Personne :
El Refai, Ahmed

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El Refai
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Ahmed
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Université Laval. Département de génie civil et de génie des eaux
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ncf11860451
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  • Publication
    Restreint
    Bond performance of basalt fiber-reinforced polymer bars to concrete
    (American Society of Civil Engineers, 2014-08-11) Ammar, Mohamed Amine; El Refai, Ahmed; Masmoudi, Radhouane
    This paper presents the test results of a study on the bond behavior of basalt fiber-reinforced polymer (BFRP) bars to concrete. Thirty six concrete cylinders reinforced with BFRP bars and twelve cylinders reinforced with glass fiber-reinforced polymer (GFRP) bars were tested in direct pullout conditions. Test parameters included the FRP material (basalt and glass), the bar diameter, and the bar embedment length in concrete. Bond-slip curves of BFRP and GFRP bars revealed similar trends. BFRP bars developed average bond strength 75% of that of GFRP bars. All BFRP specimens failed in a pullout mode of failure along the interfacial surface between the outer layer of the bar and the subsequent core layers. The influence of various parameters on the overall bond performance of BFRP bars is analyzed and discussed. The well-known BPE and modified-BPE analytical models were calibrated to describe the bond-slip relationships of the bars. Test results demonstrate the promise of using the BFRP bars as an alternative to the GFRP bars in reinforcing concrete elements. Read More: http://ascelibrary.org/doi/10.1061/%28ASCE%29CC.1943-5614.0000487
  • Publication
    Restreint
    Bond durability of basalt fibre-reinforced polymer bars embedded in concrete under direct pullout conditions
    (American Society of Civil Engineers, 2014-12-01) El Refai, Ahmed; Farid, Abed; Altalmas, Ahmad
    The use of basalt fiber–reinforced polymer (BFRP) bars as a reinforcing material has gained increasing interest worldwide. However, few studies have reported on these bars’ performance in concrete when exposed to harsh environments. This paper investigates the effect of five different accelerated environments, namely (1) tap water, (2) seawater, (3) elevated temperature, (4) elevated temperature followed by tap water, and (5) elevated temperature followed by seawater, on the bond stress-slip response, adhesion to concrete, and bond strength [of two types of BFRP bars and one type of glass fiber–reinforced polymer (GFRP) bar]. The bond-slip responses of all specimens were governed by the surface treatment of each bar and its manufacturing quality, regardless of the fiber type. Sand-coated BFRP bars showed higher bond characteristics than helically grooved bars after conditioning. Moister environments caused enhanced adhesion at the early loading stages for all specimens. Nevertheless, such environments had a detrimental effect on the bond strength at later stages depending on the bar material’s moisture absorption. Finally, exposure to elevated temperatures caused insignificant variation in the bond strength of all tested specimens. Read More: http://ascelibrary.org/doi/10.1061/%28ASCE%29CC.1943-5614.0000544
  • Publication
    Restreint
    Durability and fatigue of basalt fiber-reinforced polymer bars gripped with steel Wedge anchors
    (American Society of Civil Engineers, 2013-07-18) El Refai, Ahmed
    This paper presents the test results of a durability study on a novel basalt fiber-reinforced polymer (BFRP) bar-anchor system. The BFRP bars were exposed to saline and alkaline solutions for 10 weeks before being anchored and tested under static and fatigue loading. Unconditioned basalt, glass, and carbon specimens were also tested and served as controls. Regardless of the fiber material, all the bar-anchor systems withstood their ultimate tensile loading with no sign of slippage or premature failure in the anchor zones. Conditioning of the BFRP bars in saline and alkaline solutions resulted in 7 and 9% decreases, respectively, in the systems’ tensile capacity. A decrease of 11% in the modulus of the alkali-conditioned BFRP specimens was also observed. The fatigue test results showed that the fatigue life of the bar-anchor system was primarily affected by the applied stress range. In addition, continuous immersion of the BFRP bar in the alkaline solution increased its tendency to fracture prematurely in the anchor zone. The fatigue limit of the BFRP bar-anchor system was determined to be 4% of its ultimate capacity, compared with 3 and 10% for the glass and carbon systems, respectively.
