بکارگیری آزمون انتقال اصطکاک برای بررسی مقاومت فشاری ملات های تعمیری و تأثیر پیش فشار بر چسبندگی بین ملات و بتن پایه

نوع مقاله : پژوهشی اصیل (کامل)

نویسندگان
علی صابری ورزنه 1
محمود نادری 2
1 دکتری، دانشکده فنی و مهندسی، دانشگاه بین‌المللی امام خمینی (ره)، قزوین، ایران
2 استاد، دانشکده فنی و مهندسی، دانشگاه بین‌المللی امام خمینی (ره)، قزوین، ایران
10.22034/22.4.12
چکیده
با توجه به آسیب های وارده به سازه‌های بتنی که ممکن است به دلیل عوامل مختلفی پدید آید، موادی برای تعمیر و تقویت این سازه‌ها مورد نیاز است. معمولاً برای ترمیم و تعمیر سازه های بتنی از ملات‌های پایه سیمانی استفاده می‌گردد. جمع شدگی و تراکم نامناسب ملات های تعمیری می تواند باعث کاهش مقاومت چسبندگی بین ملات و بستر بتنی گردد. فصل مشترک ملات و بستر دارای اهمیت فراوانی می باشد، زیرا عدم تراکم مناسب باعث ایجاد حفرات ریز بین سطح مشترک شده و یکی از عوامل اصلی در کاهش مقاومت چسبندگی می باشد. لذا در این تحقیق با اعمال پیش فشارهای متفاوت روی ملات تعمیری، تاثیر آن بر مقاومت چسبندگی برشی و کششی بین ملات تعمیری و بستر بتنی با استفاده از آزمون های "انتقال اصطکاک" و "کشیدن از سطح" مورد بررسی قرار گرفته است. برای ساخت ملات های تعمیری از نسبت سیمان به ماسه برابر 1 به 3 و نسبت آب به سیمان نیز برابر 5/0 استفاده شده است. همچنین تاثیر عمل آوری بر کاهش جمع شدگی ملات ها ارائه گردیده است. در ادامه نیز برای ارزیابی مقاومت فشاری درجای ملات های سیمانی از آزمون های نیمه مخرب "انتقال اصطکاک" و "کشیدن از سطح" استفاده شده و با اندازه گیری ضریب همبستگی و رسم نمودارهای کالیبراسیون، معادلات تبدیل قرائت های حاصل از آزمون های نیمه مخرب به مقاومت فشاری ملات ها ارائه شده است. در انتها نیز با استفاده از نرم افزار اجزا محدود ABAQUS ترک‌ها و تنش‌های بوجود آمده در نمونه ها ارائه شدند. نتایج حاصله بیانگر این می باشد که اعمال فشار 5/0 کیلوگرم بر سانتی مربع باعث افزایش مقاومت چسبندگی برشی و کششی بین لایه تعمیری و بتنی در سن 90 روز به ترتیب برابر 1/30 و 4/31 درصد گردیده است. با استفاده از معادلات y=10x-0.805 و y=17.32x+1.83 به ترتیب می توان با جایگذاری نتایج حاصل از آزمون های "انتقال اصطکاک" و "کشیدن از سطح" در معادله به جای عبارت x، مقاومت فشاری ملات تعمیری را تعیین نمود.

کلیدواژه‌ها

موضوعات

عنوان مقاله English

Using Friction-Transfer test to Study the Compressive Strength of Repair Mortars and the Effect of Prestress on the Adhesion between Mortar and Concrete Substrate

نویسندگان English

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

Given the damages to concrete structures caused by different factors, some materials should be used to repair and strengthen them. In general, cement-based mortars are used to repair concrete structures. The shrinkage and inappropriate compaction of repair mortars can reduce the bond strength between mortar and concrete substrate. the shrinkage is an important problem that has an adverse effect on the adhesion between repair mortar and concrete substrate. The shrinkage can create tensile stress inside mortars, leading to cracking due to their low tensile strength. The mortar-substrate interface is of great importance since the improper compaction can create fine pores and lower the bond strength.The suitable compaction of repair mortar while applying it on the concrete substrate is an effective factor in increasing the adhesion between the mortar and concrete. The mortar-substrate interface is of great importance since the improper compaction can create fine pores and lower the bond strength. Therefore, in this study, different prestresses were imposed on repair mortar to evaluate their effects on the shear and tensile bond strength between repair mortar and concrete substrate using friction-transfer and pull-off tests. The role of curing in reducing the shrinkage of mortars was also evaluated. The semi-destructive friction-transfer and pull-off tests were then used to assess the in-situ compressive strength of cement-based mortars. By calculating the correlation coefficient and plotting the calibration curves, relationships were provided to convert the measurements obtained from the semi-destructive tests to the compressive strength of the mortars. Eventually, the cracks and stresses that appeared in the specimens were presented using finite element ABAQUS software. The obtained results indicated the effect of prestress on increasing the shear and tensile bond strength between the concrete substrate and repair layers. Moreover, a high correlation coefficient was found between the measurements of the in-situ and laboratory tests. A good agreement was also observed between the finite element modeling and the experimental results. In some researches, friction transfer and pull-off tests have been used to compare the compressive strength of fiber-reinforced mortars and polymer-modified mortars with the results of the above tests, which has resulted in a very high correlation coefficient between the results.

Imposing a prestress of 0.5 kg/cm2 resulted in an increase of 30.1% and 31.4%, respectively, in the shear and tensile bond strength between the repair mortar and the concrete substrate at the age of 90 days. Imposing a prestress of 0.1 kg/cm2 resulted in an increase by 7.5% and 5.8%, respectively, in the shear and tensile bond strength between the repair mortar and the concrete substrate at the age of 90 days. Keeping the specimen in the free space resulted in 64% more shrinkage compared to the one cured in water. The friction-transfer and pull-off test results had a correlation coefficient of more than 0.98 with the repair mortar's compressive strength. Therefore, these tests can be used to evaluate the in-situ compressive strength of mortars. The compressive strength of repair mortar can be calculated by substituting x for the friction-transfer and pull-off test results, respectively, in the equations y=10x-0.805 and y=17.32x+1.83.

کلیدواژه‌ها English

Friction transfer
Prestress
Bond
Mortar
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مهندسی عمران مدرس
دوره 22، شماره 4
خرداد و تیر 1401
صفحه 173-187