Abstract Exposure to cadmium and other pollutants is a major environmental problem. Cadmium is causing acute liver injury but the mechanism of hepatotoxicity is poorly understood. The present study ...aimed to assess the possible reasons by which cadmium causes liver toxicity. Furthermore, the protective role of selenium against this toxicity was investigated. The hepatic level of lipid peroxidation (malondialdehyde, MDA), the antioxidant system (reduced glutathione, glutathione peroxidase, and thioredoxin reductase), as well as the levels of different lipid classes and the fatty acids pattern were determined in three groups of rats of 15 each. The first group (control group) received saline solution intraperitoneal (i.p.) daily for 10 days. The second group (cadmium chloride-treated group) received 2 mg/kg body weight cadmium chloride solution i.p. for a period of 10 days. The third group (cadmium chloride/sodium selenite-treated group) received cadmium chloride as in the second group and received i.p. sodium selenite (1 mg/kg body weight) at the first and sixth day of treatment (two separate injections within 10 days). The results showed that cadmium treatment increased the hepatic level of malondialdehyde (MDA) and the mean percent of total saturated fatty acid in all lipid classes, whereas the levels of antioxidant system, the levels of hepatic cholesterol esters, triglycerides, total phospholipids, mono- and polyunsaturated fatty acids in all lipid classes were decreased compared to control rats. These changes resulting from Cd-treatment were prevented due to treatment of rats with selenium since the levels of reduced glutathione, glutathione peroxidase, and thioredoxin reductase were induced in Se/Cd-treated group compared with either Cd-treated or control group. In addition, selenium maintained the low levels of cholesterol esters, triglycerides, total phospholipids, mono- and polyunsaturated fatty acids in all lipid classes caused by cadmium to their normal levels. It is concluded that cadmium-induced oxidative stress by increasing the levels of free radicals and by decreasing antioxidants level. This oxidative stress could be the primary cause of Cd-induced hepatotoxicity. Also, selenium can be used as a protective agent against Cd-toxicity. This study could provide a possible explanation to hepatotoxicity resulting from exposure to cadmium in the environment. In addition, selenium could ameliorate cadmium-induced hepatotoxicity since it reduced MDA levels and increased the activities of antioxidant enzymes in this tissue.
Thirteen reinforced concrete (RC) beams strengthened with partially and fully bonded near surface mounted (NSM) reinforcement and one unstrengthened beam (CB) were prepared and tested in order to ...study the effect of bond length, construction details and fiber reinforced polymer (FRP) characteristics on flexural performance. Carbon fiber reinforced polymer (CFRP) bars and strips and glass fiber reinforced polymer (GFRP) bars were used as the NSM reinforcement. Two bonded lengths (384mm and 480mm in each shear span) were studied for beams strengthened with partially bonded NSM reinforcement, while the bond length was 2000mm in beams strengthened with fully bonded NSM reinforcement. The effect of transverse wrapping and end anchorage on the behavior and load capacity of strengthened beams was also studied. The results showed that the RC beam strengthened with fully bonded NSM FRP had greater stiffness and bearing capacity than the beams with partially bonded NSM FRP. The use of NSM FRP with end anchorage or with transverse wrapping for the strengthening of RC beams increased their load carrying capacity and stiffness. The analytical model predicted well the response of the tested beams.
•The strengthened beams without confinement suffered from concrete cover failure.•The used confinement methods enhanced the performance of the NSM technique.•A critical value of the stiffness ratio ...for NSM system efficiency was identified.
An experimental and numerical study was performed to study the effectiveness of axial stiffness and of the type of confinement of near-surface mounted (NSM) fibre reinforced polymer (FRP) reinforcement on the strengthened beam bearing capacities and failure modes. To improve the performance in front of concrete cover separation and enhance bond strength, the use of mechanical interlocking with shear connectors (concrete cover confinement) or transverse wrapping was also investigated. The experimental results showed that confinement significantly enhanced the load carrying capacity of the RC beams with small increase in their steel reinforcement yielding load. The ultimate load of the strengthened beams without concrete cover confinement ranged between 150% and 170% of the ultimate load of the control beam. By applying mechanical interlocking with shear connectors or transverse wrapping, the load carrying capacity was increased by up to 23.3% for strengthened beams and by 33% for the ultimate load of conventional strengthened beams. The results indicated that the yield load ratio of the strengthened beams (with respect to the control beams) was proportional to the axial stiffness ratio of NSM FRP reinforcement. It was found that the failure of the strengthened beams became concrete cover separation when the axial stiffness ratio reached a critical value, and subsequently the ultimate load of strengthened beams was not affected by increasing axial stiffness ratio beyond this value.
This critical value of stiffness ratio was experimentally found to be at about 1.25. The numerical results also showed excellent agreement with the experimental ones in terms of load–deflection behaviour and maximum load capacity.
