Showing papers by "Rami A. Hawileh published in 2022"

Geopolymer concrete incorporating recycled aggregates: A comprehensive review

Abstract: Several industrial by-products are extensively used again as a supplementary cementitious material or aggregates in the interest to reduce environmental footprints in terms of energy depletion, pollution, waste disposition, resource depletion, and global warming related with conventional cement. A remarkable quantity of industrial scrap materials, primarily designated as construction and demolition waste from the construction industry, has transformed into crucial apprehension of governments. In the recent past, substantial explorations have been accomplished to appreciate the distinct characteristics of concrete, employing recycled aggregates from construction and demolition waste. Geopolymer composite is a new cementitious material, and it appears to be a potential replacement for conventional cement concrete. This paper summarises the previous research concerning the utilisation of recycled aggregate as a partial or complete supplants for conventional aggregates in geopolymer concrete. The influence of recycled aggregate addition on the fresh and hardened properties of geopolymer concrete is comprehensively reviewed in this paper. The studies suggest significant improvement in the workability on addition of recycled aggregates to geopolymer concrete. However, the addition results in increased water absorption and sorptivity.

Influence of nano-TiO2, nano-Fe2O3, nanoclay and nano-CaCO3 on the properties of cement/geopolymer concrete

Abstract: In past decades, researchers have tried to improve the durability of concrete by integrating supplementary cementitious materials into concrete. Recent advancements in the field of nano-engineered concrete have reported that nanomaterials significantly improve the mechanical and durability properties of concrete. This paper provides a comprehensive summary of recent developments on the use of nanomaterials as a performance enhancer in cement/geopolymer concrete. Many significant correlations associated with the reinforcement of cementitious matrices using nano-TiO2, nano-Fe2O3, nanoclay/metakaolin, and nano-CaCO3 were studied. Performance aspects such as fresh properties, microstructure, mechanical and durability characteristics, and the influence of various particle sizes have been reviewed. The findings from this review confirm the feasibility of using the nanomaterials in cement concrete, with the required properties of building materials. It is also expected that this review provides better insight into using nanomaterials in concrete for the benefit of academic and fundamental research and promotes its practical application in the construction industry.

FEA Investigation of Elastic Buckling for Functionally Graded Material (FGM) Thin Plates with Different Hole Shapes under Uniaxial Loading

Abstract: In this paper, an investigation of linear eigenvalue buckling of functionally graded material (FGM) plates under uniaxial loading is carried out. The computer model is analyzed using the finite element (FE) package ABAQUS. An analysis is carried out to study the effect of the size and geometry of openings in the FGM plate on the critical buckling load. The circular, square, and diamond openings vary in size based on the ratio of the opening diameter to the width of the FGM plate. Moreover, the effect of the aspect ratio (width to thickness) of the FGM plate on the critical buckling load is examined. Further, the effect of the power law index on buckling behavior is investigated. The results show that the increase in the size of the opening and the aspect ratio reduces the critical buckling load of the FGM plate. Moreover, the lower the power law index, the higher the critical buckling load. The diamond shape opening shows the best performance in terms of the critical buckling load, and the effect of the plate thickness has a more significant influence on the critical buckling load of the FGM plate compared to the size of the opening.

Flexural Performance of RC Beams Strengthened with Pre-Stressed Iron-Based Shape Memory Alloy (Fe-SMA) Bars: Numerical Study

