Structural Concrete Applications Research Articles

Experimental and analytical behavior of one-way fiber foamed concrete slabs reinforced with/without glass fiber grid under 4-point flexural test

PurposeThe primary objective of this study is to produce one-way slabs made of LWFC with low density and sufficient compressive strength suitable for structural purpose then investigate their flexural behavior under various types of reinforcement and thickness of the slab and the influence of addition of PP fibers reinforcement on the mechanical behavior of reinforced concrete slabs. The specimens were tested using four-point loading. The results concerning load capacity, deflection and failure mode and crack pattern for each specimen were obtained. Also, an analytical investigation of PP fiber and GFG contribution on the flexural behavior of foamed concrete slabs is studied to investigate the significant role of PP fiber on the stress distribution in reinforced foam concrete and predict the flexural moment capacity.Design/methodology/approachThe materials used in this study are cement, fine aggregate (sand), water, PP fibers, foaming agent, chemical additives if required, steel reinforcing rebars and glass fiber grid. The combination of these constituent materials will be used to produce foamed concrete in this research Then this study will present the experimental program of one-way foamed concrete slabs including slabs reinforced with GFR grids and another with steel reinforcements. The slabs will be tested in the laboratory under static loading conditions to investigate their ultimate capacities. The flexural behavior is to the interest of the slabs reinforced with GFR grids reinforcements in comparison with that of one with steel reinforcing rebars. Three groups are considered. (1) Group I: two slabs of PP fiber foamed concrete with minimum required reinforcements. (2) Group II: two slabs of PP fiber foamed concrete with glass fiber grids. (3) Group III: two slabs of PP fiber foamed concrete with the minimum required reinforcements and glass fiber grids.FindingsThe experimental results proved the effectiveness and efficiency of this the new system in producing a low density of concrete below 1900 kg/m3 had a corresponding strength of about 17 MPa at least. Besides, the presence of PP fibers had a noticeable improvement on the flexural strength values for all the examined slabs. It was found that the specimens reinforced with steel reinforcement mesh carried higher flexural capacity compared to these reinforced with GFG only. The specimens reinforced with GFG exhibited the lowest flexural capacity due to GFG separation from the concrete substrate. Also, an analytical investigation to predict the flexural strength of all tested specimens was carried out. The analytical results were agreed with the experimental results. Therefore, LWFC can be used as a substitute lightweight concrete material for the production of structural concrete applications in the construction industries today.Research limitations/implicationsFoamed concrete is a wide field to discuss. To achieve the objectives of the project, the study is focused on the foamed concrete with the following limitations: (1) because the aim of this research is to produce foamed concrete suitable for structural purposes, it is decided to produce mixes within the density range 1300–1900 kg/m3. (2) Simply-supported slabs are of considered. (3) This study also looks out by using GFR and without it.Originality/valueThe main objectives of this study were producing structural foamed concrete slabs and investigate their flexural response for residential uses.

Effects of low temperatures and cryogenic freeze-thaw cycles on concrete mechanical properties: A literature review

In recent years the application of concrete material in environment with very low temperatures is on the rise. However, systematic knowledge on the mechanical behavior of concrete at low temperatures are not readily available for most researchers and engineers. In the 1970s to 1980s the cryogenic behavior of concrete was intensively studied by researchers from western countries, but after that relevant research activities decreased until it regains researchers’ interests in recent years. Boosted by the rapid development of economy in China, Chinese researchers start to focus on this topic again and have contributed some new knowledge in this respect. To help researchers and engineers design, analyze and construct concrete structures in the cryogenic environment, this paper presents a literature review on the mechanical properties of concrete subjected to low temperatures and cryogenic freeze-thaw cycles. First the effects of low temperatures on the main properties of concrete including compressive strength, tensile strength, elastic modulus, etc., are reviewed and the existing mathematical models are summarized and compared. In the second part, the concrete damage induced by cryogenic freeze-thaw cycles is discussed, and emphasis is put on the mechanism of cryogenic freeze-thaw damage. The complied conclusions by the review paper can facilitate and safeguard the application of concrete structures at very low temperatures.

