مقايسه ي عملكرد الياف پليمري ماكرو و الياف فولادي به لحاظ كنترل ترك خوردگي ناشي از جمع شدگي خشك شدن بتن

COMPARISON OF THE PERFORMANCE OF MACRO-POLYMERIC FIBERS an‎d STEEL FIBERS IN CONTROLLING DRYING SHRINKAGE CRACKS OF CONCRETE

در اين مطالعه تاثير الياف پليمري ماكرو در كنترل ترك خوردگي جمع شدگي ناشي از خشك شدن نظير زمان وقوع اولين ترك، نرخ توسعه ي تنش هاي كششي و عرض ترك ها با استفاده از آزمايش حلقه ي مقيد مورد بررسي قرار گرفته است. همچنين اثر الياف پليمري ماكرو بر روي برخي از ويژگي هاي مكانيكي و فيزيكي بتن نظير مقاومت فشاري، مقاومت كششي و جمع شدگي آزاد بتن مورد بررسي قرار گرفت. براي مقايسه، مخلوط هاي حاوي الياف پليمري ماكرو و الياف فولادي نيز ساخته و بررسي شدند. نتايج نشانگر عملكرد مشابه الياف پليمري ماكرو و الياف فولادي در مقادير استفاده كم و متوسط)0٫25 و 0٫5 درصد مصرف(هستند. در 0٫5 درصد مصرف الياف توانسته اند عرض ترك ها را تا حدود 50 درصد كاهش دهند. با افزايش مقدار مصرف به 1 درصد، عملكرد الياف فولادي در كنترل ترك خوردگي جمع شدگي به ميزان قابل توجهي بهتر از الياف پليمري ماكرو بوده است.

This study investigates the effect of polymeric and steel fibers in controlling drying shrinkage cracking of concreteby the restrained ring test according to ASTM C1581 and determines the cracking potential of various mixes. In addition the effect of various fibers on physical and mechanical properties of concrete such as a compressive and tensile strength and free shrinkage was investigated. Fibers used include macro polymeric fiber of single-strand type, spun multi-strand type and a hooked end steel fiber, which were used at dosages of 0.25, 0.5 and 1 %. Furthermore a micro polymeric fiber at dosage of 0.25% was investigated. The results showed that the use of steel fibers up to 1% and macro polymeric fibers up to 0.5% have no appreciable effect on compressive strength. With regards to tensile strength, the effect of fibers up to 0.5% was similar to that described for compressive strength. However, at the dosage of 1%, the use of steel fibers increased the tensile strength while macro polymeric fiber slightly decreased this parameter. Free shrinkage test results indicate that the effect of fibers on free shrinkage was negligible. The effect of micro and macro polymeric fibers at the dosage of 0.25% in decreasing the cracking potential of concrete is low, and cracking potentials are classified as ``High''. At this dosage, steel fiber showed a slightly better performance and the cracking potential was ``Moderate to High''. By increasing the dosage of fibers to 1%, the cracking potential for macro polymeric fibers and steel fibers were determined as ``Moderate to Low'' and ``Low'' respectively. Crack width measurements showed that macro polymeric fiber and steel fiber at a dosage of 0.25% decreased crack widths by about 35% relative to the control mix. At fiber contents of 1%, the maximum crack opening for the macro polymeric fibers showed a decrease of about 60% compared to the control mix. The steel fiber showed the best performance at this dosage and was able to completely prevent shrinkage cracking.