpose of this research is to identify the role of the most common modifying agents in the formation of the structure, properties, and durability of artificial stone. It has been revealed that the maximum resistance to cyclic effects is achieved only through the simultaneous introduction of water-reducing and pozzolanic additives, which ensure the stability of the structural characteristics of hardened cement paste. During the operation of reinforced concrete structures in aggressive environments, the cause and the degree of aggressive character are determined, and primary, secondary and special protection are designed. Modification of hardened cement paste with polycarboxylate ether and microsilica additives contributes to the formation of hydrosilicate phases in the form of an uncrystallized gel or slightly crystallized gel-like C-S-H(I) phase with C/S = 1.1–1.3, and separate inclusions of calcium hydroxide are observed.

ОПТИМИЗАЦИЯ ПРОЦЕССА ВЫБОРА ТИПА ЦЕМЕНТА ДЛЯ ИЗДЕЛИЙ, ЭКСПЛУАТИРУЮЩИХСЯ В АГРЕССИВНЫХ СРЕДАХ

Currently, in industrialized countries in order to prevent corrosion of the hydration-hardened building products a tendency to use methods reducing the permeability of concrete to aggressive agents of the environment is applied. The authors believe that to protect concrete and reinforced concrete against corrosion, it is necessary to use all available means at the disposal of specialists, the most important of which is the correct choice of cement. Increasing corrosion resistance by reducing the water-cement ratio of the concrete mixture is a universal way, but not always it can ensure preserving the performance properties of concrete products and structures in aggressive environments for their entire service life. In this regard, recommendations for choosing the type of cement for the most frequently encountered aggressive environments are given. The analysis of literature sources shows that in many cases it is advisable to use cement with active mineral admixtures.

Effect of fly ash on the service life, carbon footprint and embodied energy of high strength concrete in the marine environment

Durability is one of the primary considerations in designing concrete structures in aggressive environments. This paper presents a study of concretes containing fly ash as 30% and 40% of the total binder in regards to service life, carbon footprint and embodied energy. A simple deterministic service life estimation technique using the well-known Fick’s law was applied to assess the service life of similar grade concrete mixes against the corrosion due to chloride diffusion. The parameters needed to predict the service life of concrete were determined from laboratory experiments. Compared to control concrete, fly ash concretes showed less chloride diffusion which is considered as the dominant form of attack in reinforced concrete structures in the marine environment and thus the latter is more durable or has a longer service life than the former. Finally, this paper presents the application of life cycle assessment to measure carbon footprint and embodied energy consumption saving benefits of the use of more durable fly ash concretes in the aggressive marine environment. About 36%–43% of carbon footprint and 36%–38% of embodied energy consumption can be avoided for different concrete covers due to replacement of 40% cement with fly ash.

Application of sensitivity analysis in the life cycle design for the durability of reinforced concrete structures in the case of XC4 exposure class

The aim of this study is to develop a new design procedure for the durability of the Reinforced Concrete (RC) structures in aggressive environments. The study approach developed here includes: (i) a qualitative analysis phase to characterize the design parameters and environmental exposure conditions of RC structures; (ii) a quantitative analysis phase, to establish the relationship between service life and design parameters and environmental exposure conditions using the service life prediction model firstly, and then to determine the most influential design parameters on service life using sensitivity analyses; and (iii) a final design phase, to design RC structures using some favorable values of the most influential design parameters firstly, and then to compare the service life thus obtained with that of RC structures designed using a standardized approach. An application is also proposed on simulated RC structure exposed to carbonation in Madrid (Spain). This RC structure follows the recommendations of the European standard EN 206–1 for XC4 exposure class. The sensitivity analysis results are discussed in detail including influence trends, importance ranking, non-monotonic effects and parameter interaction influences. The most influential design parameters obtained are cement strength class (fcem), water-to-cement ratio (W/C) and cement type (CEM). By using W/C of about 0.4, fcem of about 52.5 MPa and CEM I cement type instead of their limiting value as recommended by EN 206–1, the service life of the RC structure is significantly improved.

Wear and corrosion properties of HVOF coatings from Superduplex alloy modified with addition of boron

Fe-based protective coatings are promising alternatives to replace large or expensive mechanical structures in aggressive environments, such as, in petrochemical industries. In this work, we have evaluated the corrosion and abrasive wear resistance of coatings produced by the HVOF thermal spray process using the commercial SAF2507 Superduplex alloy modified by the addition of 3.0 wt% boron. Three coatings were obtained from different metal powders produced by different routes (spray forming and high energy ball milling). The coatings had a partially amorphous structure containing a dispersion of nanocrystalline borides, such as Fe3B and (Fe,Cr)2B. The coatings showed significant improvement in abrasive wear resistance and preserved the high corrosion resistance of the commercial SAF2507 Superduplex alloy.

Frame Construction Composites for Buildings and Structures in Aggressive Environments

In this paper, the new composite materials received on frame technology are presented. Theoretical bases of receiving frame composites from hydrodynamic, structural and mechanical and heatphysical positions are given. Physics and technology properties of new materials are considered. This work is devoted to researches in the field of development and creation of polymeric composite materials for production of monolithic sheetings and coverings of floors. It is shown that the frame technology gives the chance to receive construction materials and products with a combination of the most various and even incompatible properties knitting with in advance set complex and opens a way to the directed materials science. Theoretical bases of receiving materials of frame structure are established. Their main physics and technology properties are investigated. Improvement of physics and technology properties offrame composites in comparison with composites of usual structure is revealed.