Structural Concrete Applications Research Articles

Bonding Performance of Fiber-Reinforced Polymer-to-Concrete Joints under the Effect of Corrosion Cracking

Externally bonded (EB) carbon fiber-reinforced polymers (CFRPs) have been progressively considered for application in concrete structures. However, the corrosion of reinforcing steel bars (rebars) in reinforced concrete (RC), which is more common in coastal environments than in inland environments, can degrade structural performance. The bonding performance of FRP-to-concrete joints can be further deteriorated by the degradation of the interfacial bonding behavior between the rebar (or rebars) and concrete cross-sectional area reduction at the steel bar plane induced by rust expansion. In this study, the effect of rebar corrosion on the FRP bonding performance of RC components was experimentally investigated for the first time. Single shear tests assisted by a 3D optical displacement measurement system were used to obtain the full-field distribution of specimen displacements. The test results show that, although the corrosion level and diameter of the steel bar slightly affected the bonding strength of FRP-to-concrete, the corrosion crack width increased as the steel bar corrosion level increased, which affected the failure mode. Hence, as the corrosion level of the steel bars increased, the likelihood of concrete cover separation increased. Finally, a modified strength design model accounting for the rebar corrosion level was proposed in this paper.

Modeling of shear mechanisms and strength of concrete deep beams reinforced with FRP bars

With the growing application of concrete structures reinforced with fiber reinforced polymer (FRP) composite materials, it is necessary to develop more rational mechanical models for their load-carrying capacity evaluation. Firstly, this study numerically analyzed the influences of differences in bond behavior and axial stiffness between FRP and steel bars on the shear behavior of concrete deep beams. It was identified the reinforcement stiffness is the main influencing factor, and an explanation on how the reinforcement stiffness influences the shear performance of deep beams at the mechanism-level was also provided. On this basis, a mechanical cracking strut-and-tie model (CSTM), which theoretically considered the effect of the critical shear crack on the diagonal strut capacity, was proposed to predict shear mechanisms and strength of concrete deep beams reinforced with FRP bars. The proposed CSTM was verified by a shear database of 52 existing tests and compared with predictions of other models. In addition, for purpose of practical design, a simplified CSTM was proposed and verified to be superior to the shear models of CSA S086-12 and ACI 440.1R-15 in terms of safety margin and accuracy.

Temperature variation rates in concrete at low installation temperatures of bonded fasteners

AbstractPost‐installed bonded fasteners, also known as adhesive anchors, are used for the fastening of structural as well as nonstructural elements in a large variety of applications in concrete structures. The performance of these anchors is affected by the temperature conditions during the installation as well as over the design service life of the fastener. In this contribution, the temperature rates in the concrete, as relevant in the context of the installation of bonded fasteners at low installation temperatures, during winter months are investigated. Temperature sensors were installed in the concrete element at different depths. The concrete elements were stored in outdoor conditions for the period of this investigation. In addition, the temperature of the surrounding air as well as the solar radiation was measured. To investigate the influence of the color of the concrete, concrete elements with dark color as well as light color were used. The investigation shows that the temperature in the concrete at depths related to bonded fasteners may increase during the winter months at a rate of several degree Kelvin per hour. These results provide important information for the assessment of bonded fasteners installed at low installation temperatures.

Compressive strength evaluation of coral aggregate seawater concrete (CAC) by non-destructive techniques

Coral aggregate concrete (CAC) is a material that is becoming increasingly popular in reef concrete structural applications. In the present work, CAC was cast in a wide range of compressive strength varying from 30 to 75 MPa. The ultrasonic pulse velocity (UPV), the rebound hammer (RH) and the compressive strength (fcu) test were conducted at 28 and 90 days. The influence of sisal and age on the relationship between fcu - UPV and fcu - RH were discussed. Additionally, the mathematical model of strength prediction by UPV, RH and the combined method were established (testing strength curve, TSC). Finally, the applicability of TSC of Portland concrete (OPC) and lightweight aggregate concrete (LAC) to CAC were also discussed. The results show that the curing ages have a certain influence on the TSC. Therefore, the 28 d and 90 d strength test curves for special engineering by UPV, RH and combined methods were established. For ease of use, the TSC for regional engineering by various methods were also established. The relative standard error (er) of the TSC can meet the requirements of the specification for special and regional. In addition, the TSC of OPC and LAC does not apply to the strength prediction of CAC through the error analysis.

