جستجوی مقالات مرتبط با کلیدواژه « ریزساختار » 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.

The expansion of oil-dependent industries has caused a growing rate of oil extraction and increasing oil- and its derivatives-contaminated water and soil. The impacts and damages caused by oil pollution on human resources, water, and the environment have been very complicated. Oil and its derivates leakages into the soil can change its physical and mechanical properties. Oil-contaminated lands are thought of as the main challenge to the environment. Fuel and oil-reserve sites are common oil leak sites that may penetrate the soil. However, most Bandar Abbas refineries are situated on marl soil beds. Marl is composed of clay, and calcium carbonates of varying degrees of 20-65%, which, having been hardened, are converted into marl soil, thus becoming physically stiff and impermeable. Marl soil has high stiffness and shear strength under dry conditions, as these properties experience lower rates under wet conditions. The volatile behavior of the marl soil in water and organic pollutants makes it problematic when used in geotechnical projects. Thus, the present research takes a microstructural approach to investigate the geotechnical properties and environmental geotechnics of the marl soil contaminated with varying degrees of crude oil.

Using different additives in order to increase the durability and mechanical resistance of concrete is one of the new approaches in concrete technology. In recent years, graphene has attracted attention due to its unique properties. However, the phenomenon of graphene accumulation in cement mixtures and high production costs have challenged its application in the concrete industry. For this purpose, it is necessary to use a graphene dispersing agent in the cement structure. This research used surfactants to spread graphene sheets in cement structures. This method has resulted in producing a cheap solution compared to typical methods, which can be used as an additive. The results of this research showed that the surfactant solution can increase mechanical properties at early ages. Detailed microstructure examination by FESEM analysis showed that the compounds containing 0.56 g/l of surfactant have a denser structure than the control sample, and also the compressive strength of the cement paste increased by 28.66% compared to the control sample at the age of 7 days. TGA and XRD analyses show that graphene played an effective role in nucleation and produced CH and C-S-H products in the cement structure. This solution can be used as a new additive in many construction projects.

The high cost and the accumulation phenomenon of graphene in the cement matrix are the main obstacles to its use in the concrete industry. In this study, both of the above challenges were solved by producing graphene through the combination of graphite and polycarboxylate ether-based superplasticizer by exfoliation method. In this regard, mechanical properties and permeability, as well as comprehensive microstructural studies, were investigated for the feasibility of using graphene produced based on superplasticizer in cement composites. The SEM and TEM analyses revealed that the multilayer graphene sheets produced with a polycarboxylate ether-based superplasticizer are of high quality and have few defects. According to the results of this research, the sample containing graphene based on the combination of 5 grams per liter of graphite and superplasticizer at the rate of 0.1% of the cement used, the compressive and bending strength was increased by 82.05% and 33.56%, respectively, compared to the control sample at the age of 3 days. On the other hand, the porosity in the graphene-containing mixture is reduced by 50% compared to the control sample. Besides, the results demonstrated that graphene has an effective influence on capillarity absorption due to increased twisting and modification of cement matrix pores. Also, the XRD results showed that using solution containing graphene led to the consumption of C3S and C2S at the age of 3 days and more CH, CSH phases were formed in the cement structure. These results together with TGA and FESEM characterization results showed that the effect of graphene nucleation is more evident at early ages.

In the present paper, results of a study on the use of Bacillus pasteurii to reduce wind and water erosion in alkaline silty soils are presented (Kim et al., 2014). The treated soil specimens were prepared in different periods and different concentrations and amounts of bacteria on different surfaces and were exposed to a wind tunnel constructed and calibrated for the present study and their surface erosion was measured. For further analysis of the samples, melting and freezing tests, cone penetration, electrical conductivity, pH and SEM, XRD, and EDS analyzes were also performed on the treated and untreated specimens. The results of this study showed that the use of MICP as a surface crust is an effective and environmentally friendly process to control dust caused by wind erosion in the Meighan Wetland. 

2.1. Experimental study The treated soil specimens were prepared in different periods and different concentrations and amounts of bacteria on different surfaces and were exposed to a wind tunnel constructed and calibrated for the present study and their surface erosion was measured. For further analysis of the samples, water erosion test (Gao et al., 2020), freeze and thawing test (Qi et al., 2006), cone penetration, electrical conductivity, pH and SEM, XRD, and EDS analyzes were also performed on the treated and untreated specimens. To compare the stabilization method with bacteria and conventional stabilizers, surface stabilized samples were prepared by spray method (Ivanov & Stabnikov, 2016) of cement and lime and exposed to wind tunnels and surface erosion was measured. 

