clay
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امروزه سیمان به عنوان پرمصرف ترین و رایج ترین تثبیت کننده خاک، است. ولی با توجه به آثار نامطلوب زیست محیطی سیمان، ضرورت استفاده از ژئوپلیمرها بدلیل جنبه های مطلوب زیست محیطی به عنوان جایگزینی مناسب برای سیمان حائز اهمیت می باشد. در این مطالعه از ژئوپلیمر بر پایه آهک و نانومواد که شامل نانوکلوئیدسیلیس والیاف می باشد، برای تثبیت خاک کائولینیت استفاده شده است. پارامترهای مختلف مانند نوع نانومواد، مقدار نانومواد، نسبت محلول فعال کننده قلیایی و زمان عمل آوری به عنوان عوامل موثر بر رفتار نمونه های تثبیت شده مورد توجه قرار گرفت. برای ارزیابی تاثیر ژئوپلیمر و نانومواد بر رفتار مکانیکی نمونه ها، آزمایش مقاومت فشاری محدودنشده و مقاومت کششی وسیکل ذوب ویخ که معیار اصلی مقایسه نمونه ها بوده اند، انجام شده است. از طرفی تحلیل XRD و SEM جهت بررسی ریزساختاری خاک تثبیت شده، انجام گرفت. نتایج نشان می دهد که ژئوپلیمر بر پایه الیاف و نانومواد، جایگزین مناسبی برای مواد سیمانی در تثبیت خاک هستند، طوری که افزودن الیاف و نانومواد به خاک باعث افزایش مقاومت و بهبود رفتار مکانیکی نمونه ها می شود. از طرفی با افزایش میزان نانومواد تا5 (درصد(و محلول قلیایی، مقاومت فشاری و کششی نمونه ها افزایش می یابد. مقاومت های به دست آمده، با مقاومت نمونه های تثبیت شده با سیمان مورد مقایسه قرار گرفته شده است. همچنین نتایج تحلیل ریزساختاری نشان دهنده واکنش شدید افزودنی های شیمیایی و تشکیل ژل آلومینوسیلیکاتی در ترکیبات ژئوپلیمری است که خود باعث افزایش ظرفیت باربری خاک و تثبیت آن می شودکلید واژگان: خاک رس، الیاف، نانومواد، ریزساختاری، سیکل ذوب ویخcement is used as the most widely used and common soil stabilizer. However, due to the adverse environmental effects of cement, the need to use geopolymers is important because of the favorable environmental aspects as a suitable alternative to cement. In this study, geopolymer based on lime and nanomaterials, which includes nanoclucosilica , was used to stabilize kaolinite . Various parameters such as type of nanomaterials, amount of nanomaterials, the ratio of alkaline activating solution and the curing time were considered as factors affecting the behavior of stabilized samples. To evaluate the effect of geopolymer and nanomaterials on the mechanical behavior of the samples, unrestricted compressive strength and tensile strength and melting cycle tests were performed, which were the main criteria for comparing the samples. On other hand, XRD and SEM analysis were performed to investigate the microstructure of the stabilized soil. The results show that fiber-based and nanomaterial based geopolymers are a suitable alternative to cementitious materials in soil stabilization, so that the addition of fibers and nanomaterials to the soil increases the strength and improves the mechanical behavior of the samples. other hand, with increasing the amount of nanomaterials to 5% (and alkali solution), the compressive and tensile strength of the samples increases. The obtained strengths have been compared with the strength of cement-stabilized samples. the results of microstructural analysis show Gives a strong reaction to chemical additives and the formation of aluminosilicate gels in geopolymer compounds, which in turn increases the soil bearing capacity and stabilizes it.Keywords: Clay, Fiber, Nanomaterials, Microstructure, Cycle melting
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Scientia Iranica, Volume:29 Issue: 6, Nov-Dec 2022, PP 2940 -2952Freeze-thaw (F-T) cycles cause substantial detriment to geotechnical structures, especially roads, every year. Recently, researchers have increasingly used nanomaterials to improve soil resilience. This study evaluated the effect of soil stabilization by cement and nanocement on resistance changes subjected to F-Tcycles.For this purpose, clayey soil was combined with 1, 2, 3, and 4% stabilizers based on dry unit weight. Atterberg limits and standard compaction tests were performed on the prepared mixtures. The results showedthat increasing the stabilizers enhanced the optimum moisture content, liqid limit, and plastic limitwhile decreasingthe maximum dry density and plastic limit. Then, the cylindrical specimens of the pure and stabilized soilswere prepared and curedwithin 42 days. Finally, unconfined compressive strength(UCS) tests were conducted on the samples after applying zero, three, six, and nineF-T cycles. UCSin the stabilized soil increased to a value about12 times thatin the pure soil. The UCSvalue was reduced on average to 49%inthe pure soil specimens by applying nine F-T cycles, whichfurther decreased on averageto 36% and 31%after adding cement and nanocement, respectively. However, the lowest UCS value was observed in the stabilized soil specimens, reaching 26% and 19%in 42 daysafter applying nineF-T cyclesand adding 4% cement and nanocement, respectively.Keywords: Clay, freeze-thaw, Soil improvement, Cement, nanocement