Abstract: The iron-based shape memory alloy (Fe-SMA) has promising applications in strengthening and repairing aged steel-reinforced concrete structural elements. Fe-SMA bars can produce pre-stressing forces on reinforced concrete members by activating their shape memory phenomenon upon heating. This study aims to numerically evaluate the impact of pre-stressed Fe-SMA bars on the structural behavior of reinforced concrete (RC) beams at the serviceability and ultimate stages. Nonlinear finite element (FE) models were developed to predict the response of RC beams externally strengthened with Fe-SMAs. The model shows to correlate well with published experimental results. A parametric investigation was also carried out to examine the effect of various concrete grades, pre-stressing levels, and Fe-SMA bars’ diameter on load-deflection behavior. In light of the innovative nature of the Fe-SMA strengthening technique, a comparison investigation was established between RC beams strengthened with Fe-SMA bars against different pre-stressing systems, such as carbon fiber reinforced polymer (CFRP) bars, glass fiber reinforced polymer (GFRP) bars, and steel strands. The numerical findings showed a significant increase in the beams’ load-carrying capacity with larger Fe-SMA bars’ diameter. Specifically, using 12 mm Fe-SMA bars instead of 6 mm increased the beam’s strength by 73%. However, a 14% reduction in ductility was recorded for that case. Moreover, the pre-stressing level of Fe-SMA bars and concrete grade showed a negligible effect on the ultimate strength of the examined beams. Moreover, increasing the pre-stressing level and concrete strength significantly enhanced the load-deflection response in the serviceability stage. Furthermore, using 2T22 mm of Fe-SMA bars resulted in a better structural performance of RC beams compared to other techniques with 2T12 mm, with a comparable cost. Thus, it can be concluded that using Fe-SMA bars embedded in a shotcrete layer attached to the beam’s soffit is a viable and promising strengthening strategy. Nevertheless, further experimental investigations are recommended to further ascertain the reported findings of this numerical investigation.

Buckling Analysis of Functionally Graded Materials (FGM) Thin Plates with Various Circular Cutout Arrangements

Abstract: In this paper, several analyses were conducted to investigate the buckling behavior of Functionally Graded Material (FGM) thin plates with various circular cutout arrangements. The computer model was simulated using the Finite Element (FE) software ABAQUS. The developed model was validated by the authors in previous research. A parametric analysis was employed to investigate the effect of plate thickness and circular cutout diameter on the buckling behavior of the FGM thin plates. The normalized buckling load was also calculated to compare the buckling performance of FGM plates with various dimensions. Moreover, von Mises stress analysis was examined to understand the yield capability of the FGM plates in addition to the buckling modes that show the stress distribution of the critical buckling stress. Hence, this research provides a comprehensive analysis to display the relation between the critical buckling load and the arrangement of the circular cutouts. The results show that the critical buckling load heavily depends on the dimension of the plate and the cutout size. For instance, an increase in the plate thickness and a decrease in the cutout diameter increase the critical buckling load. Moreover, the circular cutout in a horizontal arrangement exhibited the best buckling performance, and as the arrangement shifts to a vertical arrangement, the buckling performance deteriorates.

Flexural and Bond Behavior of Concrete Beams Strengthened with CFRP and Galvanized Steel Mesh Laminates

Abstract: Carbon fiber–reinforced polymer (CFRP) composites are effectively and predominantly used for flexure strengthening of RC beams. Recently, new emerging composite materials known as galvanize...

Nonlinear Finite Element Analysis (NLFEA) of Pre-stressed RC Beams Reinforced with Iron-Based Shape Memory Alloy (Fe-SMA)

Abstract: Iron-based shape memory alloy (Fe-SMA) holds great potential for strengthening and repairing aged reinforced concrete (RC) elements. In this research study, the application of utilizing Fe-SMA reinforcement rebars in prestressed RC beams is emphasized. The main purpose of this study is to simulate the influence of utilizing Fe-SMA rebars on the structural behavior of prestressed RC using finite element modeling (FEM). The results from nonlinear finite element analysis are validated with experimental data from previous studies. These studies were conducted to evaluate the influence of utilizing the Fe-SMA on the strength and serviceability of several prestressed RC beams that were tested with different rebar configurations through flexural tests. The developed models, in this study, showed excellent agreements with the previous experimental data and models.

