دراسة خصائص طبقة اعادة الاكساء الاسفلتية الرقيقة للطرق السريعة

CHARACTERIZING THIN ASPHALT OVERLAY PERFORMANCE FOR HIGHWAY PAVEMENTS

     Over the last decades, the Europe and U.S. transportation Departments and agencies of highway changed their polices from paving new highways to increase the potential of the existed infrastructures. This is recommended by maintenance and rehabilitation using many techniques of pavement preservation such as slurry seal, chip seal, microsurfacing, fog seal, crack treatment and thin asphalt overlay. These pavement preservation techniques are known as a practices of cost-effective and are designed to enhance safety, provide long service life and keep the public budgets. Thin overlay is generally the highest level of preventive maintenance treatment, which can be performed on asphalt-surfaced pavements. Thin asphalt overlays are typically 38.1 mm or less (1.5 inch or less) in thickness. This technique offer an economical resurfacing, preservation, and renewal paving solution for roads requiring safety and smoothness improvements. Thin asphalt overlays has been performed by many transportation agencies with varying success.

     However, characterizing the performance of asphalt mixtures that used as thin asphalt is still under the question by different researchers and highway agencies worldwide. Thus, this research work focused on characterizing thin asphalt overlay suitable for local infrastructure highways network that provides acceptable resistance to rutting, raveling, cracking, and wet weather skid resistance by optimizing mixture constitutions.

    In this study, the experimental program included: design the thin asphalt overlay mixtures using one gradation type (9.5 NMAS), three filler types (Conventional Mineral Filler (CMF), Ordinary Portland Cement (OPC), and Quick Lime (QL)), and five percentages of asphalt content to identify the optimum asphalt content. Then, SBS modified polymer binder was introduced for performance enhancement. This polymer was utilized in percentages of 2%, 4% and 6% of the bitumen content. Different volumetric (e.g., bulk density, air void, void in mineral aggregate and void filled with binder), mechanical (e.g., Marshall stability and flow, indirect tensile strength, creep compliance, wheel track, and skid resistance), and durability (cantabro test, and tensile strength ratio) testing methods were performed to identify the variations in thin asphalt mixtures characteristics due to such incorporations.

    The results disclosed that the filler type have a great impact on the thin asphalt overlay (TAO) mixtures performance in terms of mechanical, durability and volumetric  properties; for example, mixture containing quick lime as a filler showed an increase in stability, indirect tensile strength, creep stiffness, and dynamic stability of (12, 39, 75, 71%) respectively when compared with the mixture comprising conventional mineral filler. On other hand, the addition of SBS modified polymer to the binder with three percentages led to significant improved in mechanical and durability properties such as creep stiffness, skid resistance and rutting resistance, abrasion loss and water damage resistance. The percentage of 2% SBS showed an increase in stability and indirect tensile strength of (118, 7.8, 15%), (93, 35, 38%) respectively compared with other percentage of SBS (0, 4, 6%) respectively when using filler type (CMF). It is worthy to mention that modeling some of these characteristics were achieve and verified for prediction purpose.

     However, the extensive experimental and analytical program disclosed two vital conclusions which are the ability of producing high performance thin asphalt mixtures using local materials with some additives, and the sensitivity of these mixture performance to their constitutions.              ‏ ‎    ‏