Flexural rigidity and ductility of RC beams reinforced with steel and recycled plastic fibers

Walid Mansour,Sabry Fayed 국제구조공학회 2021 Steel and Composite Structures, An International J Vol.41 No.3

This study compares between the mechanical properties of concrete either reinforced with recycled plastic (RP) or end-hooked steel (EHS) fibers with volume fractions of 1, 2 and 3%. Also, the effects of the fiber type and volume fraction on flexural responses were investigated using experimental program composed of seven reinforced concrete (RC) beams. Generally, results showed that the RP and EHS fibers remarkably enhanced both the mechanical characteristics of concrete and the flexural capacity of RC beams. Specifically, concrete matrix that reinforced with 2% volume fraction of RP or EHS fibers exhibited the highest capacities among all tested specimens. On the other hand, the compressive and the tensile strengths of the fibrous concrete which strengthened with 3% volume fraction (either RP or EHS fibers) were lower than their counterparts that reinforced with lower volume fraction (2%). As the fiber volume fraction increased up to 2%, the peak load of the RC beams increased followed by a reduction for higher fiber volumes. The peak load of the RC beam specimens reinforced with 2% of RP and EHS fibers were 57.1 kN and 60.7 kN, respectively compared to 39.6 kN for the control RC beam. Both RP and EHS fibers had a positive effect on the (effective/gross) flexural rigidity ratio, especially when used with volume fraction lower than 3%. RC beams reinforced with 1% of RP and EHS fibers yielded higher ductility in comparison with 2 and 3%. An analytical model constructed based on the distribution of stress-strains along the height of the RC beam was used to estimate the bending moments at different stages. Results well agreed with the experimental records.

Experimental and numerical analysis of the punching behavior of RC isolated footings

Walid Mansour,Sabry Fayed,Ali Basha 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.5

In the current study, punching behavior of Reinforced concrete (RC) isolated footings was experimentally and numerically investigated. The experimental program consisted of four half-scale RC isolated footing specimens. The test matrix was proposed to show effect of footing area, reinforcement mesh ratio, adding internal longitudinal reinforcement bars and stirrups on the punching response of RC isolated footings. Footings area varied from 1200x1200 mm2 to 1500x1500 mm2 while the mesh reinforcement ratio was in the range from 0.36 to 0.45%. On the other hand, a 3D non-linear finite element model was constructed using ABAQUS/standard program and verified against the experimental program. The numerical results agreed well with the experimental records. The validated numerical model was used to study effect of concrete compressive strength; longitudinal reinforcement bars ratio and stirrups concentration along one or two directions on the ultimate load, deflection, stiffness and failure patterns of RC isolated footings. Results concluded that adding longitudinal reinforcement bars did not significantly affect the punching response of RC isolated footings even high steel ratios were used. On the contrary, as the stirrups ratio increased, the ultimate load of RC isolated footings increased. Footing with stirrups ratio of 1.5% had ultimate load equal to 1331 kN, 19.6% higher than the bare footing. Moreover, adding stirrups along two directions with lower ratio (0.5 and 0.7%) significantly enhanced the ultimate load of RC isolated footings compared to their counterparts with higher stirrups ratio (1.0 and 1.5%).

Bond behavior between concrete and prefabricated Ultra High-Performance Fiber-Reinforced Concrete (UHPFRC) plates

Walid Mansour,Mohammed A. Sakr,Ayman A. Seleemah,Bassam A. Tayeh,Tarek M. Khalifa 국제구조공학회 2022 Structural Engineering and Mechanics, An Int'l Jou Vol.81 No.3

Externally bonded ultrahigh performance fiber-reinforced concrete (UHPFRC) is commonly used as a strengthening material for reinforced concrete (RC) structures. This study reports the results of an experimental program investigating the bonding behavior between concrete and prefabricated UHPFRC plates. The overall experimental program is consisting of five RC specimens, which are strengthened using the different lengths and widths of prefabricated UHPFRC plates. These specimens were analyzed using the pull-pull double-shear test. The performance of each strengthened specimen is presented, discussed and compared in terms of failure mode, maximum load, load-slip relationship, fracture energy and strain distribution. Specimen C- 25-160-300 which bonded along the whole width of 160 mm recorded the highest maximum load (109.2 kN) among all the analysed specimens. Moreover, a 3D numerical finite element model (FEM) is proposed to simulate the bond behavior between concrete and UHPFRC plates. Moreover, this study reviews the analytical models that can predict the relationship between the maximum bond stress and slip for strengthened concrete elements. The proposed FEM is verified against the experimental program and then used to test 36 RC specimens strengthened with prefabricated UHPFRC plates with different concrete grades and UHPFRC plate widths. The obtained results together with the review of analytical models helped in the formation of a design equation for estimating the bond stress between concrete and prefabricated UHPFRC plates.

