ارزيابي اثر نانو رس‌ بر رفتار تغيير شكل دايم مخلوط‌هاي آسفالتي گرم (HMA)

Evaluation of Nanoclay Effects on the Permanent Deformation of Hot Mix Asphalt

تغيير شكل دايم يا شيار افتادگي در مسير عبور چرخ‌هاي وسايل نقليه يكي از مهم‌ترين مدهاي خرابي است كه بر عمر روسازي انعطاف‌پذير تاثير مي-گذارد. اين نوع خرابي بيشتر در جاده هاي كه در مناطق گرمسير واقع‌ شده‌اند مشاهده مي‌شود. ويژگي‌هاي مصالح تشكيل‌دهنده نقش زيادي در ويژگي‌هاي ساختماني روسازي بازي مي كنند. اگرچه وزن قير در مخلوط آسفالتي مقدار ناچيزي است، اما با اين‌حال قير اثر مهمي روي عملكرد مخلوط‌هاي آسفالتي دارد و هرگونه تغيير در عملكرد قير، روي عملكرد مخلوط آسفالتي اثرگذار خواهد بود. در دهه‌هاي اخير به منظور غلبه بر مشكلات قيرهاي خالص معمولي و ارتقاي عملكرد مخلوط‌هاي آسفالتي از مواد اصلاح‌كننده قير استفاده مي‌شود. يكي از افزودني‌هايي كه به تازگي در اصلاح مشخصات رفتاري قيرها به كار گرفته‌ شده است، نانو رس است. در اين پژوهش با فرض اينكه بستر و لايه هاي زيراساس و اساس از مقاومت باربري كافي برخوردار است از افزودني نانو رس براي بهبود خواص قير براي افزايش مقاومت باربري آسفالت و اصلاح خصوصيات فني آن در برابر شيار افتادگي در روسازي هاي انعطاف پذير استفاده ‌شده است. بدين منظور از مصالح سنگي آهكي با دانه‌بندي شماره 4، پودر سنگ به عنوان فيلر، قير 60 – 70 خالص و دو نوع نانو رس مونت موريلونيت Cloisite 15A و Cloisite 30B استفاده ‌شده است. آزمايش مارشال، آزمايش هاي خزش ديناميكي در دو سطح تنش 300 و 450 Kpa و شيار جاي چرخ در دماي 50 درجه براي نمونه هاي مخلوط آسفالتي حاوي 2، 4 و 6% از هر نوع نانو رس و نمونه شاهد انجام گرفته است. نتايج حاصل از اين آزمايش ها بهبود عملكرد مخلوط هاي آسفالتي حاوي نانو ذرات را نشان مي دهد

Permanent deformation or rutting in wheel paths is one of the most important failure modes in asphalt pavements that affect the pavement life. Permanent deformation in asphalt mixtures can be defined as the unrecoverable cumulative deformation that occurs mainly at high temperatures in the wheel paths as a result of repeated traffic loading. The deformation results in depressions on the pavement surface along the wheel tracks relative to other points on the surface. Permanent deformation in wheel paths is one of the fundamental defects that occur due to lack of bearing capacity in flexible pavement layers. This type of defect usually occurs in the roads in the tropical areas. Rutting occurs due to cumulative non-reversible Permanent deformations in the pavement layers under repeated traffic loading. In order to increase pavement life and consequently decrease maintenance related traffic delays, great demands are placed on permanent deformation resistance of asphalt mixtures. Hot Mix Asphalt is composed of aggregates and asphalt binder. Properties of these materials have important effects on the pavement structure performance. Although, asphalt binder is a little part of mixture (in comparison with aggregates), but has major effects on the performance, durability and stability of the asphalt concrete mixture. Any change in asphalt properties will result significant changes in the asphalt concrete mixture performance. Since asphalt cement (AC) never fully satisfying lacks the physical and mechanical properties, researchers are constantly trying to improve the asphalt cement properties. Asphalt cement modification will result improved quality and increased life of the pavement. Nano-particles is one of the additives that are used to modify the properties of asphalt cement. Nano-clays are unique materials as additives to make significant improvements in the material properties of polymer Nano-composites. Nano-clay polymer materials typically strengthen the mechanical properties, modulus and stability of these cases. In this research, it is assumed that subgrade, sub-base and base layers of flexible pavement have sufficient resistance to rutting. Nanoclay is used to modification of bitumen properties for Hot Mix Asphalt mixtures better bearing capacity and resistance to rutting. So, limestone aggregate with 4 degration number, AC 60-70 obtained from the Pasargad oil refinery and two types of montmorillonite Nanoclay: Cloisite 15A and Cloisite 30B are used in this study. In order to prepare asphalt binders, base binder was heated up to 150 °C in a small container until it flowed fully and nanoparticle is added and dispersed by using Ultrasonic mixer at the fixed power of 65 watt for 20 min into the unmodified bitumen. the marshal mix design by means of gyratory compactor was used for determining the optimum bitumen content. These values are used to prepare all sampeles. Marshall and Dynamic creep tests in two stress levels (300 and 450 KPa) at 50 ° C, as well as rutting test on the HMA samples with 0, 2, 4 and 6 percent of each Nanoclay were performed. at the end, it is concluded that both additive have great influence on improving rutting resistance of asphalt mixtures.\