بهبود حساسيت رطوبتي مخلوط‌هاي آسفالتي با افزودن كامپوزيت استايرن بوتادين لاستيك و نانورس (SBR/NC)

Improvement of Moisture Sensitivity of Asphalt Concrete Mixtures Using Nano- Composites

چكيده- همه‌ساله تعداد زيادي از راه‌هاي آسفالتي كشور در اثر ضعف روسازي‌هاي آسفالتي دچار آسيب يا خرابي زودرس مي‌شوند. از خرابي‌هايي كه بسيار مورد توجه پژوهشگران قرار گرفته است، خرابي‌هاي ناشي از حساسيت رطوبتي مخلوطهاي آسفالتي است. يكي از روش‌هاي متداول براي كاهش حساسيت رطوبتي مخلوط‌هاي آسفالتي، استفاده از مواد افزودني مانند لاستيك استايرن بوتادين (SBR) است كه بارها استفاده و آزمايش شده است. در اين پژوهش از كامپوزيت لاستيك استايرن بوتادين و نانورس استفاده شده تا آثار كمي وكيفي آن در بهبود حساسيت رطوبتي ارزيابي شود. بنابراين پليمر SBR با دو نسبت وزني مختلف نانورس و با سه درصد متفاوت قير، مخلوط شده و سپس با قيرهاي درست شده، مخلوط‌هاي بتن آسفالتي ساخته شده است. براي ارزيابي حساسيت رطوبتي مخلوط‌هاي آسفالتي از آزمون كشش غيرمستقيم، مطابق استانداردهاي ASTM D-4867 و ASTM-D6931 استفاده شده است. نتايج آزمايش‌ها نشان مي‌دهد كه با افزودن كامپوزيت لاستيك استايرن بوتادين- نانورس به قير، حساسيت رطوبتي مخلوط‌هاي آسفالتي، بهبود چشم‌گيري داشته است.

High traffic volumes and diverse weather conditions cause defects in the asphalt concrete surfaces such as excessive deformation, fatigue, rutting, ravelling and asphalt bleeding. Many researchers have examined moisture susceptibility of asphalt mixtures, because the high moisture sensitivity of asphalt pavement leads to the separation of bitumen and aggregates, and concluded that this phenomenon reduces the internal resistance of asphalt mixtures leading to failures such as rutting, raveling, and fatigue cracks under the traffic load stresses Styrene butadiene rubber, as a commonly used polymer has been focused by many researchers, and different methods have been developed for production of its composites based on nano-clay materials. According to the research results, styrene butadiene rubber nano-clay composite (SBR/NC) shows better properties compared to pure SBR. Despite extensive studies carried out on the impacts of SBR/NC on various properties of bitumen, asphalt concrete moisture susceptibility has not been addressed adequately. In this study, SBR/NC nano-composites with different ratios were prepared and used for modification of bitumen, and the indirect tensile strength, which can measure moisture sensitivity of asphalt mixtures, is being addressed. SBR/NC composite was prepared using the internal mixer apparatus and melting process method. Mixing was carried out for 12 minutes at a temperature of 140°C and 60 rpm rotation speed. Then the mixture was placed in a roller mill for 3 minutes to complete the mixing operation and cooling the resulting product. To evaluate the distribution structure of silica plates in polymer, X-ray diffraction tests were performed on the composites prepared with different ratios of SBR/NC. According to the obtained XRD spectrum the peak intensity has decreased, indicating a break down in regular layer structure. The wide range of peaks in this spectrum shows that, due to irregularity of layers, SBR is located between them. Thus it can be concluded that the silica plates to be well-distributed in the nano-composite structure. The ITS improvement of samples in dry state were up to 6 .6 percent and in wet state up to 25.30 percent and the ratio of wet to dry state up to 96.25 percent. These values indicated a significant improvement in asphalt properties against moisture permeability, which is one of the most detrimental factors in premature failure of asphalt concrete pavements.