جستجوی مقالات مرتبط با کلیدواژه "durability" در نشریات گروه "مهندسی زلزله"

Today, the tendency to use self-compacting concrete (SCC) is expanding due to its advantages. Manufacturing of SCC requires increasing the amount of cement used, which will result in the more environmental pollution due to the increased cement production, trying to use pozzolans to reduce cement consumption will be an essential step towards sustainable development. So, efforts to use pozzolans to reduce cement consumption will be an essential step towards sustainable development. Accordingly, in this study, by replacing a part of the cement and limestone powder with metakaolin as an active pozzolan, some properties of the produced concrete including rheology, mechanical and durability were evaluated. For this aim, metakaolin with 10%, 15%, 20%, 25% and 20%, 25%, 30%, 35% replaced the cement and limestone powder, respectively (without changing the cement content). The self-compacting properties of the concrete specimens were evaluated in the form of slump flow tests, L-box, U-box and J-ring, as well as mechanical properties including compressive and splitting tensile strength, and durability including water penetration depth and rapid chloride ion penetration (RCPT). The results present that the utility of metakaolin in the manufacturing of self-compacting concrete as an independent alternative to the part of cement and limestone powder has improved the mechanical properties of concrete, but has reduced its consistency. In order to solve this problem, it is necessary to increase the percentage of consumable superplasticizer used until it reaches the desired consistency level. Replacement of cement by 20% metakaolin reduced water permeability and RCPT by 35% and 20%, respectively, and replacing of the limestone powder by 35% metakaolin reduced water permeability and RCPT by 70% and 35%, respectively.

In recent years corrosion of steel reinforcement in concrete has been recognized as one of the most important reasons for early damage in reinforced concrete structures. In marine environments, the release of ion chloride and ion sulfate into concrete resulted in corrosion, are the major cause of dameges and shortening the useful life of reinforced concrete structures. Because concrete is weak in tension and it is cracked due to the operation loads, chlorine ions can easily enter concrete through these cracks, causing corrosion of the rebars. Therefore, the fibers can reduce the corrosion of the bars in concrete by delaying of cracking or reducing the crack width as well as silica fume Pozzolan can decrease the rebars corrosion through reduction of  penetration of liquids. Accordingly, in the present study 5 concrete compositions were made. Silica fume pozzolan was added to the concrete mixtures by replacing 10 wt.% of the cement and Barchip fibers with values ​​of 2.5, 3.5 and 5 kg/m3 were added to the concrete mixtures. In order to evaluate the mechanical properties, compressive and flexural strength tests, and for concrete durability, special electrical resistance and half-hour water absorption tests were performed. The results show that silica fume is effective in decreasing of half-hour water absorption and increasing of the specific electrical, compressive and flexural strength of concrete, and the combined application of silica fume and Barchip fibers enhances the flexural strength of concrete up to 65%. There is also a decrease in electrical resistance and an increase in compressive strength and half-hour water absorption by the addition of Barchip fibers to the concrete composition containing silica fume

Previous studies has shown that reinforced self-compacting concrete with fiber is more suitable for structural performance. The purpose of this study was to evaluate the effects of Metkaolin and alkali resistant glass fibers on the performance of self-compacting concrete. In this study, the rheological properties (L-Box, Slump flow, T50) and mechanical properties (compressive strength, tensile and flexural strength), and durability (chloride ion penetration and water absorption) have been investigated. The results of the experiments showed that by increasing the amount of fiber, the concrete performance decreases. It was also found that the glass fiber had no positive effect on the compressive strength of the concrete. The tensile and flexural strength of self-compacting reinforced concrete increases with increasing fiber content. Durability studies have shown that the presence of glass fiber initially increases the resistance to chloride ion penetration and then reduces it, and also increases the gradual absorption of concrete water. The results of the experiments showed that the simultaneous presence of Metkaolin and glass fibers with optimal percentages can significantly improve the mechanical properties and durability of self-compacting concrete.

Today, the wastes remaining from concrete degradation is considered as an environmental problem and is one of the biggest challenges in the building industry. Accordingly, many researchers have decided to re-use the materials of aggregates from degradation in concrete production cycles. In this paper, attempts were made to assess and if possible to promote the mechanical and durability characteristics after the addition of nano-silica and micro-silica to self-compacting concrete containing recycled aggregates (obtained from worn concrete degradation). One of the points to be considered in this paper was the attempt to use tests such as half-pole testing and concrete wave velocity. In this regard, 72 mixture designs were studied in 8 collections. In these mixture designs, with respect to the content of recycled aggregates, the nano- and micro-contents were changed. Then, the samples underwent mechanical tests including compressive strength and tensile strength, and durability tests including corrosion potential, concrete wave velocity (ultrasonic) and electrical strength. After the tests, with an increase in the use of nano-silica and micro-silica, the efficiency and fluidity of the fresh concrete were reduced, and compressive strength and tensile strength were increased. Also, at fixed strength, nano-silica caused less efficiency and fluidity than micro-silica and also, with an increase in the content of recycled aggregates in concrete, efficiency and fluidity as well as compressive strength and tensile strength of concrete were reduced.

In recent years, many researches are focused on optimizing the production of a kind of concrete with high strength and efficiency, and different methods including using fiber technology in concrete construction are proposed to achieve this goal. Fibers are one of the materials that nowadays are added to concrete as reinforcement material. Considering the low weight and good resistance of this material and using a good percent of these materials in lightweight concrete can result in smaller segments with greater resistance. In this paper, we try to study and evaluate the effects of steel fibers on the strength and also the amount of fibers in lightweight concrete. One of the strength experiments is wetting and drying which is used in this study. Also by reviewing dynamic properties of lightweight concrete made with pumice + leca and taftan and comparing with lightweight concrete which is armed with steel fiber, we can achieve the optimal percent of fiber in concrete. Experimental results are presented in graphs and charts.