جستجوی مقالات مرتبط با کلیدواژه « nano-clay » در نشریات گروه « عمران »

The construction of different paths on fine-grained soil beds is often inevitable and, it is necessary to select and design suitable methods of soil improvement. One of these methods is shallow soil mixing with different additives such as lime and Nano-clay. These particles can improve the physical and chemical properties of the soil as much as possible and make changes on a microscopic scale. In this paper, the stabilization of fine-grained soil beds and their strength properties due to the addition of Nano-clay and lime mixing are investigated. For this purpose, the series of unrestricted compressive strength tests, Atterberg limits, density, PH and microstructural tests including X-ray diffraction (XRD) and scanning electron microscope (SEM) have been performed on the mixture of soil with Nano-clay and lime with different adding percentages at 7, 14 and 28-day curing period. The obtained results indicate that the optimum soil properties were obtained by adding 3% lime and 3% Nano-clay during the 28-day curing period and according to the results of microstructural analysis, it was found that soil resistance increased due to the formation of calcium silicate hydrated gel with reducing the voids and increasing the contacts between soil particles.

Some factors such as soil mass settlement, earthquake activities, and hydraulic failure causing tensile forces in the earth's structures and, consequently, cracks creatoin and development of water leakage from cracks. In this study, in order to reduce possible damage caused by cracking and its extension to the erosion of internal structures, the effects of nano-clay on the self-healing properties of clayey soils have been investigated. In this study, the effect of nano-clay additive, pressure and time elapsed on crack restoration in clay was evaluated. In order to perform experiments, two types of cracks with thicknesses of 0.5 and 1 mm with a depth of 50 mm created in the samples and the montmorillonite nano-clay was used as an additive. Twelve tests with different percentage of nano-clay, without pressure and at pressures of 50 to 500 kPa in two steps after the cracking (first day) and 24 hours after the creation of crack (second day) was performed for samples with a thickness of 0.5 and 1 mm. The flow rate is measured in all tests and was the basis for judging the impact of each factor. The results show that when the cracked sample is made with one millimeter, under non-pressure conditions, in about 60 minutes, approximately 500 ml of water passes through the crack. However, when the sample contains 2 and 5% nano-clay, the amount of water passing through the crack within 60 minutes, would be 40 and 5 ml, respectively.

If the geometric design of a road is in a way that it has to pass through areas with weak and problematic soil layers or borrow materials are located far away from project sites, stabilization of pavement improvement operations should be performed to construct pavement layers, especially its subgrade level. Generally, stabilization method of soils is divided into chemical and mechanical procedures, and simultaneous geosynthetic materials can be used. Nowadays, nano materials are proposed in order to improve geotechnical properties of soils in terms of bearing capacity. The present study was aimed to investigate the capability of nanoclay particles and the application of polypropylene fibers in the clayey soil of Eslami Island near Lake Urmia to construct layers in pavement. In the first step, nanoclay particles with 5 and 10 percentages were mixed with soil, and then the curing process was carried out in 7, 14, and 28 days. In the second step, polypropylene fibers were added to the clayey soil in 0.4, 0.8, and 1.6 percentages. Finally, the optimal values of polypropylene fibers and nanoclay particles simultaneously mixed with soil specimens and, similar to the first step, curing operations were carried out. To this end, laboratory tests containing compaction, uniaxial strength, direct shear, and California Bearing Ratio (CBR) in dry and saturate conditions were executed according to ASTM standards. Furthermore, swelling values in the improved specimens at saturate positions were estimated. The findings revealed that optimum combination was obtained at 5% of nanoclay blended with 0.8% of polypropylene fibers in specimens undergoing a 28-day curing process since this condition was found to upgrade the stabilization of soil specimens in terms of compressibility, bearing capacity, strength, and reduction of swelling potential.

Dense clay layers are one of the most common impermeable layers in most geotechnical structures such as earth dams and urban and radioactive waste landfills. Due to the specific geotechnical properties, these layers are damaged by cracking over their lifetime. These cracks increase the permeability of the layer and reduce its efficiency. Considering the necessity of knowledge and understanding of factors affecting the stability of geotechnical structures made with these layers, in this research, it has been tried to use a self-resilient property of clay soils to improve soil yield in different conditions. In the present study, it has been shown by numerous experiments that increasing the plasticity index's clay soils can increase the crack restoration rate. The results show that the addition of nanomorillonite to soil improves the self-healing process of the cracks; the time elapses the effect of this increase in the process of repairing cracks created in the specimens. The discharge rate of the samples is measured relative to the time elapsed during the self-repair and are examined according to the graphs. The experiments showed that the percentage of nano-clay montmorillonite is unaffected and reduces the amount of flow in the specimens, which is the self-restorative symptom of cracking by the addition of nano-clay. The total amount of discharge outflow in nano-clay samples from the non-additive samples was much lower, and nano-clay can be used as repairing cracks in clay soils at a depth of 5 cm.

