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This paper investigates experimentally and analytically the shear performance of RC beams made of recycled coarse aggregate (RCA). Previous studies showed that the partial replacement of the virgin coarse aggregate by recycled one results in decrease the shear strength of RC beams. Consequently, the main target of the this research was to compensate such decrease in the shear strength by providing internal short fibers and using cured recycled coarse aggregate instead of crude recycled coarse aggregate. A total of eleven simply supported RC beams made of recycled coarse aggregate along with one conventional concrete beam were tested under incremental four-point loading scheme. The considered parameters were the recycled coarse aggregate replacement ratio (15, 30 and 45%), the shear span-to-depth ratio (1, 2 and 3) and the fiber volumetric ratio (1, 1.5 and 2%). In addition, to improve the physical and mechanical properties of the recycled coarse aggregate (RCA), two curing methods for the RCA were implemented using cement slurry and Styrene Butadiene Rubber (SBR) compound. The experimental results showed that increasing the replacement ratio of the RCA resulted in decrease the shear capacity proportionally. The percentages of decreases in the shear capacities were about 8%, 14% and 19%, respectively, for RC beams provided by RCA replaced by 15%, 30% and 45%. In addition, it was shown that providing internal short fibers by volumetric ratios of 1%, 1.5% and 2% enabled the RC beams made of 30% partial replacement of the recycled coarse aggregate to compensate the decreases in the shear capacities (14%) and to increase their shear capacities by about 13%, 15% and 22% compared to those of the control beam, respectively. Furthermore, for RC beams made of 30% partial replacement of the RCA, the shear capacities decreased by about 2%, 14% and 37%, respectively, for beams having shear span-to-depth ratio of 1, 2 and 3. Besides, it was shown that, the cured recycled coarse aggregate enabled the RC beams made of 30% partial replacement to exhibit improved shear performance. However, the curing method based on cement slurry showed higher improvement since the restored shear capacities were about 15% and 3% for beams provided by cured coarse aggregate based on cement slurry and compound SBR, respectively compared to that of the beam made of crude RCA. Finally, an equation for estimating the shear capacity of RC beams made of recycled coarse aggregate was proposed and it showed satisfactory results when verified against the experimental findings of the current research as well as of other researches where the maximum variations were about 8.5% and 22%, respectively.

Glass Fiber Reinforced Polymer (GFRP) bars as a proper substitute for traditional reinforcing steel bars not only eliminate the durability problem due to corrosion of reinforcing steel, but also provide remarkably enhanced capacity due to their high tensile strength compared to that of the steel bars. This paper presents the experimental findings of 180 pullout tests conducted on GFRP bars embedded into high-strength concrete blocks covering different parameters. The studied parameters were bar diameter size (12 or 16 mm), embedment length (4 or 6 times the bar diameter), bar end condition (straight and headed), and concrete cover (1.5, 2.5, and 5 or 7 times bar diameter for straight bars and 8 or 10.5 times bar diameter for headed bars) in addition to a case of no embedment length except the head length for headed-end bars. In total, 30 variables were studied, while each variable was conducted on 6 identical specimens in order to increase the reliability of the results. Based on the results of the parametric study, the bond stress was shown to be inversely proportional to the embedment length and bar diameter as expected. In addition, the smaller concrete cover appeared to have significant effect on bond stress, leading to side blow-out failure rather than bar pullout or concrete splitting in the case of headed-end GFRP bars. In addition, the GFRP bar with headed-end showed significant increase in pullout strength compared to that for the straight-end bars. Finally, an empirical expression was proposed to calculate the development length of GFRP bars with either straight or headed-end, and then compared with the available design standards such as CSA-S806-02, CSA S6-06, ACI 440-1R-06, and JSCE-97. The comparison showed that the results developed by CSA S6-06 standards was the closest to the experimental findings showed about 2% safety margin exceeding the obtained development length by the proposed expression.

Pre-cast and cured Engineered Cementitious Composites (ECC) strips were placed in the tension cover zone of one-way reinforced concrete (RC) slabs beside the main steel reinforcement. Using pre-cast and cured ECC mitigates issues associated with volumetric changes associated with the ECC material. In order to assess the structural performance enhancement of the new hybrid system, four point bending tests were performed on two different sizes of RC slabs. The tested slabs were geometrically similar in thickness but and differed in their width and span. Small, 300 mm wide × 900 mm long, slabs were strengthened using one 150 × 500 × 20 mm ECC strip. Larger, 300 × 2000 mm slabs were strengthened with two 150 × 1600 × 20 mm ECC strips. A small amount of conventional reinforcing steel was provided inside the ECC strips in order to enhance the strain hardening behavior of the ECC strengthening strip, and thereby increase its efficiency. The structural evaluation of the slabs considered crack width and spacing, deflection at the service load level, and ultimate capacity and ductility. Test results showed that the ECC strips enhanced the structural performance of the slabs at both service and ultimate limit states. Providing additional internal reinforcement by a reinforcing ratio of 1.88% exhibited outstanding performance in terms of decreased crack width, better crack distribution, and improved capacity and ductility compared to control slabs without internal ECC strips.

In this paper, a thin layer of Strain-Hardening Cementitious Composites (SHCC) is provided in either tension or compression side of RC slabs aiming to improve their impact resistance under the effect of drop weight loading. The main parameter of the current study is the condition of the contact surface between the substrate slab and the SHCC overlay that was prepared by grinding, grinding plus steel dowels or grinding plus epoxy adhesive. Accordingly, 63 RC slabs were prepared and tested under the effect of drop weight falling from three different heights; 1, 1.5 and 2 m. It was found that the SHCC strengthening layer enhanced the impact resistance of the strengthened slab when added at either tension or compression side. However, in order to attain the outermost impact resistance showing ductile performance, it is better to provide a thin layer of the SHCC at the tension side of the slab connected to the substrate slab by epoxy resin applied on pre-prepared grinded surface. Furthermore, numerical simulations based on ABAQUS software package were performed on the strengthened slabs. Their results showed good agreement with the experimental findings from the viewpoint of the kinetic energy. Besides, the impact failure loads were determined numerically for the studied slabs and compared with those obtained from incremental static loading tests.