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This study analytically investigated the axial-flexural (P-M) interactions of quare reinforced concrete (RC) columns discontinuously strengthened swith fibre reinforced polymers (FRP). Six FRP confined concrete stress-strain models and two sectional analysis methods were used to develop the analytical P-M interactions of discontinuously FRP strengthened square RC columns. The developed analytical P-M interactions were validated against experimental data available in the literature. It was found that the selection of the stress-strain models had a substantial effect on the analytical P-M interactions, while the influence of the sectional analysis methods heavily depended on the selected stress-strain models. It was also found that the three available design codes for concrete structures externally strengthened with FRP yielded different analytical P-M interactions of discontinuously FRP strengthened square RC columns. A parametric analysis was undertaken and found that the corner radius and confinement ratio significantly affected the P-M interactions of discontinuously FRP strengthened square RC columns. Also, discontinuously FRP strengthened square RC columns with a higher number of FRP layers and smaller corner radius obtained lower flexural and axial strengths than their counterparts with a lower number of CFRP layers and higher corner radius. [ABSTRACT FROM AUTHOR]

This study presents new neural‐network (NN)‐based models to predict the axial load‐carrying capacities of fiber‐reinforced polymer (FRP) bar reinforced‐concrete (RC) circular columns. A database of FRP‐reinforced concrete (RC) circular columns having outside diameter and height ranged between 160–305 and 640–2500 mm, respectively was established from the literature. The axial load‐carrying capacities of FRP‐RC columns were first predicted using the empirical models developed in the literature and then predicted using deep neural‐network (DNN) and convolutional neural‐network (CNN)‐based models. The developed DNN and CNN models were calibrated using various neurons integrated in the hidden layers for the accurate predictions. Based on the results, the proposed DNN and CNN models accurately predicted the axial load‐carrying capacities of FRP‐RC circular columns with R2 = 0.943 and R2 = 0.936, respectively. Further, a comparative analysis showed that the proposed DNN and CNN models are more accurate than the empirical models with 52% and 42% reduction in mean absolute percentage error (MAPE) and root mean square error (RMSE), respectively involved in the empirical models. Moreover, within NN‐based prediction models, the prediction accuracy of DNN model is comparatively higher than the CNN model due to the integration of neurons in each layer (9‐64‐64‐64‐64‐1) and embedded rectified linear unit (ReLu) activation function. Overall, the proposed DNN and CNN models can be utilized as paramount in the future studies. [ABSTRACT FROM AUTHOR]

This paper proposed a new approach for the strength interaction diagram (N‐M diagram) of FRP strengthened square steel reinforced high strength concrete (SSRHSC) column, considering the influence of the applied load eccentricity on the ultimate conditions of FRP strengthened high‐strength concrete (HSC). The analytical model for the strength interaction diagram of FRP strengthened SSRHSC (FRPS‐SSRHSC) columns, which incorporated the stress–strain models of constitutive materials into the rectangular stress block (RSB) method, was developed and verified against test data. The strength interaction diagrams of FRPS‐SSRHSC columns developed based on the proposed analytical model matched well with the test results, while the strength interaction diagrams developed using available design codes overestimated the experimental strength interaction diagrams. The effect of confinement ratio and longitudinal FRP strengthening on the strength interaction diagrams was examined via parametric analyses. It was found that longitudinal strengthening had a negligible influence on the axial load and bending moment when the axial load was applied at a small eccentricity but had a substantial influence when the axial load was applied at a large eccentricity. [ABSTRACT FROM AUTHOR]

This study investigated the feasibility of using two types of waste glass sand as fine aggregate replacement in ambient cured alkali‐activated mortars (AAMs). Fly ash (FA) and ground granulated blast furnace slag were used as aluminosilicate source materials to produce the AAMs. The waste glass sand was used to replace 0%, 25%, 50%, 75%, and 100% fine aggregate (by mass) in AAMs. The influences of the use of waste glass sand, for the replacement of fine aggregate, on slump flow, setting time, compressive strength, and flexural strength of ambient cured AAMs were evaluated. It was found that the slump flow and setting time of ambient cured AAMs significantly increased as the percentage of replacement of fine aggregate by waste glass sand increased. However, the compressive and flexural strengths of ambient cured AAMs decreased when 50% and over fine aggregate were replaced by waste glass sand. The ambient cured AAMs with 25% replacement of fine aggregate with waste glass sand achieved the highest compressive and flexural strengths. Scanning electron microscope analysis indicated that the increase in the compressive strength and flexural strength of AAMs was due to the bridging‐like effect and filling effect provided by the waste glass sand. The use of waste glass sand as a partial replacement of fine aggregate in ambient cured AAMs was found to be feasible. In addition, 25% of the fine aggregate replaced by waste glass sand resulted in the best mechanical properties for ambient cured AAMs. [ABSTRACT FROM AUTHOR]

