Concrete Structures In Aggressive Environments Research Articles

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.

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.

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.

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.

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.

Review of Thaumasite Sulfate Attack on Cement Mortar and Concrete

AbstractDurability is one of the most important considerations regarding the design of new concrete structures in aggressive environments. Thaumasite sulfate attack (TSA) is one durability consideration. This paper reviews the features of TSA, factors affecting TSA, thaumasite formation mechanisms, and prevention measures. Finally, some needs for future studies are also suggested. TSA can completely destroy the cementitious binding ability of concrete by transforming it into a mush. Many factors affect thaumasite formation and TSA. The four primary factors affecting TSA on portland cement-based materials are low temperatures (below 15°C) and the presence of sulfates, carbonates, and moisture. Apparently, the dissolution–precipitation mechanism can be used to explain most phenomena during TSA. A procedure for field studies is also proposed. Both material compositions and surrounding environments should be considered for the prevention of TSA in concrete structures.

Durability properties of concrete with blended cements

AbstractThe study of chloride‐induced corrosion started more than three decades ago, after extensive cases of damage were observed on reinforced concrete structures in coastal regions and on infrastructural objects exposed to salt action. Nowadays, the basis for sustainable concrete industry lies in these three aspects: reducing CO2 emissions by using by‐products of other industries (slag, fly ash, silica fume) for cement production, conservation of natural resources by replacing part of the aggregate with recycled construction waste, as well as use of recycled water in concrete production, and finally, construction of durable concrete structures. Durability design procedures for reinforced concrete structures in aggressive environments are still to a large extent empirical, especially in the case of using blended cements. The type of cement has a considerable effect on the properties of concrete, especially concrete resistance to the penetration of chloride ions. The paper presents results of testing durability and deformational properties of concrete produced with quaternary‐blended cement. A clearer insight into these properties is a necessary starting point for the performance‐based design of concrete prepared with blended cements, leading to more durable and corrosion‐free concrete structures in aggressive environments.

Integral Water Repellent Concrete Produced by Addition of Metal Soaps

Laboratory testing and subsequent verification in practice has shown that surface impregnation of cement-based materials with silane prevents capillary uptake of water and aqueous salt solutions such as seawater or water containing deicing salts. Integral water repellent concrete can also be manufactured by adding silane-based compounds, such as silane emulsions to the fresh mix of concrete or mortar. Thus, service life of reinforced concrete structures in aggressive environments can be significantly extended by efficient water repellent treatment. This contribution presents the results of measurements carried out on integral water repellent concrete produced by addition of metal soaps. Four different types of metal soaps were added to the fresh concrete mix to achieve its integral water repellency. Chloride penetration into both reference and treated concrete was determined after exposure to seawater for 28 days. The distribution of the metal soaps in the treated concrete was also determined. It could be shown that chloride penetration into integral water repellent concrete prepared in the manner described was slowed down considerably. Although a complete chloride barrier could not be achieved by the addition of metal soaps, the service life of reinforced concrete structures can certainly be extended significantly by means of this technology.

Effect of fly ash and slag on the fracture characteristics of high performance concrete

The premature deterioration of concrete structures in aggressive environments has necessitated the development of high performance concrete (HPC). The major difference between conventional concrete and HPC is essentially the use of chemical and mineral admixtures. The improved pore structure of HPC achieved by the use of chemical and mineral admixtures causes densification of paste-aggregate transition zone, which in turn affects the fracture characteristics. Hence, studies were taken up to investigate the effect of fly ash and slag on the fracture characteristics of HPC. Beam specimens (geometrically similar and single size variable notch) with locally available fly ash (25%) and slag (50%) as cement replacement materials were prepared and tested in a servo-controlled Universal Testing Machine (UTM) under displacement control. From the value of the peak load for each beam, various fracture parameters were calculated. The results show that there is a reduction in the fracture energy due to addition of fly ash or slag, which can be attributed to the presence of unhydrated particles of size larger than that of normal flaws in concrete. Also due to densification, the post peak behaviour is steeper for the fly ash or slag based HPC mixes. The results of the investigation are presented in this paper.

Cellular Automata Approach to Durability Analysis of Concrete Structures in Aggressive Environments

This paper presents a novel approach to the problem of durability analysis and lifetime assessment of concrete structures under the diffusive attack from external aggressive agents. The proposed formulation mainly refers to beams and frames, but it can be easily extended also to other types of structures. The diffusion process is modeled by using cellular automata. The mechanical damage coupled to diffusion is evaluated by introducing suitable material degradation laws. Since the rate of mass diffusion usually depends on the stress state, the interaction between the diffusion process and the mechanical behavior of the damaged structure is also taken into account by a proper modeling of the stochastic effects in the mass transfer. To this aim, the nonlinear structural analyses during time are performed within the framework of the finite element method by means of a deteriorating reinforced concrete beam element. The effectiveness of the proposed methodology in handling complex geometrical and mechanical boundary conditions is demonstrated through some applications. Firstly, a reinforced concrete box girder cross section is considered and the damaging process is described by the corresponding evolution of both bending moment–curvature diagrams and axial force-bending moment resistance domains. Secondly, the durability analysis of a reinforced concrete continuous T-beam is developed. Finally, the proposed approach is applied to the analysis of an existing arch bridge and to the identification of its critical members.