تاثیر پیش فشار بر چسبندگی بین بتن و ملات های مسلح به الیاف و ارزیابی مقاومت فشاری ملات ها با به کارگیری آزمون های درجا

فصل مشترک بین بتن و ملات تعمیری از اهمیت فراوانی برخوردار است. جمع‌شدگی و عدم تراکم صحیح ملات باعث ایجاد حفره‌ها و در نتیجه افت چسبندگی می‌شود. لذا در این نوشتار با به کارگیری آزمون‌های «انتقال اصطکاک» و «کشیدن از سطح» و همچنین عکسبرداری و تحلیل با میکروسکوپ الکترونی روبشی و الگوی پراش اشعه‌ی ایکس، تاثیر الیاف پلی‌پروپیلن و پیش فشار، بر مقاومت چسبندگی برشی و کششی بین ملات و بتن بررسی شده است. همچنین با ارزیابی مقاومت فشاری ملات‌ها به صورت درجا، نمودارهای کالیبراسیون رسم و معادلات برای تبدیل نتایج آزمون‌های فوق به مقاومت فشاری ملات‌های مسلح به الیاف ارائه شده است. در ادامه نحوه‌ی توزیع تنش‌ها و شکست در ملات با نرم‌افزار آباکوس مدل‌سازی شد. نتایج حاصله بیانگر تاثیر مثبت پیش فشار و الیاف بر چسبندگی است.همچنین همبستگی بالایی بین آزمون‌های درجا و آزمایشگاهی مشاهده شد.

The Effect of Precompression on Adhesion between Concrete and FiberReinforced Mortars and Assessment of Compressive Strength of Mortars Using InSitu Tests

The interface area between substrate concrete and repair mortars is of great importance. Shrinkage and incorrect compaction of the mortar causes fine cavities, and consequently, the bond strength decreases at the interface area. Therefore, in this paper, the influence of different precompressions on the shear and tensile bond strength between polypropylene fiberreinforced mortar and substrate concrete has been investigated. Frictiontransfer and pulloff tests were applied to measure shear and tensile bond strength, respectively. Furthermore, the effect of polypropylene fibers on shrinkage and bond strength is presented. Subsequently, using photography and analysis by Scanning Electron Microscopy (SEM) and XRay Diffraction (XRD) pattern, the effect of polypropylene fibers and precompression on the bond strength between fiberreinforced mortars and the concrete substrate has been studied. Moreover, the compressive strength of fiberreinforced mortars was evaluated by using semidestructive insitu tests. In addition to determining the correlation coefficient between insitu tests and laboratory tests, calibration diagrams, and transformation equations of records obtained from semidestructive tests to the mortar compressive strength, are presented. Finite element software ABAQUS has also been used to model the tests mentioned above and compare the outputs with laboratory results. The gained results reveal a positive effect of precompression on the bond strength between concrete and the repair layer. Polypropylene fibers also reduce the shrinkage of mortars and hence increase adhesion. In the XRD test, it was observed that adding polypropylene fibers to the mortar diminishes calcium hydroxide and thus increases calcium silicate hydrate, which has a positive effect on the properties of the mortar. Besides, the SEM photos reveal that the process of hydration and formation of calcium silicate hydrate (CSH) gel in the fibers' vicinity is carried out well and has made a better uniformity to the mortar composition. The results of numerical modeling are highly consistent with laboratory results. Due to the high correlation coefficient between insitu and laboratory tests, it is possible to evaluate fiberreinforced mortars' compressive strength by using frictiontransfer and pulloff tests.