3.1. Effect of bacteria on reducing wind erosion The results of this study showed that the use of MICP as a surface crust is an effective and environmentally friendly process to control dust caused by wind erosion in the Meighan Wetland. With this method, the surface resistance of 28-day-old samples can be increased up to 95% and the rate of wind erosion can be reduced to 89.8%. 3.2. Effect of bacteria on water erosion The formation of biological crust in a scouring cycle by 98.59% has reduced the surface scouring, which can indicate the stability of this crust against water erosion in the study area. 3.3. Effect of bacteria on freeze and thawing cycles Freeze and thawing cycles do not cause surface crust loss and increase wind erosion in bacterial-modified soil samples. 

The use of bacteria to improve the soil and create a biological crust by spraying has shown a significant effect on the rate of erosion of samples exposed to wind and this method can be used in fine-grained soils of Meighan area and soils with similar conditions to prevent surface erosion. This method increases the surface resistance of the soil against melting and freezing, scouring, and penetration of the cone. Soil bacterial stabilization in the study area is more suitable than cement and lime stabilizers in terms of reducing erosion and reducing pollution.

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.

Recently, the excellent performance of graphene-based materials has attracted civil engineering researchers in its application in cementitious mixtures. However, the application of graphene is hindered by its high cost and the agglomeration phenomenon in cementitious mixtures. In this regard, it is necessary to choose a dispersing agent with the ability to effectively separate graphene layers as well as improve mechanical properties and impermeability of cementitious mixtures. In this study, the effect of surfactant as a graphene separating agent from graphite on the mechanical properties and microstructure of cement paste containing water-dispersed graphene was investigated. The microstructure of the produced graphene reveals that the process of manufacturing graphene by peeling the surfactant leads to fragmentation and rupture of graphite. After 7 days of curing, the compressive strength of cement paste containing a mixture of 5 g / l graphite and 0.56 g / l surfactant increased by 28.66% compared to the control mixture. The crystallography and thermogravimetric results showed that graphene accelerates the formation of CH and C-S-H due to its nucleating effect in the cement matrix. Furthermore, the incorporation of graphene and surfactant into cement paste reduced the voids by 18.6%. This study shows that graphene dispersed in water produced by 0.56 g / l surfactant has the potential to be used as a novel additive in cement-based mixtures.

Global oil production exceeds two million tons per year, contaminating the soil around oil facilities. Consequently, the soil’s geotechnical properties are modified. Since Iran is an oil-rich country with numerous refineries and oil extraction facilities, it is crucial to study the mechanical behavior of contaminated clay soils. This study examines the stabilization of oil-contaminated clay (CH) soils in the Masjedsoleyman contaminated clay soils by adding lime. To this end, laboratory tests were conducted to determine the chemical properties, Atterberg limits, standard compaction, and unconfined compressive strength (UCS) of the soil and conduct a microstructural analysis. As a result, 144 contaminated soil samples (76 mm in height and 38 mm in diameter) containing 0, 4, 7, and 10% oil were synthesized by adding 0, 3, 6, and 9% lime. The samples were subjected to unconfined strength tests and microstructural analyses after 1, 14, and 28 curing days. The results of the standard compaction test revealed that the optimum moisture content (OMC) of samples with greater oil contamination decreased by 44.4%, while their maximum dry density (MDD) increased. The unconfined compressive tests indicated that adding 6% lime resulted in the highest unconfined strength (416.6%) compared to other cases. As curing time increased for lime-stabilized samples, the unconfined compressive strength of the samples improved due to the cementation of lime particles with clay soil. The microstructural analysis results demonstrated that the 7% oil-contaminated clay soil had a laminar and discontinuous structure and numerous porous spaces between soil particles. However, longer curing times reduced the porosity and cavities in samples stabilized with different lime percentages. This confirmed the high cation exchange capacity of lime and the presence of pozzolanic reactions, which increased the unconfined compressive strength of the samples. Overall, this study demonstrates the efficacy of adding lime in stabilizing the contaminated clay and the potential use of stabilized contaminated clay as an alternative construction material and practice in the environmental protection of sites.

