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سال سیزدهم شماره 2 (تابستان 1399)

Box-shaped damper (BSD) is a new type of yielding dampers that have been introduced recently. It does not require sophisticated technology and can be easily mounted in any type of diagonal steel brace. Adjustable geometrical parameters available in this damper allow the designer to easily select appropriate properties needed for dissipating seismic energy induced in the structure. In this research, behavior of reinforced concrete moment resisting frame with intermediate ductility and strengthened by BSD dampers were numerically studied. In total twenty-two frames were considered for numerical analyses. The models consisted of 6 and 9 story frames with different configurations of BSD dampers. All models were subjected to seismic forces and analyzed by nonlinear static methods. The results show that implementing the BSD dampers in reinforced concrete moment resisting frames, significantly reduces target displacement. Also, the average response modification factor calculated from the analyses is at least 20% higher than those of bare frames.

Corrosion of reinforcement in concrete structure is the main factor of determination in the world. Therefore evaluation of concrete on durability base is essential for construction in coast of Persian Gulf and Oman sea. The most important test method is measurement or prediction of diffusion coefficient of concrete. There are different direct and indirect methods for determining of diffusion coefficient. The methods include, chloride profile and Fick law, rapid chloride permeability test, conductivity, and resistivity. Formation factor is considered as an important indicator of concrete performance against chloride diffusion. Because this indicator contains both the resistivity of the concrete and resistivity of the pore solution. In otherwords, the formation factor indicates the amount of porosity in the concrete and the type and amount of ions in the pores. The porosity and ions determine the intensity of chloride diffusion in concrete. The target of researchers is to achieve accurate diffusion methods or proposing simple models, in last 30 years. In this paper beside literature review, a novel and simple model for prediction of diffusion is presented.

Roller Compacted Concrete is defined as a concrete with zero slump. It will support a roller while being compacted in its unhardened state. RCC is used in two general areas of engineered constructions: dams and pavements. In this study, RCC will be discussed only in the context of its use in pavements. In this regard, Some material savings may be possible due to the lower cement content normally needed in RCC pavement mixtures to achieve strengths equivalent to those of conventional concretes. The other advantages of using RCC include cost savings as a result of the construction method and the increased placement speed of the pavement.Unreinforced concrete has a low tensile strength and a low strain capacity at fracture. It was reported in many studies that NS significantly improved the mechanical properties and durability of cement-based materials. In this study we carried out a comprehensive investigation of the results caused by the addition of steel fibers and nano silica particles in mechanical properties of RCCP. Therefore, with varying amounts of steel fibers (0.00%, 0.33%, 0.67% and 1.00% by the volume of concrete) and nano silica particles (0.0%, 0.5%, 1.0% and 1.5% by the weight of cement), RCCP was prepared and consistency and mechanical properties (compression strength, tension strength, flexural strength, and thoughness) were investigated. The results indicated that the addition of steel fibers and nano silica leads to positive mechanical properties of RCCP.

Geopolymer concrete is a new material in the construction industry with optimal performance and efficiency. On the other hand, geopolymer concrete has mechanical characteristics and durability against chemical attacks. Microstructural changes on the mechanical properties of geopolymer concrete in sulfate environments can be strongly affected. Accordingly the present study is a microstructrul analysis of the influence of sulfate environmental condition on the mechanical propertiese of geopolymer concrete.

In this regard, for the production of geopolymer concrete-based slurry, a sodium bicarbonate solution with sodium concentration of 10 M and sodium silicate as activating material have been used. This study evaluated about 200 concrete samples. The samples were preserved for 3 months in simulated environments with 0.1%, 0.25%, 0.5%, 1%, 2.5%, 5% and 7.5% sulfuric acid concentrations. Compressive strength, weight percentage, ultrasonic wave, permeability and pH change tests were then performed after 1, 3, 7, 14, 28 and 90 days on all the samples in the preserving environment.

The results indicate that the strength of samples preserved in the sulfate environment compared to the control sample depended on the amount of sulfate. After 90 days, the compressive strength of samples preserved in the 7.5% concentration sulfuric acid sulfate environment was reduced by about 45% compared to control samples. This reduction in compressive strength is inversely related to the results from the ultrasonic test of samples preserved in the 7.5% percent concentration sulfate environment.

The purpose of this research is producing geopolymer concrete in order to reduce the consumption of cement in the construction industry to preserve environmental benefits. In this study, the production of geopolymer concrete using mineral soils of different regions of Iran and industrial by-products has been studied and parameters such as type of raw material, curing temperature, applying pressure during construction, type of alkaline solution and age of samples on compressive strength of concrete samples have been studied. 120 cubic samples with dimensions of 50 × 50mm and 64 cubic samples with dimensions of 100 × 100mm for compressive strength test, 76 cylindrical specimens with a diameter of 150 mm and a height of 300 mm for compressive and tensile strength test and 9 beams with dimensions of 150×150×1200 mm for flexural strength test were made. The ductility and load bearing capacity of the geopolymer and cement concrete samples were compared and the results were analyzed. The compressive strength of the geopolymer concrete produced in this study by using slag, which are the by-products of the industry, and the mineral soils of zeolite, perlite and bentonite, was obtained between 10 and 62 MPa under different curing conditions. Geopolymer concrete showed better results in tensile tests on cylindrical specimens and four-point bending tests than conventional concrete on steel reinforced beams. The ductility of beam samples made of geoplymer concrete containing zeolite and slag is about 14% and 43% higher than that of cement concrete samples in the flexural strength test, respectively

