جستجوی مقالات مرتبط با کلیدواژه "سرباره کوره آهنگدازی" در نشریات گروه "عمران"

One of the disadvantages of using conventional concrete in road paving is its low resistance to traffic loads. But today, scientists have been able to improve the strength of concrete by using new materials such as slag in the composition of concrete. These materials contain adhesives and fillers such as aluminate and silicate, which ensure the improvement of strength in concrete after the process of chemical reaction with alkaline solutions. The purpose of this laboratory research is to make concrete with higher strength than ordinary concrete used in road pavement. In this regard, a mixing plan was made of ordinary concrete with a cement grade of 450 kg/m3. A mixing design was also made of fermented concrete based on composite kiln slag to compare and evaluate the ultrasonic pulse (UPV) rate of concrete under ambient temperature and temperature of 500 °C, at a 90-day curing age. Continuation of X-ray diffraction (XRD) spectroscopy and scanning electron microscopy (SEM) imaging tests to further evaluate and verify the UPV test results at 90 days of processing at ambient temperature and 500 °C on the sample Concrete works were carried out. Based on the results, the amount of UPV at ambient temperature was 5930 m/s for ordinary concrete and 4920 m/s for alkaline concrete, which had a difference of 17.03%. By applying heat to concrete samples, the rate of UPV drop in ordinary concrete was 37.26% and in quilted concrete was 45.93%. The results of XRD and SEM tests were in agreement with each other and overlapped with the results of UPV test.

Today, the use of nanomaterials in various sciences has found a wide perspective. In this regard, nanoscale additives in the concrete industry with the aim of improving the mechanical properties and durability of concrete, have been considered by researchers. In the preparation of geopolymer concrete, materials containing abundant aluminosilicate materials are combined with alkaline solution. In this laboratory study, a mixing design was made of control concrete containing Portland cement. Then, slag geopolymer concrete was made in three mixing designs containing 0, 4 and 8% nanosilica (4 mixing designs in total). Then, SEM test at 90 days of curing age and tests of water permeability, compressive strength and modulus of elasticity at 7 and 28 days of curing at room temperature were performed on concrete samples. Laboratory results indicate that increasing the curing age of concrete has improved the results of compressive strength, modulus of elasticity and water permeability. In the test of water permeability, modulus of elasticity and compressive strength, the addition of 8% nanosilica to geopolymer concrete improved the results by 26, 13 and 19%, respectively, compared to the design of nanosilica-free geopolymer concrete at 28 days after curing.

In recent decades, the use of alkaline materials in concrete has found a wide perspective in the concrete industry due to its pozzolanic properties and the presence of aluminosilicate materials with high filling and adhesion properties. The use of this type of concrete (due to its superior advantages over ordinary concrete) in paving roads can improve the strength and increase the useful life of roads. In this laboratory research, a mixture ratio of normal concrete with a cement grade of 450 kg/m3 was made. A mixture ratio was also made of activated alkali concrete based on blast furnace slag to compare and evaluate the modulus of elasticity of concrete under ambient temperature and heat of 500 ℃, at the age of 90 days. Next, X-ray Diffraction Spectroscopy (XRD) and Scanning Electron Microscope (SEM) tests were carried out in order to further investigate and verify the results of the modulus of elasticity test, at the processing age of 90 days at ambient temperature and It was done on concrete samples under the heat of 500 ℃. The modulus of elasticity at ambient temperature was 32 GPa for ordinary concrete and 35 GPa for activated alkali concrete, which had a difference of 8%. By applying heat to concrete samples, the amount of modulus of elasticity drop in normal concrete reached 59% and in activated alkali concrete 42%. The results of the XRD and SEM tests were in agreement with each other and overlapped with the results of the modulus of elasticity test.