Physical and Mechanical Properties of Reinforced Concrete from 20th-Century Architecture Award-Winning Buildings in Lisbon (Portugal): A Contribution to the Knowledge of Their Evolution and Durability

The use of concrete materials in Portugal, namely reinforced concrete, began in the 19th century. However, during the 20th century, the increase in the application of this composite material, alongside the use of hydraulic binders, led to a disruption of traditional construction techniques and enhanced generalized application in concrete structures, combining aesthetics with functionality. In this paper, the authors will present and discuss several physical and mechanical characteristics of reinforced concrete materials from 12 award-winning architectural buildings constructed between the 1930s and the end of the 20th century in Lisbon, Portugal. These results are vital to evaluate their durability, as those buildings have an undiscussable heritage value in the context of 20th-century buildings’ valorization. Furthermore, the results will contribute to the knowledge of the current state of conservation of these materials and will allow an understanding of the evolution in the application of national regulations during this period.

Multi-Technique Approach to Enhance the Properties of Fine Recycled Aggregate Concrete

This study investigated the properties of fine recycled aggregates (FRA), with a view to enhancing their properties for structural concrete applications. The study explored several approaches including mixing; curing; systematic screening of FRA particles below 1.18 mm to reduce the adhered cement paste (ACP) content; and the use of fly ash as 30% cement replacement to modify the microstructure of FRA concrete. To test these approaches, two series of concrete mixes were prepared at 0.45 and 0.55 w/b ratio, with FRA replacing natural sand at 0, 25, and 50% by mass, and tests were carried out after 3, 28, and 180 days of curing. Results show that the combination of ACP reduction and fly ash treatment significantly enhanced the compressive strength and elastic modulus of FRA concrete, especially at 180 days, through microstructure modification and pozzolanic reactions.

Fundamental Studies on the Use of Distributed Fibre Optical Sensing on Concrete and Reinforcing Bars.

Distributed fibre optical sensing (DFOS) allows for quasi-continuous strain measurement in a broad range of gauge lengths and measurement frequencies. In particular, Rayleigh backscatter-based coherent optical frequency domain reflectometry has recently registered a significant application increase in structural concrete research and monitoring thanks to its numerous merits, such as high resolution and low invasiveness. However, it is not a plug-and-play technique. The quality of the acquired data depends highly on the choice of the fibre optical sensor and the methods of instrumentation and post-processing. Furthermore, its unprecedented resolution and sensitivity allow capturing local effects not well documented so far. This paper analyses the suitability of DFOS based on Rayleigh backscatter for reliably measuring strains and discusses the origin and structural relevance of local variations in the results. A series of experimental investigations are presented, comprising tensile tests on bare reinforcing bars and concrete compression tests. A critical analysis of the results leads to a best practice for applying DFOS to reinforcing bars and concrete, which establishes a basis for reliable, accurate measurements in structural concrete applications with bonded reinforcement.

A review of studies on concrete structures prestressed with external fiber reinforced polymer composites tendons

The studies on concrete structures prestressed with external fiber reinforced polymer (FRP) tendons are reviewed in the aspects of FRP tendon, key technology and structural component, in this review. The tensile properties and long-term behaviors of FRP tendon are firstly introduced. The design-oriented values of creep-rupture stress, relaxation rate and the limits of maximum fatigue stress and fatigue stress range are provided. The advantages and deficiencies of three main types of anchor for FRP tendon, and the methods of reducing the stress concentration on FRP tendon at anchor are elaborated. The newly-developed composite-wedge anchor is emphasized, which possesses an anchor efficiency coefficient exceeding 90%. Meanwhile, the curvature radius of deviator is recommended to be larger than 200 times of the radius the cross-section of FRP tendons, and the bending angle of FRP tendons should not exceed 5°, based on the experimental results on the mechanical properties of deviated FRP tendons. The experimental results of concrete beams prestressed with external FRP tendons are reviewed, including monotonic loading, sustained loading and cyclic loading. The design methodologies in the codes at home and overseas are introduced. The accuracies of the calculating methods in the codes are evaluated using the experimental data of forty-two beams, and the methods in the Chinese code GB 50608—2020 are validated to be accurate in the design calculation for concrete structures prestressed with external FRP tendons. This paper is expected to actively promote the popularization and application of concrete structures prestressed with external FRP tendons.

