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This paper was made possible by NPRP grant # NPRP 7-1720-2-641 from the Qatar national research fund (a member of Qatar Foundation). The findings achieved herein are solely the responsibility of the authors.

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.

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.

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This research aims at creating finite-element models for fiber-reinforced polymer (FRP) shear strengthened concrete beams. It is inspired by the fact that the determination of the structural behavior of shear strengthened beams requires advanced numerical methods of which results are substantiated by credible experimental findings. The models are developed here to assess the shear and interfacial types of behavior of beams strengthened using one of three different schemes, namely, externally bonded (EB), mechanically fastened (MF), and hybrid EB/MF FRP schemes. The interfacial behavior between the EB, MF, and hybrid EB/MF FRP and the concrete is accounted for using interface elements for both vertical and inclined FRP strips. A user-defined subroutine for the microplane constitutive law for the concrete material is incorporated in the model. Results are presented in terms of the ultimate load-carrying capacities, load-deflection relationships, and interfacial stress/slip distributions. Numerical results are validated against available experimental data and show reasonable agreement. Models for hypothetical cases of MF FRP strengthened beams are created to enrich the discussion on the interfacial bearing stress distributions.

Reinforced concrete (RC) beams are bound to lose their strength while in service due to numerous causes.Thus, proper strengthening and rehabilitation techniques are required to restore the strength and extend the service life of the structures.Steel reinforced grout (SRG) has recently been introduced as an efficient and economical strengthening solution, however, the study on its application for the strengthening of shear-deficient RC beams is scarce.Thus, this paper is aimed to investigate the efficacy of SRG for shear strengthening of RC beams with the focus on SRG/stirrups interaction.Six T-cross section beams were grouped into three series based on their internal shear reinforcement ratio and tested under three-point bending.Each series comprised of one reference and one SRG-strengthened beam.The test results revealed that SRG laminates are an effective technique to increase the shear capacity of RC beams.Up to 71% increase in the load-carrying capacity of the strengthened beams was achieved.The increase in the internal shear reinforcement has shown to reduce the shear-strengthening performance of SRG.

This pioneering research involved an in-depth experimental evaluation of the mechanical properties of ambient-cured alkali-activated mortar (AAM), while assessing an innovative machine learning (ML) driven solution for sustainable construction. A comprehensive dataset was used, comprising 635 compressive strength and 94 flexural strength data points, including data from previous studies. The performance of six ML algorithms in predicting the compressive and flexural strengths of AAM was evaluated. Hyperparameter optimisation was performed with Optuna and ten-fold cross-validation. Multi-objective optimisation aimed to maximise compressive strength while minimising the carbon dioxide footprint. The findings highlight the significant impact of ground granulated blast-furnace slag (GGBS) content on strength, with higher GGBS improving compressive and flexural strengths but reducing workability. The highest compressive strength was 56.28 MPa at 28 days, for the AAM with 100% GGBS. The highest flexural strength was 0.580 MPa at 28 days, with 75% GGBS. Extreme gradient boosting was found to be the most reliable model in predicting the compressive strength, achieving a coefficient of determination (R2) of 98.1% on training data and 86.8% on testing data. Extra tree regression showed high accuracy in predicting the flexural strength of the AAM, achieving R2 = 90% on the testing dataset. A user-friendly interface was developed for predicting the mechanical properties of AAMs.

Fiber-reinforced polymer (FRP) composites have become popularly utilized in structural engineering applications.The common use of the FRP composites is related to their economic benefits that can be observed right away or in a long-time period.With increasing concern about global warming and the shortage of natural resources, it is essential to study the environmental implications of the use of FRP composites.Life cycle assessment (LCA) is one of the most common techniques that can be used to take the environmental impact of the FRP into consideration.This paper presents a literature review about the LCA of FRP composites in concrete beams.The LCA results reported in the literature confirmed the use of FRP composites for reinforcing the RC beams instead of conventional steel rebars or that the strengthening of RC beams instead of demolishing and reconstruction is a more environment-friendly approach.

This paper constitutes a special importance for developing countries where an affordable trowel-based strengthening system is needed. This paper also provides an affordable strengthening solution when it is not possible to entirely remove the effect of live load on the strengthened element. A series of 13 ferrocement strengthened beams of 2,400 mm in length and a rectangular cross section of 120×200 mm were tested. The beams were cast and preloaded to different load fractions (45 and 60%) of its ultimate capacity; then the load was partially released (by 15% of the ultimate load) and maintained, while the beams were then strengthened and reloaded until failure. The load released simulates the removed live load while strengthening an actual beam. The research reported in this paper features designing and manufacturing a special loading frame to apply, release, and reapply the loads on the tested beams. The frame allows implementing the strengthening process while maintaining the strengthened beams partially loaded. The use of flat and U-shaped ferrocement layers of three different volume fractions (VFs) of mesh reinforcement have been assessed. The overall response of the specimens was investigated in terms of the load carrying capacity, crack patterns, and propagation and modes of failure, and the deformational characteristics that include deflection, ductility, and energy absorption characteristics. The results indicated that the ferrocement strengthening system is effective in enhancing both strength and ductility of the RC beams.