  • Publication
    Restreint
    Effect of corrosion damage on the flexural performance of RC beams strengthened with FRCM composites
    (Elsevier, 2017-08-18) El Refai, Ahmed; Elghazy, Mohammed; Ebead, Usama; Nanni, Antonio
    This paper reports on the flexural behavior of corrosion-damaged reinforced concrete (RC) beams strengthened with different fabric-reinforced cementitious matrix (FRCM) composites. Three groups of beams were subjected to accelerated corrosion for 70, 140, and 210 days to obtain theoretical mass loss in their tensile steel bars of 10%, 20%, and 30%, respectively. The test parameters included the fabric type (PBO and carbon), the number of FRCM layers (two, three, and four), and the strengthening Scheme (end-anchored and continuously wrapped). Test results showed that FRCM composites governed the failure of the strengthened beams rather than the damage level to which the beam was subjected due to corrosion. The reported load-carrying capacities of the corrosion-damaged beams confirmed that the contribution of FRCM composites significantly offset the impact of corrosion damage on strength. FRCM-strengthened beams exhibited an increase in strength that ranged between 7 and 55% of that of the virgin beam based on the type, the axial stiffness, and the Scheme of the FRCM used. The strengthened beams showed energy absorption indices that ranged between 111 and 153% of that of the virgin beam. The theoretical formulations of ACI-549.4R-13 reasonably predicted the ultimate strengths of the end-anchored strengthened beams but underestimated those continuously anchored beams.
  • Publication
    Restreint
    Fatigue and monotonic behaviors of corrosion-damaged reinforced concrete beams strengthened with FRCM composites
    (American Society of Civil Engineers, 2018-08-06) El Refai, Ahmed; Elghazy, Mohammed; Ebead, Usama; Nanni, Antonio
    This paper provides a comprehensive account of using fabric-reinforced cementitious matrix (FRCM) composites to strengthen corrosion-damaged reinforced concrete (RC) structures subjected to monotonic loading and fatigue. Twelve beams were constructed and tested to failure under four-point loading configuration. Prior to testing, 10 beams were subjected to accelerated corrosion for 140 days, leading to an average mass loss in the steel reinforcement of 19%. Eight corrosion-damaged beams were strengthened and tested while the other two beams remained unstrengthened. Two other virgin beams that were not subjected to corrosion were used as benchmarks. The test parameters included the fabric material (polyparaphenylene benzobisoxazole and carbon), the number of FRCM plies, the strengthening configuration, and the type of loading (monotonic and fatigue). Test results showed that the corrosion of steel bars dramatically decreased the fatigue life of the beams. After strengthening, the corrosion-damaged beams fully restored the load-carrying capacity of the virgin beam. The FRCM-strengthened beams endured more load cycles than those endured by their unstrengthened benchmarks but could not restore the original fatigue life of the virgin beam. The effect of FRCM configuration was more pronounced in the beams subjected to fatigue than those tested monotonically. PBO-FRCM composites were more effective than the carbon counterparts in enhancing the fatigue performance of the corrosion-damaged beams.