Recent developments in Polyvinyl-chloride tube filled with concrete

This study highlights the recent developments in the use of Polyvinyl-chloride (PVC) in the construction technology. The PVC is a very versatile plastic, resistant to fire (prevents the spread of fire) wear and rupture, with excellent anti-chemicals and anti-corrosion characteristics. The material could be produced with plasticizers (PVC, more flexible) or without (uPVC, more rigid). The thermoplastic polymer is the most widely used polymer for structural concrete applications; either as a simple tube for pour-in concrete or the more complicated Stay-in-place formwork (SIPF) systems. In this study, the structural performance of uPVC-encased concrete (uPEC) used as a compression member is reviewed, for the period start-end of 2020, with emphases on the resistance of these members to the applied axial load. The study is extended to cover the seismic behavior of these confining devices when used in combination with the brittle concrete. Several strength models have been proposed for evaluating the bearing capacity of uPEC columns under monotonic axial compression load. Most of these models are based on limited number of test results and might yield unsatisfactory predictions. On the other hand, the number of models for predicting the strain at peak stress are limited. The main features of these models were reviewed and recommendations presented for future research.

Enhanced durability performance of cracked and uncracked concrete by means of smart in-house developed superabsorbent polymers with alkali-stable and -unstable crosslinkers

For the past two decades, research on the use of superabsorbent polymers (SAPs) in cementitious materials has proven that these innovative materials have the potential to become a suitable admixture in the concrete industry. Not until recently, most of the applications studied made use of SAPs originally designed to be used in other industries, such as in food, agricultural and hygiene products. In this paper, an innovative “in-house” developed SAP (SAPX) is presented, designed with a double crosslinking system specifically for applications in concrete structures. Its efficiency is compared with two commercially available SAPs (SAP1 and SAP2) for different applications. The “in-house” developed SAP promoted an immediate sealing effect of cracked concrete specimens as reflected by a reduction of 72% in the water permeability of specimens with cracks up to 250 µm compared to specimens without SAPs. A superior performance was also found against frost attack in salt scaling after 28 cycles of freezing and thawing. Although no complete mitigation of shrinkage was noticed, SAPX promoted a significant reduction in the shrinkage strain at early ages and up to 28 days. In terms of mechanical properties, SAPX reduced the strength to a comparable extent as SAP1 and less than SAP2. To conclude, SAPX showed a better performance compared to the already commercialized SAPs and has a high potential towards large-scale production to be exploited for concrete applications.

Sodium hydroxide-free geopolymer binder for prestressed concrete applications

Geopolymer is a sustainable binding material which can be produced from industrial by-products, such as fly ash and ground granulated blast furnace slag. Despite having higher mechanical strengths and durability properties than conventional ordinary Portland cement (OPC) concrete, geopolymer concrete has not been widely used in structural grade concrete, so far. The safety hazards in mixing and handling of concrete due to the use of liquid sodium hydroxide in geopolymer binder is one of the barriers to the adaptation of geopolymer in the concrete industry. This study aims to use sodium hydroxide-free one-part geopolymer binder for structural concrete applications, such as prestressed concrete beams. In this study, the mechanical and serviceability properties of grade 50 MPa geopolymer concrete cured at ambient temperature are investigated and compared against same grade OPC concrete. The effects of tensile strength of concrete in load–deflection behaviours of prestressed concrete beams of different spans and sizes are investigated using finite element analysis for short-term and long-term durations. This study finds that geopolymer concrete has around 27% higher indirect-tensile and flexural strengths than OPC concrete of same strength grade which contributes to geopolymer prestressed concrete beams to withstand around 20% higher first-crack load than OPC concrete beams of same span. In addition, geopolymer prestressed concrete beams show a relatively smaller loss in prestressing stress which results in a smaller loss in flexural capacity of beams over the service life of the structure.

Strength, permeation, freeze-thaw resistance, and microstructural properties of self-compacting concrete containing sandstone waste

This investigation aims to identify the possible utilization of sandstone slurry (SS) as an eco-friendly alternative material in self-compacting concrete (SCC). The SCC mixes made with six percentages (0, 5, 10, 15, 20, 25, and 30) of SS as partial substitution of Portland Pozzolana cement (PPC). Characterization of SS has been performing through the microscopic image, X-ray diffraction (XRD) analysis, methylene blue, and particle size distribution (PSD) analysis. The modified concrete’s strength parameters report via microstructure, compressive strength, pull-off strength, and flexural tensile strength. Sorptivity, carbonation, chloride ion penetration, mercury intrusion porosimetry, and freeze and thaw tests measure durability, along with the economic indexes. The compressive strength, flexural strength, and pull-off strength results of the modified concrete were lower than that of the control concrete. However, it improved gradually with increased curing ages. Mercury intrusion porosimetry test revealed an enhancement in the porosity with an increment in the percentage of SS, leading to an augmentation in the capillary water absorption capacity, depth of carbonation, and chloride penetration. However, at lower water to powder ratio (0.33) and up to 15% of SS content, the durability test results commensurate with that of the control concrete, also supported by microstructural analysis. The specimens were highly resistant against freeze and thaw cycles from weight loss as well compressive strength point of view. Economic index analysis shows a decrement in the index values with an increment in the SS content. It deduces that the partial substitution of SS up to 15% may recommend for structural concrete applications.

