Publications

This paper presents a comprehensive experimental work to study the interaction between the internal and external shear reinforcement for strengthened reinforced concrete (RC) deep beams.For this purpose, a total of twelve medium-scale RC deep beams have been designed, fabricated, and loaded monotonically till a completed failure.Four beams were kept unstrengthened to act as reference beams, while others have been strengthened using hybrid carbon-glass Fiber-reinforced polymer (FRP) strips.All beams have been designed to be shear deficient in one side, which will be called herein as a critical shear span (CSS).The study included three test parameters: strengthening technique (externally bonded and near-surface mounted), number of internal and external shear reinforcement (two and three) in the CSS, and the alignment of the internal and external shear reinforcement (aligned and unaligned) to each other.The results revealed that the near-surface mounted (NSM) technique could be able to mitigate the premature debonding mode of failure which was dominant with the beams strengthened by the externally bonded (EB) counterpart.The NSM technique could be able to increase the shear capacity of the strengthened beams up to 45% compared to the corresponding technique.The results also showed that the unaligned configuration of the internal and external shear reinforcement was better than the aligned one for both NSM and EB techniques.

This paper presents an experimental study on the efficacy of a recently introduced hybrid “near surface embedded/ externally bonded” NSE/EB fabric reinforced cementitious matrix (FRCM). Seven medium scale RC beams, deficient in shear, were constructed and tested under three-point loading. Six beams were strengthened using hybrid NSE/EB-FRCM technique and one beam was left un-strengthened as a reference. Two main test variables were considered; viz., strengthening configuration: full versus intermittent strengthening configuration and FRCM type: glass FRCM versus polyparaphenylene benzobisoxazole (PBO). The test results revealed that the hybrid NSE/EB-FRCM strengthening technique is effective in enhancing the shear capacity of the strengthened beams. The strengthened specimens showed an average of 67% higher shear capacity relative to the reference specimen. With regard to the FRCM type, G-FRCM strengthened specimens showed an average of 73% enhancement in the shear capacity, which was 12% higher than the value for PBO-FRCM counterpart. Moreover, the strengthened beams showed higher deflection at the ultimate load than that of the reference specimen. Furthermore, the hybrid NSE/EB-FRCM technique has shown to be a promising alternative to the conventionally used externally bonded FRCM system with the potential to reduce the debonding of FRCM from the concrete substrate.

Recently, seawater has emerged as viable mixing water for concrete, especially in the case of non-reinforced concrete applications or with the use of non-corrosive reinforcement. Previous studies concerning seawater-mixed concrete mostly revealed an initial slight increase in its strength performance (i.e., till Day 14 following mixing), followed by a strength reduction of 7–15% (i.e., after 28 days or longer) as compared to the conventional freshwater-mixed concrete. With an attempt to explain such observations, this paper aims at comparing the microstructure of freshwater-and seawater-mixed cement pastes. Scanning electron microscopy was utilized to observe the microstructure of freshwater and seawater pastes at Days 3 and 28 following mixing. At Day 3, seawater paste was observed to have more densified microstructure as compared to that of the freshwater counterpart, resulting in relatively higher strength performance. At Day 28, the microstructure was almost similar for the two cement pastes. However, seawater paste was observed to have salt impurities as a result of seawater ions, which possibly cause a slightly lower strength performance as compared to the freshwater paste.

The structural performance of corrosion-damaged reinforced concrete (RC) beams repaired with fabric-reinforced cementitious matrix (FRCM) was investigated. Eleven RC beams were constructed and tested in flexure under four-point load configuration. Nine beams were subjected to an accelerated corrosion process for 70 days to obtain an average mass loss of 13% in the tensile steel reinforcing bars while two other beams were tested as controls. One corroded beam was repaired with carbon fiber-reinforced polymer (CFRP) before testing for comparison. The test parameters included the number of fabric plies (1–4), the FRCM repair scheme (end-anchored and continuous U-wrapped strips), and FRCM materials [carbon and polyparaphenylene benzobisoxazole (PBO)]. Test results showed that corrosion slightly reduced the yield and ultimate strengths of the beams. The use of FRCM increased the ultimate capacity of corroded beams between 5 and 52% and their yield strength between 6 and 22% of those of the uncorroded virgin beam. Beams repaired with U-wrapped FRCM strips showed higher capacity and higher ductility than those repaired with the end-anchored bottom strips having a similar number of layers. A high gain in the flexural capacity and a low ductility index were reported for specimens with a high amount of FRCM layers. A new factor was incorporated in the design equations of the ACI 549.4R-13 to account for the FRCM scheme.

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 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 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.

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.

Fabric-reinforced cementitious matrix, (FRCM) system has shown to be promising for the strengthening of reinforced concrete (RC) beams. However, the available experimental investigation on the shear strengthening efficacy of FRCM system is limited, particularly for deep beams. Moreover, to the authors' knowledge, no literature is available on the effect of the stirrups' configuration relative to the FRCM strips on the shear capacity of FRCM-strengthened beams. Studying this effect will aid in a better understanding of the FRCM/stirrups interaction. Thus, in this paper the experimental study on the shear behavior of RC deep beams strengthened in shear using FRCM system is presented. The test matrix involved two unstrengthened and six FRCM-strengthened deep beams tested under three-point bending. The primary test variable was the effect of stirrups' configuration relative to the FRCM strips. The other test variable includes the effect of different types of FRCM fabric (made of carbon, glass, and polyparaphenylene benzobisoxazole, PBO). Experimental results demonstrated an effective application of the FRCM in improving the load capacities of RC deep beams, up to 40.3% increase in the load capacity was achieved.