The construction sector is well known for its critical environmental impact resulting from the consumed amounts of raw materials and the tremendous emissions of greenhouse gases. Therefore, scientists need to promote and study the environmental implications of using alternative solutions such as fiber-reinforced polymers (FRP) throughout their service life. FRPs have gained increasing popularity in the last few years due to their durability, high corrosion resistance, light weight and high strength. Life cycle assessment is considered one of the most important methods to investigate the environmental impacts of the FRP. The aim of this paper is to present an overview of fiber-reinforced polymer composites in concrete structures with an investigation focusing on their environmental and mechanical properties in civil engineering structures. The main focus is set on the properties of fiber-reinforced polymers, their use as a strengthening technique in concrete structural members and their environmental impact using the life cycle assessment method. The reported results from the literature reveal that utilizing FRP composites in structural members instead of traditional materials improves their strength and stiffness and reduces environmental impacts.
The use of seawater and recycled coarse aggregate (RCA) in concrete mixtures leads to the production of a very sustainable concrete. The potential risk of steel reinforcement corrosion (due to chloride in the seawater) in such mixtures may be eliminated when considering plain concrete or noncorrosive reinforcement (e.g., fiber-reinforced polymer). This study investigated the fresh and hardened properties of a proposed green concrete mixed using seawater and recycled coarse aggregates. Two different concrete mixtures were studied, namely conventional concrete (Mix 1) and seawater-mixed concrete with RCA (Mix 2). Blast furnace slag was used as supplementary cementitious material at a 65% replacement level in both concrete mixtures. Fresh and hardened properties of the two concretes, including workability, strength gain, drying shrinkage, permeability, and microstructure, were characterized and compared. The results suggest that the use of seawater and RCA together has negative effects on concrete performance. Compared with the reference (Mix 1), Mix 2 concrete had approximately 5% lower density, 25% lower slump flow, 50% lower setting time, 33% lower strength gain, 10% higher drying shrinkage, 60% higher water absorption, and 100% higher charge passed (in rapid chloride permeability tests). Consequently, strategies to improve the performance of such concretes, such as a reduction in the water:cementitious materials ratio and the use of chemical admixtures, are suggested. These strategies, however, may somewhat reduce the green aspect of the proposed seawater-mixed concrete with RCA.
The externally bonded (EB) fabric reinforced cementitious matrix (FRCM) has successfully been used as a structural strengthening for various applications including flexural and shear strengthening of reinforced concrete (RC) beams, flexural strengthening of RC slabs and column confinement. However, the EB-FRCM system is characterized by poor FRCM/concrete bond leading to premature debonding of FRCM off the concrete substrate, particularly for thicker FRCM. The present paper reports on an experimental study on the efficacy of a pioneer form of hybrid near surface embedded and externally bonded technique using FRCM composites (NSEEB-FRCM) for shear strengthening of RC beams. With such a technique, higher thickness of FRCM composites can be applied with less likelihood of debonding that is normally experienced when using the EB-FRCM system. Thirteen shear-deficient medium-scale RC beams were constructed, strengthened in shear and tested under three-point bending test. The test parameters were: (a) FRCM type (polyparaphenylene benzobisoxazole, carbon, and glass), (b) strengthening configuration (full versus intermittent strips), and (c) number of fabric layers. The percentage enhancement in the shear capacity of the beams ranged from 43% to 114% indicating the successful implementation of the strengthening methods provided. An average enhancement in shear capacity of 83%, 72% and 62% were observed in carbon FRCM, glass FRCM and PBO-FRCM, respectively. The failure mode of the strengthened specimens was sensitive to the type and configuration of FRCM in addition to the number of FRCM layers. The strengthening systems also resulted in higher deflection at failure and energy absorption value of the strengthened beams with an average of 94% and 204% relative to the reference specimen, respectively.
Results from nonlinear finite element analyses of fibre reinforced polymer (FRP)-strengthened concrete beams and slabs are presented. The direct shear test, a basic application that provides insight into FRP-concrete interfacial behaviour, is also considered. The motivation for this work is the fact that, although there is a large amount of experimental data available on the FRP strengthening of concrete structures, a full understanding of the various load–deformation behaviours and debonding phenomenon is still lacking. The numerical models presented in this paper adopt a displacement-controlled solution and are capable of simulating FRP-strengthened beams either in shear or in flexure, as well as slabs strengthened using either passive or prestressed FRP laminates. Results of the different applications are presented and compared with published test data, and a very good agreement in terms of the ultimate load carrying capacities, load–deflection behaviour and modes of failure, is obtained.
The use of a recently introduced "near surface embedded" (NSE) technique for fabric reinforced cementitious matrix (FRCM) system is shown to be a viable alternative to the conventionally used externally bonded FRCM counterpart with the potential to mitigate FRCM/concrete debonding. This paper presents a study on the interaction of FRCM and stirrups for RC beams strengthened in shear using the NSE-FRCM system. The experimental program involved eight (8) rectangular RC beams with and without internal shear reinforcement. Two test variables were considered; namely, fabric type (carbon, glass and polyparaphenylene benzobisoxazole) and internal shear reinforcement within the critical shear span (with and without stirrups). The experimental results revealed that the NSE-FRCM can successfully be used to enhance the shear capacity of the strengthened beams. Carbon FRCM was the most effective of all the fabric types. Moreover, an interaction between the stirrups and the NSE-FRCM system has been observed. The percentage gain in the shear strength was reduced from 69% to 38% due to the presence of stirrups within the critical shear span. Moreover, the NSE-FRCM strengthening has reduced the strain in the stirrups owing to the load sharing between the stirrups and the strengthening system.
