جستجوی مقالات مرتبط با کلیدواژه « fly ash » در نشریات گروه « عمران »

Applying stone columns (SCs) is an economical method to improve loose soil. This laboratory study is conducted on the effects of simultaneous use of crumb tire (CT) and fly ash (FA) on the shear behavior of SCs encased with geotextile and fiber-reinforced polymer (FRP) in soft clay. A large-scale direct shear device was utilized to do the desired tests. The samples were exposed to normal stress values of 20, 40, and 70 kPa. First, optimal percentages of CT and FA were determined to be used with granular materials in the SCs. The impact of installing ordinary reinforced and unreinforced SCs on the shear behavior of the assembly was examined. Installing the SCs in soft clay bed and adding the CT-FA composite to the SC materials increased the shear strength. Supplementing the CT-FA composite to the SC materials increased shear strength of the assembly to 4.6%-10%. The shear strength rose more than twice when the normal stress increased from 20 kPa to 70 kPa and it was mobilized more since CT-FA composite is present. It increased due to a rise in the replacement ratio of the SCs in the assembly. By installing the ordinary composite SCs in clay bed under the normal stresses of 20 kPa and 70 kPa, the shear strength increased to 34% and 41.7% and it would rise in the encased mode more than in the ordinary mode. Furthermore, the FRP-based reinforcement enhanced the shear strength more than the geotextile reinforcement did.

In the present study, due to sustainable development and eco-friendly aims, alkali activated slag and fly ash were used as the geopolymer binder instead of cement in self-compacting concretes. The alkaline solution consisted of sodium hydroxide and sodium silicate solutions. Binder content was between 500-700 kg/m³ and water to binder (W/B) ratio varied from 0.45 to 0.48. Na₂O percentages were in the range of 5 - 7% and three ratios of coarse to fine aggregate (25/75, 30/70, 35/65) were used. Design of experiments was based on orthogonal L9 array of Taguchi methodology. A total of nine main mixes and three validation mixes were prepared. Fresh concrete characteristics and mechanical properties including compressive strength, splitting tensile strength, modulus of elasticity and water absorption were evaluated. The results demonstrated that the binder content and coarse to fine aggregate ratio were the most influential parameters on the mechanical properties. The highest compressive strength, splitting tensile strength and modulus of elasticity were belonging to the mixture with low W/B ratio and higher binder content by 58 MPa, 4.5 MPa and 32 GPa, respectively. Moreover, Taguchi method has a good capability (R²≥0.967) to analyze and predict the mechanical properties of self-compacting geopolymer concrete.

In this article, one of the solutions to reduce greenhouse gases in block concrete pavements, i.e. the use of recycled materials investigated. concrete pavers blocks containing micro silica gel, fly ash, macro and micro polymer fibers, as well as reclaimed asphalt pavement (RAP) were made and in terms of compressive strength, bending resistance, durability against periods of freezing and thaw, skid resistance by the British pendulum method and wear resistance, by wide wheel abrasion method, were tested. The results showed that micro silica gel has the greatest effect in improving the compressive strength of the samples. The result of the flexural strength test was that micro silica gel increase the flexural strength by nearly 20%. Although polymeric fibers did not affect improving the compressive strength, they improved the modulus of rupture by about 5%. Meanwhile, two other materials, i.e. fly ash and RAP were not able significantly increase the flexural strength. The evaluation of the results of the durability test showed that the presence of three-tenths volume percent of macro polymeric twisted fibers preserves the compressive strength before and after 50 cycles of freezing and thawing. overall, the comparison of the ratio of the compressive strength of the samples after freezing and thawing to the strength of the samples before the test showed that the use of high percentages of micro silica gel, fly ash and macro polymer fibers is more than RAP and fibers and Micro polymers affect improving durability. The results of the abrasion and sliding resistance test also showed that different types of polymer fibers were more effective in improving the skid resistance of the samples. The test of abrasion resistance with wide wheel abrasion method also showed that micro silica gel plays a more effective role in keeping the surface of the sample blocks unified