Experimental study on the enhancement of additional ribs to the bond performance of FRP bars in concrete

The deficient bond performance of Fiber-reinforced polymer (FRP) bars has impeded their application in concrete structures. To enhance this weak characteristic of FRP bars, the additional ribs as a new anchorage system applied on the bars was proposed in this paper. Its effect on the bond performance of the FRP bars was experimentally investigated through 36 pull-out tests with a centric FRP bar placement in concrete blocks. After the tests, the failure mode and bonding mechanism were discussed. The effects of the types of FRP bar, the anchorage length and the number of additional ribs on the bond properties of bars in concrete were also evaluated. Based on the results, it can be concluded that the additional ribs with radial force contributed greatly to the anchoring force. The utilization of additional ribs also changed the bonding force transferring mechanism between the FRP bars and the concrete. The end bearing that arose from the additional ribs reduced the occurrence of concrete splitting, and thus, the tensile strength of the FRP bars can be fully utilized. The test results also indicated that the additional ribs significantly improved the anchorage performance of the FRP bars in concrete. This improvement would continue with the increase in the number of additional ribs.

Residual behaviour of glass FRP bars subjected to high temperatures

The adoption of glass fiber reinforced polymer (GFRP) bars is becoming an interesting solution for different structural application, as a replacement of ordinary steel reinforcement, mainly for durability performance. The behavior of GFRP reinforcement, after high temperature exposure, is of critical importance for applications in concrete structures potentially subjected to fire. Accordingly, the aim of this study is the experimental evaluation of the residual behavior of GFRP bars subjected to different temperatures treatments, ranging between 100 and 700 °C. In particular, tensile tests on E-CR Glass FRP bars with nominal diameter of 14 mm were carried out after thermal treatment in an electric muffle, in order to characterize the degradation of the material residual properties after high temperature exposure. Young’s modulus and tensile strength decay were recorded. The experimental results are discussed with reference to practical structural applications as tunnel segmental lining.

Potential use of recycled construction and demolition waste aggregates for non- structural concrete applications

Promoting recycled aggregates from construction and demolition (C&D) waste for producing concrete will reduce the demand on conventional aggregates and it is an alternative to effectively manage C&D waste. Application of recycled C&D aggregates as a substitute to conventional aggregates in low strength concretes is the best way to initiate this in the industry. Therefore, this study focused on investigating the strength properties and the influence of time on the behaviour of strength gaining of concrete elements made by mixing the conventional aggregates and recycled C&D aggregates. The grade of the concrete was 25. The research methodology involved replacing the conventional coarse aggregates partially with 0 %, 20 %, 40 % and 60 % recycled C&D aggregates in concrete mixtures. Test cubes were cast for each percentage of the materials and other conditions were kept as constants. The test cubes were then subjected to compressive strength test under three test series. The test series were focused on different curing periods of the specimens as 7, 28 and 90 days to determine the behaviour of strength gaining with time. The conclusion drawn from the study is that it is feasible to substitute up to 40 % of coarse aggregates by recycled C&D aggregates in conventional low-intermediate strength concrete applications with the specified mix design.

Axial behaviour of circular steel tubed concrete stub columns confined by CFRP materials

Carbon fibre reinforced polymer material has many advantages, including high strength, light weight and good durability, resulting in good performance when it is used in concrete structures; however, the construction procedures of concrete columns confined by a CFRP tube are very complicated, leading to a relatively high cost. Therefore, CFRP-steel composite tubed concrete columns are suitable for application in concrete structures because of their excellent mechanical properties and convenient construction. In this paper, the axial static mechanical behaviour of circular CFRP-steel composite tubed concrete stub columns was investigated, including an experimental study and a theoretical analysis. Based on investigation of the strain efficiency of CFRP material, the calculation methods for the axial ultimate loading capacity of circular CFRP-steel composite tubed concrete stub columns were compared, and recommendations for practical design were provided.

Development and application of an environmentally friendly ductile alkali-activated composite

