اثر هندسه ي مقطع نمونه در مقاومت فشاري بتن خودتراكم مسلح به الياف پلي وينيل الكل

Specimen shape effect on the compressive behavior of PVA fiber-reinforced self-consolidating concrete

در پژوهش حاضر، اثر هندسه‌ي مقطع نمونه در مقاومت فشاري بتن خودتراكم مسلح به الياف پلي‌وينيل الكل بررسي شده است. بدين منظور، سه طرحاختلاط مربوط به بتن‌هاي خودتراكم مسلح به درصدهاي مختلف از اليافپلي‌وينيل الكل، در ابعاد متفاوت از قالب‌هايي با شكل‌هاي استوانه‌يي و مكعبي طراحي شده‌اند. تأثير اضافه شدن الياف پلي‌وينيل الكل در ويژگي‌هاي تازه و مقاومت فشاري 28 روزه‌ي بتن خودتراكم بررسي و رابطه‌ي ميان مقاومت فشاري قالب‌هاي استوانه‌يي و مكعبي به‌صورت توابع خطي ارائه شده است. همچنين از رابطه‌ي بازانت به‌منظور تعيين شدت اثر اندازه استفاده شده و ضرايب مجهول اين رابطه با استفاده از رگرسيون غيرخطي نتايج آزمايشگاهي به دست آمده است. اضافه شدن 0٫08٪ حجمي از الياف پلي‌وينيل الكل، مؤلفه‌ي اندازه‌ي انتقالي رابطه‌ي بازانت (D_{0}) را براي نمونه‌هاي استوانه‌يي و مكعبي به‌ترتيب به ميزان‌هاي 170٫39 و 105٫86 درصد افزايش داده است، كه نشان از تأثير چشم‌گير الياف پلي‌وينيل الكل در كاهش شدت اثر اندازه در بتن خودتراكم دارد.

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 laboratory-made 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 fiber-reinforced self-consolidating concrete. To do so, three self-consolidating 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, V-funnel flow time test, and L-box test. Also, the 28-day compressive strength of the designed samples was obtained using a pressure jack. The specimen shape and size effect of PVA fiber-reinforced self-consolidating 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 fiber-reinforced SCC, and the Bazant's size effect model became functional for the designed concretes. To do so, non-linear 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 self-consolidating concretes