ارزیابی مشخصات مکانیکی ملات های اصلاح شده با پلیمر و چسبندگی آن ها با فولاد

نوع مقاله : پژوهشی اصیل (کامل)

نویسندگان
علی صابری ورزنه 1
محمود نادری 2
1 دانشکده فنی و مهندسی، دانشگاه بین‌المللی امام خمینی (ره)، قزوین، ایران
2 استاد، دانشکده فنی و مهندسی، دانشگاه بین‌المللی امام خمینی (ره)، قزوین، ایران
چکیده
با توجه به آسیب­های وارده به سازه­های بتنی، لزوم استفاده از لایه­های تعمیری مناسب امری ضروری می­باشد. در ساختمان­های بتن آرمه، بتن و فولاد در ارتباط با یکدیگر بوده و در اکثر موارد نیز لایه­های تعمیری در ارتباط مستقیم با فولاد اعمال می­گردد. لذا در این تحقیق با بکارگیری آزمون­های "انتقال اصطکاک" و "کشیدن از سطح" اقدام به اندازه گیری مقاومت چسبندگی برشی و کششی بین ملات­های اصلاح شده با پلیمر و فولاد شده است. همچنین تاثیر پلیمر بر جمع شدگی ملات­ها و تاثیر آن بر مقاومت چسبندگی مورد بررسی قرار گرفته است. تاثیر پلیمر بر ملات­ها با استفاده از عکسبرداری با میکروسکوپ الکترونی روبشی و نرم افزارهای Image J و Origin مورد مطالعه قرار گرفت. در ادامه نیز برای ارزیابی مشخصات مکانیکی ملات­ها، با استفاده از آزمون های فوق، مقاومت فشاری و خمشی درجای ملات­ها تعیین و ضمن مقایسه با آزمون­های استاندارد آزمایشگاهی، نمودارهای کالیبراسیون رسم گردیدند. سپس معادلات تبدیل نتایج آزمون­های درجا به مقاومت فشاری و خمشی ملات­های اصلاح شده با پلیمر ارائه گردیدند. در انتها نیز با استفاده از نرم افزار ABAQUS ترک­ها و تنش­های بوجود آمده در ملات­ها ارائه شدند. لایه تعمیری اعمال شده روی بستر فولادی حاوی نسبت ماسه به سیمان برابر 3 و نسبت آب به سیمان برابر 5/0 می باشد. برای ارزیابی مشخصات مکانیکی ملات های تعمیری، پلیمر استایرن بوتادین رابر با نسبت های 10، 15 و 20 درصد وزن سیمان به ملات اضافه گردید. نتایج حاصله بیانگر تاثیر پلیمر بر کاهش جمع شدگی ملات­ها و افزایش مقاومت چسبندگی برشی و کششی بین فولاد و ملات می باشد بگونه ای که افزودن پلیمر به میزان 10، 15 و 20 درصد باعث کاهش جمع شدگی ملات ها به ترتیب به مقدار 3/35، 2/41 و 4/45 درصد در سن 90 روز شده است. مقاومت چسبندگی برشی و کششی 90 روزه بین ملات و فولاد نیز با افزودن پلیمر، به ترتیب به مقدار 1/303 و 2/291 درصد افزایش داشته است. همچنین ضریب همبستگی بالایی بین قرائت­های بدست آمده از آزمون­های درجا با آزمون های آزمایشگاهی مشاهده شد به گونه ای که می توان با بکارگیری آزمون های "انتقال اصطکاک" و "کشیدن از سطح" به ترتیب با استفاده ازمعادلات y=0.113x و y=0.063x مقاومت فشاری ملات های اصلاح شده با پلیمر را تعیین نمود. در ضمن همخوانی بالایی بین نتایج عددی و نتایج آزمایشگاهی بدست آمد.

کلیدواژه‌ها

موضوعات

عنوان مقاله English

Evaluation of mechanical properties of polymer modified mortars and their bond strength to steel

نویسندگان English

Ali Saberi Varzaneh 1
Mahmood Naderi 2
1 Imam Khomeini International University, Qazvin, Iran
2 Professor, Imam Khomeini International University, Qazvin, Iran
چکیده English

Today, the use of different kinds of polymer, as the modifier of some repair mortars properties, is growing. Given the damages to concrete structures, it is necessary to use appropriate repair layers. In concrete structures, concrete and steel are connected, and in most cases, repair layers are applied in direct connections with steel. Therefore, in this research, the shear and tensile bond strength between steel and styrene-butadiene rubber polymer modified mortars was measured using semi-destructive friction-transfer and pull-off tests. In the "pull-off" test, to determine the bond between the mortar and the steel, a core with a 50mm diameter and is first mounted on the test surface using a diamond drill bit and a metal cylinder with a diameter of 50 mm and a thickness of 20 mm is attached to the partial core. Then, the tensile force is applied to the cylinder by means of a "pull-off" device to make the partial core fail. To measure adhesion with friction transfer method, first a small core was created from the mortar surface to the steel substrate surface using the coring machine. Thereafter, the friction transfer metal device was fixed onto the core and the torsional moment was applied using a typical torque wrench in order to cause failure in the core. Moreover, the effect of polymer on the shrinkage of mortar was evaluated. Shrinkage is one of the important problems that negatively affects the adhesion of repair mortar and steel. Due to the fact that hydrated cement paste has capillary pores that contain some water, shrinkage occurs after this moisture leaves the pores. The effect of polymer on mortars was investigated by taking images with a scanning electron microscope and using the “Image-J” and “Origin” software programs. Afterward, in order to evaluate the mechanical properties of mortars, the in-situ compressive and flexural strengths of the mortars were determined, and the calibration curves were plotted by comparing them with standard laboratory tests. Then, relationships were proposed to convert the results of in-situ tests to the compressive and flexural strength of the polymer modified mortars. Eventually, the cracks and stresses that appeared in the mortars were provided using ABAQUS software. The obtained results indicated the effect of polymer in reducing the shrinkage of mortars and increasing the shear and tensile bond strength between steel and mortar, along with a high correlation coefficient between the measurements in the in-situ and laboratory tests. Comparing the modified mortars with polymer and ordinary mortar, it is observed that at the age of 90 days, adding 10, 15 and 20% of SBR reduced the amount of shrinkage to 35.3%, 4.2% and 45.4%, respectively. Addition of styrene butadiene rubber to the repair mortar increased the shear bond strength obtained from the "friction transfer" test between the mortar and steel at the ages of 7, 42 and 90 days by 44.4, 178.2 and 303.1%, respectively. Adding SBR to the repair mortar increased the tensile strength of the "pull-off" test between the mortar and the steel at the ages of 7, 42 and 90 days by 58.7, 183.4 and 291.2%, respectively. A good agreement was also observed between the numerical and experimental results.

کلیدواژه‌ها English

SBR
Mortar
Steel
ABAQUS
Friction transfer
Pull-off
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مهندسی عمران مدرس
دوره 22، شماره 1
فروردین و اردیبهشت 1401
صفحه 83-98