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Scientia Iranica, Volume:27 Issue: 4, Jul Aug 2020, PP 1740 -1750
Settlement-based designs for foundations, using subgrade reaction modulus (K_s), is an important technique in geotechnical engineering. Plate load test (PLT) is one of the commonly applied methods to directly determine K_s. As the determination of the K_s from PLT—especially at depths—is relatively costly and time-consuming, it is necessary to develop models that can handle simply determinable properties. In the present study, the suitability of the Group Method of Data Handling (GMDH)-type neural network (NN) to estimate the subgrade reaction modulus of clayey soils has been investigated. In order to derive GMDH models, a database containing 123 datasets compiled from geotechnical investigation sites in Qazvin, Iran, has been used. The performance of the GMDH models has been compared with other available correlations for clayey soils, and it has been demonstrated that an improvement in estimating the K_s has been achieved. Finally, a sensitivity analysis has been conducted on the proposed models, showing that the proposed K_s is considerably influenced by changing the LL value.
Keywords: Subgrade reaction modulus, Plate load test, Neural network, Clay, Group method of data handling -
A series of bitumen/nano clay nanocomposite have been prepared through solvent intercalation technique by using mechanical agitation and sonication process. The structure of nanocomposite coatings was investigated by TEM, low angle X-ray diffraction and Fourier-transform infrared spectroscopy. To investigate barrier properties of nanocomposite coatings, polarization, salt fog test and pull-off adhesion tests have been employed. The results showed that bitumen/MMT nanocomposite coatings were superior to the pristine bitumen coating in corrosion protection effects. Also, it was observed that the corrosion protection of bitumen/clay nanocomposite coatings improved as the clay loading is increased up to 4 wt.%.Keywords: Bitumen, Nanocomposite coating, Clay, Corrosion
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Application of tire crumbs on mechanical properties of a clayey soil subjected to freeze-thaw cyclesDuring recent years, processed used tires such as tire shreds, tire chips, tire bungs, and tire crumbs have been applied in order to improve the mechanical properties of soil mixtures. Finding more bene cial ways of using waste tires, this paper assessed the influence of adding tire crumbs to a clayey soil which was a ected by freeze-thaw cycles. Freeze-thaw cycling is a weathering process which occurs in cold climates during winter and spring and considerably changes the engineering properties of soils. In the present study, a clayey soil was mixed with six di erent percentages of tire crumbs (0, 0.5, 1, 1.5, 2, 2.5) and evaluated by triaxial compression tests under three di erent con ning pressures (30, 60, 90 kPa) after the soil was subjected to 1, 3, 6, and 9 cycles of freeze-thaw. It has been found that for the investigated soil, using 2.5% of tire crumbs decreases the cohesion reduction ratio by about 24% and the resilient modulus reduction ratio by about 6-42% during the cycles. Hence, although the addition of tire crumbs does not considerably a ect the strength reduction of soil during freeze-thaw cycles, it can reduce the changes of cohesion and resilient modulus of the soil, e ectively.Keywords: Freeze, thaw cycling, Clay, Tire crumbs, UU triaxial test, Cohesion, Resilient modulus
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Scientia Iranica, Volume:22 Issue: 5, 2015, PP 1643 -1660In conventional elastic-plastic constitutive models for clays, elastic strains are usually calculated by isotropic hypo-elastic models. However, this class of elasticity has two major deficiencies: (a) it ignores the influence of shear stress-induced anisotropy and; (b) it does not conserve energy. Another class of the elasticity theory, the so-called hyper-elasticity theory, is capable of eliminating both deficiencies simultaneously. In this study, constitutive equations of a recently proposed elastic-plastic platform for clays named SANICLAY are generalized in order to enable it to consider the possibility of the anisotropic response in the elastic domain. The generalized formulation allows shear-volumetric coupling not existing in the basic platform. Then, the elastic moduli obtained from a hyper-elastic model are implemented within the generalized SANICLAY formulation. The refined model predictions are directly compared with the experimental data of various clays. It is shown that more realistic stress paths are achieved from the refined model.Keywords: clay, anisotropy, elasticity, Gibbs free energy, plasticity
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