This paper presents a development of a ductile alkali-activated fly ash (FA) and ground granulated blast furnace slag (GBFS) based composite as an environmentally friendly material for structural concrete application. For this purpose, polyvinyl alcohol (PVA) fibres and sand aggregate were combined with alkali-activated paste. Workability, setting time, mechanical properties and failure mode of PVA fibres in the mixture were studied by slump test, Vicat needle test, flexural and compression tests, and Scanning Electron Microscopy (SEM) imaging, respectively. Although the mixture sets in a short period of time (less than 30 min), the workability was good and the developed fibre reinforced composite was used for a large scale application in a canoe. Casting a large volume (45 l compared to 3 l, as initially designed) did not affect the workability and the setting time of the mixture. Mechanical properties of specimens coming from “small” (3 l) and “large” (45 l) batches were tested at different ages (up to 120 days) and compared. It was shown that their flexural and compressive strength are similar, i.e. not affected by the upscaling. Furthermore, it was shown that the mixture with PVA fibres exhibits deflection hardening behaviour even with aggregate particles as large as 4 mm, although single crack localization led to failure. The SEM images of fractured surfaces indicated that combined fibre pull-out and fibre rupture occurred, with the latter one causing the final failure. The developed mixture, additionally reinforced with the plastic fiberglass mesh, was used in the 5.8 m long and 16 mm thick canoe for the student competition, which for the very first time, was constructed without the use of Ordinary Portland cement (OPC). The upscaling was successful and the results show the potential of fibre-reinforced alkali-activated FA and GBFS composite to be used as a durable and resistant material suitable for the structural application in thin shell elements, exemplified by the canoe. Such an application and a low risk project was suitable to gain the necessary experience and confidence with this innovative, “concrete like”, material for which no codes or regulations are available. Furthermore, similar applications are the first step for larger scale structural applications, like structural elements in the building industry, bridges and other civil engineering structures.

Ultrasonic tests in the evaluation of the stress level in concrete prisms based on the acoustoelasticity

The ultrasonic pulse velocity method is a nondestructive test commonly used for the determination of the elastic properties of materials and verification of non-homogeneities and damages in structural elements. Another application for the ultrasound is the measurement of the stress state in a material. However, the use of ultrasonic waves for the latter purpose has been poorly studied, mainly regarding application in concrete structures. This paper addresses the use of ultrasound for the evaluation of stresses in concrete structures. Uniaxial compression tests were performed on concrete prisms. During the tests, longitudinal and shear ultrasonic waves were emitted to specimens subjected to different compressive stress levels. The results showed the increase of compression stress leads to higher velocities of ultrasonic waves, which proved the acoustoelastic effect. Such behavior was not observed in longitudinal waves emitted perpendicularly to the direction of the stress application. The largest increase in velocity was observed for longitudinal waves propagating in the same direction of the load application (variations on the order of 1%). Acoustoelastic coefficients were determined for each tested prism, according to the change in the velocities of the ultrasonic waves. The present study contributed to the knowledge on the acoustoelastic behavior of the concrete elements and shows the potential of ultrasonic tests to evaluate the stress state in concrete structures.

Enhanced bamboo composite with protective coating for structural concrete application

Potential application of newly developed bamboo composite material as structural reinforcement called forth for durability test and bond strength examination. Firstly, durability of bamboo composite material and effectiveness of protective epoxy coating were evaluated by subjecting samples to various corrosive environments normally encountered during the life span of construction materials. At accelerated conditions, samples were immersed in water, simulated acidic rain solution and simulated concrete pore water solution for 28 days. Tensile tests and microstructural analysis were conducted to investigate the impact of different corrosive environments on the bamboo composite material’s behavior. The results revealed that the application of epoxy coating successfully protected bamboo composite material’s integrity without substantially affecting its mechanical capacity, particularly in acidic environment. Secondly, bond strength between bamboo composite material and concrete was investigated through pull-out tests. The epoxy coating improved the bond strength, especially with addition of sand particles. The findings of this study suggest that epoxy coating can be an effective approach to simultaneously enhance the bamboo composite material’s resistance towards acid attack and improve its bond strength with concrete for concrete reinforcement application.

Fatigue performance of prestressed concrete beams using BFRP bars

Basalt fibers have recently been introduced as a promising addition to the existing fiber reinforced polymer (FRP) family. A limited amount of information is available on basalt FRP (BFRP) bars and their structural concrete applications. This paper presents the flexural behaviour of sixteen prestressed concrete beams using BFRP bars under monotonic and fatigue loading. The investigated parameters were the level of prestress of the bars (0%, 20% and 40% of their static tension capacity) and the fatigue load ranges. The experimental findings showed that beams with the bars prestressed to 40% of the bar strength had a higher fatigue strength than those prestressed to 0% and 20%. For 40% and 20% prestressed beams, there is no improvement in fatigue performance for load ranges above 20% and 13% of the ultimate capacity of the beams a level at which calculations showed that the remaining prestress did not close cracks at the minimum load in the fatigue load cycle. When compared on the basis of load range versus cycles to failure, the data for the three beam types fell onto a single curve at load levels where the remaining prestress after fatigue creep relaxation no longer closed the crack at the minimum load.

