جستجوی مقالات مرتبط با کلیدواژه « sem » در نشریات گروه « عمران »

The proliferation of petrochemical industries and oil refineries in the western region of Hormozgan province has led to the placement of numerous concrete structures in close proximity to organic pollutants. This proximity has the potential to significantly influence the resistance parameters and durability of concrete. Therefore, the primary objective of this article is to investigate the short-term and long-term effects of exposure to organic pollutants from crude oil on the microstructural properties and strength of concrete. This research entailed the evaluation of approximately 360 concrete samples. These samples underwent a 12-month curing process in emulsions containing varying concentrations of crude oil (0.5%, 1%, 1.5%, 2.5%, 5%, 10%, 25%, 50%, and 100%). Compressive strength tests were conducted at intervals of 1, 3, 7, 28, 90, and 365 days, with concurrent analysis of changes in permeability coefficient. Microstructural examination was carried out using Scanning Electron Microscope (SEM) images, while structural analysis was performed using EDX. Additionally, X-ray Diffraction (XRD) tests were conducted to study the formation of hydration products in environments contaminated with crude oil and to analyze the crystalline structure of the materials. The results reveal that the resistance of concrete samples cured in crude oil emulsions depends on the concentration of the emulsion. Notably, the compressive strength of samples cured in 100% crude oil concentration emulsion decreased by approximately 41% after 365 days when compared to the control sample. Specifically, the compressive strength dropped from 41 MPa to 24 MPa, while the permeability coefficient increased from 3.2*10-7cm/h to 15.3*10-7cm/h.

Proximity of soil with pollution caused by landfills changes its pH.On the other hand, due to the heat generation potential of high-level waste, the used clay coating is exposed to different thermal regimes, which leads to changes in its physical, mechanical, and microstructural characteristics. Based on this, the aim of this article is to investigate the simultaneous effect of pH changes and thermal regimes in high-level waste disposal centers. In this study, the combined effect of pH and temperature on the behavior of marl soil was evaluated using unconfined compressive strength tests, weight loss and Atterberg limits, determination of carbonate amount by titration, X-ray diffraction (XRD) and SEM images. For this purpose, HCl and NaOH solutions have been used to change the pH. After the pH of the marl soil was fixed at 4, 6, 8.3, 11 and 13, the samples were dried in the oven, then exposed to the thermal levels of 25, 100, 300, 500, 700 and 900 degrees Celsius for 2 hours. One of the most important results of this research is the removal of carbonate in acidic conditions and prominent changes in the engineering characteristics of marl soil in the thermal range of 500 ℃ to 900 ℃. Palygorskite mineral is destroyed in stable acidic and alkaline environment at 700 ℃ with the occurrence of dihydroxylation. On the other hand, the removal of carbonate in an acidic environment has led to an increase in plasticity properties and a change in the classification of marl soil.

Industrial activities, particularly in petrochemical and refinery sectors, have introduced a wide range of organic pollutants into the environment, leading to the pollution of aggregate materials with crude oil or petroleum products. This study investigates the influence of aggregate materials contaminated with crude oil and diesel on the cement hydration process and concrete properties. Around 90 concrete samples with polluted aggregates were evaluated over a 6-month period. Compressive strength tests and water absorption percentage tests were conducted at different ages. Microstructural analysis through SEM, structural analysis via EDX, and XRD analysis for hydration product characterization were performed. Results showed a significant reduction in compressive strength (47% and 31%) for samples contaminated with crude oil and diesel, respectively, compared to the control. Water absorption and permeability increased in polluted samples. SEM, and XRD, results indicated increased ettringite production, decreased nanostructure C-S-H, reduced strength and durability, and increased water absorption and permeability in the concrete. This study highlights the detrimental effects of organic contaminants on concrete properties, emphasizing the need for pollution management in aggregate materials for sustainable construction practices.

