This paper reports on the efficiency of fabric-reinforced cementitious matrix (FRCM) in enhancing the flexural capacity and deformational characteristics of RC beams. In the main experimental part of the paper, 12 RC beams, 2,500 mm long, 150 mm wide, and 260 mm deep, were fabricated. The beams had two different steel reinforcement ratios, namely, ρsD12=0.72% and ρsD16=1.27%, representing typical underreinforced beam sections. The strengthened beams utilized two FRCM types, carbon and polyparaphenylene benzobisoxazole (PBO) FRCM systems. In the second part of the work, tensile material characterization tests were performed on the FRCM coupons to determine the tensile characteristics of the FRCM composites. The beams were tested in flexure under four-point loading until failure. Two beams without FRCM strengthening were used as a benchmark. Six beams were externally strengthened using one, two, and three layers of carbon FRCM system. Four beams were strengthened with one and two layers of PBO FRCM system. Test results showed that the flexural capacity of the strengthened beams increased by 77% for the carbon FRCM system (three layers) and to 27% for the PBO FRCM system (two layers) over that of their benchmark (unstrengthened) beams.
Given the increasing global concern of freshwater scarcity, the use of seawater in concrete mixtures appears to be a way forward towards achieving sustainable concrete, especially in the case of non-reinforced concrete applications or with the use of non-corrosive reinforcement. This paper reports on the results of an experimental study to compare the freshwater-and seawater-mixed concretes in terms of their strength, shrinkage and permeability performance. The experimental program included the following: (i) compressive strength test (at 3, 7, 28, and 56-day ages); (ii) concrete shrinkage test (at Days 4, 7, 14, 21, 28, and 56 following mixing); and (iii) permeability tests (rapid chloride permeability and water absorption at Days 28 and 56 following mixing). As for the study results, seawater concrete showed a slightly higher early-age (i.e., till Day 7) strength performance than that of freshwater-mixed counterpart, followed by a strength performance that is 7–10% inferior to the freshwater concrete after 28 days or later. Also, the shrinkage of seawater concrete was slightly higher than that of freshwater concrete, with a difference of 5% reported after 56 days following mixing. Finally, the permeability performance of hardened concrete in seawater and freshwater mixtures was similar.
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.
Abstract Fabric reinforced cementitious matrix (FRCM) is a composite consisted of high‐strength fibers impregnated in a cement‐based mortar, and is commonly used for strengthening reinforced concrete and masonry structures. Comprehending the tensile behavior of FRCM is important to achieve a reliable and accurate design of FRCM strengthening systems. The current paper reports on the results of an experimental study on the tensile characterization of FRCM. A total of 40 FRCM specimens (410 × 50 mm, varied in thickness) were prepared and tested. The tensile characterization tests were conducted according to AC 434 guidelines using clevis‐grip mechanism. The tests were used to assess the effect of two parameters: (a) fabric type (carbon/glass) and (b) number of fabric plies (one/two/three/four). The results showed that the tensile strength of carbon‐FRCM specimens was approximately 1.33 times that of the glass‐FRCM counterparts. Three distinct failure modes were observed, namely, (a) ductile fabric slippage in carbon‐FRCM (up to three plies of fabric); (b) brittle fabric delamination in carbon‐FRCM with four plies of fabric; and (c) brittle fabric rupture in glass‐FRCM systems. The FRCM tensile load‐carrying capacity had proportionally increased with the number of fabric plies; less significant effect (within 20%) was observed on the corresponding ultimate tensile stresses (considering the net fabric area as the effective area).
This study investigates the influence of basalt fiber on the rheological, mechanical, and microstructural properties of sustainable self-compacting concrete (SCC) incorporating fly ash and microsilica as supplementary cementitious materials (SCMs). Various SCC mixes were prepared, incorporating five different volume fractions of basalt fiber (0.05%, 0.1%, 0.5%, 1%, and 1.5%), along with a control mix. The rheological properties of fresh SCC were evaluated using slump flow and V-funnel flow tests. Subsequently, the mechanical properties, including compressive strength, splitting tensile strength, and flexural strength, were measured after 28 days of curing. Additionally, microstructural analysis was conducted using scanning electron microscopy (SEM) on fractured specimen surfaces. The results indicated that the inclusion of basalt fiber adversely affected the flowability of fresh SCC mixes, with increased fiber volume. However, the hardened concrete exhibited significant improvements in mechanical properties with the addition of basalt fibers. The optimal performance was observed in the SCC70-85/0.10 mix specimens, which demonstrated a 69.90% improvement in flexural strength and a 23.47% increase in splitting tensile strength compared with the control specimen. SEM analysis further revealed enhanced microstructural density in the concrete matrix containing basalt fiber. A two-factor analysis of variance (ANOVA) with repetitions was conducted to evaluate the effects of varying basalt fiber concentrations on the compressive, flexural, and tensile strengths of SCC mixes. The ANOVA results indicated significant effects for both SCC grade and basalt fiber concentration, demonstrating that each factor independently affected the compressive, tensile, and flexural strengths of SCC. These findings suggest that the incorporation of basalt fibers holds promise for extending building lifespans and enhancing concrete quality, representing a valuable advancement in structural engineering applications.