Behavior of reinforced concrete beams cast with a proposed geopolymer concrete (GPC) mix

Abstract: The aim of this paper is to examine the effects of using Ground Granulated Blast Furnace Slag (GGBFS) as a complete replacement to Ordinary Portland Cement (OPC) in Reinforced Concrete (RC) beams. The proposed GGBFS mix had an air content of 1.4%, a unit weight of 2480 kg/m3, a slump of 201 mm, and a compressive strength of 30 MPa after 56 days of curing. In addition, the GGBFS-based sample have shown an increased durability as it passed less chloride ions when compared to conventional concrete. A total of four beams were cast using the proposed mix and then tested under three-point loading and four-point loading. The beams were categorized into group 1, samples designed to fail in flexure, and group 2, samples designed to fail in shear. The performances of the GGBFS-based specimens were evaluated and compared to the control beams. In flexure, the GGBFS-based sample carried 83% of the control sample’s ultimate load which is considerably less than the expected 96%. Whereas the GGBFS-based shear deficient sample carried 79% of the load carried by the control beam. Although GGBFS samples carried less load, it is concluded that use of GGBFS as a full replacement to OPC is practical as the normalized capacity of GGBFS samples is comparable to that of the control samples. Additionally, using GGBFS contributes to the reduction of CO2 emissions and hence promotes the use of sustainable and green concrete.

Comparative analysis of design guidelines for FRP contribution to shear capacity of strengthened RC beams

Abstract: In the past few years, strengthening and retrofitting of reinforced concrete (RC) structures using externally bonded (EB) fiber-reinforced polymers (FRP) laminates has been deemed as a promising rehabilitation technique. Structural applications of FRP include flexural and shear strengthening of RC beams and confinement of columns. Many guidelines and standards were developed to predict the contribution of FRP to the strength of structural members. For shear strengthening applications, in particular, most of the design guidelines tend to underestimate the capacity of the strengthened members, whereas other models provide unsafe predictions. The accuracy of the models is dependent on many factors, such as but not limited to the wrapping scheme, amount of internal shear reinforcement, shear crack angle, concrete compressive strength, number of FRP layers, and FRP type. For this purpose, this paper focuses on comparing and evaluating the accuracy of the available FRP shear design guidelines. The design standards that are considered in this study are the ACI440.2R-17, CSA-S806.12 (R2017), fib bulletin 90, and TR55. The accuracy of the design models was assessed against an experimental database collected from the literature. The database included RC beams externally strengthened in shear with different FRP types, configurations, and wrapping schemes. In addition, the database included strengthened beams with varying types of anchors. Results showed that most design codes provide reasonable predictions to the FRP shear strength in case of U-wraps. However, the guidelines are significantly conservative in case of complete wraps and anchored specimens. Overall, the ACI440.2R-17 and TR55 predictions are very conservative while fib bulletin 90 and CSA-S806.12 predictions are accurate and can be safely used to design FRP shear strengthened members.

Comparison of shear behavior of normal and recycled aggregates beams strengthened with CFRP U-Wraps

Abstract: In recent years recycled aggregates, from construction demolition waste, has been used as a replacement to normal (natural) aggregates in concrete. This is to preserve the depletion of natural resources and to further reduce carbon footprints in terms of energy depletion and waste disposition. Mechanical properties, such as compressive and tensile strengths, of recycled aggregates concrete (RAC) have been investigated by several researchers and were compared with that of normal aggregate concrete (NAC). In this investigation, the shear strengths and modes of failure of RAC and NAC beams have been investigated. In addition, the behavior of RAC and NAC beams strengthened with carbon-fiber-reinforced-polymer (CFRP) U-wrapped laminates have been examined. Four RAC and NAC shear-deficient rectangular beams were cast, two of which were strengthened in shear with CFRP U-wraps. The beams were tested to failure under four-point bending. The test results indicate that the shear capacity of all specimens strengthened with CFRP composites increased significantly compared to the control beam specimens. The performance of the RAC and NAC beams before and after strengthening were compared. It was observed that the RAC specimens provided similar shear strength as that of the NAC beams. The percentage increase in the shear capacity of RAC beams reached almost 60% of the control beam for the beams with U-wraps. The ACI 318-19 and ACI440.2R-17 codes are also used to predict the shear strength of the tested RAC and NAC beams and it was observed that the predicted capacities were close to the experimentally measured ones.

