اثر هندسه ی مقطع نمونه در مقاومت فشاری بتن خودتراکم مسلح به الیاف پلی وینیل الکل

در پژوهش حاضر، اثر هندسه‌ی مقطع نمونه در مقاومت فشاری بتن خودتراکم مسلح به الیاف پلی‌وینیل الکل بررسی شده است. بدین منظور، سه طرحاختلاط مربوط به بتن‌های خودتراکم مسلح به درصدهای مختلف از الیافپلی‌وینیل الکل، در ابعاد متفاوت از قالب‌هایی با شکل‌های استوانه‌یی و مکعبی طراحی شده‌اند. تاثیر اضافه شدن الیاف پلی‌وینیل الکل در ویژگی‌های تازه و مقاومت فشاری 28 روزه‌ی بتن خودتراکم بررسی و رابطه‌ی میان مقاومت فشاری قالب‌های استوانه‌یی و مکعبی به‌صورت توابع خطی ارائه شده است. همچنین از رابطه‌ی بازانت به‌منظور تعیین شدت اثر اندازه استفاده شده و ضرایب مجهول این رابطه با استفاده از رگرسیونغیرخطی نتایج آزمایشگاهی به دست آمده است. اضافه شدن 0٫08٪ حجمی از الیاف پلی‌وینیل الکل، مولفه‌ی اندازه‌ی انتقالی رابطه‌ی بازانت (d_{0}) را برای نمونه‌های استوانه‌یی و مکعبی به‌ترتیب به میزان‌های 170٫39 و 105٫86 درصد افزایش داده است، که نشان از تاثیر چشم‌گیر الیاف پلی‌وینیل الکل در کاهش شدت اثر اندازه در بتن خودتراکم دارد.

Specimen shape effect on the compressive behavior of PVA fiberreinforced selfconsolidating concrete

The mechanical properties of concrete are dependent on the specimen size and shape. This phenomenon is caused by the heterogeneous nature of concrete and results in significant dissimilarities between the laboratorymade samples and larger concrete elements in the construction fields. Thus, it is required to develop experimental and numerical models to translate the strength of different concrete specimens with varying sizes and shapes. In this research, the effect of specimen shape is evaluated for PVA fiberreinforced selfconsolidating concrete. To do so, three selfconsolidating mix proportions were designed, containing two different dosages of PVA fibers and various sizes of cylindrical and cubic specimens were cast in order to account for the influence of specimen size and geometry. The fresh properties of the designed SCC concretes were assessed using several experiments such as slump flow time and diameter tests, Vfunnel flow time test, and Lbox test. Also, the 28day compressive strength of the designed samples was obtained using a pressure jack. The specimen shape and size effect of PVA fiberreinforced selfconsolidating concrete was studied based on specimen geometry and fracture mechanism, and the influence of PVA fiber addition on the compressive strength of samples was presented in the form of linear equations. By analyzing the obtained data, relations were proposed to translate the strength of cylindrical specimens to cubic specimens. Also, for the first time, the experimental coefficients of Bazant's model were achieved for PVA fiberreinforced SCC, and the Bazant's size effect model became functional for the designed concretes. To do so, nonlinear regression analysis was conducted on the obtained experimental data. According to the achieved results, the addition of 0.08% of PVA fibers increased the transitional size coefficient (D0) of cylindrical and cubic specimens by 170.39% and 105.86%, respectively, reduced the size effect, and enhanced the ductility in the designed selfconsolidating concretes.