JOURNAL OF CONCRETE RESEARCH
Year:2015 | Volume:8 | Issue:1|Papers Count:10

Marin environments such as Qheshm Island, are the most destructive environments for reinforced concrete structures. Concrete quality is one of the important factors in corrosion. Nowadays use of pozzolanic materials is one of the methods to improve the concrete qualities. In this study, by placing specimens with different water to cement ratios and different amounts of Metakaolin in splash zone and measuring the rate of corrosion and half-cell potential using GalvaPulse method, the effect of these factors on corrosion of reinforcements during 32 month is evaluated. The test results indicate that the specimen with lower water to cement ratio has lower likelihood of corrosion. Increasing the water to cement ratio from 0.35 to 0.45, decreases the time-to-corrosion to 50%. Using Metakaolin also reduces the rate of corrosion.

Reactive Powder Concrete (RPC) is one of the latest achievements in concrete technology. Development and application of this concrete depends on the knowledge on its specifications and characteristics. Shear strength is one of the most important specifications in design of RC structures. One of the effective methods to determine the shear strength of concrete is to estimatethis strength using concrete’s compressive strength. In this study, RPC and normal concretes with different mixture designs and using the existing materials in Iran were produced. Than their compressive and shear strengths evaluated. Two methods (JSCE G553, Afshin Aliloo’s) were used to measure the shear strength. The result show that there are difference between reactive powder concrete shear properties and normal concrete. Also, shear strength that measured by either of two methods is close together. Using the results of the experiments, an equation is developed to estimate the shear strength of RPC using its compressive strength.

According to significant of bridges as infrastructures, and need for serviceability after earthquakes, it is necessary to design this group of structures adequately. In this way the determination of the location of nonlinear response in these structural systems is an important step to predict the performance of the system under different loading conditions. In reinforced concrete bridge piers, these nonlinear deformations generally occur over a finite hinge length.A model of hinging behavior in reinforced concrete bridges pier will help guide, detailing and drift estimates for performance-based design. In this paper, by using experimental results that conducted on the reinforced concrete bridges piers and also applying artificial neural networks algorithm, predict the plastic hinge length of reinforced concrete bridges pier.The results show that the accuracy of artificial neural networks algorithm for predicting of this parameter in compare with other formulations that were proposed as for calculated error is appropriate.

This paper evaluates the impacts of the addition of steel fibers with two different percentage by weight, on flow ability parameters and hardened properties of self-compacted lightweight concrete containing lightweight aggregate of Scoria. For this purpose, was used from the steel fibers with a length of 50mm the amount 20& 40 kg/m3.With a good mix design, fresh and hardened properties of each plans was evaluated. Fresh properties such as slump flow, V-funnel, and L-box and physical properties such as, density measurements, compressive strength, splitting tensile strength, flexural strength, ultrasonic pulse velocity (UPV), flexural toughness, and dry unit weight were determined in hardened conditions. The samples were stored in water until the age 7, 14, 28, 42 and 90 days.From the result, it is clear that fibers decrease flow ability of fresh concrete, however mixes were in the acceptable range of EFNARC. The results of hardened concrete indicate, all mixes are in the range of structural lightweight concrete too. Moreover, the addition of fibers significantly increases tensile strength, flexural strength and flexural toughness.

The behavior of light weight concrete at elevated temperature is of significant importance in providing safety of structures in response to certain accidents or particular service conditions. Thispaper deals with the physical and mechanical properties of light weight concrete “containing leca” such as: compressive strength, water absorption, mass loss and spalling. Specimens with different amount of Nano Silica by applying the Taguchi method for an optimal mix design had been made and after curing for 28 days and being subjected to 200, 400 and 600oC specimens had been compared with the specimen without Nano silica and cured at room temperature. It was found that by increase temperature to 600oC physical properties of light weight concrete like water absorption goes bad and in some condition an improvement in mechanical properties like compressive strength had been emerged surprisingly.

There are a large number of old arch bridges in Iran designed to carry the service loads that have been increased in the past decades. Capacity assessment of these bridges has become a vital need. Due to their complex behavior, essential field and loading tests are required. An accurate and appropriate modeling of these types of bridges was the first key paid attention to, in this research. Parameters such as number, length and geometry of spans and strength of materials are the most significant features to achieve this goal. Field load testing of old railway bridge in km–24 of Tehran–Qom railway have revealed important characteristics of the bridge such as primary stiffness, rigidity and pattern of fraction. The bridge is a plain concrete arch with five identical six-meter spans. The effect of number of spans on the yielding strength of the bridge has been carried out using ANSYS software. Based on the results obtained, a plain concrete arch bridge with a single span has a totally different behavior with the multi span ones. Also it has been revealed that bridges with more number of spans have less yielding strength and higher amount of crown displacement value. At last, novel relations for computing the yield strength and displacement value of six-meter span plain concrete bridges have been suggested.