Structural Behavior of Reinforced Concrete Beams Incorporating Foamed Glass as Aggregates

Natural resources that are utilized in civil engineering applications can be saved by replacing them with some recycled materials to produce sustainable concrete with required mechanical and durability properties. In recent years, recycled glass is being used as aggregates in concrete production in many countries across the world. In the present study, the structural properties of reinforced concrete beams containing foamed glass (FG) as a partial natural coarse aggregate replacement are investigated. Five concrete mixes were employed to conduct the present study. The coarse aggregate was replaced with 0%, 25%, 50%, 75%, and 100% (by volume) of FG. Four point-loading flexural tests on beams were conducted up to failure. The results showed that the compressive strength was decreasing linearly with the increasing amount of FG. It was also observed that the ductility of the reinforced concrete beams significantly improved. However, the load-carrying capacity of the beam and load at which the first crack occurs was reduced. It was concluded that the inclusion of FG in structural concrete applications is possible and the structural behavior of concrete beams proved to be similar to that of other types of lightweight aggregate concrete such as wood and plastic aggregates used in similar structural elements.

Optical fiber sensors based on sol–gel materials: design, fabrication and application in concrete structures

This review provides an overview of the state-of-the-art of OFS based on sol–gel materials for diverse applications with particular emphasis on OFS for structural health monitoring of concrete structures.

Bond behavior of iron-based shape memory alloy reinforcing bars embedded in concrete

Iron-based shape memory alloys (Fe-SMA) have shown a strong potential for strengthening applications in concrete structures. This paper presents an experimental study on the bond strength and bond-slip behavior of ribbed Fe-SMA bars embedded in concrete. A total of nineteen pullout tests were conducted to study the bond behavior of 16-mm Fe-SMA bars embedded in concrete specimens with different levels of passive confinement. Prior to specimen fabrication, the bars were pre-strained (at 4% or 8%) and then activated by resistive heating after concrete casting. The experimental study considered different activation temperatures (160 °C, 300 °C, and no activation) to evaluate their effects on bond performance. Five specimens with conventional steel bars were also tested to establish a direct comparison with conventional reinforcement. Unconfined pullout specimens failed by splitting of concrete in most of the cases, while confined specimens presented pullout failures and higher bond strengths. In general, the Fe-SMA bars presented similar bond performance as conventional steel bars. However, the bond strength of unconfined specimens was reduced with the activation temperature. For confined specimens, the activation temperature had a minor effect on the bond strength. Local bond stress-slip relations derived from tests have also been compared with two analytical bond-slip laws available in the literature. Finally, the transfer length of Fe-SMA bars in prestressing applications has been estimated based on the experimental data and a simple analytical model of the bond stress distribution along the embedment length of a bar.

Durability characteristics of high and ultra-high performance concretes

Durability characteristics of high-performance concrete (HPC) and ultra-high performance concrete (UHPC) are evaluated in comparison to normal strength concrete (NSC). HPC and UHPC are cast using commonly available materials with no special heat treatment. Concrete resistivity, rapid chloride permeability, sorptivity, porosity, and resistance to chloride migration and carbonation of these three types of concrete are assessed. Microstructure and hydration products are investigated using scanning electron microscope (SEM) imaging and X-ray diffraction (XRD) analyses, respectively. Potential enhancement in the service life of reinforced concrete (RC) structures when concrete is replaced with HPC and UHPC is predicted using the time-to-corrosion model. Dense microstructures, high electrical resistance, negligible chloride permeability, low sorptivity, no carbonation ingress are observed in HPC and UHPC. The chloride diffusion coefficient was found to be at least three orders of magnitude lower in UHPC compared to NSC, which could delay the corrosion initiation of steel reinforcement. With such positive attributes, these concretes are expected to find more widespread application in concrete structures in harsh-climatic conditions. This paper provides additional data and analysis that could accelerate the adoption of these materials in practice.