One Of the effective parameters in the final strength and durability of self-compacting concrete is post-fabrication curing. External Curing with water Supply and moisture retaining coating are commonly used despite the limitation of these methods. Internal curing is one of the main issues in the implementation of reinforced concrete and bulk concrete structures with much less restrictions, especially in high performance concrete. The aim of this study was to investigate the effect of internal curing of self-compacting concrete using superabsorbent polymers on mechanical properties and durability of concrete. These polymers absorb some water and gradually release it during the hydration process. Using this method, the curing process is performed more efficiently, not only on the surface but also in the depth of concrete elements. Two types of superabsorbent polymer powders based on sodium and potassium with two different amounts have been used in this research. Concrete samples at 7 and 28 days of age were subjected to compressive strength, electrical resistance, water permeability, thaw-freeze cycle and microstructure tests including SEM, XRD and XRF. Compressive strength of samples with internal curing increased by 11.4% compared to control samples. In terms of durability parameters, the samples with internal curing show a reduction of more than 100% in water permeability and 16.7% improvement in electrical resistance. The result of microstructural experiments showed an improvement in evolution of the hydration process by at least 2.4% and at most 8.3% due to internal curing.

One of the crises facing humanity is damage to the environment. Inadequate management and attention to greenhouse gas emissions threaten human life on Earth. Given the CO2 emissions from cement production, finding a way to reduce cement consumption in concrete as the most widely used building material is a priority. In this paper, a natural pozzolan from Iran with suitable physical and chemical properties for replacing part of cement in concrete was introduced and its engineering properties were investigated. To strengthen its strength, steel and polypropylene fibers were used separately and hybrids with new mineral pozzolans were used in concrete. According to previous studies and optimizations, mineral pozzolan with a weight fraction of 15% cement in concrete was used. A comparison of the strength of local mineral pozzolan samples with other famous pozzolanic concretes showed that concrete with local pozzolan is more resistant than ordinary cement concrete. Also, concrete containing steel fibers and local pozzolan has higher compressive strength than other samples. Pozzolanic concrete samples containing a combination of steel fibers and polypropylene had better performance in flexural strength than other samples and the impact toughness of these samples was better than other samples. Investigations showed that the impact resistance of samples containing local mineral pozzolans was 3.75 and 8.33% higher than conventional cement concrete at 28 and 90 days, respectively. The test results generally indicate that the local mineral pozzolans studied can be a good option to replace part of the cement in concrete and while improving the engineering properties of concrete, not only greatly reduce cement consumption but also a valuable finding for environmental protection. Biology, construction, and production of green concrete.

The abundance of saline water at ground level and their progression to freshwater and onshore sources, landfill leachate chemicals, or industrial plant effluents into the soil are factors that can change the amount and type of soil salinity and, as a result, their geotechnical properties (Ouhadi et al, 2015). Also, due to the size of the large dams reservoirs and the impossibility of changing the axis of the dams due to different constraints, it is possible that after the filling, the dam lake water will come into contact with the salt formations and may cause risks such as changing the geotechnical behavior of the clay core, after exploiting embankment dams. Therefore, due to the presence of contaminants, which is sometimes unavoidable, an understanding of basic mechanisms in modifying the physical and engineering properties of soils under the influence of chemicals or chemical salts is essential (Sen et al, 2017). In general, the concentration of ions affects the intermolecular forces of the soil (ie double-layer repulsion and van der Waals attraction) and the structure of the materials (Weimin et al, 2014; Zhu et al, 2015). As a result, such changes in soil structure alter its engineering properties (Yan and Chang, 2015). According to the extensive studies on the influence of pore fluid on clay soils, however, a comprehensive study from the microstructural perspective with regard to permeability coefficient changes on clay soils has not been conducted. The purpose of this study was to investigate the permeability coefficients and engineering properties of clay soils with a special attitude to clay core in the presence of sodium chloride solution salt as a pore fluid from a microstructural perspective..

Marl soils with their complex behavior can be found in different parts of the world, such as Spain, the United States, Italy, Britain, France, Canada, and the Gulf states. In Iran, also, Marls can be located in abundance in the marginal zones of the East Azerbaijan Province, Persian Gulf, Hormozgan, and Qeshm Island. Marl soils' engineering behavior and durability in dry and wet conditions are entirely different and cause challenges in construction projects. Marl-like soils are widely observed in different parts of the world. The behavioral characteristics of marl typically depend on the distribution and size of the particles and their plastic properties. Under dry conditions, the deformation of marl soil is due to the breakdown of particles and creating a new structure. However, when this type of soil is exposed to moisture, the aggregate bond will degrade and cause swelling in the soil and, at the same time, a change in its hardness and strength on the other hand, many polluting industries are located on marl soils. Usually, the pollution caused by these industries changes the pH and creates acidic and alkaline conditions in marl soils. Therefore, this study aims to study the effect of initial pH on the durability of marl soils from a microstructural perspective.