  • Publication
    Restreint
    Experimental and finite element investigation of the shear performance of BFRP-RC short beams
    (Hindawi Publishing Corporation, 2019-07-06) Abed, Farid; El Refai, Ahmed; Abdalla, Suliman
    This paper reports on the experimental, analytical, and numerical results of deep concrete beams reinforced with basalt fiber-reinforced polymer (BFRP) bars without web reinforcement. Ten beams of 2.0 m long and rectangular cross sections of 140 mm width with and variable heights were tested under four-point loading configuration. Three beams were reinforced with steel bars to act as controls while the other beams were reinforced with BFRP bars. The investigated parameters included the effective depth, d, the longitudinal reinforcement ratio, ρ, and the shear span-to-depth ratio, a/d. All of the BFRP-reinforced beams recorded slightly higher load-carrying capacities but lower post-cracking stiffness than their steel-reinforced counterparts. The strut-and-tie model of CSA-S806-12 conservatively predicted the shear capacities of the BFRP-reinforced beams whereas that of ACI-318-14 overestimated the capacities of most of the beams. A finite element model was developed using ABAQUS to predict the behavior of the tested beams. The model adequately predicted the shear capacities of the beams and captured well their failure modes. The verified FE model was used to expand on the experimental test matrix and include additional beams to further investigate a wide variation of the experimental parameters. The results indicated that the shear capacities of BFRP-reinforced beams were linearly proportional to the cubic root of the effective depth, ∛d, the longitudinal reinforcement ratio, ∛ρ, and the reciprocal of the shear span-to-depth ratio, 1/∛(a/d), which was in agreement with the provisions of CSA S806–02. Furthermore, a linear correlation between the shear capacities and the square root of the effective depth √d was observed indicating a good correlation with the provisions of ACI-440.1R.
  • Publication
    Restreint
    Assessment and modeling of the debonding failure of fabric-reinforced cementitious matrix (FRCM) systems
    (ScienceDirect, 2021-07-24) El Refai, Ahmed; Mandor, Ahmed
    This paper aims at developing a model that is capable to accurately predict the debonding strains in reinforced concrete (RC) members strengthened with fabric‐reinforced cementitious matrix (FRCM) systems. A large database consisting of 393 shear bond specimens strengthened with Polyparaphenylene Benzobisoxazole (PBO), Carbon (C), Glass (G), and Steel (S) FRCM systems was firstly compiled from the published literature. A sensitivity analysis was carried out to identify the key parameters that most affected the debonding mechanism in FRCM. The notable influence of the compressive and tensile strengths of the concrete substrate, the compressive strength of FRCM mortar, and the axial stiffness of FRCM system on the debonding strains in FRCM systems was evidenced. Contrarily, the tensile strength of FRCM mortars showed slight or no impact on the FRCM debonding strains. Based on the results of the sensitivity analysis, three simple models were developed using a multivariate nonlinear regression analysis. The models were then optimized and validated against the experimental results of 41 flexural members strengthened with different types of FRCM systems. Two of the three models proved an excellent prediction performance of the debonding strains with an average predicted–to–experimental strain ratios, ɛpred=ɛexp, of 0.99 ± 0.27 and 1.02 ± 0.27 with coefficients of variation (COV) of 0.28 and 0.26, respectively. Both models could safely predict the debonding strains in FRCM‐ strengthened members regardless of the type of FRCM system used. Neglecting the tensile strength of the concrete substrate in the third model resulted in an average ɛpred=ɛexp ratio of 0.85 ± 0.37 with a COV of 0.44
  • Publication
    Accès libre
    Bond performance of tensile lap-spliced basalt-FRP reinforcement in high-strength concrete beams
    (Applied Science, 2021-11-14) Eltantawi, Islam; El Refai, Ahmed; Alnahhal, Wael; Younis, Adel; Alnuaimi, Nasser; Kahraman, Ramazan
    This paper investigates the bond between high-strength concrete (HSC) and tensile lap-spliced basalt fiber-reinforced polymer (BFRP) bars. Ten large-scale BFRP-reinforced concrete beams (300 × 450 × 3900 mm) were fabricated and tested under four-point loading until failure. The parameters investigated included the BFRP bar diameter (10, 12, and 16 mm), the splice length (400–1200 mm range), and the bar surface texture (sand-coated (SC) and helically wrapped (HW)). Test results demonstrated that the flexural capacity of the beams reinforced with SC-BFRP bars was almost similar to that of beams reinforced with HW-BFRP bars. However, SC-BFRP bars showed a slightly higher bond with concrete compared to that of helically wrapped counterparts. The bond strength of spliced BFRP bars was inversely related to the splice length. Also, BFRP bars with larger diameter bars require longer splice lengths to reach their maximum capacity. Finally, the experimentally estimated critical splice lengths were compared to those calculated by existing models and code-based equations. Both ACI 440.1R-15 and CSA S806-12 provisions were conservative in predicting splice length for BFRP bars. However, the CSA-S6-14 design code was more accurate in estimating the splice length for BFRP with bigger diameters. Though, it was not conservative with smaller diameters.
