جستجوی مقالات مرتبط با کلیدواژه « میدان مغناطیسی یکنواخت » در نشریات گروه « عمران »

The present study was an attempt to investigate the effect of direct and uniform magnetic field on concrete-steel rebar bond strength in fresh and hardened concrete specimens containing quartz aggregates using pull-out test. Moreover, compressive strength test was performed on all magnetic and non-magnetic specimens at 28 days of concrete age in order to investigate the effect of compressive strength of concrete on bond strength. In the present study, a concrete mixture containing smart quartz aggregate was designed for a compressive strength of 30 MPa, . The water to cement ratio was selected to be 0.4 for concrete mixes. The method of fabrication and processing of samples was performed according to ASTM C192 . Accordingly, first one-third of the fine-grained and one-third of the mixing water were added to the mixer with one-third. The remaining cement and water were gradually added to the concrete mix. At the end, superplasticizer was gradually added to the concrete mix for 1 to 2 minutes and then the concrete mixing process was continued for 3 minutes. In order to prevent the magnetic field from being absorbed by the concrete mold, concrete samples were sampled in plastic molds. Concrete samples were covered with a wet sack at a temperature of 20–22 ° C for 24 hours and then removed from the formwork and stored under moist conditions until the experimental age. The device used in this study is able to convert electricity into a uniform magnetic field with an intensity of 0.5 Tesla. According to the results, the failures in all specimens are of slip type with no fissure cracks. The results also showed that applying a magnetic field to the concrete can lead to enhancement of bond strength by about 55% and 73%, in 14 and 20 mm rebar respectively.

In this research, the effect of applying magnetic field directly to steel fiber reinforced concrete specimens containing 1.5% volume of steel fiber on bond strength between reinforcing steel bar and concrete was experimentally investigated using a direct pull-out test. For this purpose, magnetic field was applied externally to the fresh specimens by means of an electromagnetic instrument, capable of causing the flux density of 5000 Gauss. In this study, the pull-out specimens were tested with two different bar diameters: 14 and 20 mm. The study also investigated, mechanical properties of the specimens in the terms of compressive, splitting tensile and flexural strengths at an age of 28 days. In addition, the microstructure of the specimens was analyzed by the SEM images. The experimental results demonstrated that the pull-out failure occurred for all the specimens. Furthermore, the bond strength of the specimens increased by about 83 and 51% correspond to the #14 and #20 rebars, respectively. In addition, thoughness parameter of concrete exposed to magnetic field increased by 82 and 53% correspond to the #14 and #20 rebars, respectively. Applying magnetic field to fresh concrete caused an increase in its compressive strength more than 21%. Following this, splitting tensile and flexural strengths of concrete specimens were inhanced up to 9 and 13%, respectively. Magnetic field also has the ability to compact the microstructure of concrete.