In this research, the mechanical properties of concrete in the conditions of using natural aggregates and comparing the results with the replacement of recycled aggregates with values of 10, 20, 30 and 40% have been investigated. In the first part of the study, the results showed that the specific gravity of concrete in the presence of 40% of recycled sand and gravel was 1.02% and 2.38%, respectively. Also, in terms of compressive strength, the lowest decrease in compressive strength occurred in 10% of recycled sand and the highest decrease in compressive strength occurred in 40% of recycled sand. Then, the mechanical properties of ordinary concrete with concrete containing waste plastic (PET) were compared with 2, 4, 6, 8 and 10% of concrete volume. In this regard, the results of the study indicate a decrease in compressive strength of concrete compared to control concrete. In this regard, the lowest reduction in compressive strength was 2.01% in the presence of 2% waste plastic (PET) and the highest reduction in compressive strength was 16.39% in the presence of 10% waste plastic (PET). Regarding flexural strength, the results showed an increase in flexural strength; So that the lowest increase in flexural strength of 6.27% occurred in the presence of 2% waste plastic (PET) and the highest increase in flexural strength of 39.49% occurred in the presence of 10% waste plastic (PET). In the end, the results showed that increasing the presence of waste plastic (PET) has led to a decrease in water absorption of samples. In this regard, the lowest decrease in water absorption by 5.26% and the highest decrease in water absorption by 23.08% occurred in the presence of 2 and 10% waste plastic (PET), respectively.

Self-compacting composite concrete is known as a cement composite with high performance and adhesion. This composite has a lot of psychological capability and efficiency. Concrete failure depends on the formation of cracks and microcracks. As the load increases, the microcracks join together to form cracks. To solve this problem and also to create homogeneous conditions, in recent years, thin fibers of fiber in the entire volume of concrete are used. Fiber concrete is actually a type of cementitious composite that increases its tensile and compressive strength by using reinforcing fibers inside the concrete mix. In this study, the effect of adding materials (Microsilica Fume, Fly Ash, GGBFS) and sinusoidal steel fibers (corrugated) on the mechanical properties of self-compacting cement composite was investigated in 9 mixing designs. For this purpose, cement alternative additives in the amount of 10% by weight of cementitious materials and steel fibers in the amount of 1% of the volume of cement composite were used in the mixing design. In the compressive strength test, the sample with 1% steel fibers had a 4.5% increase in strength compared to the reference sample, which showed a very low effect of steel fibers on the compressive strength. Also, the use of microsilica by 10% by weight of cement substitute increased the amount of compressive strength by 6.6%, which due to the property of microsilica in increasing resistance, this result was not far from the eye. In general, the use of steel fibers had no effect on the results of compressive strength, capillarity, and water absorption, but the changes in other test results compared to the reference sample were quite noticeable and expected due to the use of steel fibers.

The fly ash obtained from the extraction of exhaust gases from coal and silt furnaces, is non-plastic and fine, which is a different combination based on natural coal fuel. Fly ash is one of the waste materials in thermal power plants. The use of waste materials such as fly ash in the concrete industry offers an alternative and valuable solution to create an environmentally friendly environment. However, experimental work is time-consuming and expensive, and the use of soft computing techniques can speed up the process of predicting concrete's resistance properties. In this study, artificial neural network (ANN) was used to predict the compressive strength of fly ash-based high-performance concrete. A number of 471 experimental data were extracted from valid sources and parameters such as cement, fly ash, water, superplasticizer, fine and coarse aggregate and age of the samples were considered as input parameters and compressive strength of samples was considered as output parameters. Among the networks with different number of neurons, a network which has the best correlation coefficient values obtained from training, evaluation and testing data and also has the lowest mean square error (MSE) value was selected as the optimal network. In this study, the network with the number of 6 neurons provided the best results. Also, the effect of each parameter in different numerical ranges on the compressive strength of concrete was investigated and presented, and it was found that the age of the samples and the amount of cement, fly ash and water have the greatest relative importance.