When subjected to a magnetic field, the hydrogen bonds between water molecules become weakened, and the water molecule clusters break down into smaller ones. This allows for the water to more easily penetrate into cement particles, causing a faster and more effective hydration process. In order to assess the effect of magnetic water on curing and workability of cement past and wet concrete, also the compressive strength of condensed cement as well as concrete, first, a magnetic treatment device was designed and built in this study. The magnetic water produced was mixed with cement to make cement pastes with different water-to-cement (w/c) ratios. Curing time, workability, and compressive strength of such cement pastes were investigated. Then, using well balanced aggregates, magnetic water, cement with different proportions, and micro-silica, concrete with different mix designs were made and tested. Among the results from this study are: 1) The optimized magnetic field intensity for producing magnetic water is 0.8 to 1.0 tesla.2) Magnetic water reduces the primary and secondary curing of cement by 50% and 19%, respectively.3) The best compressive strengths are obtained if the water is circulated through the magnetic field for about 15 minutes, and the best workability is obtained if this time is about 65 minutes.4) For higher proportions of cement in mix design and the application of magnetic water, the resulted concrete compressive strength may be increased by 20% and even higher.5) In addition to enhancing the level of cement hydration, application of magnetic water takes more advantage of micro-silica in improving concrete strength. For example, the simultaneous application of micro-silica and magnetic water increases the 7-day-strength by 46% and the 28-day-strength by 39%. It is noteworthy that if one were to choose either application of micro-silica or the magnetic water for enhancing the concrete compressive strength, results here show that the application of micro-silica is slightly more effective. In general, the application of magnetic water increases the speed of concrete strengthening and/or the hydration process. In fact the rate of this strengthening for the 7-day-concrete is much more than that for the 28-day-concrete.

In order to select the most suitable concrete for the construction of high-rise buildings, method of analytic hierarchy process (AHP) based on expert knowledge has been used.In this study conducted a series of laboratory works, to compare the effect of steel fibers used in various categories of resistance on concrete behavior parameters. Mixing the samples is set for the three categories of resistance 25, 35 and 45 MPa. Strength parameters that are chosen to identify concrete actions are tensile strength, impact strength, compressive strength and flexural strength. Also the samples in each resistance category are made with four fibers quantity: without fibers, 15, 25 and 35 kg fibers per cubic meter. The results suggest that using of steel fibers, increases the impact resistance, time of the first crack and ultimate strength of concrete significantly. Also the addition of this type of fibers, increases tensile strength and flexuralstrength but don’t have significant effect on the compressive strength of concrete.

Determination of optimal steel reinforcement layout for shear wall with opening is an important topic in designing this structural member. Strut-and-Tie Method (STM) is one way to design such members, where steel reinforcement is arranged based on the selected model. In this study, a strategy was introduced to determine optimal Strut-and-Tie model by selecting a good volume fraction in continuum topology optimization problem. The elastic strain energy was selected as the objective function to achieve the optimal pattern, and the modified Solid Isotropic Material with Penalization (SIMP) with continuous penalty function was used to prevent local minimum solution. Finally, By using Nonlinear Finite Element and defining qualitative and quantitative conditions for optimal STM, the resulting models, obtained with topology optimization for three shear wall with various opening, were compared with previous models and models with manufacturing constraint. The results show that, topology optimization models have the best ultimate load to steel weight ratio and get the optimal steel reinforcement layout for shear wall with opening.

Using concrete reinforcement fibers improves the concrete desirable features including its strength, and sometimes provides the engineers with very light materials by reducing theconcrete’s weight. In the current study, type 2 Dashtestan cement, polypropylene, steel and glass fibers, and Superplasticizer were used in 9 mixture patterns to make the concrete. After they were built, concrete samples were kept in a regular water tank. Then, compressive and flexural strength of samples were measured in 7, 28, and 90 days. Results indicated that polypropylene fiber reinforced concrete’s compressive strength curve, which was ascending at 1 percent range of fibers (the curve was upward), and descending at 2 to 3 percent fiber range (the curve was downward). In addition, Propylene fiber reinforced concrete’s flexural strength curve which was ascending at 1 and 2 percent range of fibers (the curve was upward). At 3 percent range of fiber, it was descending (the curve was downward) and the highest compressive and flexural strength occurred at 1 and 2 percent range of polypropylene fiber respectively. Steel and glass fibers cause an increase in concrete samples compressive and flexural strength. The compressive strength of steel and glass fibers reinforced concrete at 1 to 3 percent range of fiber with an upward curve. The flexural strength of steel fiber reinforced concrete at 1 to 2 percent range of fiber with an upward curve, and at 3 percent range it had a downward curve, and the curve of flexural strength of glass fiber reinforced concrete at 1 to 3 percent of fiber with an upward curve. The highest compressive and flexural strength in steel fiber reinforced concrete occurred at 2 and 3 percent range of fiber respectively, and for glass fiber reinforced concrete, it was at 3 and 3 percent range of fiber respectively.