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.

One of the main objectives of infrastructure managers is the timely and rapid operation of airports and freeways. A goal that is challenging when utilizing concrete pavements, due to their different behavior during the initial stages of implementation. This research aims to improve the mechanical characteristics of concrete pavements and increase their durability against the combined effects of the freeze-thaw cycle and surface desalination, especially during early ages. This paper examines the use of cementitious material in combination with hydrated lime, metakaolin, and zeolite to remove the hurdles to the early operability of concrete pavements. To this end, micro-structural studies have been performed using XRD and SEM analysis and comparisons in two states of water processing and exposure to freeze-thaw cycle. During which replacing cement with zeolite and metakaolin in calcareous concrete resulted in reduced porosity and homogeneous density with the formation of CSH in the concrete structure.  Accordingly, improvements in the mechanical properties and durability of concrete pavements against the combined effects of freeze-thaw cycle and surface desalination were studied and analyzed in four mixtures of Control Concrete (CC), 15% lime (CL), 15% lime, and 15% Metakaolin (CLM) and 15% lime and 15% Zeolite (CLZ). It was noted that at age of 7 days the CLM, CL, and CLZ samples showed an increase of 20%, 32%, and 48% respectively compared to the CC sample. This increase continued throughout the study. During the freeze-thaw test and after 55 cycles the CLM and CLZ samples always exhibited lower degradation and showed a weight loss of 48.7% and 75.2% less than the CC sample. In addition, as per the results of the capillary absorption test the CLM and CLZ mixtures had at lower ages had less permeability than the CC mixture and this behavior continued with better performance at older ages.    Also, the results of flexural strength indicate the positive effect of additives in all samples over time, and at 28 days, the CL, CLM, and CLZ samples increased flexural strength by 39%, 42%, and 57% respectively in comparison to the CC sample. The positive effect of hydrated lime due to its high paste property in increasing the flexural strength of mixtures containing metakaolin and zeolite is quite evident and has increased the mechanical properties at all ages of the samples, but has weakened the durability performance compared to the control sample. This issue has been addressed in composite mixtures containing lime with metakaolin or zeolite, and the results of durability tests indicate a significant improvement in both pozzolans, especially in the zeolite. It can therefore be concluded that with improving mechanical characteristics and durability of CLM and CLZ mixtures, utilizing metakaolin and zeolite in concrete containing hydrated lime is a suitable solution to eliminate the challenges of early usage in concrete pavements.

Using fibers to reduce cracks and increase the joint spacing of concrete slabs has become popular in the concrete pavements of airports and freeways recently. However, their durability behavior against acid rain has been less studied. The purpose of this paper is to investigate the mechanical performance and durability of concrete reinforced with polyolefin and polypropylene fibers containing 15% of pozzolanic materials (pumice or metakaolin) instead of Portland type II cement. In this regard, compressive and flexural strength were measured to investigate the mechanical behavior of the studied mixtures at different ages. On the other hand, chemical resistance against acid rain simulated was investigated through the visual examination and weight loss, and also microstructural analysis was performed by SEM analysis and CT scan testing. Based on these results, the addition of both of these fibers in concrete reduces the compressive strength of concretes compared to the similar content in the control concrete. On the contrary, fibers increased the flexural strength, which became much more significant with the addition of pozzolanic materials. However, ordinary and fibrous concrete containing pozzolanic materials showed a weak performance against acid rain. Based on the results of CT scan and SEM analysis, concretes containing pozzolanic materials have a porous structure. Besides, the ratio of calcium to silicon in them is much lower than the control concrete due to decalcification reactions caused by acid attacks.

