Publications

In this paper, experimental work has been reported to investigate the efficiency of fiber-reinforced cementitious matrix (FRCM) in enhancing the flexural capacity and deformational characteristics of reinforced concrete (RC) beams.The aim of the experimental work is to assess the parameters that contribute to such enhancement.Twelve RC beam specimens, 2500 mm long, 150 mm wide and 260 mm deep, were prepared with two different reinforcement ratios of: ρ s D12 = 0.72% and D16 =1.27% , representing under-reinforced beam sections.The strengthened beams utilized two FRCM types; namely carbon and polyparaphenylene benzobisoxazole (PBO) FRCM systems.The RC beam specimens were tested in flexure under four-point loading until failure.Two beams without FRCM strengthening were used as control specimens.Six beams were externally reinforced by one, two and three layers of carbon FRCM system.Four beams were strengthened with one and two layers of PBO FRCM system.From the experimental observations, a reasonable gain in flexural strength was achieved for both the FRCM systems.Results showed that the flexural capacity of carbon FRCM strengthened beams (FRCM stiffness = 1422 MPa) can be increased by 78% and of PBO FRCM counterparts (stiffness = 605 MPa) by 27.5% over that of their control (un-strengthened) specimens.

Fibre reinforced cementitious matrix (FRCM) systems are mostly externally bonded (EB) for the strengthening of reinforced concrete (RC) and masonry structures. In this paper, the relatively new concept of near-surface embedded (NSE) FRCM, has been introduced for the flexural strengthening of beams. The process of the application of NSE-FRCM strengthening technique involves the removal of the concrete layer at beam soffit, being the most deteriorated in actual practices. Experimental evidence of the flexural strengthening efficacy of this technique is provided here. Eight RC beams were prepared and tested under four-point loading with the consideration of two test parameters: (a) FRCM material (polyparaphenylene benzobisoxazole (PBO)/carbon/ glass); and (b) the reinforcement ratio (0.5% representing flexure-deficient beams and 1.28% representing typical under-reinforced beams). The strengthening led to gains in ultimate loads that ranged between 31.4% and 84.3%.

There are very limited studies on bond of spliced fiber-reinforced polymer (FRP) bars as a reinforcement of flexural concrete members. The current standards for steel reinforcement cannot be used for the FRP bars due to the inherent differences in their mechanical properties and surface configurations. The results of 12 concrete beams of dimensions 250 mm (9.85 in.) in width and 400 mm (15.76 in.) in thickness and spanned at 4200 mm (165.48 in.) are presented. The beams were reinforced with spliced carbon or glass FRP bars. The effects of the bar diameter and splice length on the bond strength are investigated. Furthermore, an evaluation of the existing recommendations for the spliced FRP bars (ACI 440.1R-03, CAN/CSA-S806-02, ISIS-M03-01, and CAN/ CSA-S6-00) is presented. Tests indicated that the FRP stress limit is directly proportional to the splice length. Moreover, the ultimate strength analysis method can be used to predict the maximum stress in the spliced FRP bars. In addition, the average bond strengths and the critical splice lengths for the FRP bars with different diameters are outlined.

Exiting literature revealed that fabric reinforced cementitious matrix (FRCM) is a promising material for the strengthening of shear deficient reinforced concrete (RC) beams. However, most of the available experimental studies are devoted to the use of FRCM system for the strengthening of slender beams and limited literature is available on the strengthening of deep beams using FRCM system. Moreover, there is no available literature on the analytical modelling of FRCM-strengthened deep beams. In this paper, a simple strut and tie model (STM) has been used to predict the ultimate load carrying capacity of RC deep beams strengthened in shear using FRCM system. The model accounts for the internal transverse reinforcement ratio and axial rigidity of the FRCM system. The proposed model is validated against an experimental results of RC deep beams strengthened with different types of FRCM system available in the literature.

Predictions show that more than half of the world population will lack sufficient freshwater by 2025. Yet, the construction industry uses a considerable amount of freshwater to produce concrete. To save resources of fresh water, using seawater seems to be a valid potential alternative that can replace freshwater for mixing concrete. This paper presents a short review performed on existing literature related to the usage of seawater in concrete structures. As a summary of the work presented: (a) It is noticeable that the current literature, generally, reports little or no negative effect of seawater on the characteristics of plain concrete, both in the short and in the long term; (b) steel corrosion caused by the presence of chloride appears to be the sole reason for not accepting the use of seawater in concrete preparation; (c) Fiber reinforced polymer (FRP) is discussed as a promising alternative to steel for seawater-concrete reinforcement, owing to their light weight, high tensile strength, and adequate corrosion resistance; and (d) A future outlook for using seawater accompanied by FRP reinforcement in concrete structures is discussed in terms of achieving sustainability goals.

