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Deterioration of concrete structures in the Gulf region is a serious problem. Penetration of Chloride ion into concrete is responsible for such early deterioration. Determination of chloride diffusion coefficient is an effective way to predict the service life of concrete structures. In order to investigate the performance of concrete mixtures in such environments, ordinary and silica fume concrete mixtures containing various water to cementitious materials ratios were used. Rapid chloride permeability test and determination of diffusion coefficient of chloride ion penetration in accordance with bulk diffusion test under laboratory conditons simulated to Persian Gulf climate, and site investigation were performed. Concentration of chloride ions in various depths of concrete specimens was measured using acid soluble chloride test method. Test results show that silica fume reduces the chloride penetration and the diffusion coefficient in concrete mixtures. Different models were made for rapid chloride test results, and diffusion coefficient, of concretes maintained in the hot and corrosive environments of the Persian Gulf. The models which were calibrated with real data obtained from the concrete structures are capable to predict the penetration and service life of concrete structures in such corrosive environments.

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Rice Husk Ash (RHA) is a by-product of the agricultural industry which contains high amount of silicon dioxide (SiO2). In this research, for the first time in the Middle East, in order to supply typical RHA, a special furnace was designed and constructed in Amirkabir University of Technology. Afterwards, XRD and XRF techniques were used to determine the amorphous silica content of the burnt rice husk. Attempts were made to determine the optimum temperature and duration of burning. Results show that temperature of 650 degrees centigrade and 60 minutes burning time are the best combination. Then various experiments were carried out to determine properties of concretes incorporating optimum RHA. Tests include compressive strength, splitting tensile strength, modules of elasticity, water permeability and rapid chloride permeability test. Results show that concrete incorporating RHA had higher compressive strength, splitting tensile strength and modulus of elasticity at various ages compared with that of the control concrete. In addition, results show that RHA as an artificial pozzolanic material has enhanced the durability of RHA concretes and reduced the chloride diffusion.

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The use of epoxy-bonded FRPcomposite for structural repair is emerging as an efficient and cost-effective technique for restoring and upgrading the capacity of concrete structures. Considerable researches have been reported in the last decades on the mechanical behavior and failure modes of the FRPstrengthened RC elements but actual data on its durability are scarce. This study intends to examine the durability of concrete specimens strengthened with FRP laminates under accelerated laboratory conditions and mimic harsh environmental situation which is the penetration of chloride ions. In this study three groups of specimens were examined. Each of these groups includes several concrete cylindrical specimens full confined with FRP laminates for investigating different types of fiber (Glass and Carbon), number of fiber layers and temperature influences. Furthermore, an apparatus was fabricated to simulate wetting and drying cycles for the second group of specimens. Moreover group III specimens were placed in a marine environment for 3 years to monitor their performance. Test results show that addition of FRP laminates reduces chloride ions penetration up to 70 percent. Results also indicate that although chloride ions penetration decreased the ultimate strength of cylindrical specimens up to 11 percent but FRP strengthened specimens achieved their initial strengths. Moreover wetting and drying cycles reduced the strength of cylinder specimens up to about ten percent especially in the high temperature laboratory condition.

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Self Compacting Concrete (SCC) specimens with limestone (L) and quartz (Q) powders were formulated. The influence of the type

of the powder on the properties of fresh and hardened concrete was evaluated. Dense packing theories were used for mix design

of samples. The equation of Fuller and Thompson for particle size distribution (PSD) of aggregates was modified with considering

fine particles and a proper PSD curve was obtained for SCC. Experimental results showed that this method needs use of less

powder content and results in higher strength/cement ratio compared to traditional mixing methods. No significant difference was

observed between the compressive strengths of specimens containing limestone (L-specimens) and quartz (Q-specimens) powders,

with similar proportions of materials. The residual compressive strength of specimens was examined at 500°C and contradictory

behaviors were observed. One Q-specimen suffered from explosive spalling, while no spalling was occurred for L-specimens. On

the other hand, the residual strength of remained Q-specimens showed considerable increase compared to L-specimens. The results

show the necessity for more detailed investigations considering different effective parameters.