It has been demonstrated, through laboratory investigations and various field projects, that the external bonding of fiber- reinforced polymer (FRP) laminates is an effective technique for the structural enhancement of reinforced concrete slabs. In such applications, failure is generally governed by debonding of the FRP laminate. Nevertheless, numerical simulations to date of FRP-strengthened slabs have usually been based on the assumption of full bond between the concrete and FRP. In this study, the interfacial behavior between the FRP laminates and the concrete substrate is accounted for by introducing appropriate bond-slip models for the interface in a nonlinear finite-element analysis of FRP-strengthened two-way slabs. The numerical model is capable of simulating slabs strengthened in shear or in flexure; it can be applied to arbitrary FRP configurations, and can also accommodate both passive as well as prestressed FRP strengthening schemes. Results are presented in terms of load-deflection relationships, ultimate load capacities, failure modes, and interfacial slip and stress distributions. When compared to test results reported in the literature, the analysis is shown to lead to excellent predictions in that, for the entire set of FRP-strengthened specimens considered, the average of the numerical-to-experimental load capacity ratios is 0.966, with a standard deviation of 0.066. Furthermore, in all cases when FRP debonding was observed experimentally, the analysis correctly predicted the mode of failure.

There is considerable investment in construction industry in Qatar for civil infrastructures and taking into account the severe environmental conditions, they would entail for proper maintenance, repair and strengthening for safe, continuous, uninterrupted, and efficient functionality. Reinforced concrete (RC) structural members, which constitute majority of construction works in Qatar, can be easily deteriorated by the deleterious effect of seawater exposure in the form of humidity or direct splashing for sea-level and offshore structures. Such deterioration can also be due to the exposure to extreme high temperatures, severe humidity and high chloride. All such environmental effect can significantly reduce the life-span of RC structures by up to 10-15 years. The cost of rehabilitation and strengthening is usually estimated in millions of dollars. Traditional methods of strengthening corrosion-damaged structures involve the replacement of the corroded bars and the substitution of deteriorated concrete layers with new concrete. Our study proposes an “optimum strengthening technique” for RC structures to mitigate the prevailing conditions of Qatar. This relatively new technique utilizes “textile-reinforced mortar (TRM)” to strengthen concrete beams. TRM systems consist of one or more layers of textiles made of carbon, glass, or Polyparaphenylene benzobisoxazole (PBO) grids that are sandwiched between layers of associated cementitious mortars. The cement-based mortar used in TRM acts as a barrier against chloride ions penetration thus protecting the main reinforcing bars from corrosion attack. Textiles' lightweight, high tensile strength, corrosion resistance, and ease of application make the strengthening system appealing. The potential of TRM for the repair and strengthening of concrete structures is not just the result of its physio-mechanical performance but also the ease and simplicity of installation that does not require any sophisticated equipment or retraining of the construction work. In addition, the compatibility between the mortar used and the concrete substrate is inherited since both materials have the cement as a common “base”. TRM systems, with their innovative features, ensure the endurance of the rehabilitation process and consequently the sustainability of the strengthened structure. Recently in the last few years, several research works in the USA and Europe in the field of TRM strengthening technique have been reported for masonry and concrete structural members. Majority of these works is limited to single type of textile (either carbon, PBO or glass) and on limited types of reinforcement levels. The work presented here compares two different types of TRM systems in the same domain, performed on three different levels of reinforcement ratios representing flexural deficient, lightly reinforced and typical under-reinforced beams. Experimental works were done to state the efficiency and effectiveness of textile reinforced mortar (TRM) in increasing the ductility and the flexural capacity of reinforced concrete (RC) beams. The aim of the experimental work was to investigate the parameters that contribute to the increase in the load carrying capacity of beams strengthened with TRM system. Eighteen medium-scale rectangular RC beam specimens, 2500 mm long, 150 mm wide and 260 mm deep, were prepared at