Ever-growing concern to protect the environment concentrated the attention of the society on the possible re-use of different agricultural and industrial wastes in road construction. This research study depicts the effect of using wastes like rice husk ash (RHA) and fly ash (FA) as a replacement of conventionally used hydrated lime (HL) as fillers in hot-mix asphalt (HMA). Primarily, the dense graded bituminous macadam (DBM) mix specimens were made in the laboratory with varying proportions ranging from 2% to 8% of HL, RHA and FA by following design mixes according to the Marshall method and compared the results with control mix as prepared by utilizing 2% HL. The performances of the said mixes were studied through the Marshall Quotient, indirect tensile strength and tensile strength ratio. Results of investigation show better performance of HMA with the addition of RHA and FA and also proved to be economical as the optimum bitumen content is reduced by 7.5% from that of control mix when added at 4% filler ratio. Further, RHA shows a greater affinity to the bitumen attributing the highest stiffening effect of the bituminous mastic droplets compared to that of other used fillers with good compatibility at the micro level by satisfying the essential criterion.

The durability of a concrete structure is highly dependent on the strength and permeability of the surface layer, as it is the surface layer that must prevent the entry of materials that can initiate or enhance the harmful effects on concrete. Sulfates are one of the most common destructive factors in concrete in most parts of Iran, especially in the southern regions of the country where concrete is exposed to seawater (which contains sulfate compounds). Also, the lack of compaction of the surface layer, due to the difficulty of vibration in limited spaces between molds and rebars and other accessories, is one of the main reasons for the poor durability of reinforced concrete structures exposed to environmental factors. Naturally, incorrect vibration results (worming, detachment, dehydration) have stronger negative effects on permeability and therefore durability. Self-compacting concrete with suitable properties is free from these defects and as a result, materials with less inconsistency and uniform permeability have less weaknesses for environmental harmful factors and, therefore, have better durability. Therefore, considering that the "torsion" test shows good sensitivity to surface changes of concrete, so in this study, using the "torsion" test, the effect of magnesium sulfate on the surface strength of self-compacting concretes has been investigated. In the "twist" test, a 5 cm diameter metal cylinder is glued to the surface of the test site using epoxy resin adhesive. Then, using a conventional hand-held tachometer, a torsion anchor is inserted into the metal cylinder to break the test object. The equipment used in the "twist" test is very cheap, simple and accessible compared to other corresponding tests. The damage from the "torsion" test is very superficial and minor, and by causing failure in the test object itself, it directly determines its strength. Self-compacting concrete mixing designs were studied by replacing 25, 35 and 45% cement with fly ash filler, and a conventional concrete mixing design as a control to study the effect of magnesium sulfate on the strength of self-compacting concrete. Self-compacting concrete tests including slump flow test, slump flow time of 50 cm, V-shaped funnel, V-shaped funnel increase time (5 minutes) and L-shaped mold were performed on self-compacting concrete acceptance criteria on self-compacting concrete mixing designs. . The results indicate that sulfated water not only does not have a negative effect on the surface strength of self-compacting concrete containing fly ash, but also provides better curing conditions for these samples. The use of fly ash also makes the magnesium sulfate solution a more suitable medium than ordinary water for the surface strength of self-compacting concretes. The process of obtaining surface strength in almost all self-compacting samples treated in magnesium sulfate solution is more than that in ordinary water. However, in the case of ordinary concrete, the process of obtaining the surface strength of all samples placed in magnesium sulfate solution is less. For self-compacting samples treated in magnesium sulfate solution, with increasing the percentage of fly ash, the surface resistance of 3 and 7 days decreases. But the 28-day surface resistance increases.