Abstract In this study, steel reinforced grout (SRG) is proposed for shear strengthening of reinforced concrete (RC) beams using the near‐surface embedded (NSE) technique. It is believed based on several research contributions in the literature that the NSE technique precludes or delays the onset of premature debonding and achieves higher strength increase in strengthened beams compared to the externally bonded (EB) counterpart. The tests conducted in this study used 13 RC beams to determine the shear behavior of RC beams strengthened in shear using SRG. The effect of the strengthening technique (NSE versus EB), SRG fabric density, strengthening scheme (side‐bonded vs. U‐wrapped), and the strengthening configuration (continuous vs. discontinuous) on RC shear enhancement was studied. The strengthening effectiveness of the SRG system was assessed in terms of the shear capacity, failure mechanism, load‐deflection response, and strain results. The NSE‐SRG increased the beam shear strength by an average of 100%, alleviated SRG debonding, and enhanced the deformation characteristics. The average increase in the shear strength of the EB‐SRG strengthened beam was 54% and 105% for the continuous and discontinuous SRG strips, respectively. An analytical model is proposed to predict the shear capacity of both the NSE‐SRG and EB‐SRG strengthened beams and give accurate and safe predictions.
Abstract Concrete bridge piers reinforced with conventional steel bars experience large permanent (residual) deformation that may lead to uneconomical repair or demotion of bridges due to their non-functionality post strong seismic event. Thus, sufficiently ductile materials are required to reinforce concrete bridge piers in the plastic hinge zone in order to limit their permanent damage and deformation post-earthquake event. Previous studies showed that partial replacement of conventional steel reinforcement bars with superelastic shape memory alloy (SMA) bars in the plastic hinge zone of concrete bridge piers has the capacity to limit the residual deformation owing to the superior self-centering properties of SMA bars. In this study, the efficacy of hybrid SMA/steel reinforcement for hollow section concrete bridge piers under combined reverse cyclic and constant axial loading is numerically investigated for the first time. The responses of the piers were evaluated in terms of different performance indices including hysteretic characteristics, residual deformation, energy dissipation capacity, and self-centering capacity. A sensitivity analysis was used to explore the main effects of key design parameters and their interactions on each performance index at four damage states, namely, complete, extensive, moderate, and slight damage states. The results of this study demonstrate the effectiveness of hybrid SMA/steel reinforcement for enhancing the seismic behavior of hollow section concrete bridge piers.
The focus of this work was to study the reactivity of glass powder of a certain fineness by using a new experimental approach and to establish specifications for the use of glass powder as a pozzolanic material in concrete by developing glass powder hydration reaction equations. Experiments were carried out to determine the different quantities and proportions of glass powder, calcium hydroxide and water to establish the hydration reaction. Models that describe the hydration of the glass powder with and without calcium hydroxide are also developed in this paper. The developed models are validated using the results of the experiments. Using these models, predictions of the structure of the hydration products are obtained.
In spite of the availability of different models proposed to predict the shear capacity of reinforced concrete (RC) beams strengthened in shear using fabric reinforced cementitious matrix (FRCM) system, accurately predicting this value remains a challenge. The simplified compression field theory has shown to accurately predict the shear capacity of RC beams. This paper presents an analytical model based on the simplified compression field theory for predicting the shear capacity of RC beams strengthened in shear using FRCM strengthening system. The model has been validated against a data series of over sixty RC beams strengthened in shear using different FRCM types with different strengthening configuration and orientation. The results showed that the model can reasonably predict the load carrying capacity of the beams. The ratio of theoretically predicted and experimental results for the load carrying capacity ranged between 0.67 and 1.33 while average of this ratio was 1.01 with a coefficient of variation of 0.16.
The application of inorganic composites has proven to be an effective strengthening technique for shear-critical reinforced concrete (RC) beams. However, accurate prediction of the shear capacity of RC beams strengthened with inorganic composites has been a challenging problem due to its complex failure mechanism and the interaction between the internal and external shear reinforcements. Besides, the predictive capabilities of the existing models are not satisfactory. Thus, this research proposed machine learning (ML) based models for predicting the shear capacity of RC beams strengthened in shear with inorganic composites, for the first time, considering all important variables. The results of the analyses evidenced that the proposed ML models can be successfully used to predict the shear capacity of shear-critical RC beams strengthened with inorganic composites. Among the ML models examined herein, the extreme gradient boosting (xgBoost) model showed the highest prediction capability. The comparison among the predictions of the proposed xgBoost and existing models evidenced that the efficacy of the xgBoost model is superior to the existing models in terms of accuracy, safety, and economic aspects. Finally, reliability analysis is performed to calibrate the resistance reduction factors in order to attain target reliability indices of 3.5 and 4.0 for the proposed model.