Applicability of seawater as a mixing and curing agent in 4-year-old concrete

In certain scenarios, seawater may be the only mixing/curing agent available; hence, it is necessary to optimize conditions for its application in concrete structures. In this study, the applicability of seawater as a mixing and curing agent in 4-year-old mortar cement specimens is evaluated. Unlike previous studies, we focused on evaluating the long-term performance of reinforced mortar specimens exposed to seawater. Specimens comprised ordinary Portland cement (OPC), grand granulated blast furnace slag (GGBFS), and reinforced concrete with plain steel, epoxy-coated, or stainless-steel bars; they were subjected to wetting–drying cycles (mimicked for tidal/splash zones) in the laboratory, and the corrosion was evaluated through electrochemical techniques. The results indicate that the effect of seawater on corrosion activity is considerably higher as a curing agent than that as a mixing agent. Further, GGBFS exhibited better performance than OPC; similarly, epoxy-coated and stainless-steel bars exhibited better corrosion resistance than plain steel bars. The results obtained in this study highlight the need to study the application of seawater in concrete mixing.

From numerical prototypes to real models: a progressive study of aerodynamic parameters of nonconventional concrete structures with Computational Fluid Dynamics

Abstract The practical evaluation of aerodynamic coefficients in unconventional concrete structures requires specific studies, which are small-scale models evaluated in wind tunnels. Sophisticated facilities and special sensors are needed, and the tendency is for modern and slender constructions to arise with specific demands on their interaction with the wind. On the other hand, the advances obtained in modern multi-core processors emerge as an alternative for the construction of sophisticated computational models, where the Navier-Stokes differential equations are solved for fluid flow using numerical methods. Computations of this kind require specialized theoretical knowledge, efficient computer programs, and high-performance computers for large-scale calculations. This paper presents recent results involving two real-world applications in concrete structures, where the aerodynamic parameters were estimated with the aid of computational fluid dynamics. Conventional quad-core computers were applied in simulations with the Finite Volume Method and a progressive methodology is presented, highlighting the main aspects of the simulation and allowing its generalization to other types of problems. The results confirm that the proposed methodology is promising in terms of computational cost, drag coefficient estimation and versatility of simulation parameters. These results also indicate that mid-performance computers can be applied for preliminary studies of aerodynamic parameters in design offices.

Influence of structural parameters on the properties of fibred-foamed concrete

The demand for novel technology for manufacturing lightweight concrete has increased in the global construction industry. Therefore, studies that explore alternative lightweight concrete systems for structural applications are urgently needed. The objective of this study is to develop structural fibred-foamed concrete (SFFC) by the addition of polypropylene (PP) fibre, fly ash (FA), and silica fume (SF). Foamed concrete (FC) was obtained by replacing sand with FA. The properties of the FC were enhanced with PP fibre and fine SF. SFFC with dissimilar densities of FC (1000, 1300, 1600, and 1900 kg/m3) is essential for examining compressive, flexural, and splitting tensile strengths, drying shrinkage, and creep. The FC with a density of 1000–1900 kg/m3 and compressive and splitting tensile strengths of 10–70 MPa and 1.1–4.81 MPa, respectively, have been made by the addition of PP fibre and fine SF. Fine SF and PP fibre considerably improved the hardened strength of the FC. Additionally, the inclusion of PP fibre significantly enhanced the tensile strength and increased the creep resistance and drying shrinkage. Therefore, SFFC can be used as a substitute lightweight concrete material for the production of structural concrete applications in the construction industries today.

Performance properties of structural fibred-foamed concrete

Abstract The demand for novel technology for manufacturing lightweight concrete has increased in the global construction industry. Therefore, studies that explore alternative lightweight concrete systems for structural applications are urgently needed. The objective of this study is to develop structural fibered foamed concrete by the addition of polypropylene fiber, fly ash, and silica fume. Foamed concrete was obtained by replacing sand with fly ash. The properties of the foamed concrete were enhanced with polypropylene fiber and fine silica fume. Structural fibered foamed concrete with dissimilar densities of foamed concrete (1000, 1300, 1600, and 1900 kg/m3) is essential for examining compressive, flexural and splitting tensile strengths, drying shrinkage and creep. The foamed concrete with a density of 1000–1900 kg/m3 and a hardened strength of 10–70 MPa have be made by the adding of polypropylene fiber and fine silica fume. Fine silica fume and polypropylene fiber considerably promoted the hardened strength of the foamed concrete. Besides, the addition of polypropylene fiber significantly enhanced the tensile strength and increased the creep resistance and drying shrinkage. Therefore, structural fibered foamed concrete can be used as a substitute lightweight concrete material for the production of structural concrete applications in the construction industries today.

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.