In the past, fiber reinforced concretes (FRC) was used mainly in pavements and industrial floors however, FRC has a number of other uses as well, with recent uses including bridges, hydraulic structures, tunnels, pipes, canal linings and safety vaults. On the other hand, the resistance of FRC against to penetration of chloride ions, especially bonded chloride, has received less attention. In addition, the prior literature's results on chloride ions bound in different concretes have always been varied. This study analyses the mechanical characteristics of fibrous and normal concretes (NC) containing two pozzolans of metakaolin and pumice using microstructural investigation. Also, the chloride isothermal under marine environment was studied by simulating the immersion and tidal conditions. This study can be beneficial for use in different applications such as paving and bridges which are under the influence of chloride ion penetration. The first goal of this study is to increase the flexural strength of the pavement layer in order to reduce its thickness which can be economical, and the second goal is to study the durability performance of NC and FRC containing of cementitious material (pumice and metakaolin) with respect to the aggressive medium that is a determining factor in the lifetime of concrete structures. It is generally acknowledged that blocking the paths of chloride penetration by densifying the microstructures of the concrete can be a fundamental solution using pozzolanic reaction produced by pozzolans to enhance the durability of concrete. In the last years, metakaolin and pumice has been introduced as a highly active and effective pozzolan for the partial replacement of cement in concrete. Metakaolin and pumice consumes the Ca(OH)2 that is produced from the cement hydration process rapidly and effectively and in addition to CSH, phases like C2ASH8 (stratlingite), C4AH13 and C3ASH6 (hydrogarnet) are produced. These pozzolanic products enhance the structural properties of concrete and also contribute to total pore refinement. In this study, six concrete mixtures with a control mixture without any addition are prepared and tested in hardened states. Afterwards, the resistance to chloride penetration both in immersion and tidal conditions is investigated. Accordingly, first, the compressive strength and flexural strength test were performed on hardened states to assess the mechanical resistance of the different prepared mixtures at early ages and up to 365 days. Then, the microstructure study of six prepared mixtures were investigated by using Scanning Electron Microscope (SEM), EDX spectrum and CT scan test. Finally, the chloride penetration resistance of the different concrete mixtures was evaluated by measuring water-soluble chloride profile, bonding and total chloride in immersion and tidal conditions. In both the immersion and the tidal conditions, durability results show that metakaolin and pumice have a significant effect on the increasing chloride penetration resistance. This impact was far more apparent in pumice-containing samples. However, the concretes containing pozzolans have a porous structure, according to computed tomography scan (CT scan) analysis and microstructure results in this study, and the Ca / Si ratio is considerably lowered owing to decalcification. Also, the results showed that despite the structural porosity in concretes containing pozzolans, factors such as Ca / Si ratio and pore solution concentration play a very important role in their durability against chloride ion in the simulated marine environment.

Salt scaling of concrete pavements is known as a serious problem in cold regions. In the present study the effect of water-binder (W/B) ratio, silica fume and air entraining on the salt scaling resistance, compressive strength and electrical resistance were investigated. Microstructure of the concretes was assessed by mercury intrusion porosimetry and scanning electron microscope. Water-binder ratios were 0.35, 0.40 and 0.45. Silica fume was used, by 8% weight of cement, in the predetermined mixtures. The results showed that the best salt scaling resistance was correspondent to the air entrained silica fume specimens. By reducing the water-binder ratio, the amount of surface scaling was decreased. The MIP results declared that silica fume refined the microstructure and also decreased the total porosity and critical pore radius compared with those for the reference specimens. Furthermore, the MIP results of the silica fume specimens declared that the pores smaller than 10 nano were increased, due to the effective pozzolanic reaction. The scanning electron microscope images showed that the concrete containing silica fume had a denser gel compared with those for the reference ones. Introducing silica fume into the specimens had remarkable effect on the later age electrical resistance of the concrete. It was concluded that the highest electrical resistance belonged to the durable specimens. The results of the present study clarify how the micro structure may influence the salt scaling resistance of concrete pavement, this achievement will surely reduce the cost of rehabilitation of concrete pavements in the cold regions.

Ultra-high performance concrete (UHPC) is a new type of composite materials that can develop a compressive strength up to 200  MPa and high tensile strength around 10 MPa, given the low water-to-binder ratio (W/B). The fracture energy of UHPC can vary from 8560 to 40,000 J/m2, which is approximately 220 times greater than that of conventional mortar. Due to its superior properties, Ultra-high performance concrete has received great attention among researchers recently. Very high compressive strength leads to a significant weight loss of the structure and makes it possible to build slender structural elements. In this paper, the ultra-high performance fiber reinforced concrete specimens exposed to two different curing regimes, a 23°C limewater tank, and a 70°C hot-water tank. Then, the compressive and flexural strength and the electrical behavior of specimens were evaluated. Mechanical strength at the age of 28 days and six months were measured, in order to in conjunction with durability-related properties offer an overall view of UHPFRC characteristics. Results showed that the PVA fiber affected the mechanical strengths by preventing the propagation of cracks and by increasing the total porosity of the matrix. Moreover, its influence on resistivity was highly dependent on the concentration of silica fume particles.