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.
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Abstract The process of desalination results in the production of a hypersaline waste by-product known as reject brine. In some locations, this reject brine is dumped back into the ocean, which has potentially detrimental effects on water quality and marine life. This study was carried out to investigate whether this brine could potentially be used to manufacture cementitious materials. The effects of different concentrations of simulated reject brine on hydration kinetics, compressive strength, and drying shrinkage of cement paste and mortar were investigated. Cement paste and mortars were prepared using a water-to-cement ratio of 0.45 and were mixed with simulated reject brine, tap water, and diluted reject brine (an equal mass mixture of reject brine and tap water). The results show that the reject brine causes an acceleration of early cement hydration; however, this effect is negligible at later ages. Mixtures containing reject brine have higher compressive strength at early ages, although this difference is reduced at 91 d. The reject brine causes a drastic increase in the drying shrinkage. The difference between the results obtained using reject brine and diluted reject brine were generally insignificant, which suggests that the effects of solution composition on the observed properties were not strong when solution concentrations were greater than a threshold value. Although these results are preliminary and further feasibility studies, including research on concrete durability, are required, the results suggest that reject brine may be used to make unreinforced concrete or concrete reinforced with noncorrosive materials.
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%.
This paper presents a data-driven approach to determine the load and flexural capacities of reinforced concrete (RC) beams strengthened with fabric reinforced cementitious matrix (FRCM) composites in flexure. A total of seven machine learning (ML) models such as kernel ridge regression, K-nearest neighbors, support vector regression, classification and regression trees, random forest, gradient boosted trees, and extreme gradient boosting (xgBoost) are evaluated to propose the best predictive model for FRCM-strengthened beams. Beam geometry, internal steel reinforcement area, FRCM reinforcement area, and mechanical characteristics of concrete, steel, and FRCM are the main input parameters included in the database. Among the studied ML models, the xgBoost model is the most accurate model with the highest coefficient of determination (R2=99.3%) and least root mean square (RMSE), mean absolute error (MAE), and mean absolute percentage error (MAPE). A comparative study of the performance of the proposed and existing analytical models revealed the superior predictive capability and robustness of the proposed model. The predicted flexural and load capacities of the beams based on the existing analytical models are highly scattered and either over-conservative or unsafe. A unified SHapley Additive exPlanations approach is employed to explain the output of the best ML model and identify the most significant input features and interactions that influence the capacity of FRCM-strengthened RC beams in flexure. Furthermore, a reliability analysis is performed to calibrate the resistance reduction factor (ϕ) to achieve a specified target reliability index (βT=3.5).
This paper investigates the effectiveness of fabric reinforced cementitious matrix (FRCM) systems in shear-strengthening of reinforced concrete beams. Three types of FRCM systems were considered, namely, polyparaphenylene benzobisoxazole (PBO)-FRCM, Carbon-FRCM, and Glass-FRCM. At first, tensile characterization test was performed on 15 FRCM coupons with the aim of identifying the tensile properties of the FRCM systems adopted. After that, seven shear-critical RC beams were tested under three-point loading, with the consideration of two test parameters: (a) FRCM material (glass/carbon/PBO); and (b) strengthening configuration (full/intermittent). The study results revealed the use of FRCM as a strengthening material to achieve a considerable improvement in the structural capacity of shear-critical RC beams. The average gain in the shear capacity of the FRCM-strengthened beams was 57%. The beam specimens strengthened with carbon-FRCM showed the highest improvement as compared to those strengthened with glass-and PBO-FRCM systems. As intuitively expected, the shear capacity improvement achieved with the full-length strengthening systems was generally higher than that with the intermittent counterparts.
This paper presents an experimental study on the flexural behaviour of RC beams strengthened with fabric reinforced cementitious matrix (FRCM) system. Eight T-shaped RC beams with two different flexural reinforcement ratios (ρs = 0.40% and ρs = 1.02%) were constructed and tested as simply supported under monotonic three-point loading. Two beams were kept unstrengthen to act as references while the remaining six beams were strengthened with different types and geometric schemes of FRCM system. Three different test parameters have been considered: (a) FRCM type (carbon and glass), (b) FRCM strengthening scheme (side bonded versus U-shaped scheme), and (c) internal flexural reinforcement ratio. The strengthening system increased the ultimate load carrying capacity by 16.52 – 46.73% in carbon FRCM strengthened beams and 4.84 – 29.41% for glass fRcM strengthened beams relative to the reference beams. The strengthening performance of FRCM system decreased with an increase in the amount of internal flexural reinforcement. Moreover, U-shaped strengthening scheme performed better than the sided bonded counterparts in terms of the gain in the ultimate load and failure modes.
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