Durability performance of sustainable structural concrete: Effect of coarse crushed concrete aggregate on rapid chloride migration and accelerated corrosion

The increasing use of crushed concrete aggregates (CCA), formerly referred to as recycled concrete aggregates (RCA), has led to research into the effects of coarse CCA in higher value structural applications. Concerns exist regarding the effect on chloride ion ingress which ultimately can cause deterioration of reinforced concrete. This concern is reflected in existing European and British concrete design standards as limitations prevent their use in environments where chlorides may be present. The rapid chloride migration coefficient and rate of accelerated corrosion of structural CEM I and CEM III/A CCA concretes was measured to determine the effect on chloride ion ingress. Three sources of coarse CCA were evaluated; results show that coarse CCA generally had a detrimental effect on the chloride ion ingress of structural concrete. However, these effects can be mitigated by the inclusion of GGBS to produce structural CEM III/A concretes, thus allowing higher proportions of coarse CCA. It is recommended that the GGBS and coarse CCA content be limited to 50% and 60% respectively as this reduces the risk of a significant detrimental effect on chloride ion ingress. The results also suggest that the limitations in existing European and British standards are conservative and sustainable structural CEM III/A concrete with the inclusion of coarse CCA could be a viable option for future responsibly sourced projects, provided that a reliable and consistent source of CCA can be obtained. This is a positive outcome for the wider implementation of coarse CCA into structural concrete applications.

Microstructure, dielectric and piezoelectric properties of 0–3 lead free barium zirconate titanate ceramic-Portland fly ash cement composites

Piezoelectric ceramic – Portland cement composites have been developed for sensor application in concrete structures to overcome the acoustic matching problem that may occur for piezoelectric ceramic or polymers with concrete. Pozzolanic materials such as fly ash are commonly used in concrete to enhance durability. The objectives of this research were to investigate the effects of fly ash addition on the physical properties, dielectric properties and piezoelectric properties of 0–3 barium zirconate titanate ceramic– Portland cement composites. The results showed that the dielectric constant of these composites decreased when the fly ash content in the composite increases. However, the piezoelectric coefficient (d33) value of BZT–PC composite with fly ash 10% by volume was found to be similar to that of BZT–PC composites.

A novel embeddable spherical smart aggregate for structural health monitoring: part II. Numerical and experimental verifications

The newly developed spherical smart aggregate (SSA) based on a radially polarized spherical piezoceramic shell element has unique omnidirectional actuating and sensing capabilities that can greatly improve the detection aperture and provide additional functionalities in health monitoring applications in concrete structures. Detailed fabrication procedures and electrical characterization of the SSA have been previously studied (Part I). In this second paper (Part II), the functionalities of the SSA used in both active sensing and passive sensing approaches were investigated in experiments and numerical simulations. One SSA sample was embedded in a 1 ft3 concrete specimen. In the active sensing approach, the SSA was first utilized as an actuator to generate stress waves and six conventional smart aggregates (SA) mounted on the six faces of the concrete cube were utilized as sensors to detect the wave response. Conversely, the embedded SSA was then utilized as a sensor to successively detect the wave response from each SA. The experimentally obtained behavior of the SSA was then compared with the numerical simulation results. Further, a series of impact tests were conducted to verify the performance of the SSA in the detection of the impact events from different directions. Comparison with the wave response associated with different faces of the cube verified the omnidirectional actuating and sensing capabilities of the SSA.

Strength and stiffness of concrete with recycled concrete aggregates

By crushing old concrete to make recycled concrete aggregates (RCA) for use in new concrete, the overall environmental impacts of concrete are reduced. However, a better understanding of the use of RCA in new concrete is necessary before adoption in structural concrete applications can be widely realized. In particular, the strength, stiffness (Modulus of Elasticity), workability, and durability of concrete using RCA can be different than concrete that uses natural aggregate (NA). Variability in RCA properties from source to source also must be addressed if guidelines for RCA use are to be adopted. This paper describes properties of RCA and recycled aggregate concrete (RAC) with materials from four distinct areas of the United States (Northeast, South, Midwest and Southwest regions), making this study the most geographically varied study of RCA known. Variability in aggregate properties and the relationships between them are addressed within the paper. Equations allowing concrete mix designers to predict strength and stiffness of mixes are shown to be applicable across a much broader range of RCA properties than previously known. Similarly to concrete with natural aggregates, the strength and stiffness of RAC is shown to be impacted by the gradation of the coarse aggregates – smaller aggregates make stronger, stiffer concrete.