•The GFRP bars were used as NSM to augment the load capacity of GFRP RC beam.•Replacing internal steel with GFRP enhanced capacity of NSM CFRP upgraded beams.•Increasing the internal reinforcement ...area diminished the NSM GFRP efficiency.
Strengthening the steel-reinforced concrete (RC) beams by fiber-reinforced polymer (FRP) elements have become common several years ago. Recently, the RC beams internally reinforced with FRP reinforcement, especially Glass FRP (GFRP) bars, became popular worldwide. The carbon FRP (CFRP) elements (strips and bars) were recently used to strengthen the internally GFRP RC beams. In contrast, using the GFRP elements to upgrade the RC beams, especially those with GFRP bars as the main tensile reinforcement, was rarely studied. In this paper, the GFRP bars were implemented as near-surface mounted (NSM) elements to upgrade the beams reinforced in their tension side with GFRP or steel bars. All beams were experimentally loaded in flexure using a four-point loading scheme. The experimentally studied parameters were the main tensile reinforcement area, NSM area, and main reinforcement properties. Moreover, a numerical model was established and validated using the available experimental data to investigate the impact of main and NSM materials properties and areas on RC beam response. The experimental results highlighted that increasing the internal and NSM GFRP area by 96% and 100 % increased the beam capacity by 61.6% and 59.7%, respectively, which underlined a slightly higher efficiency of the main reinforcement than NSM bars on the beam load capacity. In addition, substituting the main steel with GFRP bars for the beams upgraded with NSM GFRP reinforcement enhanced their capacities by 11.33–15.1%. This emphasized the great effect of the linear response of the FRP materials and their higher tensile strengths than steel on the interaction between the main and NSM reinforcement, especially after the steel yielding. The FE results showed the highest load capacity using CFRP and GFRP bars as main and NSM reinforcement for the simulated beams. Conversely, using CFRP bars as NSM strengthening was more efficient than GFRP bars for the RC beams with steel or GFRP bars.
The behaviour of RC beams strengthened with NSM FRP bars was experimentally investigated. Eight beams were tested under four point bending. The effects of material type, epoxy properties, bar size ...and the number of NSM bars were studied. The tested beams were strengthened with a limited bond length in order to imitate as much as possible work-place conditions, as the grooves could only be cut up to the faces of the supporting columns with difficulty. The load capacity, deflection, mode of failure, FRP strain, concrete strain, free end slip and the transverse strain in epoxy and concrete of the tested beams were all analysed. Comparison of strengthened and control beams showed enhancement of 155.8% and 129.8% in the yielding loads, while the increase in the ultimate loads was 166.3% and 159.4% for beams strengthened with carbon fibre reinforced polymer (CFRP) and glass fibre reinforced polymer (GFRP) respectively. The beams strengthened with CFRP bars experienced higher stiffness than the corresponding beams with GFRP bars. Epoxy properties, size and number of bars had little effect on the load capacity of the strengthened beams with failures mainly occurring either in epoxy or as a result of concrete cover separation.
Near-surface mounted (NSM) fiber reinforced polymer (FRP) reinforcement has proven to be an efficient technique for strengthening concrete members. The bond behavior of the NSM system depends on the ...bond in the two existing interfaces, while the response in terms of load–slip curves and load capacity may be strongly affected by many other parameters. As a consequence of the variety of factors affecting the bond, different studies into the behavior of NSM FRP reinforcement have been carried out in recent years. In this paper, an experimental study is performed in which the effect of adhesive properties, bar type, bar size, FRP properties, groove geometry and the use of mechanical interlocking on the capacity and bond behavior of a NSM joint is investigated. The failure load, average bond stress, loaded end slip, free end slip, transverse strains (on adhesive and concrete), and the mode of failure for the tested joints are reported and discussed. The results show that the adhesive properties, FRP bar size and bar surface treatment were critical factors in the capacity and mode of failure of the specimens tested.
•Steel-bar reinforced-mortar layer (SBRML) method proposed to strengthen RC beams.•Bearing-capacity efficiencies of up to 214% was achieved with SBRML.•Large reinforcement area of SBRML lead to ...enhanced beam stiffness.•Prediction model of yield / peak load during flexural failure was proposed.
Reinforced concrete (RC) elements can be strengthened using several techniques. Among these techniques are the externally bonded (EB), near-surface-mounted (NSM), textile-reinforced mortar (TRM), and ultra-high-performance concrete (UHPC). The NSM and EB methods are primarily based on the efficiency and thickness of the concrete cover, while the UHPC method demands excessive surface preparation. This study presents a new technique to strengthen RC beams using a limited steel-bar-reinforced mortar layer (SBRML). This method reduces the installation time and cost and combines the advantages of existing techniques. An experiment with eight concrete beams, one unstrengthened beam (CB), and seven strengthened beams is performed. The RC beams are tested until failure under a four-point bending load. The effect of the SBRML reinforcement area, internal reinforcement configuration, adhesive type, concrete cover condition (with or without), position (bottom or side), and application type (casting or bonding) on the failure mechanism and capacity of the RC beams are studied. The results show an increase in the bearing capacities of RC beams strengthened with epoxy-bonded SBRML and cast SBRML in the range of 152.5–213.9% and 122.7–158.1%, respectively, compared to those of CB. The values of yield and ultimate loads for RC beams strengthened with epoxy-bonded RML are analyzed. A numerical simulation is performed and verified against the experimental results. A parametric study was conducted to reveal the effect of fiber-reinforced polymer reinforced mortar layer FRP-RML on the behavior of the strengthened beams.
