بررسی اثر ترکیب الیاف‌های فولادی و پلی‌اولفین بر خواص مکانیکی و دوام بتن حاوی پودر پومیس و فلدسپار

بتن یک ماده ترد محسوب می شود، به طوری که رفتار آن تحت اثر نیروهای فشاری و کششی متفاوت است و مقاومت بتن در کشش بسیار کمتر از مقاومت فشاری آن است. برای جبران این ضعف، استفاده از ماده‌ای که بتواند مقاومت کششی بتن را افزایش دهد امری ضروری است. یکی از راهکارهای پیشنهادی که در سال های اخیر بسیار مورد توجه محققین قرار گرفته است، استفاده از انواع الیاف در مخلوط بتنی است. در پژوهش حاضر از ترکیب دو نوع الیاف فولادی و پلی اولفین در ساخت نمونه های آزمایشگاهی استفاده شده است. الیاف فولادی با درصد حجمی 1% و الیاف پلی اولفین با درصدهای حجمی 1% و 2% مورد استفاده قرار گرفته است. همچنین پودر پومیس و فلدسپار با درصدهای وزنی 10% و 20% به صورت تکی و ترکیب (با نسبت‌های مساوی) مورد استفاده قرار گرفته اند. نتایج به دست آمده نشان داده است که استفاده از ترکیب الیاف های فولادی و پلی اولفین باعث افزایش مقاومت فشاری 28 روزه مخلوط های حاوی پودر پومیس و فلدسپار می شود، به طوری که درصد بهینه ترکیب 1% الیاف فولادی و 1% الیاف پلی اولفین است. استفاده از ترکیب الیاف های فولادی و پلی اولفین اثر قابل توجهی بر بهبود مقاومت خمشی نمونه های حاوی پودر پومیس دارد به طوری که استفاده از ترکیب 1% الیاف فولادی و 1% الیاف پلی اولفین در طرح حاوی 10% پودر پومیس باعث دستیابی به بهترین عملکرد خمشی در سن 28 روزه می شود.

investigation of the effect of the combination of steel and polyolefin fibers on the mechanical properties and durability of the concrete with pumice powder and feldspar

concretes have different behavior in the tensile and compressive loading. concretes have a strong compressive strength, but the tensile strength of them is weak. to compensate for this weak tensile strength, it is necessary to use materials with high tensile strength. steel fibers have been widely used in recent years because of their high energy absorbing capacity, scientific improvement of the concrete behavior after the creation of the first crack, and improvement of the bending and impact strength. fiber concretes are a type of composite materials. in this concrete, fibers were used in the concrete mix design and increased significantly the tensile and compressive strength of the concrete. in this paper, the combination of steel fibers and polyolefin fiber in the construction of the concrete cube specimens was used. the steel fibers with a volume percentage of 1% and polyolefin with a volume percentage of 1% and 2% were used in the concrete mix design. also, pumice powder and feldspar with a weight percentage of 10% and 20% individually and in combination with the same proportion were used. the 19th concrete mix design was constructed and experimental tests were performed on them to investigate the mechanical properties of the specimens. the compressive test on the 100×100 mm cubic specimens according to astm c109 and the three-point flexural test according to astm c348 at the age of 7 and 28 days of the specimens were conducted. the results exhibited that the combination of the steel fibers and polyolefin fibers led to an increase in the 28-day concrete compression strength test of the specimens with pumice powder and feldspar. the optimal percentage of the combination is the steel fiber with 1% and polyolefin with 1%. also, the use of fiber and polyolefin fibers improved the flexural strength of the specimens with pumice powder. it should be mentioned that a combination of the steel fiber and polyolefin with 1% in the specimens with 10% pumice powder achieves the best flexural strength at the age of 28 days. also, the combination of the steel fibers and polyolefin fibers improved the compressive strength of the specimens with pumice powder and feldspar at the age of 7 days, but they resulted the lower compressive strength in comparison with the control specimen. also, the use of these fibers led to an increase in the energy-absorbing capacity and the ductility of the specimens by increasing the fracture strain of the concrete. depending on the amount of the pumice powder and feldspar in the concrete mix design, increasing the volume percentage of the fibers has a positive or negative effect on the ductility of the specimens. also, increasing the weight percentage of the pumice powder and feldspar reduced the electrical resistance of the specimens. it should be noted that a combination of steel fibers and polyolefin fibers has a significant effect on the decrease of the electrical resistance. the use of the pumice powder and feldspar increased the water-absorbing capacity of the specimens and it intensified due to the use of the fibers.