Reinforced concrete is one of the most widely used building materials in the construction industry. The sulfate attack on concrete structures is one of the factors effectively causing the reduced durability of concrete and structural damage. In the design and construction of concrete structures, service life, sustainable development, and environmental issues are important indicators considered by researchers in optimizing materials to achieve sustainable concrete with high strength by substituting various types of pozzolans for cement. The present study aims to compare the effects of fly ash and micro-silica on the development of the compressive strength, and electrical resistance of concretes exposed to sulfate-rich waters. The plans of this study include two types of conventional concretes and concretes containing pozzolanic material. Concrete mixing plans in sulfate medium were divided into 11 groups. The first group, with no additive material as a substitution for cement, included one plan (control plan), and the other 10 groups included 8 plans with the substitution of different percentages of micro-silica and fly ash powders for cement in concrete. Accordingly, 81 plans, each with 4 samples (7, 14, 28, and 42-day ages), were constructed to test compressive strength (N=324 plans). The results indicate that in the sulfate medium, with an optimal mixing design, the concrete containing standard sand reinforced with fly ash and microsilica pozzolans had higher strength compared to the concrete with no pozzolan, Moreover, the maximum (a 6% reduction in strength) and minimum (a 28% reduction in strength) durability was obtained for Samples # 5 and 6 of Group 2 and Samples #30 and 31, respectively. Also, with the substitution of 15% microsilica, a 1.58-fold increase in the electrical resistance was observed in the 90 day-old concrete sample compared to the 28 day-old sample

Most studies show that some certain fiber can enhance to some extent both mechanical properties as well as ductility of lightweight concrete. On the other hand, due to high industrial potential as well as less damage to the environment, basalt fibers have gradually become an appropriate option to be used in the composite industries and thus is considered as a special competitor to other fibers (Ralegaonkar et al., 2018; Sadrmomtazi et al., 2018). In recent years, there has been a growing interest in the use of the intelligent inference and reasoning methods, including ANFIS and ANN to approximate nonlinear and complex concrete behaviors and predict its properties (Tesfamariam and Najjaran, 2007; Sadrmomtazi et al., 2013). Therefore, this study aimed to investigate mechanical properties of the lightweight structural concrete containing different amounts of basalt fibers (0, 0.1, 0.2, 0.3, 0.4, and 0.5%) as well as pozzolanic materials (silica fume and fly ash). In addition, the modified ANFIS was used as a robust method to predict results to evaluate the experimental results.

In this study, different combinations of replacement of metakaolin, zeolite and fly ash in single, binary, and ternary mix designs were investigated in order to determine the optimal amount of suitable pozzolans. Fifty mix designs with constant water to cement ratio were made and the results of compressive strength, tensile strength, slump, specific gravity, water absorption, and volumetric electrical resistivity of concrete were recorded in order to evaluate the effect of type and amount of pozzolans and the effect of their compositions. The results showed that the highest amount of compressive strength was related to the ternary composition of pozzolans, and the amount of replacement was 3% (M3Z3F3). 3-, 7-, 28- and 90-days compressive strength increased by 14.8%, 24.1%, 41.1% and 54.1% compared to the reference sample, respectively. Compressive strength of samples containing single, binary and ternary mixes with a total of up to 45% will increase the compressive strength by different percentages and will have a further downward trend. The tensile strength of concrete in all samples containing binary and tertiary compounds of pozzolanic materials was higher than the reference sample with the highest increase related to M5Z5, M5F5, Z5F5 with 84.2%, and M3Z3F3 with 94.7%. The maximum reduction of water absorption is in the ternary mix designs M13Z13F13 and M15Z15F15 with a decrease of 75.8% compared to the reference sample. In all samples containing pozzolanic materials, the amount of electrical resistance has increased compared to the reference sample (from 1.3 to 9.1 times). The amount of electrical resistivity of concrete samples containing ternary composition was higher than binary and single. The maximum is related to M13Z13F13 and M15Z15F15 designs, which increased 9.1 times more than the reference sample. The presence of more than 40% pozzolanic values has almost no effect on the mechanical properties of concrete.