Contribution of Longitudinal NSM-CFRP Bars on the Shear Strength of RC Beams with Varying Depths and Concrete Strengths

Abstract: To assess experimentally the effect of flexural near surface mounted (NSM) carbon fiber-reinforced polymer (CFRP) bars mounted on the sides of beams on the shear strength of reinforced concrete (RC) beams, 18 shear-deficient RC beams were built, strengthened with flexural NSM-CFRP bars, and tested under three-point bending until failure. The variables of the experimental program included the beam depth, the concrete compressive strength, and the flexural fiber-reinforced polymer (FRP) reinforcement ratio. It was observed that the strengthened beams exhibited up to 35% increase in shear capacity over the control beams. It was also observed that the increase in shear strength provided by concrete after strengthening was higher for beams with normal strength concrete when compared to those with higher strength concrete. The results have also revealed that the percent change in shear strength provided by concrete for the strengthened beams decreased with the increase in beam depth. Experimental data from this study showed that current standards become unconservative for beams with large depths. Five different beam shear strength models found in the literature were utilized to predict the shear strength of the tested beams. The models that exhibited the closest agreement with the experimental data were those of the University of Houston and the second order simplified modified compression field theory. It was concluded that flexural longitudinal NSM bars are a viable solution to enhance the shear strength of RC beams and that the shear strength provided by concrete can be accurately quantified using published models.

Modeling the behavior of CFRP-strengthened RC slabs under fire exposure

Abstract: This paper presents the development of a numerical model that simulates the fire response of reinforced concrete (RC) slabs externally strengthened with carbon fiber-reinforced polymer (CFRP)laminates using two different techniques, externally bonded (EB) and near-surface mounted (NSM). A three-dimensional (3D) nonlinear finite element (FE) model is developed to predict the thermal and structural behavior of strengthened RC slabs subjected to fire. The model incorporates temperature-dependent thermal and mechanical properties of concrete, steel reinforcement, and CFRP, as well as mechanical bond interaction between CFRP and concrete interfaces. The predicted temperature profiles, ultimate loads, and midspan deflections are compared with previously published experimental data. Results from the proposed model show a good correlation with the experimental data throughout the fire exposure duration. The validated model can be adapted to conduct parametric studies intended to inspect the effect of important factors that influence the behavior of strengthened RC slabs under fire.

Heat Transfer Analysis of Reinforced Concrete Walls in ANSYS and ABAQUS: A Comparative Study

Abstract: This paper presents a comparison of the numerical results from heat transfer analysis of reinforced concrete (RC) walls under standard fire exposure. A three-dimensional (3D) finite element (FE) model was constructed using the FE modeling software ABAQUS and ANSYS to compare the simulation results of thermal analysis and cross-sectional temperature distribution of two RC walls. The predicted temperature distribution of the two FE models was verified using published experimental data. Results from the numerical analysis show that both models created using the two FE software can reasonably predict the nodal temperatures and temperature distribution through the wall. The results also indicated that ANSYS was slightly more sensitive to mesh size which resulted in higher predicted temperatures at the colder face of the wall.

Performance of RC beams externally strengthened with hybrid CFRP and PET-FRP laminates

Abstract: The use of fiber-reinforced polymers (FRP) composite materials in strengthening applications of reinforced concrete (RC) structures has been gaining wide popularity in recent decades. This is due to its superior properties such as high strength to weight ratio, durability, and versatility. In fact, it is well established that bonding FRP materials to the soffit of RC beams enhances the flexural capacity of such beams. However, the non-yielding characteristic of FRP materials is a major concern, and often results in sudden and brittle failure mode of the strengthened member. To encounter this issue, a new type of FRP materials composed from polyethylene terephthalate (PET) fibers have been developed. Compared to conventional FRPs, PET-FRP have large deformability and possess a nonlinear stress-strain relationship. Employing PET-FRP in the retrofitting industry reduces construction waste, enhances the capacity of structures and provides a solution that encourages the concept of sustainability. However, these types of large rupture strain (LRS) FRPs have lower stiffness and tensile strengths than conventional FRPs. Therefore, the main aim of this study is to combine the lower stiffness and large rupture strain of PET-FRP sheets with that of the higher stiffness and strength of carbon FRP (CFRP) sheets resulting in a new hybrid composite system. The research program consists of four RC beams externally strengthened with CFRP, PET-FRP, and their hybrid combinations, in addition to a control unstrengthened beam specimen. The beams are tested under four-point bending and load-displacement curves along with the failure modes, strength, strain in the FRP, and ductility of the beam specimens are examined. Test results indicate that strengthening with PET-FRP laminates significantly enhances the deformation capacity of the strengthened specimens compared to that with CFRP. In addition, the hybrid mix between CFRP and PET-FRPs resulted in 46-48% strength improvement compared to the unstrengthened control beam. However, the effectiveness of the hybrid system was not pronounced in terms of ductility due to the premature debonding of the concrete cover that occurred before utilizing the full strain of the hybrid system. Hence, it is advised for future research studies to anchor the hybrid sheets by means of end U-wraps or FRP spike anchors to delay the debonding failure and to exploit the benefits of the proposed hybrid system.