Evaluate the effect of steel, polypropylene and recycled plastic fibers on concrete properties

Fayed, Sabry,Mansour, Walid Techno-Press 2020 Advances in concrete construction Vol.10 No.4

The impacts of reinforcing concrete matrix with steel fibers, polypropylene fibers and recycled plastic fibers using different volume fractions of 0.15%, 0.5%, 1.5% and 2.5% on the compressive and tensile characteristics are experimentally investigated in the current research. Also, flexural behavior of plain concrete (PC) beams, shear performance of reinforced concrete (RC) beams and compressive characteristics of both PC and RC columns reinforced with recycled plastic fibers were studied. The experimental results showed that the steel fibers improved the splitting tensile strength of concrete higher than both the polypropylene fibers and recycled plastic fibers. The end-hooked steel fibers had a positive effect on the compressive strength of concrete while, the polypropylene fibers, the recycled plastic fibers and the rounded steel fibers had a negative impact. Compressive strength of end-hooked steel fiber specimen with volume fraction of 2.5% exhibited the highest value among all tested samples of 32.48 MPa, 21.83% higher than the control specimen. The ultimate load, stiffness, ductility and failure patterns of PC and RC beams in addition to PC and RC columns strengthened with recycled plastic fibers enhanced remarkably compared to non-strengthened elements. The maximum ultimate load and stiffness of RC column reinforced with recycled plastic fibers with 1.5% volume fraction improved by 21 and 15%, respectively compared to non-reinforced RC column.

Variation of the Hydraulic Conductivity and the Mechanical Characteristics of Plastic Concrete with Time

Ali Basha,Walid Mansour 한국콘크리트학회 2023 International Journal of Concrete Structures and M Vol.17 No.4

Sand-bentonite-cement are commonly used as cut-off walls to isolate polluted soils or in ground improvement technologies and as retaining structures as secant pile wall. In this research, a laboratory program consisted from 105 sample were prepared and tested between different tests, such as hydraulic conductivity, porosity, and compressive strength to monitor the mechanical behavior of sand-bentonite-cement at different ages. Based on the experimental relationships between hydraulic conductivity coefficient and samples age; there were reduction due to added bentonite to mixture reach about 35.0% at 7 days. Moreover, the average reduction in the compressive strength of plastic concrete samples with bentonite was lower by average range about 51.0% than the compressive strength of plastic concrete samples without bentonite at 7 days. In this study, proposed formulas were derived to estimate the splitting tensile strength based on the compressive strength and the hydraulic conductivity in terms of the bentonite/cement ratio and testing age. The predicted values showed well agreement with the experimental records for samples of sand-bentonite-cement mixtures where the standard deviation and coefficient of variation were 0.02, and 0.94%, respectively.

Buckling performance of pultruded glass fiber reinforced polymer profiles infilled with waste steel fiber reinforced concrete under axial compression

Emrah Madenci,Sabry Fayed,Walid Mansour,Yasin Onuralp Özkılıç 국제구조공학회 2022 Steel and Composite Structures, An International J Vol.45 No.5

This study reports the results of a series of tests of pultruded glass fiber reinforced polymer (P-GFRP) box section composite profile columns, geometrically similar with/without concrete core, containing 0-1-2-3% steel fiber, with different lengths. The recycled steel wires were obtained from waste tyres. The effects of steel fiber ratio on the collapse and size effect of concrete filled P-GFRP columns under axial pressure were investigated experimentally and analytically. A total of 36 columns were tested under compression. The presence of pultruded profile and steel wire ratio were selected as the primary variable. The capacity of pultruded profiles with infilled concrete are averagely 9.3 times higher than the capacity of concrete without pultruded profile. The capacity of pultruded profiles with infilled concrete are averagely 34% higher than that of the pultruded profiles without infilled concrete. The effects of steel wire ratio are more pronounced in slender columns which exhibit buckling behavior. Moreover, the proposed analytical approach to calculate the capacity of P-GFRP columns successfully predicted the experimental findings in terms of both pure axial and buckling capacity.

