بررسي آزمايشگاهي تاثير الياف پلي‌پروپيلن بر رفتار بتن تراورس

Laboratory Study on the Effect of Poly-Propylene FiberReinforced Concrete for Application in Sleeper

از آن جايي كه تراورس بتني به‌عنوان يكي از اجزاي روسازي خط راه‌آهن بالاستي در معرض شرايط آب و هوايي متنوعي قرار مي‌گيرد، مسيله كنترل خوردگي و افزايش دوام آن از اهميت به‌سزايي برخوردار است. از اين رو اگر بتوان با به‌كارگيري مواد افزودني مناسب در قالب مسلح‌كننده‌ها، ميزان ايجاد و گسترش ترك‌هاي سطحي را در اين عضو محدود كرد، اين موضوع تاثير مستقيمي بر بهبود دوام و افزايش عمر آن خواهد داشت. در اين مقاله تلاش شده است تا ميزان افزايش مقدار مقاومت‌هاي كششي و خمشي و هم‌چنين كاهش مقاومت فشاري بتن مسلح شده به الياف پلي پروپيلن با نظر به كاربرد آن در تراورس بتني بررسي شود. براي اين منظور با اضافه كردن مقادير مختلفي از الياف پلي‌پروپيلن به بتن تراورس و بررسي تاثير آن بر رفتار 72 نمونه ساخته شده، در‌نهايت مقدار بهينه‌اي برابر kg/m37/0 شناسايي شد كه اين مقدار با مقادير اعلام شده به‌وسيله ساير محققان همخواني دارد. بررسي و تحليل نتايج به‌دست آمده از آزمايش‌ها نظير مقدار بهينه الياف، نشان‌دهنده كاهش مقدار مقاومت فشاري، افزايش مقادير مقاومت كششي، مقاومت خمشي و افزايشVB به‌ترتيب به ميزان 7/8 ، 33 ، 10 و 51 درصد مي‌باشد.

Abstract: Concrete sleeper as an important component of super-structure has a remarkable role in proper performance of ballasted track. Nowadays, railroads companies of the world are willing to increase strength of concrete sleepers and use new solutions for repairing and rehabilitation of these elements with low cost. Sleeper damage is usually occurred in forms of cracks that have appeared by repetitive loadings and thermal effects. Corrosion of reinforcement tendons in some special regions is another problem that causes serious damage in sleeper. Since these concrete elements are being exposed to various weather conditions, enhancing their resistance against corrosion and improving their durability has a great importance as well. there are many ways to improve concrete characteristics like using FRP by covering concrete in regions that have high stress, but this solution will not increase corrosion resistance.Using epoxy resins that can be sprayed as nano material on concrete is another way to reduce permeability, but it is an expensive way. One of the useful and cost benefit ways to increase the corrosion resistance and reduce the cracks extension is using Poly-Propylene fibers in mixture of concrete. Many researchers have been studied on using Poly-Propylene fibers in mixture of concrete and shotcrete.these reasearches are presented below : reaseraches have been accomplished on using Poly-Propylene fibers in shotcrete.the results have shown that rebounding of shotcrete has been being decreased 30% volume of cement, and cracks have been being decreased about 20% .In case of fiber reinforced concrete also reasearches have been accomplished the result of test on a concrete cube; the compression strength of specimens till 28 days , decreases but it increases till the day 90.As mentioned, many researches have been accomplished on using Poly-Propylene fibers in mixture of concrete and shotcrete. Moreover the Poly-Propylene fibers can control the propagation and extension of the surface cracks. Regarding SEM results, this increase is due to enlargement of Poly-Propylene fibers that can fill micro cracks, and of course the bonding of the concrete structure will be enhanced. Considering the significant effect of Poly-Propylene fibers on concrete behavior, the current research is devoted to investigating the influence of Poly-Propylene fibers on improving the electrical resistance, tensile and flexural strengths of the concrete in sleeper. In this matter an optimal value of 0.7 kg/m3 of Poly-Propylene fibers was achieved during the laboratory tests on fresh and hardened concrete, including 72 laboratory specimens.