Shear Strengthening of Reinforced Concrete T-Beams using Carbon Fiber Reinforced Polymer (CFRP) Anchored with CFRP Spikes

Abstract: Reinforced Concrete (RC) structures deteriorate over years due to many reasons including corrosion of reinforcing steel, carbonation of concrete, overload on structural members, among others. This may result in flexural or shear deficiency in RC beams. The failure of shear-deficient RC beams is usually brittle, sudden and with little warning, if any. Diagonal shear cracks will form due to load increase that may result in complete fracture of the RC beam. Therefore, deteriorated and shear-deficient RC beams need to be strengthened to avoid such undesirable shear failure. This paper investigates shear strengthening of RC T-Beams using carbon fiber reinforced polymer (CFRP) laminates anchored with spike anchors. The beams have been strengthened in flexure to avoid flexural failure and then strengthened in shear using CFRP sheets that were anchored with CFRP spikes. Six beams were strengthened with CFRP laminates at 45o and at 90o inclination angles and anchored with embedded CFRP spikes with different depths (50 mm and 75 mm) and different diameters (10 mm and 12 mm). Wrapping (U-Wrapped) was also used for anchoring the flexural CFRP laminates. The beams are tested to failure and their capacity were compared with that of an unstrengthen control beam. It is observed that the capacity of the strengthened beams is increased up to 45% compared to that of the control beam. Anchoring with U-wraps enhanced the beam capacity further. The inclination of the CFRP sheets, dowel diameter, and the embedment depth of the spike anchors influenced shear and deformation capacity of the tested RC T-Beams.

Finite Element Simulation of FRP-Strengthened Thin RC Slabs

Abstract: This study aims to investigate the flexural behavior of high-strength thin slabs externally strengthened with fiber-reinforced polymer (FRP) laminates through a numerical simulation. A three-dimensional (3D) finite element (FE) model is created to simulate the response of strengthened reinforced concrete (RC) slabs under a four-point bending test. The numerical model results in terms of load-deflection behavior, and ultimate loads are verified using previously published experimental data in the literature. The numerical results show a good agreement with the experimental results. The FE model is then employed in a parametric study to inspect the effect of concrete compressive strength on the performance of RC thin slabs strengthened with different FRP types, namely carbon fiber-reinforced polymers (CFRP), polyethylene terephthalate fiber-reinforced polymers (PET-FRP), basalt fiber-reinforced polymers (BFRP) and glass fiber-reinforced polymers (GFRP). The results showed that the highest strength enhancement was obtained by the slab that was strengthened by CFRP sheets. Slabs that were strengthened with other types of FRP sheets showed an almost similar flexural capacity. The effect of concrete compressive strength on the flexural behavior of the strengthened slabs was moderate, with the highest effect being a 15% increase in the ultimate load between two consecutive values of compressive strength, occurring in the CFRP-strengthened slabs. It can thus be concluded that the developed FE model could be used as a platform to predict the behavior of reinforced concrete slabs when strengthened with different types of FRP composites. It can also be concluded that the modulus of elasticity of the composite plays a major role in determining the flexural capacity of the strengthened slabs.