In this regard, marl soils with different initial pHs were prepared by adding 1 M sodium alkali hydroxide (NaOH) and hydrochloric acid (HCl). Changes in geotechnical and geoenvironmental characteristics were investigated by macrostructural experiments (Atterberg Limits, permeability, and unconfined compressive strength, durability, and water absorption testing) as well as microstructural experiments (Laser diffraction particle size analysis (PSA), X-ray diffraction (XRD), X-ray fluorescence (XRF), carbonate percentage determination and scanning electron microscopy (SEM) images) and the effect of initial soil pH change on marl engineering behavior was investigated.

One of the most important results of the present paper is the durability and stability of marl soils with initial pH ≤4 against moisture. Based on the SEM images and XRF analysis results, the formation of magnesium chloride in the structure of palygorskite and sepiolite has caused the stability of marl soils with initial pH≤ 4. Also, the initial strength of marl soil does not affect the durability of indentation.

Due to the fact that stripping is one of the main failures of asphalt mixtures, special methods and tests have been proposed to evaluate this phenomenon by various regulations. These include AASHTO T283 and boiling water test. Among the methods mentioned, the results of AASHTO T283 are more accurate in investigating moisture sensitivity due to the numerical results, but qualitative tests such as boiling water can also be useful due to the ease of testing as well as visual acuity. Accordingly, in this study, the stripping of asphalt mixtures containing nano-stripping anti-stripping materials such as Zycotherm, Ivanic and nano-lime has been investigated. SEM images were also taken from these samples and converted to numbers using MATLAB software to examine the relationship between the results of AASHTO T283 and visual methods more carefully. In addition to stripping experiments, Marshall Resistance tests, modulus of resistance, and dynamic creep have also been used to investigate the properties of the mixtures. The results of this study show that the use of qualitative analysis such as the use of SEM images can determine the overall result of the stripping of asphalt mixtures.

Low compressive and tensile strength, high water absorption of the AAC leading to excessive absorption of the mortar’s water as well as low impact resistance, are the technical and executive drawbacks of using the ACC in the construction projects. To address these issues, in this paper, it has been attempted to replace cement with Nano-Graphene (NG) at ratios of 0.2, 0.4 and 0.8% and study mechanical properties of the modified NG-incorporated AAC, using the compressive and tensile strength tests (cylindrical specimens with diameter and height of 10 and 20cm, respectively), impact resistance and water absorption tests (cubic specimens with size of 15cm) as well as SEM and XRD tests. Based on the results, replacement of cement with NG, could enhance the compressive, tensile strength and impact resistance by 45, 81 and 130% compared to the control specimen. Moreover, it was observed that inclusion of the NG reduced the water absorption up to 61%. Finally, the SEM results revealed that incorporation of the NG strengthened the bonds between the compounds and the particles were downsized by 30%.

In this work, the effect of MgO on the treatment of a natural and contaminated clay soil with phenanthrene was studied through conducting various experimental tests including Atterberg limits, standard compaction, uniaxial compressive strength (UCS), and SEM tests. The contaminated soil was prepared artificially in the lab. Natural and contaminated soil were mixed with 5, 10, 20, and 30% of MgO as an agent. The results showed that phenanthrene changes the structure of the soil and causes a reduction in Atterberg limits, wopt, UCS, and E50 of the soil. The results also indicated that the UCS and E50 of mixture natural and contaminated soil with different percentages of MgO are increased and the amount of increasing of them is dependent on the percentage of MgO and curing time. SEM results also showed that the formation of carbonation products due to hydration of MgO is effective in increasing the strength of treated soil samples.

Economic concerns and environmental issues have led to increased use of recycled materials in cementitious mortars. In fact, to mitigate the adverse effects of cement, it can be partially replaced with recycled materials. In this paper, cement was partially replaced with iron, rubber, glass and eggshell powders (IP, RP, GP and EP) by 7, 14, 21 and 28% and then, compressive and tensile strength, water absorption and microstructure of the specimens were assessed. The strength tests, as well as microstructure analysis, were conducted at the age of 28-day and the water absorption was tested at the ages of 7, 28, 56 and 90 days. Based on the results, use of all powders by 14%, enhances the compressive strength up to 14%. Moreover, it was found that up to replacement ratio of 28%, the tensile strength is greater than that of the control specimen although, in the case of 7% admixtures, maximum tensile strength is achieved. In addition, water absorption of the specimens containing GP and EP up to 35% replacement ratio, is less than that of the other specimens, which was well observed in the SEM analyses.