In this paper, the effect of bacteria on self-healing concrete with fly ash has been studied. Sporosarcina bacteria with four different concentrations were used for evaluation. In concrete with fly ash, fly ash is replaced by 20% by weight of cement of mixing design has been used. In order to evaluate and control the specimen, destructive and non-destructive tests such as ultrasonic, permeability, water absorption and compressive strength have been used. To evaluate the effect of bacteria on self-healing of concrete cracks, concrete cracks were studied using scanning electron microscopy (SEM) and light microscope. The results show that the concentration of 10.46 × 106 is the most suitable concentration of Sporosarcina for the production of calcite and filling the pores of concrete by products such as calcium carbonate. The mentioned concentration resulted in a 36% increase in compressive strength in specimen with fly ash and a 30% increase in specimen without fly ash. The results also showed that increasing the bacterial concentration did not cause significant changes in compressive strength, water absorption, impermeability and ultrasonic wave velocity.

The use of concrete in industry is expanding. Self-compacting composite concrete is known as a cement composite with high performance and adhesion. This composite has a lot of psychological capabilities and efficiency, so that the use of this concrete, in addition to reducing construction time, also reduces costs. Self-compacting composites fit into the mold without the need for vibration and pass through the smallest seam. In this study, the effects of adding microsilica, fly ash and GGBFS pozzolan on the mechanical properties of self-compacting cement composite were investigated in 8 mixing designs. In making samples, 3 alternative cement additives at the rate of 10% were used in different mixing designs. In the compressive strength test, the sample with 10% microsilica increased the resistance by 5.4% more than the reference sample, which showed that the addition of microsilica increases the strength and water absorption in the samples. However, these pozzolans reduce the flow of self-compacting concrete. On the other hand, in the design of air ash mixtures, the resistance was reduced, but no significant changes were observed for slag. In total, other experiments such as tensile strength, flexural strength, water absorption, capillary, ultrasonic pulse velocity and impact resistance were performed on the mixing design.

Even though incineration has been extensively studied by many researchers, a few bibliometric analyzes have been presented in this area. This bibliometric paper aims to value the research trend and identify the most used topics in the field of "incinerator ash" during the years 2000 to 2020 by social network analysis comprehensively. This research includes examining document type, distribution of journals, the activity of institutes and countries, language, and keywords. The results show that among the 6,179 publications surveyed related to incinerators, more than 57% of them belong to the field of environment and the number of publications in 2020 was almost four times larger than the ones in 2000. “China” has played a key role in publishing among the countries, followed by Japan and the United States. “Waste Management” was the leading scientific journal in the field with a total of 579 articles related to incinerators, and the “Journal of Cleaner Production” had the most growth. The keywords “fly ash”, “heavy metals” and “bottom ash” have been the most frequently used keywords in 21 years. In recent years, words related to stabilization and solidification have been among the most widely used words, which shows the growth of this category of research. The significant growth of the words in the newfound fields of “life cycle assessment”, “sustainable development” and laboratory incineration-related research containing “XRD” and “SEM” can also be seen. The paper results provide a better comprehension of recent research and can also affect forthcoming research in this field.

Chloride ions cause the most common corrosion, so chloride ions can enter the concrete through contaminated aggregates and additive materials or infiltration from external sources, such as seawater. If the concrete is exposed to the aforementioned ions, there will be severe loss of durability and expansion of corrosion. In this case, there will be a tangible effect on the development process of resistance reducing the concrete's strength. Therefore, the extant study was conducted to compare the effect of fly ash and micro silica on the development, compressive strength, and electrical resistance of concretes exposed to chlorinated waters. The plans of this study included two types of ordinary concretes and concretes containing pozzolanic material. Concrete mixing plans in chloride medium were divided into 11 groups, which included 8 plans with substitution of micro silica and fly ash powders with different percentages in exchange for cement. The first group included no additive material as a cement substitute and included one plan as the base plan. Accordingly, 81 plans that each consisted of 4 samples were constructed and examined to test compressive strength in 7, 14, 28, and 42-days ages (N=324 plans). According to the results of laboratory samples in chloride medium, there was an increase in the development process of compressive strength, and electrical resistance of concrete while using concrete with standard aggregates reinforced with micro silica and fly ash by selecting the optimal mixing plan and lower cost. The above mentioned case was cost-effective for project implementation.

