كليدواژه :
پوميس , ريزساختار , متاكائولن , يون كلريد
چكيده فارسي :
در سال‌هاي اخير استفاده از الياف در بتن جهت افزايش فاصله درز اتصال دال‌هاي بتني و كاهش ترك در روسازي‌هاي بتني و سازه‌هاي پل متداول شده است. بااين‌حال، رفتار دوام بتن اليافي در برابر نفوذ يون كلريد به‌خصوص در اندازه‌گيري غلظت يون كلريد مقيد كمتر مورد مطالعه قرار گرفته است. در اين مطالعه 6 طرح مخلوط شامل بتن معمولي (به‌عنوان بتن شاهد) و يك طرح مخلوط از بتن اليافي (بدون پوزولان) حاوي الياف پلي الفين(kg/m3 4) و پلي‌پروپيلن(kg/m3 8/0) به همراه دو طرح از بتن معمولي و دو طرح از بتن اليافي حاوي پوميس يا متاكائولن (با 15 % جايگزيني سيمان) در نظر گرفته شد. پس از مطالعه خواص مكانيكي نمونه‌هاي بتني، عملكرد بتن‌هاي مذكور در برابر نفوذ يون كلريد به كمك شبيه‌سازي محيط دريايي موردبررسي قرار گرفت. همچنين جهت ارزيابي منافذ موجود در طرح مخلوط‌ها مطالعات ريزساختاري به‌وسيله آزمون ميكروسكوپ الكتروني روبشي (SEM) و آناليز اسكن توموگرافي كامپيوتري (سي‌تي‌اسكن) انجام شد. نتايج آزمايشات نشان داد كه افزودن متاكائولن و پوميس موجب افزايش مقاومت مكانيكي و دوام در برابر نفوذ كلريد در هر دو بتن معمولي و بتن اليافي شده است. براين اساس، مقاومت فشاري پوميس و متاكائولن به نسبت نمونه معمولي 30 % و 15 % افزايش در سن 365 روز نشان داد. همچنين، حداكثر عمق ميزان نفوذ يون كلريد آزاد، مقيد و كل در بتن اليافي با 15 درصد جايگزيني سيمان با متاكائولن به ترتيب 44%، 40% و 40% كاهش نسبت به نمونه شاهد در شرايط غوطه‌وري داشت و همچنين در شرايط جزر و مد نيز به ترتيب 25%، 25% و 33% درصد كاهش مشاهده شد. بر اساس آناليز سي‌تي‌اسكن و نتايج SEM در اين مطالعه، بتن‌هاي حاوي پوزولان داراي سطح متخلخل‌تر مي‌باشند و نسبت Ca/Si به دليل رسوب‌زدايي به ميزان قابل‌توجهي در آن‌ها كاهش مي‌بايد كه اين ميزان براي نمونه حاوي متاكائولن 4/0 نشان مي‌دهد كه به نسبت نمونه كنترلي 1/1 كاهش داشته است. همچنين، نتايج نشان داد كه عليرغم تخلخل سطحي در بتن‌هاي حاوي پوزولان، نسبت Ca/Si و غلظت مايع منفذي نقش اساسي در دوام آن‌ها در برابر نفوذ يون كلريد ايفا مي‌كنند.
چكيده لاتين :
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.