Collapse refers to sudden decrease in the soil volume upon wetting which is attributed to loss in the strength of the inter-particle bonds. Collapsible soils can be founded at vast areas around the word and subtropical areas of Iran. Collapse characteristics contribute to various problems to infrastructures that are constructed on loess soils. For this reason, collapse behavior of loess soils has been subject of interest. In this study, stabilization of Semnan loess which is composed of fine sand and silt bonded by weak clay bonds has been investigated. The loess was mixed with Portland cement in the order of 0.5%, 1%, and 2.5% for and with nano-clay in order of 0.05%, 0.1%, and 0.25%. The specimens were prepared to achieve dry density of 14 kN/m3 and water content of 5%. Oedeometer tests were performed to determine the collapse potential according to ASTM D5333 after 7, 14, and 28 days. Results showed that both Portland cement and nano-clay can reduce collapse potential. Improvement performance was significantly dependent on the binder content and curing time. The best improvement performance was observed at low nano-clay content and it was reduced by increasing nano-clay content. Unlike the cement stabilization, treatment process with nano-clay was relatively fast that terminated when soil moisture content was evaporated. In addition, in this study micromechanical soil behaviors were investigated by scanning electron microscopy (SEM) image of the treated and untreated specimens.

Permanent deformation or rutting is one of the most important distress modes that affect the life of flexible pavements. This type of distress is often observed on the roads that are situated in tropical regions. The properties of the constituent materials play a significant role in the construction properties of the pavement. The use of porous gradation and high binder grade for proper binding in the structure of mixes is known as the methods for improving the properties of mixtures. One of the mixtures made on this basis is Stone Matrix Asphalt mixtures (SMA). These mixes are a type of hot mixed with the coarse skeleton and the high binder and filler, which plays a key role, with the importance of the type and the tar properties used, as the binder of rock particles and the factor that has to endure the stress of the shear stress between aggregates.  On the other hand, due to the high percent of binder and the prevention of binder, the use of additives such as fibers or polymer materials is inevitable. The use of polymeric additives in addition to improving the binder properties, with the increase binder viscosity, also decreases binder drain down. Also, one of the recently applied additives to enhance the binder properties is Nano - clay. The aim of this study is to evaluate the effects of Nano clay as the main additive to binder to improve the binder properties alongside the SBS and fibers, in order to increase the loading resistance of asphalt and to correct its technical properties against the rutting. So, control asphalt mixtures containing of 60-70 binders with 0/4% fiber blended into mixture or modified bitumen mixed by 5 %, along with a montmorillonite additive of 1 %, 2 %, 3 % and 4 % for both pure and polymer bitumen. In this study, the Marshall test, dynamic creep tests and delamination were performed on different samples. The results of these experiments show improved performance of samples containing Nano - nanoparticles with an addition of Nano clay to 3%, which is best achieved performance in polymer modified mixtures.

Durability of reinforced concrete (RC) structures has been increased using different additives under corrosive environments in the recent years. In the present study, 0, 0.5, 1 and 1.5 percentage of nano clay particles were substituted as cement. Therefore, 24 RC beams divided in three groups after 28 days of curing. The first group consists of 8 beams which were tested after 28 days of moist curing. The second and the third groups consist of 8 beams in each group, which were tested after 6 months exposure in chloride solution and wetting and drying cycles, where the third group beams were additionally under service loads. Also, compressive strength and water absorption of the mixtures were evaluated at different ages. Results showed that the addition of nano-clay particles considerably reduces the compressive strength of concretes which consequently decreases the flexural capacity of the beams. In addition, nano-clay particles reduce the half-hour water absorption and increase 24-hour water absorption. Also, results showed that the wetting and drying cycles of chloride solution for 6 months reduces the flexural capacity of the beams, but service loads reduces the negative effect of the exposure. Also, the beams containing nano-clay particles showed better performance under chloride attack.