A significant number of engineering structures around the world are exposed to fire on a daily basis. The most important effect of fire on the structure is elevated temperatures, which may reach more than 1000 degrees Celsius and cause not only thermal stresses and deformations but also diminished mechanical properties of materials comprising the structure. Fire-related collapses have been observed in numerous structural fires. However, many reinforced concrete structures exposed to fire do not demonstrate notable apparent damage and survive despite having experienced elevated temperatures before the fire is put out. Estimating the residual strength of such structures is of critical importance when deciding whether such structures can be safely used after fire. Moreover, in many industrial applications, there is a need to concrete that can withstand repeated long-term cycles of elevated temperatures without diminished mechanical properties. The objective of this paper is to investigate the effects of silica fume and fly ash as two widely used supplementary cementitious materials on the residual strength of concrete exposed to elevated temperatures and evaluate while such materials can be of benefit in improving the strength retention in case of heat exposure. Using 19 mix designs, a series of 570 concrete cylinders was fabricated using different water to cement ratios (0.35, 0.5, and 0.65), silica fume replacement ratios (0, 10, and 15 percent), and fly ash replacement ratios (0, 10, 20, and 30 percent). The specimens were cured in water for 56 days, after which they were placed in a rate-controlled large-scale electrical furnace, and their residual compressive and tensile strengths were measured before heat, and after heat exposure for 2-, 12-, and 24-hour heating cycles with temperatures reaching 200, 400, and 600 degrees Celsius. To eliminate the risk of explosive spalling, all specimens were preheated at a temperature of 100 degrees for 24 hours before the main heating cycle. Results showed that the compressive and tensile strengths did not reduce noticeably after exposure to 200 degrees but demonstrated a significant drop after exposure to 400- and 600-degree cycles. In many cases, the residual compressive and tensile strengths of specimens were found to be smaller than those predicted in previous studies. The square root equation widely used in the literature was found to provide a reasonable lower-bound estimate of the residual splitting tensile strength of concrete from the residual compressive strength; however, a linear trend was identified to provide a more accurate estimate for the results of this study. Moreover, due to less scatter, the splitting tensile strength was found to be a better indicator of heat damage in the structure than the compressive strength. The use of silica fume did not result in a meaningful trend in the residual compressive strength but reduced the residual tensile strength of specimens. Fly ash, on the other hand, could increase the residual compressive strength of the specimens but reduces the residual tensile strength. The results suggest that generally, and with few exceptions, these two supplementary cementitious materials are not recommendable choices for improving the strength retention of concrete in case of heat exposure.

Pervious concrete is a special type of concrete comprised of cement, water, coarse aggregate, little or no sand which is sometimes mixed with the additives. The uniformly graded coarse aggregates in combination with low water content (i.e., water-to-cement ratios ranging from 0.25 to 0.35) were used to produce a concrete mixture whose pore content ranges from 11% to 35%. In this paper, performance of pervious concrete containing silica fume, zeolite, fly ash and granulated blast furnace slag (10% and 20% of cement weight) was investigated at the ages of 7 and 28 days. To this end, The compressive and tensile as well as water absorption tests were conducted on cubic and cylinderical specimens whise dimensions are 10 and 10×20 cm, respectively. In order to provide the required materials, the fine-grained gravel extracted from the Hamesh Bar mine Located in Semnan Province, was used. The results imply that compared to the other materials, application of silica fume and granulated blast furnace slag leave the greatest effects on the concrete performance in a way that averagely, the compressive and tensile strength were improved nearly 1.6 and 3 times in comparison with the control specimen (i.e. reference specimen). Moreover, the water absorption was reduced following addition of various pozzolanic materials excpet silica fume such that according to CEB-FIP Standard, they are classified as average and good concretes.