The combined use of recycled concrete aggregate (RCA) and glass fiber reinforced polymer (GFRP) reinforcement in reinforced concrete (RC) structures is deemed plausible to achieve sustainable construction. This paper aims to examine the effect of such a combination (RCA + GFRP reinforcement) on the shear behavior of RC beams. Six medium-scale RC beams (150 × 260 × 2200 mm) critical in shear were tested under three-point loading until failure. The test variables were the aggregate type (natural/recycled) and the shear reinforcement (steel/GFRP/none). The failure modes, cracking patterns, load-carrying capacities, deformational and strain characteristics were analyzed and compared among the tested specimens. It was found that using 100% RCA in the concrete mix reduced the shear strength of RC beams (by 12% on average). Minor effects were observed on the shear strength of the beam specimens (∼2%) with altering the transverse reinforcement (GFRP versus steel). Theoretical load-carrying capacities of the tested beams were obtained as per contemporary design guides and compared with the experimental results.

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Textile reinforced mortar (TRM) is applied on the concrete surface with the aim of strengthening reinforced concrete structures. The performance of the strengthened structural system is directly related to the bond between the existing concrete substrate and the freshly applied TRM layer. This paper presents the results of an experimental study carried out to investigate the significance of concrete surface preparation, performed prior to strengthening, on the bonding behavior of the TRM system. For this purpose, concrete slabs of size (500 mm × 500 mm × 100 mm) were prepared and strengthened using a 10-mm thick TRM layer. After that, the bond performance of the strengthening layer with the concrete slab was assessed using the pull-off test. Three different levels of surface roughening were considered before strengthening: (i) no roughening (regarded as the reference), (ii) low roughening level, and (iii) high roughening level. Two types of textile materials are used in strengthening systems: carbon and polyparaphenylene benzobisoxazole (PBO). A total number of 72 pull-off tests were performed, of which the results were analyzed to examine the significance of the test variables. Results revealed that as the concrete surface is more roughened before strengthening, the bond between concrete substrate and TRM layer becomes stronger. Moreover, the PBO-TRM systems exhibit more desirable bonding behavior compared to the carbon-TRM counterpart.

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This paper is aimed at studying the bond and shear-strengthening performance of fabric reinforced cementitious matrix (FRCM) systems. Three FRCM systems were compared, namely, polyparaphenylene benzobisoxazole (PBO)-FRCM, Carbon-FRCM, and Glass-FRCM. At first, six double-shear specimens were tested to investigate the FRCM/concrete bond, with the test variables including the fabric type and the bond length. After that, seven shear-critical reinforced concrete (RC) beams were tested under three-point loading, considering the fabric type and strengthening configuration (full/intermittent) as the test variables. As for the double-shear test results, the failure observed was fabric/matrix debonding in carbon-FRCM, matrix/concrete debonding in PBO-FRCM, and fabric rapture in glass-FRCM. The FRCM/concrete bond increased with the bonded length, and the PBO-FRCM showed the highest bond to concrete. Regarding the RC beam tests, the FRCM-strengthened beams showed the same failure mode that is debonding at the FRCM/concrete interface. Nonetheless, FRCM had successfully strengthened the beams in shear: an average gain of 57% in the load carrying capacity was achieved as compared to the non-strengthened reference. Indeed, the full-length strengthening resulted in a better structural improvement compared to the intermittent-strengthening configuration. Amongst the three systems, carbon-FRCM systems were the most efficient in shear-strengthening RC beams.

The feasibility of strengthening concrete slabs in flexure, with and without cutouts, using the mechanically fastened (MF) FRP technique is investigated. Two series of large-scale reinforced concrete slabs are tested. The first series is comprised of five slabs without a cutout, and measuring 2,600×2,600×120mm; the second series consists of four slabs of the same dimensions with a central cutout measuring 800×800mm. The mechanically fastened system is found to be a valid alternative to the externally bonded system resulting in a rapid, economic, and effective strengthening technique for two-way concrete slabs. The increases in ultimate capacities of the MF FRP-strengthened slabs range between 30 and 70% over those of the unstrengthened specimens. In addition, finite-element modeling of MF FRP-strengthened slabs is introduced in this study. The interfacial behavior between the MF FRPs and the concrete substrate is accounted for by using appropriate interfacial models. Very good agreement is obtained between the test results and the numerical predictions.

This paper presents an experimental study on the efficacy of a lately introduced "near surface embedded" technique (NSE) for fabric reinforced cementitious matrix (FRCM) for the strengthening of reinforced concrete (RC) beams in shear; considering two test variables: (a) fabric type (glass and carbon) and (b) strengthening configuration (intermittent versus full). For this purpose, five (5) simply supported medium-scale RC rectangular beams have been tested under displacement controlled monotonic three-point loading. The experimental results showed that the FRCM system is effective in strengthening of shear deficient RC beams. An average of 62% gain in the shear capacity has been achieved due to the FRCM strengthening system. Carbon FRCM owning the higher axial rigidity showed better performance than that of glass FRCM. The average gain in the shear capacity for carbon FRCM strengthened beams was 22.5% higher than that for glass FRCM strengthened beams. Moreover, full strengthening configuration showed better performance than that for the intermittent configuration counterparts confirming the significance of the FRCM continuity and its quantity in enhancing the shear capacity of the strengthened beams.