Experimental Study of the Flexural Behaviour of RC Beams Made of Eco-friendly Sawdust Concrete and Strengthened by a Wooden Plate

Ahmed M. Maglad,Walid Mansour,Sabry Fayed,Bassam A. Tayeh,Ahmed M. Yosri,M. Hamad 한국콘크리트학회 2023 International Journal of Concrete Structures and M Vol.17 No.6

In this paper, the effectiveness of the strengthening by a wooden plate for reinforced concrete (RC) beams that incorporate waste sawdust (SD) as a partial substitute for fine aggregate (sand) has been investigated. To this end, two types of concrete mixtures were made: normal concrete (NC) and sawdust concrete (SDC), which was made by substituting 15% of the volume of sand with SD. Five RC beams (100 mm in depth, 200 mm in width, and 1500 mm in length) were experimentally tested for flexural behavior under four-point loading. Three strengthening schemes were used in this study. The first scheme used a wooden plate that was only fixed by an adhesive layer. The second and third schemes were applied by a wooden plate, which was fixed by an adhesive layer and steel angles (two and eleven angles). The findings of the study indicate that although the concrete's workability, compressive, and splitting tensile strengths were reduced with the addition of SD, the ultimate load of the beam with SD was lower than that of the control beam, with a slight variation of approximately 4%. Moreover, strengthening the RC beam with a wooden plate and two steel angles yielded the highest load capacity among all tested beams, 20% higher than the control specimen. The study's findings offered useful information for developing eco-friendly sawdust concrete beams with efficient strengthening techniques for potential future uses.

Flexural strengthening of RC one way solid slab with Strain Hardening Cementitious Composites (SHCC)

Basha, Ali,Fayed, Sabry,Mansour, Walid Techno-Press 2020 Advances in concrete construction Vol.9 No.5

The main aim of the current research is to investigate the flexural behavior of the reinforced concrete (RC) slabs strengthened with strain hardening cementitious composites (SHCC) experimentally and numerically. Seven RC slabs were prepared and tested under four-points loading test. One un-strengthened slab considered as control specimen while six RC slabs were strengthened with reinforced SHCC layers. The SHCC layers had different reinforcement ratios and different thicknesses. The results showed that the proposed strengthening techniques significantly increased the ultimate failure load and the ductility index up to 25% and 22%, respectively, compared to the control RC slab. Moreover, a three dimensional (3D) finite element model was proposed to analyze the strengthened RC slabs. It was found that the results of the proposed numerical model well agreed with the experimental responses. The validated numerical model used to study many parameters of the SHCC layer such as the reinforcement ratios and the different thicknesses. In addition, steel connectors were suggested to adjoin the concrete/SHCC interface to enhance the flexural performance of the strengthened RC slabs. It was noticed that using the SHCC layer with thickness over 40 mm changed the failure mode from the concrete cover separation to the SHCC layer debonding. Also, the steel connectors prevented the debonding failure pattern and enhanced both the ultimate failure load and the ductility index. Furthermore, a theoretical equation was proposed to predict the ultimate load of the tested RC slabs. The theoretical and experimental ultimate loads are seen to be in fairly good agreement.

Experimental and Analytical Investigation of Fracture Characteristics of Steel Fiber-Reinforced Recycled Aggregate Concrete

Ahmed M. Maglad,Walid Mansour,Bassam A. Tayeh,Mohamed Elmasry,Ahmed M. Yosri,Sabry Fayed 한국콘크리트학회 2024 International Journal of Concrete Structures and M Vol.18 No.1

Fracture parameters of fiber concrete (FC) are currently a hot research area. Fracture mechanics is the field of solid mechanics that helps to study the type and propagation of cracks in materials. It uses methods of calculating the driving force on a crack and characterizes the material's resistance to fracture. Behavioral characteristics are determined by crack mouth opening displacement and the load–deflection method. This research identifies the fracture parameters of 33 notched simply supported beams made by recycled aggregate cement concrete with steel fiber. The recycled aggregate ratio in concrete has been altered to determine the effect on the mechanical and fracture properties. For determining fracture parameters, a 3-point bending single-edge notched fracture test was used. The results indicated that the steel fiber-reinforced concrete made with recycled aggregate showed similar performance and fracture characteristics compared to normal concrete. Thus, adding steel fibers to various concrete mixes considerably improved the fracture characteristics, while the brittleness was reduced with increased steel fiber content. Linear regression analysis also showed the accuracy of mechanical strength results as the value of R-square was close to unity. Displacement, ultimate load, brittleness (B), fracture toughness (KIC), crack mouth opening displacement (CMOD), fracture energy (GF), modulus of elasticity (E), and characteristic length (lch), were determined for both conventional and recycled aggregate specimens. The “work of fracture"—by definition the formula—is the most reliable to calculate the fracture energy as the nonlinearity is related to the performance of FC.