Finite Element Modeling and Prediction of Tensile Behavior of PE-ECC Dogbones

Abstract: This study presents the development of 3-dimensional Finite Element (FE) models of Engineered Cementitious Composite (ECC) dogbones. The main aim of this study is to investigate the uniaxial tensile behavior of ECC dogbones exposed to elevated temperature and to validate the accuracy of the corresponding FE predictions. Two dogbones were tested, one at room temperature and the second was tested after exposing it to a temperature of 200 °C. Comparisons between dogbones FE models confirmed that the models are capable of effectively predicting experimentally measured values.

Finite Element Modeling of Engineered Cementitious Composite (ECC) Prisms and Beams

Abstract: In this study, 3-dimensional Finite Element (FE) models of prisms and beams subjected to 4 point-loading setup were developed. The objective is to investigate the flexural behavior of Engineered Cementitious Composite (ECC) prisms exposed to different temperatures and to verify the effectiveness of the corresponding FE predictions. Two ECC prism models were analyzed; one model was for an ECC prism tested at room temperature, while the second was for an ECC prism tested after exposure to a temperature of 200° C. Moreover, analysis was conducted and the results were compared for Reinforced Ultra-High-Performance Engineered Cementitious Composite (UHP-ECC) beams and traditional Reinforced Concrete (RC) beams. The impact of two different reinforcement ratios was analyzed for both (UHP-ECC) and RC beams. Comparison between FE models for prisms and beams confirmed that the models provide reasonable predictions of experimental results.

Enhancing fire resistance of reinforced concrete beams through sacrificial reinforcement

Abstract: Due to the superior properties of concrete, structural members made of concrete often satisfy fire requirements specified in codes and standards without special installations or the use of external insulation. A closer examination into fire codal provisions shows that they are primarily founded for new constructions or that which does not suffer from aging or in-service trauma; such as cracking, reinforcement corrosion, creep, etc., all of which can adversely affect the structural response of concrete structures, especially under fire conditions. In order to enhance the fire resistance of concrete structures, this paper presents insights into simple and cost-effective solutions by utilizing sacrificial layer(s) of reinforcement. These solutions capitalize on the natural synergy between reinforcement and concrete and have the potential to mitigate fire-induced cracking and the development of fire-induced large deformation, thereby extending the fire resistance of reinforced concrete beams. The validity and applicability of the proposed concepts are highlighted through a highly complex three-dimensional thermo-mechanical nonlinear-based finite element model. This model was utilized in a series of parametric studies to examine critical parameters influencing the fire response of concrete beams reinforced with steel and fiber-reinforced polymer reinforcement. These parameters include sacrificial reinforcement scheme, size, and material type. It was concluded that the use of sacrificial reinforcement could be beneficial for mitigation purposes or as a repair solution for postfire events.

Enhancing fire resistance of reinforced concrete beams through sacrificial reinforcement

Abstract: Due to the superior properties of concrete, structural members made of concrete often satisfy fire requirements specified in codes and standards without special installations or the use of external insulation. A closer examination into fire codal provisions shows that they are primarily founded for new constructions or that which does not suffer from aging or in-service trauma; such as cracking, reinforcement corrosion, creep, etc., all of which can adversely affect the structural response of concrete structures, especially under fire conditions. In order to enhance the fire resistance of concrete structures, this paper presents insights into simple and cost-effective solutions by utilizing sacrificial layer(s) of reinforcement. These solutions capitalize on the natural synergy between reinforcement and concrete and have the potential to mitigate fire-induced cracking and the development of fire-induced large deformation, thereby extending the fire resistance of reinforced concrete beams. The validity and applicability of the proposed concepts are highlighted through a highly complex three-dimensional thermo-mechanical nonlinear-based finite element model. This model was utilized in a series of parametric studies to examine critical parameters influencing the fire response of concrete beams reinforced with steel and fiber-reinforced polymer reinforcement. These parameters include sacrificial reinforcement scheme, size, and material type. It was concluded that the use of sacrificial reinforcement could be beneficial for mitigation purposes or as a repair solution for postfire events.