Geopolymers, as a type of mineral polymers, are nano-structural Amorphous solid. They are usually produced in temperatures below 120 °C by polymerization of aluminosilicate monomers in alkaline solutions. The compressive strength of geopolymer concretes mainly depends on its chemical ingredients, including Aluminosilicate minerals and alkaline solution. This paper presents the results of an experimental study on compressive strength of geopolymer concretes made by using Khorasan province pozzolan. Effects of various parameters such as solution-to-solid ratio, sodium silicate-to-sodium hydroxide ratio, setting tempertature, setting time, Sodium hydroxide Concentration, base water, silice-to-aluminium ratio, sodium silicate chemical composition on geopolymer compressive strength was studied. It was observed that the compressive strength of geopolymer concrete is increased by increasing the sodium silicate and silica in the mixture and increasing sodium hydroxide molarity and setting temperature, the concrete compressive strength is increased. On the other hand, increasing the water and sodium oxide weights in the mixture and sodium silicate-to-sodium hydroxide ratio results in decreasing the concrete strength.

The arrangement of the centers of mass, resistance and stiffness has a great influence on the stability of the structure and its behavior against the moderate and strong earthquakes. In this study, three structural models with 6, 9 and 12 stories with dual bending system of intermediate steel frame coupled with concrete shear walls in three types of regular, irregular with stiffness and resistance eccentricity has been modeled using finite element software and fragility curves are depicted for different structural performance levels. Survey results showed that at immediate occupancy (IO) performance level the structure is still in the linear region and the probability of exceeding from collapse prevention (CP) performance level in the stiffness eccentricity model is higher compared to other models. Also, the probability of exceeding from the CP performance level in the resistance eccentricity model is higher than the other models because the structure arrives at the plastic region.

The reusing of recycled aggregates produced from waste concrete is a sustainable solution to reduce the shortage of natural resources. This paper presents the effects of the addition of Nano silica and polyvinyl alcohol (PVA) fiber on the mechanical and microstructural properties of recycled aggregate concrete containing coarse and fine recycled aggregates. Recycled aggregate concrete was produced by 50% and 100% volume substitution of natural fine and coarse aggregate with recycled aggregate. In total, 21 series of concretes are evaluated. The Nano silica in weight ratios of 0%, 2%, 4%, and 6%, and the polyvinyl alcohol fibers in volume fraction of 0%, 0.5%, and 1% were used. The compressive strength, tensile strength, and flexural strength at the different ages of 7, 28, and 90 days are measured in this research. Also, the microstructure of the recycled aggregate concrete was studied via scanning electron microscopy on the selected mixtures.Test results show that the addition of Nano-silica and polyvinyl alcohol fiber can improve the mechanical and microstructural properties of the recycled aggregate concretes. Also, it was seen that polyvinyl alcohol fiber improves the post-peak behavior of specimens. Moreover, high ratios of Nano silica and PVA fiber in the concrete mixture caused negative effects on the compressive strength of recycled aggregate concrete.

Mineral additives are one of the used methods to prevent the decrease in strength of concrete against sulfate attack. In this paper, after identifying the characteristics and properties of Qotursui spa construction site, the effects of mineral additives (fly ash and micro-silica) on mechanical and durability parameters of the concrete specimens have been investigated before and after immersion in the Qotursuyi spa pool. Results showed that, in the improved samples with single component additives (e.g. micro-silica only) and two components, in the short-term cement type II and in the medium and long-term cement type V has been resulted greater compressive strength and durability. Fly ash has more positive effect on compressive strength in the long-term. The compressive strength of concrete samples containing type V cement with microsilica showed a greater increase than that of type II cement. Optimum amount of microsilica for concretes made of type II and type V cements are 10-15 percent and 10 percent replaced with cement, respectively. Similarly, optimum amount of flyash for concretes made of type II and type V cements are 15 for both, percent replaced with cement. The highest compressive strength in the two component additives is the F10S10 compound.

Today, Concrete is one of the main materials used in the industry. Today, the recycling of construction waste and the construction of concretes with the environment has found many fans. Heavy metal chromium is one of the most important environmental pollutants. In this study, glass and bricks recycled from building demolition are used to build concrete (green mixing concrete). This concrete has non-structural standard concrete properties, which was added by adding bentonite adsorbent to remove chromium from industrial wastewater. Various samples were made with different absorbent percentages . Concrete samples were mixed with various concentrations of chromium mg / L, different pH at different contact times Solution 6, was tested and compared in vitro. The results showed that maximum adsorption in the concentration of sewage was 25 mg / L, contact time 8 hours, absorbent dose of 8% and pH, 6 in laboratory (25 ° C). Maximum adsorption in optimal conditions was 95.65% and the absorption capacity was 123.3 mg / g. Experiment with optimal parameters obtained on the actual sample of industrial wastewater was repeated and the rate of adsorption was 97.29%. Absorption of chromium from a quasi-second-order model and absorption isotherm follows the Freundlich model. 28-day resistance of concrete specimens with optimum mixing plan before contact with chromium metal at 114 kg / cm2, after contact with chromium-containing solution with optimal laboratory parameters of 101.1 kg / cm2 and after contact with the actual sample of sewage containing chromium 4 / 127 kg per square centimeter.