Today, in order to reduce the harmful effects of the environment and increase the mechanical properties and durability of concrete, particles with high pozzolanic properties are used as a suitable alternative to ordinary cement in concrete. And filler, as an alternative to cement, has attracted the attention of researchers. In this laboratory study to investigate the effects of slag and nanosilica slag consumption on the microstructure of geopolymer concrete and compare it with the characteristics of control concrete containing Portland cement, 1 mixing design of control concrete and 3 mixing designs of geopolymer concrete containing 92, 96 and 100% composite kiln slag was fabricated with 0, 4 and 8% nanosilica, respectively. X-ray fluorescence (XRF) was performed. In order to investigate the effect of microstructural changes on the macro structure of concrete, compressive strength and tensile strength tests were performed on concrete samples at 90 days of age. Examination of the images obtained from the SEM test shows the superiority of the microstructure of the geopolymer cement matrix in all designs, compared to the microstructure of the control concrete containing Portland cement. Celsius), the effects of improvement and cohesion in the microstructure of geopolymer concrete are evident due to the presence of silica nanoparticles, in this regard, the presence of 8% nanosilica in mixture 4 (geopolymer concrete), accelerates the reactivity process and increases the volume of hydrated gels Geopolymerization was compared to other geopolymer concrete mixtures (containing 0 and 4% nanosilica). Images of concrete samples heated to 500 ° C show signs of weakening of the concrete microstructure compared to images taken of concrete at room temperature. The results of XRF test indicate the presence of the highest amount of oxidilica and aluminum oxide (the main factors in improving the density in the microstructure of concrete), in the combination of designs 4 and 2 by 36 and 8%, respectively. The high peaks created in the XRD spectrum diagram often occur in areas with angles (θ2) of 28 °, and their height varies according to the presence of aluminosilicate particles in the concrete mix. The application of high heat to the concrete specimens caused a decrease in the results of the XRD test. Evaluations performed on the results of the test to determine the compressive strength and tensile strength in concrete, showed coordination and overlap with the results of microstructural tests in this study.

The use of pozzolans to make concrete with suitable and durable mechanical properties has found a special place in the last decade; because the use of these materials reduces the consumption of cement and consequently reduces environmental pollution. In the meantime, knowing the optimal amount as well as the effect of pozzolans has been an important and challenging aspect that many researchers have focused on. In this study, an attempt was made to make concrete with suitable mechanical properties using three types of high-consumption pozzolans, namely microsilica, rice husk ash and furncae slag. The compressive strength of 7, 28, and 90 days, as well as the three-point flexural strength of the experiments, was performed separately and in combination to investigate the effect of the use of these pozzolans. In this study, a wide range of alternative values of pozzolan was considered so that in addition to knowing how these pozzolanes are affected, the optimal percentage for each of the pozzolanes used can also be determined. Experimental results have shown that the effect of using microsilica separately from furncae slag is more severe. In addition, the effect of the utilization of pozzolans in combination is positive in improving the compressive strength of concrete specimens and only reduces the compressive strength at an early age. With the exception of samples containing low levels of pozzolan, other specimens cause a decrease in compressive strength at an early age. The potential for pozzolans can be an important factor in reducing resistance to overus. The electrical resistance of concrete samples containing pozzolan was higher than the control specimen, which indicates a denser structure of concrete at the age of 90. The proposed artificial neural network based on the experimental data was able to predict the compressive strength of concrete containing different pozzolan in various ages.

Alkali-activated concretes with slag base as new materials could be used to achieve a healthy environment without pollutants such as greenhouse gases and to solve the problems of water shortage and groundwater resources and use by-products produced during the processing of materials such as iron, steel and copper alloys for construction projects. On the other hand, porous concretes have economic and environmental potentials such as preventing flooding, increasing groundwater reserves, decreasing the flow of surface water. Slag-based alkaliactivated concretes have been synthesized by natural pozzolans and industrial wastes such as sodium silicate with alkaline silicate and alkali hydroxide solutions. In the current study, the performance of alkali-activated porous concrete with the different amounts of sodium hydroxide molarity and the ratio of sodium hydroxide to sodium silicate has been investigated in terms of mechanical properties such as compressive strength. The flexibility and permeability of the specimens were also investigated. The tests have been performed on 9 series of samples with three values of 8, 12 and 16 Molar of sodium hydroxide and three ratios of sodium silicate to sodium hydroxide 1, 2 and 3 under curing times of 7, 14 and 28 days. The test results show that the alkali-activated porous concrete indicated a higher initial strength compared to conventional porous concretes. The compressive strength at curing time of 14 days and flexural strength at curing time of 7 days were about 75% of its strength at curing time of 28 days which is significant. The compressive and flexural strengths have been increased with the increasing of molarity and the ratio of sodium silicate to sodium hydroxide about 20 to 25% and 9 to 13%, respectively. However, the permeability decreases with the increasing of molarity of sodium hydroxide solution or the ratio of sodium silicate to sodium hydroxide.

