بررسی تاثیر جمع‌شدگی بر چسبندگی ملات‌های اعمالی بر بتن بستر، با به کارگیری روش‌های "انتقال اصطکاک" و "کشش مستقیم"

نوع مقاله : علمی - پژوهشی

نویسندگان

1 استاد، دانشکده فنی و مهندسی، دانشگاه بین المللی امام خمینی (ره)، قزوین، ایران

2 دانشجوی دکتری، دانشگاه بین المللی امام خمینی (ره)، قزوین، ایران

چکیده

با توجه به تفاوت های موجود بین شرایط محیطی سازه‌های بتنی با شرایط آزمایشگاهی، تعیین پارامترهای مهم مصالح در محل سازه از اهمیت ویژه ای برخوردار است. به همین دلیل، در این مقاله نتایج حاصل از کاربرد دو روش درجای"انتقال اصطکاک" و "کشش مستقیم" جهت تعیین مقاومت برشی و کششی چسبندگی بین ملات های تعمیری و بستر بتنی ارائه گردیده است. از آنجا که جمع‌شدگی حاصل از خشک شدن ملات‌های تعمیری می تواند تاثیر بسزائی در مقاومت چسبندگی این ملات‌ها داشته باشد، در تحقیقات انجام شده، این پدیده بطور خاص مورد توجه واقع شده است. جهت بررسی دقیق‌تر مقاومت چسبندگی ملات‌های به کار گرفته شده، از بستر بتنی با سطح صاف (برش خورده) استفاده گردیده تا تداخل بین چسبندگی و قفل و بست مکانیکی حاصل از خلل و فرج سطحی به حد اقل برسد. سن بستر بتنی در زمان اعمال لایه تعمیری، 90 روزه بوده و پس از اعمال لایه تعمیری و عمل‌آوری مورد نظر، در سنین مختلف مقاومت برشی و کششی چسبندگی ملات‌های تعمیری با به کارگیری روش‌های ذکر شده در بالا، اندازه‌گیری گردید. جهت تخمین میزان جمع‌شدگی ملات‌‌ها‌، 9 نمونه با ابعاد استاندارد تهیه و در بازه زمانی 90 روزه، جمع‌شدگی آن‌ها اندازه‌گیری شد. همچنین با توجه به تاثیر عمل‌آوری بر خشک شدگی لایه تعمیری (جمع‌شدگی)، عمل‌آوری‌های با "پوشش گونی خیس و نایلون" برای مدت 7 و 90 روز و "رها شده در محیط آزمایشگاه" بعد از مدت 7 روز مورد بررسی قرار گرفت. نتایج حاصله نشان می‌دهد که مقدار سنگدانه و خمیره سیمان در جمع‌شدگی ملات تعمیری موثر بوده و جمع‌شدگی باعث کاهش شدید مقاومت برشی و کششی چسبندگی بین لایه تعمیری و بتن بستر می‌گردد. به علاوه مشاهده گردید که افت مقاومت برشی چسبندگی، کمی بیشتر از افت مقاومت کششی چسبندگی می‌باشد. همچنین بین نتایج روش "انتقال اصطکاک" و "کشش مستقیم"، همبستگی بالایی مشاهده گردید.

کلیدواژه‌ها


عنوان مقاله [English]

Studying the Effect of Shrinkage on the Bond Strength of Mortars, Applied to Substrate Concrete, Using “Friction-Transfer” and “Pull-Off” Methods

نویسندگان [English]

  • Mahmood Naderi 1
  • Ali Saberi Varzaneh 2
1 Professor, Department of Civil Engineering, Engineering Faculty, International Imam Khomeini University, Qazvin, Iran
2 PhD Student in Structural Engineering, Department of Civil Engineering, Engineering Faculty, International Imam Khomeini University, Qazvin, Iran
چکیده [English]

Considering the differences that exist between the laboratory and site conditions, the in-situ estimation of bond strength of repair mortars is important. Therefore, in this paper, the results obtained from the use of two methods, “Friction-transfer” and “Pull-off”, for measuring the shear and tensile bond strength of repair mortars applied to substrate concrete, are presented. Since the drying shrinkage of the repair mortar has considerable effect on their adhesion, the shrinkage of the mortars is considered. In order to increase the accuracy of the measured bond strength of the repair mortars, substrate concrete with saw cut surface was employed to minimize the interferences occurring between the pure adhesion and the mechanical keying effects of the rough surfaces. The age of the substrate concrete at the time of the application of repair mortar was 90 days and after curing under different conditions, the repair/concrete bond strength was measured at different ages. For measuring the shrinkages of the repair mortars, nine standard shrinkage samples were prepared and their shrinkages were measured. Regarding the effect of the curing process on the drying shrinkage of the repair mortars, two different curing systems of “covering with wet hessian and polythene sheet” and “stored in the laboratory”, for 7 and 90 days were considered. The results tend to show that, the amount of the aggregates and the associated cement paste have substantial effects the shrinkage of the repair mortars. It was also seen that the shrinkage causes reduction on the shear and tensile bond strength at the repair/concrete interface. Furthermore, the reduction of the shear bond strength seemed to be slightly more than the corresponding reduction of the tensile bond strength. A very high correlation was also observed between the related shear and tensile bond strength of the repair mortars.

کلیدواژه‌ها [English]

  • Concrete
  • repair mortar
  • Shrinkage
  • Bond strength
  • Friction-Transfer
  • pull-off
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