بررسی تاثیر افزودن نانورس و آهک بر خواص مکانیکی و خودترمیمی خاک‌های ریزدانه

استفاده از افزودنی‌ها در تثبیت خاک همواره مورد توجه محققان بوده است. در این مقاله تاثیر نانورس به‌عنوان یک افزودنی جدید، در کنار آهک که یکی از افزودنی‌های قدیمی در تثبیت خاک به‌شمار می‌رود، بر رفتار خاک بررسی شده است. درصدهای مختلف نانورس و آهک بر خاک رسی افزوده می‌شود و تاثیر آن بر درصد رطوبت بهینه، بیشینه دانسیته خشک، مقاومت تک‌محوری، حدود اتربرگ و خاصیت خود ترمیمی خاک‌ها بررسی می‌شود. پژوهش‌های انجام شده حاکی از آن است که اضافه کردن آهک باعث کاهش دانسیتۀ خشک خاک می‌شود این در حالی است که افزودن نانورس سبب افزایش این پارامتر در خاک‌های رسی می‌شود. افزودن آهک تاثیر زیادی بر افزایش چسبندگی دارد و بر افزایش زاویۀ اصطکاک تاثیر چشم‌گیری ندارد این درحالی است که نانو مواد علاوه بر اینکه چسبندگی را افزایش می‌دهد، سبب افزایش زاویۀ اصطکاک خاک نیز می‌شود. نکته مهم و قابل تمرکز در این کار تاثیر چشم‌گیر نانو مواد بر خاصیت خود ترمیمی خاک رس است. با افزودن 2 درصد نانورس به خاک با گذشت 24 ساعت از ایجاد صفحه گسیختگی در خاک، مصالح قادر هستند حدود 80 درصد مقاومت اولیۀ خود (زمانی که هیچ افزودنی ندارد) را به‌دست آورند.

Evaluation of the Effects of Additives of Nano Clay and Lime on the Properties of Soil

IntroductionThe use of various additives to improve the properties of soils from past years have been studied by different researchers. Such additives are lime, cement, fly ash and fiber which have been used frequently in combination with soil. Lime is one of the oldest additives that it is utilized with different types of soils. Lime has positive impact on geotechnical properties of soil that alter some of the soil characteristics. Adding lime causes to reduce plasticity ranges, enhanced efficiency, strength and shrinkage of the soil. Extensive researches in the field of sustainability of clay with lime indicate that the optimum percentage of lime in the soil modification is between 1 to 3% by weight of the soil. But some researchers believe 8% by weight of lime are effective for soil stabilization. The presence of lime in clay soil yiels to occur some reaction, that it improves the soil properties. Reactions are included cation exchange flocculation, carbonation and pozzolanic reactions. Cation exchange between the clay cations and calcium cations takes place in lime. Cation exchange causes clay particles to get closer to each other creating complex structures in the clay soil and this improves the clay soil features. In recent years the use of nanoparticles is considered in civil engineering field. The investigations have demonstrated that the use of nanomaterial increases cement reactivity and also improves density because it is filled with particles. Recent research has shown that the use of montmorillonite nanoclay soils to control swelling and to reduce failure potential in the soil. A number of researchers have expressed the use of nanoparticles causes to decrease the hydraulic conductivity of soils. In this paper, the effect of nanoclay and lime on the important soil parameters is evaluated. For this purpose, lime at 2 and 4 percentage and nanoclay at 0.5, 1 and 2 percentages have been added to clay soil and their impact on parameters such as optimized moisture, Atterberg limits, unconfined compressive strength and selfhealing properties of soil is evaluated. Selfhealing properties is one of the features, to repair damages due to internal erosion in the clay which is very efficient and important.Materials and experimental methodsIn the present research, the effect of lime and montmorillonite nano -clay to soil strength is evaluated. For this purpose, samples of clay soil (CL) has been used. In the experimental study, the percentages of additives mixed with the dry soil and then the optimum moisture and maximum specific weight of soil are determined with different percentages of additives. Soil Atterberg limits based on the ASTM D4318 standard have been determined. Dry samples have been mixed together and then the water is added and mixed well with each other. Then the sample has been prepared in the form of a steel cylinder (cylindrical specimens) with a diameter of 50 mm and a height of 100 mm. Specimens were molded immediately and the weight and dimensions were carefully measured and then placed in plastic to prevent moisture loss and put them at 20 °c and 90% moisture curing room.Results and discussion In this study, the percentage of lime is between 0, 2, 4 percent by weight and nanomaterials percentage is between 0.5 and 1 and 2 percent that can be varied in order to analyze the effect of various additives on the properties of the soil samples. The results indicate that increasing the nanoclay and lime percentage can enhance the optimum specific gravity of soil. The optimum moisture content of sample without any additive is equal to 19.5%. However, samples contain 2% nanoclay and 4% lime, the optimum moisture content increases to 23.5%. But the presence of lime reduces the maximum dry density of soil while adding nanoclay increases this amount. In samples with 4% lime and with no nanoclay, maximum dry density is 17 but in case of lime with 4% and nanoclay with 2% it is increased to 17.5 . In addition, adding lime without the presence of nanoclay only increases strength of soil. When 2 percent of lime is added, the strength of soil increases about 39 percent. As mentioned before, the effect of lime and nanoclay on increasing of unconfined compressive strength is almost the same which means by adding 2% of lime or nanoclay the strength of the soil increases about 40 percent. Using both lime and clay nanoparticles simultaneously (each 2%), a significant increase in strength of soil occurs in approximately 77 percent.ConclusionThe use of nanoclay and lime improves soil strength parameters. But economically lime is more affordable than nanoclay. Therefore, if you need to increase only unconfined compressive strength, then the nanoclay is not recommended.When it comes to selfhealing in clay, the nanoclay can improve resistance rupture of the soil. By adding 2% of nanoclay in soil, healing of soil resistance after the break and after 24 hours can reach up to 60% of the ultimate strength of the soil. This property can be used to repair of locations that are subjected to internal erosion and scouring.