The choice of concrete consumption and high strength in the structure of concrete dams is of particular importance. In this laboratory research, slag alkaline concrete containing 0, 4 and 8% nanosilica and 1 and 2% polyolefin fibers has been produced in 5 mixing designs. A design of control concrete containing Portland cement was prepared to compare with the test results of reinforced concrete. Modulus of elasticity, impact resistance of falling hammer and scanning electron microscope images were performed on concrete samples at 90 days of processing age. Addition of nanosilica to reinforced concrete improved (Module 4 compared to Scheme 2) in the modulus of elasticity test and the energy absorbed in the impact test by 13.42% and 36.36%, respectively. This superiority was increased by 7.5% and 8.26 times by adding fibers to concrete, respectively. The results of the SEM test overlap with other results.

Cement production has always been associated with environmental challenges due to carbon dioxide emissions. On the other hand, cement production is an energy-intensive process and leads to the consumption of abundant fossil fuels. In order to solve this problem, the production of geopolymer concrete is on the agenda. The researchers decided to reduce the negative effects of cement production and have superior properties than ordinary concrete . Geopolymer cement matrix, due to the production of abundant hydrated gels, has a higher density and cohesion than the Portland cement matrix, and this is the main reason for increasing the resistance of this type of concrete to high heat compared to ordinary concrete. In this study, the effect of heat on the mechanical properties of slag geopolymer concrete containing 0 to 8% nanosilica and 1 to 2% polyolefin fibers at 90 days of processing age was investigated and XRF, XRD and SEM experiments were used to study the microstructure. In the optimal design of slag geopolymer concrete (containing 8% nanosilica and free of fibers), we saw a decrease of 8 and 44% in the values after and before heating in compressive strength tests and determination of ultrasonic pulse speed of concrete, while in control concrete, the results decreased Reached 38 and 37 percent. In slag geopolymer concrete containing 8% nanosilica and 2% fibers, tensile strength and modulus of elasticity equal to 14 and 34% showed results after and before heating, for control concrete these figures decreased by 51 and 59% in the results. Received, the results of the falling hammer impact test also had a reduction in the resistance of heat-exposed concrete to hammer blows. In the end, the microstructural studies were in overlap and in coordination with the results of the tests of this study.

In the present study, in order to make geopolymer concrete for use in concrete dams, 6 mixing designs including 288 concrete samples of control concrete containing Portland cement and slag geopolymer concrete containing 0 to 8% nanosilica and 1 to 2% polyolefin fibers were prepared. 7, 28 and 90 days processing were subjected to mechanical and durability tests. In order to study the microstructure in this study, XRF and SEM tests were used. The results show that the compressive strength, tensile strength, water impermeability, capillary water absorption for geopolymer concrete containing 8% nanosilica and 2% polyolefin fibers (as an optimal design) compared to control concrete, by 3%, respectively, 9 %, 56% and 65 times at 90 days of processing. In this regard, the maximum values ​​of compressive strength and tensile strength obtained were 82.96 and 5.51 MPa, respectively, and the minimum amount of water penetration in concrete was 13 mm and the minimum rate amount of water capillary absorption was 0.049 Cm/s1/2 for geopolymer concrete. SEM images showed that the geopolymerization process was enhanced by producing more hydrated gels and improving the microstructure of geopolymer concrete by increasing the presence of silica nanoparticles.

One of the most important challenges facing civil engineering community besides cost, performance problems such as vibration, especially in thin sections, the smooth and concrete movement of reinforced and complex sections, is increased resistance with reducing or not using cement. The purpose of this research is to innovate in Portland cementless concrete industry, which is inspired by geopolymer technology and its incorporation in self-compacting concrete (SCC) to produce sustainable concrete, in order to reduce carbon emission from Portland cement (PC) production. In this regard, the furnaces slag as amorphous (cement replacement) and alkaline actuators are used and laboratory study was performed on the fresh properties (slump Flow, T50, L-Box, hopper V and J rings) and hardened properties (compressive and tensile strength). Results indicate easy filling in narrow sections, improved compression, good bonding strength, reduced maintenance, faster construction speed, about 70% increase in 28-day resistance and 86% in 90-day resistance of Type III geopolymer concrete with respect to Portland cement concrete (reference concrete) with constant grade of 400 kg / m3, Use of industrial waste and reduction of air pollution, Improve mechanical properties (according to statistical results of compressive strengths up to 65 MPa), Reduce the overall construction cost of self-compacting geopolymer concrete in comparison to the rate of acquisition of resistance of conventional self-compacting concrete, self-compacting concrete with different slag percentages, conventional geopolymer concrete and ordinary concrete. Due to the high cost of alkaline activators in the country, lack of equipment and infrastructure for slag powder, insufficient information on the durability of geopolymer concrete is predicted and thereby create new opportunities for the construction industry.