Durability performance of sustainable structural concrete: Effect of coarse crushed concrete aggregate on microstructure and water ingress

The use of crushed concrete aggregate (CCA), formerly referred to as recycled concrete aggregate (RCA) is increasing, particularly with a recent push towards sustainable sourcing of materials. Further research is required to understand the effect of coarse CCA on the mechanical properties and durability performance of structural concrete. The electrical resistivity, water absorption by capillary action and SEM analysis of CEM I and CEM III/A concretes were investigated to determine the effects on concrete microstructure and water ingress, together with compliance of characteristic (fc,cube) and target mean compressive strengths. The results show that for the three coarse CCA sources tested, the inclusion of coarse CCA generally has a detrimental effect on the microstructure and water ingress of structural concrete. These can be largely overcome through the incorporation of GGBS to produce CEM III/A concretes, allowing higher proportions of coarse CCA to be incorporated. We conclude that the GGBS and coarse CCA content be limited to 50% and 60% respectively, as this reduces the risk of a significant reduction of compressive cube strength and durability performance. The findings suggest that sustainable structural CEM III/A concrete can be a viable option for future responsibly sourced projects, provided that a reliable and consistent source of CCA can be obtained. This is a positive and significant outcome for the wider implementation of coarse CCA into structural concrete applications.

Bond-Slip Behavior of Basalt Fiber Reinforced Polymer Bar in Concrete Subjected to Simulated Marine Environment: Effects of BFRP Bar Size, Corrosion Age, and Concrete Strength

Basalt Fiber Reinforced Polymer (BFRP) bars have bright potential application in concrete structures subjected to marine environment due to their superior corrosion resistance. Available literatures mainly focused on the mechanical properties of BFRP concrete structures, while the bond-slip behavior of BFRP bars, which is a key factor influencing the safety and service life of ocean concrete structures, has not been clarified yet. In this paper, effects of BFRP bars size, corrosion age, and concrete strength on the bond-slip behavior of BFRP bars in concrete cured in artificial seawater were investigated, and then an improved Bertero, Popov, and Eligehausen (BPE) model was employed to describe the bond-slip behavior of BFRP bars in concrete. The results indicated that the maximum bond stress and corresponding slip decreased gradually with the increase of corrosion age and size of BFRP bars, and ultimate slip also decreased sharply. The ascending segment of bond-slip curve tends to be more rigid and the descending segment tends to be softer after corrosion. A horizontal end in bond-slip curve indicates that the friction between BFRP bars and concrete decreased sharply.

Evaluation of Resistance of Intermetallic Fe-Zn Coating in the Model Environment as Concrete Pore Solution

Article assesses the effectiveness of intermetallic Fe-Zn coating on steel elements due to their potential application in concrete structures. Introduction part of this article summarizes corrosion behavior of hot-dip galvanized steel in fresh and aged concrete with focusing on corrosion resistance intermetallic Fe-Zn (especially ζ phase-FeZn13). Resistance of unconventional Fe-Zn coating created on the steel was tested in model pore solution of concrete. Results were evaluated by the time flow of spontaneous corrosion potential and polarization resistance. Based on the measured data we can say that the Fe - Zn - (Al) coating has a similarly low resistance in an alkaline environment like coatings obtained with conventional hot-dip galvanizing process.

Improving the Quality of Mixed Recycled Coarse Aggregates from Construction and Demolition Waste Using Heavy Media Separation with Fe3O4 Suspension

The primary objectives of this study are to investigate the feasibility of a heavy media separation process with magnetite (Fe3O4) suspension for upgrading the quality of mixed recycled coarse aggregates from construction and demolition waste (CDW) in Korea and to determine a range of effective operating density of Fe3O4 suspension for producing high-quality RCA acceptable to structural concrete applications. For the purposes, six 200 kg recycled coarse aggregates (RCAs) samples were collected from a conventional recycling plant in Korea. Subsequently, the samples were processed by a heavy media separation process using Fe3O4 suspensions with various densities from 2.65 g/cm3 to 2.40 g/cm3 with an interval of 0.05 g/cm3. Next, a series of tests was performed in the laboratory to evaluate properties of finished sink and float products from the HMS processes, including oven-dry density, absorption capacity, and physical durability. Furthermore, compressive strength of concrete cylinders (150 mm by 300 mm) made of the finished sink products from Fe3O4 suspensions with three different densities (2.4, 2.5, and 2.6 g/cm3) was tested in this study. As a result, it was demonstrated that the HMS process using Fe3O4 suspension with a density ranging between 2.40 and 2.65 g/cm3 was effective for upgrading mixed CDW RCAs in Korea to high-quality RCAs acceptable for structural concrete applications.