Stabilization/solidification (S/S) has emerged as a cost-effective method for treating a variety of wastes, particularly heavy metal (HM) contaminated soils. Among the many available fixing agents, Portland cement (PC) has been used extensively for the remediation of contaminated sites. However, there are significant environmental and technical impacts associated with PC application. Thus, the present research was conducted to address the efficacy of cement and nano-clay mixture in enhancing the S/S process. In so doing, artificially contaminated soils were first prepared by mixing kaolinite with zinc (Zn) at levels of 0 to 2%. Afterward, tow type of nano-clay (Na-Montmorillonite and Na-Cloisite), cement and cement/nano-clay (CNC) were separately added to the sample, and then, a set of macro and micro level experiments including batch equilibrium, pH, toxicity characteristic leaching procedure (TCLP), unconfined compression strength (UCS), X-ray diffraction (XRD) and energy dispersive X-ray (EDX) analyses were carried out at various curing periods (1, 7 and 28 days) to assess the effectiveness of the additives. The results obtained show that the addition of nano-clay can increase the HM retention capability of soil; however, this may be partly lost when the treated soil are subjected to acidic TCLP solution. In addition, with increasing the HM content, due to the decrease in buffering capacity of system and the restructuring of the clay particles, the soil remediation potential at presence of nano-clay is decreased considerably. It was found that the application of sole cement may significantly enhance the HM retention capacity of soil. But in this case, the physicochemical reactions of Zn ions with cement could hinder and/or reduce the generation of hydration products phases such as calcium silicate hydrate (CSH) and calcium aluminate hydrate (CAH), resulting in the degradation of cementation structure-bonding of S/S matrix, as clearly confirmed by the formation of calcium zincate and the diminution in the cementitios compounds peak intensity in the XRD patterns of cement-treated soils. Therefore, the leaching characteristics and the mechanical properties of the S/S material with sole cement are adversely affected by increasing the amount of HM ions. As a result, a large quantity of cement (20 wt% per one percent of HM) and a long time of curing (≈ 28 days) should be employed to meet the full needs of HM immobilization in contaminated soil and give the EPA-acceptable UCS value (≥ 0.35 MPa). The TCLP and XRD test results indicate that the cement/nano-clay combination can expedite the S/S process and alleviate the deleterious influences of metal ions and acidic attack on the stabilized sample. The EDX analyses also support the increase in the development of hydration reactions and the formation of cementing materials in the presence of CNC, providing the enhancement of binding capacity that will lead to the greater strength (up to 50%) in comparison to cement application. Hence, the CNC binary system is more efficient in modifying the contaminated soil with a lower amount of binder (to about 40%) and shorter curing ages (by nearly 4 times) than that of the sole cement. Overall, it is concluded that the cement/nano-clay mixture can be utilized as an effective S/S amendment and CNC content of 15 wt% per 1% of HM can successfully remediate the contaminated soil after 7 days of curing.

Dispersive soils are vulnerable to erosion by water. In soil layers where clays are saturated with sodium ions soil can disintegrate into fine particles and wash away. In such soils, the clay particles lose adhesion in the presence of water and consequently, soil’s colloidal particles easily move away from each other. In order to deal with the adverse effects of this kind of soils, three major options are available: avoiding construction on such soils, replacing dispersive soil and using various additives to improve and stabilize the soil. In most cases, application of the first two methods is infeasible and cost effective but adding various additives is beneficial to overcome the encountered problems. In this study, the effect of nanoclays on dispersive soils of the Minab wastewater treatment plant has been investigated by using special tests for the determination of the soil dispersion. The results of the experiments indicated that, adding a low percent of nanoclays to the soil can improve the level of dispersion a little but adding excessive amounts of nanoclay increases the dispersivity potential.

Due to high expenditures, maintenance of road networks has always been one of the main concerns of pavement engineers. Effective use of Nano materials in industry, was a good reason for authors to study the capability of these kinds of materials in order to increase the service life of asphalt pavements.Considering the fact that applying Nano clay in polymers, modifies polymers characteristics e.g. stiffness, tensile strength, thermal stability, increasing flash point and resistance against moisture and vapor, also as bitumen is a thermoplastic material, the bitumen was modified by adding 20% nano clay and tested for increasing the fatigue life of asphalt pavements. The effect of nano clay additive on performance of flexible pavements is investigated through the repeated constant stress, in indirect tensile test for the core samples prepared by conventional mix and asphalt mixed with 2% of nano clay in four stress levels from 200 – 500 KPa (Steps of 100). The primary results indicated that nano core samples have almost double or even more fatigue lives in most of stress levels with less variability than conventional ones.