three different reinforcement ratios of “ “ρ” _“s” ^“1” “ = 0.5%;” o “ρ” _“s” ^“2” “ = 0.72%;” f: “ρ” _“s” ^“1” “ = 0.5%; “ “ρ” _“s” ^“2” “ = 0.72%; “ “ρ” _“s” ^“3” “ = 1.27%.” The strengthened beams utilized two TRM types namely carbon and Polyparaphenylene benzobisoxazole (PBO) TRM systems respectively. The RC beam specimens were tested in flexure under four point loading until failure with a clear span of 2.2 m. The strengthening technique was applied to the soffit of the beam (flat type) altering the number of layers of textile. Three beams (of three different reinforcement ratios) without TRM strengthening were used as control specimens. Nine beams were externally reinforced by one (“ρ” _“T-c” ^“1” “ = 0.014%”), two (“ρ” _“T-c” ^“2” “ = 0.028%”) and three (“ρ” _“T-c” ^“3” “ = 0.041%”) layers of carbon TRM system. Six beams were strengthened with one (“ρ” _“T-PBO” ^“1” “ = 0.009%”) and two (“ρ” _“T-PBO” ^“2” “ = 0.018%”) layers of PBO TRM system. From Based on the experimental observations, a reasonable gain in flexural strength and energy absorption was achieved for both the TRM systems. An increase of the initial stiffness was achieved for strengthened specimens; however, an apparent decrease in the overall ductility was observed with TRM strengthening. Results showed that the flexural capacity of strengthened beams increased to an average of 38% for carbon TRM system and an average of 26.7% for PBO TRM system over that of their control (un-strengthened) specimens. The highest increase in the load carrying capacity was 77.51% for a specimen having with the main reinforcement ratio of D12 (“ρ” _“s” ^“2” “ = 0.72%)” and was strengthened with carbon TRM system using three layers of carbon textile. Ductility index (ΔI) and energy absorption (Ψ) values were also calculated in order to know the behavior of ductility and flexural capacity in each of the beam specimen. The term ductility index (ΔI) is defined as the ratio between the deflection at the ultimate load and that at yield load, representing its ability to stretch/deform under sustained load before fracture. During experimentation, it was observed that the average values of ductility indices of using carbon as strengthening material were 1.1 × , 1.2 × and 0.5 × for “ρ” _“s” ^“1” “ = 0.5%,” “ρ” _“s” ^“2” “ = 0.72% and “ “ρ” _“s” ^“3” “ = 1.27%” beam specimens respectively to that of their control specimen. Similarly the average values of ductility indices of using PBO as strengthening material were 2.42 × , 0.75 × and 0.56 × for “ρ” _“s” ^“1” “ = 0.5%,” “ρ” _“s” ^“2” “ = 0.72% and “ “ρ” _“s” ^“3” “ = 1.27%” specimens respectively to that of the control specimen. Also the term energy absorption (Ψ) is defined as the area under the load- deflection curve up to the ultimate load, representing the amount of energy absorbed by the specimen before complete failure. The average values of energy absorption for using carbon as strengthening material were 1.8 × , 1.2 × and 1.6 × for “ρ” _“s” ^“1” “ = 0.5%,” “ρ” _“s” ^“2” “ = 0.72% and “ “ρ” _“s” ^“3” “ = 1.27%” beam specimens respectively to that of the control specimen. Similarly the average values of energy absorption for using PBO as strengthening material were 2.0 × , 1.0 × and 1.5 × for “ρ” _“s” ^“1” “ = 0.5%,” “ρ” _“s” ^“2” “ = 0.72% and” “ρ” _“s” ^“3” “ = 1.27%” specimens respectively to that of the control specimen. Therefore, both the adopted TRM systems performed exceptionally well within the scope of the work, with carbon TRM system showing a relatively higher increase in the capacity of strengthened specimens and PBO TRM systems exhibiting relatively more ductile failure with higher bond strength between the TRM surface and concrete substrate. Moreover, crack patterns for the strengthened beam showed effective distribution of cracks/damage over the length of beam as compared to severe and concentrated damage in the associated control un-strengthened beams. Further, during the experimentation, it was seen that the technique of applying the TRM system also considers the contractor's ease where the construction workers (although not very skilled) can easily implement the technique after being given simple demonstrations. The study puts forth proper procedures and standards to the construction industry on the rehabilitation and strengthening of the existing concrete structures using innovative TRM strengthening technique. Successful implementation of the project will result in “state-of-the-art recommendations for design and construction specifications”, which will place Qatar and research at Qatar University in a leadership position not only limited to the Gulf region. Furthermore, this can potentially act as an “important initiation for the development of new industrial opportunities” in the country. Keywords Reinforced concrete beams, textile reinforced mortar, flexural strengthening, ductility index, energy absorption.