Due to the high amount of CO2 emission through the production of cement and great energy consumption in the cement industry, one of the most important issues in concrete technology is to find out an appropriate replacement for Portland cement. Alkali activated materials are the new approach for solving this problem. In fact, alkali activated concrete consists of an inorganic structure containing two parts: Source material and alkaline activator liquid. In this study, the effect of the amount of source material and water to binder ratio on chloride ions ingress was evaluated. For this purpose, 5 mix designs were used to make alkali activated slag concretes and for activating slag, 6 molar potassium hydroxide and sodium silicate solutions were employed as alkaline activator liquid. Additionally, one mix design was dedicated to ordinary Portland cement concrete for the sake of comparison.
The properties of AAS concretes were examined by means of slump loss, measurement of compressive strength at the ages of 1 to 180 days and capillary water absorption test at 7, 28 and 90 days. Furthermore, chloride ions penetration was measured through electrical resistivity test, rapid chloride migration test (RCMT) and resistance against chloride ions diffusion test according to NT Build 443. The results indicated that the performance of water to binder ratio and also the amounts of source material were comparable to that of ordinary Portland cement concretes. Additionally, alkali activated slag concretes had higher compressive strength and also superior durability against chloride ions penetration compared to OPC concretes

Alkali-activated cement is a new and innovative material in the construction industry and with desirable performance that by use of natural Pozzolans and industrial waste containing aluminosilicate can be used as an eco-friendly substitute material for Portland cement. On the other hand mechanical and durability properties of concrete has made it important to research on the factors influence on these two characteristics. In this paper it’s tried to study and manufacturing high perfomence concrete based on ground blast furnace slag by using sodium base alkaline solution. Three concentrations 18.75,15 and 11.25 and three ratios of Na2SiO3 to NaOH have been used. The ratio of water to the binder material is considered constant in all mix designs. In this study, for curing samples were submerged in water at ambient temperature samples. Compressive test results show that by decreasing the NaOH concentration to 11.25 mechanical strength of this material decreases and while by decreasing this parameter from 18.75 to 15 this parameter almost stay constent. Water absorption test was done on samples at 28 days age. This test shows that increasing of NaOH concentration reduces water absorption of samples

Self-Compacting Concrete (SCC) is one of the innovative products in concrete technology which has been developed in recent years. SCC has gained great popularity due to its benefits such as reduction in labor and equipment costs, acceleration of construction, providing flexibility in filling highly reinforced sections and complex formworks, lowering the noise on job site and having superior surface quality.rnHowever, many researchers are still trying to optimize the mixture proportions and investigate the incorporation of new materials in SCC. The typical high content of Portland cement in SCC is one of the main challenges in optimization of its mixture proportions. This high cement consumption increases the production cost of SCC and is also undesirable from an environmental point of view, considering the large amount of CO2 emitted during Portland cement production. rnNowadays cement replacement materials are being widely used in concrete mixtures and blended cements allocate noticeable amount of cement consumption in the world. Still, use of these materials is negligible in Iran and needs more attention by construction industry. Use of cement replacement materials, depending on their properties, can bring about improvements such as reduction in production costs, rheological improvements, reduction of heat of hydration and concrete durability enhancement.rnIn this paper the results of an experimental study on effects of silica fume and Ground Granulated Blast Furnace Slug (GGBFS) on resistance of high-strength SCC against chloride ion penetration are presented. Five concrete mixtures were prepared and tests were conducted to investigate the effects on high-strength self-compacting concrete. Filling ability, passing ability and segregation resistance of fresh mixtures were evaluated using slump flow, T50 and V funnel tests; while compressive strength, electrical resistivity and water adsorption tests were carried out on hardened concrete at different ages. The results show that GGBFS replacement decreases the viscosity of concrete and consequently the needed superplasticizer dosage. Also, results imply that use of silica fume and GGBFS decreases permeability of concrete. Finally the mixture containing 10% silica fume and 10% GGBFS cement replacement are introduced as the optimum SCC mixture.