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.

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.

Today, the use of powdered materials and chemical additives to improve the mechanical, durability, and rheological properties of a variety of concretes is rapidly expanding. The use of naphthalene, polycarboxylate and melamine-based lubricating and thickening agents is one of the effective strategies to control the instability of concrete. One of the foundations of the new lubricant is the xanthan gum biopolymer. The substance synthesized from the vegetable gum has a high viscosity that is widely used in various industries. After observing the lubricating type, high consistency, and appropriate price of this material, we decided to observe its effect on concrete. In this research, 16 mixing schemes containing Pozzolan Microsilica with 10 wt% cement and different grades were investigated. A 0.25 wt% lubricant and xanthan gum additive were added to the concrete cube samples. The results show that the xanthan gum additive reduces slump and separation and increases compressive strength, due to the increased viscosity. A bonding between concrete materials and decreased pores and porosity would reduce the capillary coefficient and increase electrical resistance of the concrete. Microstructural studies of concrete, including scanning electron microscopy (SEM) experiments, showed that the permeability is reduced and structural bonds of concrete adhesive are strengthened, due to the use of xanthan gum, and as a result, the samples containing xanthan gum have less porosity than samples lacking xanthan gum.

Stabilization/Solidification (S/S) is an attractive technology which helps to reduce the toxicity and facilitate the disposal of sediments containing heavy metals, industrial wastes, and contaminated soils. The efficiency of the S/S technology can be enhanced by the use of clay nanoparticles. The S/S process incorporating Montmorillonite nanoparticles can be employed to prevent the dissemination of heavy metals effectively. Although many studies have addressed the stabilization of contaminant by the use of cement, few have discussed the microstructural interactions between montmorillonite nanoparticles, heavy-metal contaminants, and cement in different time intervals. In addition, there are not enough researches on the impact of montmorillonite nanoparticles in the efficiency of solidification process. Therefore, this study aims to investigate the interactions between montmorillonite nanoparticles, heavy metals, and cement in different time intervals from microstructural point of view and to determine the impact of clay nanoparticles on toxicity leaching from solidified/stabilized contaminants. To achieve the above mentioned objectives, different concentrations of heavy metal (zinc) and different percentages of Portland cement were added to nano-montmorillonite. The contaminant retention mechanism was then experimentally analyzed through monitoring the changes in pH, evaluating microstructural changes (using X-Ray Diffraction), and Toxicity Characteristic Leaching Procedure (TCLP) measurement. The results indicate the role of clay nanoparticles in retaining the heavy-metal contaminant and the lack of linear relation between the quantity of cement content of the specimen and the contaminant retention efficiency.

In this study, the effects of two types of by-product materials resulting from the manufacture of iron including GGBS and BOFS on the hydro-mechanical performance of a lime-stabilized clayey soil were investigated. The results indicate that the addition of slag particularly of GGBS has a less impact on the soil engineering properties as compared to lime treatment. It was found that the lime-slag (LAS) combination decreases the water retention potential, controls the soil settlement and causes a considerable increase in the mechanical capacity. The composite clay sample containing LAS exhibits a better performance than that of lime-treated soil particularly at short time of curing.

Adsorption has been proved to be the best process of water treatment because of its significant advantages. Clays and their minerals are abundant and cheap material successfully used for decades as an adsorbent for removing toxic heavy metals from aqueous solutions (Kashif Uddin., 2017). Environmental pollutants and their toxicity cause a major problem worldwide. New pollutants keep emerging and pose severe health and scientific challenges. Water pollution is one of the biggest environmental issue causing serious problems to living beings. The removal of various toxic substances from water and wastewater has been a core interest of many scientists and researchers around the globe over the past decades. Dyeing, battery, printing, mining, metallurgical engineering, electroplating, pigment, PVC stabilizers, nuclear power operations, electric appliances manufacturing, semiconductor, cosmetics, and so on belong to industries that generate various types of pollutants in wastewater effluent [Ali et al., 2007; Gupta et al., 2009]. By construction of engineered landfills, we can prevent the groundwater pollution. In industrialized countries, the use of compacted sand-bentonite mixture (SEB) alternatives to clay Liners due to low permeability and lack of vulnerability caused shrinkage cracks (Alston et al., 1997).