  • Publication
    Restreint
    Flexural behavior of basalt fiber–reinforced concrete slab strips with BFRP bars : experimental testing and numerical simulation
    (American Society of Civil Engineers, 2020-02-11) El Refai, Ahmed; Attia, Karim; Alnahhal, Wael
    This study investigated the flexural behavior of a new one-way concrete slab system reinforced longitudinally with basalt fiber–reinforced polymer (BFRP) bars and cast with basalt fiber–reinforced concrete (BFRC). The study included experimental testing and three-dimensional finite-element (FE) modeling of eight slab strips, 500×175×2,500  mm each. The investigated parameters included the volume fraction of the basalt fibers added to the concrete mix (0%, 0.5%, 1%, and 2%) and the BFRP reinforcement ratios (1.4 and 2.8 times the balanced reinforcement ratio). The effect of varying the fiber volume fraction on the mechanical properties of concrete was first assessed. The test results showed that increasing the fiber volume fraction increased the compressive strength and the modulus of rupture of the concrete. Slab strips with higher dosages of fibers showed an increased number of cracks and a considerable enhancement in their cracking and ultimate capacity. A volume fraction of 0.5% of basalt fibers had an insignificant effect on the flexural performance of the specimens, and therefore 1% of basalt fibers were recommended as a minimum dosage. Increasing the fiber volume fraction led to a noticeable increase in the ductility of the slab strips at all stages of loading. The FE models provided reasonable prediction of the nonlinear structural behavior of the slab strips. The Variable Engagement Model, initially developed for steel fiber–reinforced concrete, was assessed to describe the BFRC mixes. Good correlation between the numerical and experimental results in terms of cracking loads, load-carrying capacities, deflections, and crack pattern was obtained.
  • Publication
    Restreint
    Post-repair flexural performance of corrosion-damaged beams rehabilitated with fabric-reinforced cementitious matrix (FRCM)
    (Elsevier, 2018-02-22) El Refai, Ahmed; Elghazy, Mohammed; Ebead, Usama; Nanni, Antonio
    This paper presents the results of a research program examining the post-repair flexural response of corrosion-damaged reinforced concrete (RC) beams repaired with different FRCM systems. A total of nine RC beams were tested, including two beams that were neither corroded nor repaired, one beam that was corroded and not repaired, and six corroded-repaired beams that were prepared in two phases. Beams of phase I were subjected to an accelerated corrosion process for 210 days before being repaired whereas beams of phase II were initially subjected to accelerated corrosion for 70 days, then repaired and exposed to further corrosion for 140 days. Flexural test results showed that exposing the FRCM-repaired beams to corrosion after repair resulted in 23% reduction in steel mass loss. The use of U-shaped FRCM layers was more efficient in reducing the corrosion rate and increasing the ultimate strength of the repaired beams than the end-anchored FRCM layers. The PBO FRCM-repaired beams showed lower post-yielding stiffness and more ductility at failure than those of their carbon FRCM-repaired counterparts. Beams that experienced post-repair corrosive environment showed load-carrying capacities that ranged between 14 and 65% above those of the virgin beam. ACI 549.4R-13 provisions conservatively predict the ultimate capacities of the FRCM-repaired beams exposed to post-repair corrosive environment.