The bond strength of steel reinforcement bars in concrete is of prime importance for the strength and serviceability of reinforced concrete structures. The composition of concrete directly affects the bond strength of steel bars in concrete. Research is ongoing to improve the bond properties of concrete with the addition of nanoparticles. In this paper, the effect of adding graphene nanoplatelets (GNP) to geopolymer concrete on the bond strength of steel bars in geopolymer concrete was investigated and compared with the bond strength of steel bars in ordinary portland cement (OPC) concrete. Slag and fly ash were used as aluminosilicate precursors, and ambient curing conditions were adopted for preparing geopolymer concrete. Specimens were cast with geopolymer concrete without and with GNP and OPC concrete without and with GNP. Steel bars of four different diameters (10, 12, 16, and 20 mm) were used for preparing the specimens. The quantity of GNP added in the concrete was 0.5% by weight of aluminosilicate materials in geopolymer concrete and 0.5% by weight of cement in OPC concrete. The addition of GNP to geopolymer concrete enhanced the bond strength by 13%–19% for the steel bars of diameters 10–20 mm. The bond strengths of steel bars in geopolymer concrete were found to be lower than the bond strength of steel bars in OPC concrete. Furthermore, the bond strengths were calculated using equations available in the design codes and available research studies on geopolymer and OPC concrete and compared with the experimental bond strengths. [ABSTRACT FROM AUTHOR]

The durability performance of geopolymer concrete against severe environmental conditions is important for implementing geopolymer binders as alternatives to ordinary portland cement (OPC). In this experimental investigation, the impact of adding graphene on the durability characteristics of geopolymer concrete was examined. Graphene was added at 0.5% by weight of aluminosilicate precursors in geopolymer concrete. Permeability, salt ponding, capillary sorptivity, and immersion in chemical agents were performed to assess the durability characteristics of geopolymer concrete without and with graphene, which were also compared with the durability characteristics of OPC concrete without and with graphene. It was found that the addition of graphene in geopolymer concrete reduced the permeable voids by 12% and water absorption by 9%, and improved the resistance against chloride penetration and sulfuric acid exposure. The compressive strength of geopolymer concrete increased by 20% with the addition of graphene. Also, an approximately 70% reduction in the initial and final rate of water absorption was observed in geopolymer concrete with the addition of graphene. [ABSTRACT FROM AUTHOR]

Near-surface mounting (NSM) and external bonding (EB) are wildly used techniques for strengthening reinforced concrete (RC) beams using fiber-reinforced polymer (FRP) reinforcement. However, there are a few drawbacks to the use of these two techniques, including premature failure due to concrete cover separation (CCS), which can cause significant challenges for their wide practical applications. Hence, his experimental study investigates the efficiency of using a novel anchoring system for RC beams strengthened at the sides using NSM glass-FRP (NSM-GFRP) bars. The NSM-GFRP bars were anchored with either GFRP channels or GFRP channel strips. The experimental results showed that RC beams strengthened with side NSM-GFRP bars anchored with GFRP channels and GFRP channel strips increased the flexural load of the RC beams by 152% and 106%, respectively, compared to the unstrengthened reference beam. In addition, GFRP channel strips prevented the CCS failure and improved the ductility of the RC beam, using the full strength of NSM-GFRP bars. [ABSTRACT FROM AUTHOR]

In this paper, the Taguchi method was used to identify the optimum mixture proportions of alkali-activated reactive powder concrete (AARPC) by considering the most influential parameters. Five main parameters, including binder content, alkaline activator-binder ratio (Al-binder), binder-fine aggregate ratio, sodium silicate to sodium hydroxide ratio (Na2SiO3-NaOH), and sodium hydroxide (NaOH) concentration, were considered in the mixture design. A total of 18 trial batches were designed according to the L18 array obtained from the Taguchi method. The results showed that the highest average compressive strength was 110.9 MPa (16.08 ksi) and the lowest average compressive strength was 50.6 MPa (7.34 ksi). The test results of the 18 trial batches were then evaluated by the analysis of variance (ANOVA) method to determine the optimum level of each parameter. It was found that specimens with a binder content of 700 kg/m3 (0.025 lb/in.3 ), Al-binder ratio of 0.3, binder-fine aggregate ratio of 0.8, Na2SiO3-NaOH ratio of 2, and NaOH concentration of 14 M produced the highest 28-day compressive strength (116.77 MPa [16.94 ksi]) at the ambient curing conditions. [ABSTRACT FROM AUTHOR]

This paper presents the results of an experimental investigation on the behavior of glass fiber reinforced polymer (GFRP) bar‐reinforced hollow‐core (GFRP‐HC) circular concrete specimens under concentric, 25 mm and 50 mm eccentric axial loading and four‐point bending. The main parameters investigated include the type of reinforcing bars, pitch of the helices and loading conditions. The test matrix of this study consists of 12 specimens, among which nine specimens (850 mm high) were tested under concentric and eccentric axial loading and the remaining three specimens (1500 mm long) were tested under four‐point bending. The specimens were circular in cross‐section with an outer diameter of 214 mm and an inner circular hole diameter of 56 mm. The experimental results showed that, for the similar amount of reinforcement, steel bar‐reinforced hollow‐core (steel‐HC) specimens sustained higher loads than the GFRP‐HC specimens under different loading conditions. Also, the steel‐HC specimens achieved higher ductility than the GFRP‐HC specimens under 50 mm eccentric axial loading and four‐point bending. However, under concentric and 25 mm eccentric axial loading, the GFRP‐HC specimens achieved higher ductility than the steel‐HC specimens. The close pitch of the GFRP helices significantly enhanced the load carrying capacity and ductility of the GFRP‐HC specimens. [ABSTRACT FROM AUTHOR]