Fabric-reinforced cementitious matrix (FRCM) composites represent a new technique for strengthening concrete and masonry structures. Various studies confirm the efficiency of FRCM systems in terms of ultimate capacity gain, compatibility with the parent material, and viability in corrosive environments and under elevated temperatures. An appealing use of FRCM composites is to strengthen concrete bridges. Vehicular traffic imposes cycles of loading and unloading on the structure that can lead to fatigue failure, but the fatigue life of FRCM materials is yet to be investigated. This study examined fatigue performance of FRCM-strengthened reinforced concrete beams. Twelve concrete beams reinforced with carbon fabric were tested, including four benchmark beams subject to monotonic loading. The effects of fiber architecture and reinforcement ratio were accounted for by using two types of fabrics. Inspection of the fractured sections indicated that fatigue failure in the steel reinforcement was the predominant cause of failure. Analysis of applied stress range versus number of cycles to failure suggested that FRCM systems enhance fatigue life by controlling crack propagation in concrete.
In this paper, statistical analyses and a parametric study are presented for reinforced concrete beams strengthened in flexure using FRP composites. Five variables are considered in this study; namely, the FRP axial stiffness, concrete strength, steel reinforcement ratio, beam depth, and beam span. We aim to develop statistics-based design equations to predict the debonding load, the flexural capacity of the beam cross-section, the maximum deflection at the debonding load, the ductility index, and the debonding strain level in the FRP laminate. Simplifying these statistical models is then carried out to develop robust design equations. These equations hold an advantage over those available in most code specifications because they account for the effect of interactions between various variables on the predicted quantities. The statistical analyses are primarily based on the response surface methodology (RSM) technique. The proposed models are thus referred to as the RSM models. Proposed design equations are then developed by simplifying the RSM models using Monte Carlo simulations and nonlinear regression analysis. Of the five responses considered in the RSM analysis, only the debonding strain level in FRP laminates is considered in the design equations. The data required for the statistical analysis were obtained from finite element models for beams having different combinations of variables. The statistical analyses are followed by a parametric study to investigate the effect of the above five variables and their interactions on the debonding load and the corresponding debonding strain level in the FRP laminate. This involves comparisons in terms of the debonding strain between the predictions of the proposed equation and those of the ACI, fib, Chinese specifications, and Australian standards.
This paper presents an analytical study to verify the ACI 549-4R-16 code for experimentally tested Reinforced Concrete (RC) beams, which were strengthened to enhance the flexural capacity using Fiber-Reinforced Cementitious Mortars (FRCM).Twelve RC beam specimens having 2500 mm length, 150 mm width, and 260 mm depth were prepared with two different reinforcement ratios (ρ_s^D12=0.72% and ρ_ s^D16=1.27%),and were then strengthened with two different FRCM systems, namely carbon and polyparaphenylene-benzobisoxazole (PBO) FRCM systems.Two RC beams were tested as control specimens.Six beams were externally reinforced using single, double and triple layers of carbon FRCM system, while the remaining four beams were repaired with one and two layers of PBO FRCM system.The strengthened RC beams were tested in flexural under four-point monotonic loading.The experimental results revealed that a reasonable gain in flexural strength was achieved for both FRCM systems, with up to 78% increase in flexural capacity for carbon FRCM systems and up to 27.5% for PBO FRCM system over that of their control specimens.Further, the results obtained from the theoretical approach using the ACI 549 code conform well with the experimental loadcarrying capacities.Moreover, the values obtained for experimental to theoretical ratio are quite close to 1.00 which somewhat shows satisfactory computational results.
This paper reports on the results of an investigation carried out to examine the ability of fine glass to be used in the concrete industry. The pozzolanicity of the glass powder (GP) hydration with and without calcium hydroxide (CH) (lime) is assessed using different methods. A comprehensive experimental programme is carried out to investigate the chemical and physical properties of the hydrated activated GP with CH, as a cement hydration product, on the microstructural level. The experimental work focuses on the degree of hydration, pH and the alkalinity nature of the pore solution to evaluate the performance of the GP when it reacts with the CH. A flame emission spectroscopy test was used to quantify the alkali release from the GP as well as determining the rate of alkali release with time. It was found that the GP releases a small fraction of sodium ions into the solution. Test results showed that the finely ground GPs exhibited very high pozzolanic activity. It was observed that the GP–lime pastes show high non-evaporable water content. Moreover, the best performance of the GP reactivity can be obtained in the range of 10·5 < pH < 11·5 depending on the CH/GP ratio. According to the scanning electron microscope analysis, the gel product of the GP hydration precipitates on the surface of the large particle of the GP, at which the very small micro particles and the outer layer of the large GP particles react with CH.
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.
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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