•The natural sand was partially replaced by the crumb rubber (CR) with different percentages.•The rubberized concrete in beam middle layer (M) showed trivial effects on its load capacity.•30% and ...10 %CR in the M and B layers of beam, respectively achieved 99% of CB capacity.•The use of RSF delayed the steel yielding and enhanced the failure load.
The huge amount of crumb rubber (CR) produced from cars' tires and others causes environmental problems while using natural concrete components reduces their amounts in nature. So, using recycled wastes to replace the concrete components became essential. Herein, the functionally graded material (FGM) approach was implemented to reduce the bad effects of the recycled materials on the beam behavior. Nine reinforced concrete (RC) beams were tested experimentally (under four-point bending) and simulated numerically using the ABAQUS program. The first beam was a control beam (CB) made from plain concrete (PC), while the cross-section of the rest beams was divided into three equal horizontal layers along the beam span. The middle layer was cast from rubberized concrete (RuC) with CR% (30%, 50%, and 80%) as a partial sand replacement, while the top layer was made from PC. Consequently, the bottom layer was made from different patterns of RuC and recycled tire steel fiber (RSF) concrete. The numerical model was extended to involve the presence of RuC in the top layer and opening in the middle layer on the beam behavior. The test results demonstrated trivial effects on the loads' capacities compared to CB, maximum reduction = 3.8% for beams cast with RuC in their middle layers. Moreover, the beams cast with RuC containing up to 20% and 80% CR in their bottom and middle layers could attain about 94.3––99% of the CB load. These findings encouraged using CR in concrete to reduce its harmful environmental effects and save the natural sand by about 13.3–16.6%.
Near surface mounted (NSM) fiber reinforced polymer (FRP) bars became more effective in strengthening reinforced concrete (RC) beams. This is because it increases the bond capacity and makes a ...protection against external damage. Most of previous related researches stated that the failure of the tested RC strengthened beams with NSM FRP is due to debonding or concrete cover separation. In this research the ends of the NSM glass fiber reinforced polymer (GFRP) bars were bent to delay or prevent NSM FRP debonding and concrete cover separation and thus increasing the load carrying capacity of the strengthened beams. The inclination angles of GFRP bars with bent ends were 90° and 45°. Straight GFRP bars with variable lengths were also used for comparison. The test results demonstrated that the GFRP bars with bent ends prevented the concrete cover separation and increased the load carrying capacity of the strengthened beams. The load carrying capacity of the strengthened beams by straight NSM bars and those having 45° and 90° inclined ends were 177%, 201%, and 185% of that of their control beam, respectively.
In this investigation, crumb rubber (CR) was a viable substitute for concrete's conventional natural fine aggregate (FNA). This approach carries dual advantages: the conservation of natural resources ...and the environmentally conscious recycling of rubber waste, diverting it from traditional disposal methods. The study incorporated varying proportions of CR (5%, 10%, and 20%) by volume of the sand used in the mixtures. The primary study objective is to enhance the bond between CR particles and the surrounding concrete components by coating the CR with cement or fly ash slurry (CTR and FATR). For the limitation of the previous research discussed the CR effect on the beam’s behavior, fourteen beams were poured with different rubberized concrete (RuC) and tested in flexure. This comprehensive approach sought to assess the influence of diverse factors, including rubber content, treatment materials, and the nature of internal reinforcement, on the overall performance and characteristics of the beams. The results assumed that the compressive strength was raised by 6.0–11.0% and 13.0–22.0% for the mixes cast with CTR and FATR, respectively, compared to the corresponding mixes cast with UR. Consequently, the tensile strength of the RuC-integrated CTR and FATR was raised by 5.9–11.0% and 14.0–22.0%, respectively, compared to the mixes integrating uncoating CR. Moreover, the beams cast with FATR concrete experienced the highest flexural capacities among all the steel RC beams. Furthermore, using the carbon fiber reinforced polymer (CFRP) bars as internal reinforcement for the RC beams showed the highest load capacities.
•The coated and uncoated crumb rubber wastes were a viable substitute for the fine aggregate.•The compressive strength was raised by 6.0–11.0% for the CTR mixes.•The compressive strength was raised by 13.0–22.0% for the FATR mixes.•The beams cast with FATR concrete experienced the highest flexural capacities.