Heat, both in transient and steady state, changes the physical and chemical properties of concrete. In addition, the use of slag with Portland cement is very effective on development of concrete microstructure. The main products of hydration process are cement paste and slag, which plays important role in increasing concrete strength, C-S-H and C-A-Fe-H microstructures. Based on this, this paper has focused on the concrete containing varying degrees of steel slag in order to get a deeper perception of the changing behavior of C-S-H and C-A-Fe-H due to being exposed to high temperature. In this regard, 150 cubic samples of concrete with zero, 5%, 10%, 15% and 20% replacement of steel slag to Portland cement were treated for 28 days in a moisture bath. Then, all samples were exposed for 1 hour to 25 to 800 ºC. The percentage of weight change, compressive strength and cracking behavior of samples were investigated. Furthermore, in order to evaluate the microstructural behavior of test samples in different temperatures, SEM photos and EDS were used. Based on the results, the behavior of concrete samples depends on the variations of C-S-H and C-A-Fe-H microstructures under high temperature. The compressive strength of samples containing 5 to 15% steel slag increased as compared to conventional concrete sample. Based on SEM photos, the reason for this increase is higher density of C-S-H and C-A-Fe-H microstructures and FeO(OH).

The concrete structures used in various applications including iron and aluminum foundries and hazardous waste disposal lose performance when subjected to heat. As aluminum silicate materials however, geopolymers behave in a much more stable manner than normal concrete when exposed to high temperatures. Calcium silicate hydrate (C-S-H) and calcium-aluminum-silicate-hydrate nanostructures, which are products of the geopolymerization process that strengthens geopolymer concrete, undergo many changes when exposed to heat. The study therefore investigates the effect of high temperatures on geopolymer concrete’s strength parameters from a microstructural perspective and according to nanostructural changes of C-S-H and C-A-S-H.

In this regard, about 300 samples were cured in the humidity bath for 1, 3, 7, 14, and 28 days. All samples were then put in of 25, and 900°C temperatures for 2 hours. Length and weight change percentages, compressive strength, and ultrasonic and cracking behavior tests were performed on all samples. Images from the (SEM) and the energy-dispersive X-ray (EDX) analysis were also used to evaluate the microstructural behavior of samples in various temperatures.

According to the results, sample weight and length changes and compressive strength depended on the behavioral nature of C-S-H and C-A-S-H nanostructures. Nanostructural analysis of C-A-S-H points to high temperatures reducing compressive strength and weight as well as causing more cracks. The compressive strength of the 28 samples in 900°C temperature also decreased from 604 kg/cm2 to 75 kg/cm2. The complete disintegration of the C-S-H and C-A-S-H nanostructures.

Temperature changes the engineering behavior of clay soils. Clay soils are used as a protective cover for burial of high-level wastes (HLWs), where the soil is exposed to medium to high temperature regimes. Marls are a type of sedimentary deposits consisting of clay minerals and calcium carbonate. These two components can substantially influence the behavior of marl soils from an engineering standpoint. The present study focuses on the engineering characteristics of marl soils under various temperature regimes with an emphasis on the microstructural changes in permeability coefficient, settlement, and compressive strength Therefore, after determining the geotechnical properties of the marl soil, its samples were exposed to temperatures from 25℃ to 900℃. The changes in marl soil properties were analyzed via mechanical tests (measuring permeability, consolidation, and uniaxial compressive strength), and microstructural tests (measuring pH and X-Ray diffraction), and scanning electron microscopy (SEM). The microstructural analysis of marl soil samples indicates that due to the deterioration and formation of new minerals as well as soil particle arrangement and microscopic texture; temperature regimes increase the permeability coefficient. However, at 700℃ the formation of cement compounds reduces permeability coefficient by an approximate factor of 50,000.

