اثر متاکائولن بر پتانسیل واگرایی و پارامترهای ژئوتکنیکی خاک های واگرا

نوع مقاله : مقاله کامل پژوهشی

نویسندگان

دانشکده مهندسی عمران و منابع زمین، دانشگاه آزاد اسلامی واحد تهران مرکزی

چکیده

امروزه یکی از دغدغه ­هایی که در پروژه ­های صنعتی و عمرانی در برخی مناطق جنوبی کشور مطرح است پدیده واگرایی می ­باشد. در این پدیده خاک­ های رسی واگرا تحت شرایطی خاص پراکنده شده و به سرعت شسته می­ شوند. با توجه به پیشرفت روزافزون در زمینه افزودنی­ های صنعتی و معدنی، در این پژوهش از متاکائولن (Metakaolin) جهت بهسازی خاک­ های واگرا استفاده شده است. بدین منظور نمونه ­هایی متشکل از درصد وزنی صفر، 2، 4، 6 و 8 درصد وزن خاک، به خاک رس شدیداً واگرا افزوده شد و پس از پایان دوره عمل­ آوری 7 روزه، نمونه ­ها تحت آزمایش ­های مختلف ژئوتکنیکی قرار گرفتند و میزان تغییرات پتانسیل واگرایی و همچنین بهبود ویژگی های ژئوتکنیکی خاک مورد ارزیابی قرار گرفت. نتایج حاکی از آن است که با افزودن 6 تا 8 درصد متاکائولن به خاک، پتانسیل واگرایی به طور قابل توجهی کاهش می ­یابد. در این حالت مطابق نتایج آزمایش هیدرومتری دوگانه شدت پتانسیل واگرایی حدود 55 درصد کاهش یافت و در محدوده واگرایی کم قرار گرفت این موضوع در آزمایش کرامب (Crumb) هم صادق بود. در ادامه نتایج آزمایش حدود اتربرگ (Atterberg limits) نشانگر کاهش شاخص خمیری و در نتیجه کاهش انعطاف ­پذیری نمونه­ ها است. بررسی نتایج آزمایش تراکم نشان دهنده آن بوده است که با کاهش رطوبت بهینه، حداکثر دانسیته خشک خاک افزایش یافته که همین امر سبب افزایش تراکم خاک در نتیجه واکنش ­پذیری بالا متاکائولن با هیدروکسیدکلسیم و تشکیل ژل هیدرات سیلیکات کلسیم بوده است که درنهایت سبب افزایش مقاومت محصورنشده خاک و بهبود مشخصات ژئوتکنیکی خاک واگرا گردیده است.

کلیدواژه‌ها

موضوعات

عنوان مقاله [English]

Effect of Metakaolin on Dispersivity Potential and Geotechnical Parameters of Dispersive Soils

نویسندگان [English]

  • Ahmadreza Soltanian
  • Amir ali Zad
  • Maryam Yazdi
  • Amin Tohidi
Department of Civil Engineering, Faculty of Civil and Earth Resources Engineering, Central Tehran Branch, Islamic Azad University, Tehran, Iran
چکیده [English]

     Nowadays, the dispersion phenomenon is one of the main concerns for industrial and civil projects in southern regions of Iran. In this phenomenon, dispersive clay soil, under special situation, is dispersed and rapidly washed away. Due to the continuous developments in industrial and mineral additives, in this study metakaolin was used for soil improving dispersive soils. Researchers have always studied the use of additives for soil improvement. However, using cheap and environmentally friendly additives, such as natural pozzolans, are more desired. Natural pozzolans, are silica and alumina-silica materials with no apparent cement property but in presence of water, they make bonds with hydrate calcium and have cement properties. By reviewing previous studies, it can be seen that using pozzolanic materials are environmentally friendly, reduces energy consumption, reduces costs, reduces permeability and increases the chemical resistance of concrete. Metakaolin is a natural pozzolan with high permeability, with 50-55% SiO2 which reacts with Ca (OH)2 in room temperature and produces the calcium silicate hydrate (CSH) gel. Kolovos et al (2013) investigated mechanical properties of a soil improved by metakaolin. In this study, the optimum mix design of cement soil and its mechanical properties are investigated and the results show improved mechanical properties of soil. Wu et al (2016) studied the effect of metakaolin and cement on MHS strength and soil structure. The results show that adding metakaolin to soil reduces its sensitivity to water and significantly increased the uniaxial compressive strength and tensile strength of soil. Wianglor et al (2017) reviewed the effects of alkaline active metakaolin on compressive strength and particle structure of the improved mortar in 23 and 60 centigrade. The results show that increasing the amount of metakaolin and the temperature results in increased compressive strength and silicate and aluminate gel is apparently seen in mortar particle structure. In recent years, the compound effect of cement and metakaolin have rarely been studied, however there is no record for using metakaolin alone for soil improvement. This study aims to investigate the effects of different metakaolin percentages on reducing the clay dispersion potential, using crumb test, hydrometry, and also reviewing its geotechnical properties, such as Atterberg limits, maximum dry density, optimum humidity percentage, uniaxial compressive strength, and its validation using SEM.

کلیدواژه‌ها [English]

  • Dispersive soil
  • Metakaolin
  • Soil stabilization
  • Double hydrometric test
  • Crumb test

مراجع

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