In the recent years the use of phosphate fertilizer has been increased. On the other hand, the use of phosphate fertilizer causes change in micro-structure and geotechnical properties of clayey soils. This may raise the risk for groundwater contamination. The main objective of this paper is to study the permeability and microstructural change of clayey soils after interaction with phosphate fertilizer. To achieve the above mentioned objective, series of geo-environmental engineering experiments was performed and the process of interaction of bentonite with phosphate fertilizer is studied. The evaluation of permeability variations, sedimentation tests, plasticity properties, soil pH variations and results of XRD and SEM experiments show that the presence of phosphate fertilizer changes the clay soil microstructure. Based on the results of this study phosphate fertilizer causes a reduction on the quantity of intensity of basal spacing of montmorillonite. Consequently the permeability might increases around1000 times at the presence of 10 percent phosphate fertilizer.

Concrete structures undergo behavior change and instability at elevated temperatures. In most cases, these behavioral variations and instability are related to the changes in C-S-H and (C-A-S-H nanostructures, which is an important part of the cement paste hydration process and plays a crucial role in determining the strength and mechanical properties of concrete.. Application of aluminum dross as a type of pozzolanic material to cementitious composites can improve concrete behavior at elevated temperatures. Consideringly, this article aims to investigate the effects of elevated temperatures on concrete containing different percentages of aluminum slag from the microstructural perspective. For this purpose, cubic samples containing different percentages of aluminum slag powder were prepared. The specimens were cured in a humidity bath for 28 days and then heated for 60 min at temperatures of 25 to 750 °C. To evaluate the mechanical properties, the percentage of weight and compressive strength changes of concrete samples were investigated. Scanning electron microscopy (SEM) images were also used to observe the microstructural properties of the samples at different temperatures. According to the results, in samples containing slag less than 10% due to its activation as well as the hydration process and the formation of C-A-S-H and C-A-H nanostructures, the portlandite phase was formed which has improved the compressive strength. On the other hand, the elevated temperature and the occurrence of the dehydroxylation process lead to water decomposition within the bonds of C-S-H nanostructure which subsequently results in the change in compressive strength behavior.

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.

In this paper, the eect of multi-walled carbon nanotubes on the properties of concrete was evaluated in the post-heat treated condition. Following this, a number of cylindrical specimens (10 x 20 cm) including multiwalled carbon nanotubes in dierent percentages of 0.5, 1 and 1.5% by weight of cement were cast. Later on, concrete specimens in the electric furnace were exposed to temperatures of 25, 100, 250,500 and 7000C and after cooling down, compressive and tensile strength tests were carried out on them. The results showed that by increasing multi-walled carbon nanotubes in concrete, compressive and tensile strengths of concrete were increased up to 138% and 88%, respectively. In addition, dissipation of energy and modulus of elasticity of concrete specimens were up to 2 times more than that of control concrete specimens. The SEM test results indicated that a strong bond between concrete particles exists at the room temperature and upper than that.

The type and percentage of clay minerals in the soil as well as the pore fluid properties of double layer are the important parameter that influence on the strength and behavioral properties of the clay Soils. In this regard, clay soils are highly sensitive to changes in environmental conditions and their behavior and strength parameters will be affected by many factors such as soil disturbance, water content, loading and drainage conditions, loading rate, temperature, etc. Therefore, one of the important parameter that affect the results and efficiency of lime stabilized clay soil samples and optimum lime content (OLC) is the type and percentage of clay minerals in the clay soils. In common, methods of lime stabilization, the most effective innate factor of clay minerals in the soil is not considered comprehensively. So it has been observed that the results of various test methods are completely in conflict with each other. The accuracy of the test results depends on the simultaneous consideration of chemical and mineralogical properties of the soil. In this research, to study the micro and macro-structure of stabilization process of lime stabilized clay soil samples, different combination of bentonite and kaolinite clay samples with different percentage of lime were studied experimentally. Studied samples during the time of 7 and 28 days were cured and uniaxial test were performed on them. Then Scanning Electronic Microscope (SEM) images were done to investigate the effect of the percentage and clay mineral type on the lime stabilized clay samples. The results of this research indicate that lime stabilization increase the UCS of soft clay soils about 2 to 10 times. Also, the interaction of soil-additive, the pozzolanic reaction progresses over the time, the optimum mixture of soil and lime as well as the stabilization efficiency, significantly dependent on the type and percentage of clay minerals in the soil.