International Journal of Civil and Structural Engineering Research ISSN 2348-7607 (Online) Vol. 10, Issue 1, pp: (1-13), Month: April 2022 - September 2022, Available at: www.researchpublish.com
Improving the bitumen in HMA to resist the effect of Octahedral Shear Stresses on asphalt pavement surface layer Ahmed Eraky1, H. S. Ayoub 2,3, Omar Osman4 , Mohamed E. Ouf 1, Abdel Zaher E.A. Mostafa 1 1
Department of Civil Engineering, Faculty of Engineering at Mataria, Helwan University, Egypt 2
Department of Physics, Faculty of Science, Cairo University, Egypt
3
Scientific Center for Polymer Technology, 11585, El Mokatam, Cairo, Egypt
4
Department of civil Engineering, Faculty of Engineering, Cairo University, Egypt
Abstract: For a long time, standard Egyptian penetration grade 60/70 bitumen which is actually equivalent to (PG64-22), used to provide a satisfactory ACP performance with current combination of (18t IWL ,1.35 MPa tire pressure). However, by the recent changing the bitumen fractional composition due to bitumen’s origin or/ and different refining techniques, many shear related distresses has been reported. Moreover, top-down cracks (TDCs) have been also observed as one of the most surface distresses in this perspective. Moreover, creep has been reported also in (ACP) especially, in southern latitude airports, where surface layer is exposed excessively to high temperature ambient. In this decade, the criterion of admissible octahedral shear stresses (OSSs) in the flexible surface layer, has been used successfully as a judicious design tool, for the accurate assessment of ACP performance. Consequently, the aim of this work was to study the state of art of using bitumen products through different bitumen types modified by recycled low density polyethylene (LDPE), and its impact on the OSS resistance of ACP surface layer. Keywords: Airfields AC pavement distresses, Enhanced PG LPDE modified binder, Octahedral shear stress.
I. INTRODUCTION In the current decade, there is a widely acknowledgement that AC quality has went down over the recent three decades. There are also considerable evidences to show that crude oil quality has decreased, oil refining processes have become more influencing and bitumen is extended by adding what would traditionally have been waste or by-product (G. White, 2016). Airports, compromising airport pavements, are internationally regulated to provide a minimum standardized level of infrastructure at the starting and destination of international flights. In the current decade, the new-type aircraft have become ever more demanding for the airport pavement. Meanwhile, the need to minimize runway occupancy duration of landing has pushed aircraft to use excessive braking stresses (White, 2014b). It is obvious that as aircraft continue to grow, their wheel loads and tire pressures will continue to increase. Consequently, an improved understanding of how the resulting shear stresses under extreme braking impact on the surface layer of the pavement is critical. Conventionally, Marshall designed dense graded AC (Asphalt Concrete) has been adopted to meet the international standard requirements. However, changes in bitumen quality dedicated for airport AC production and more demanding new-type aircraft, together, have been the main reason for notable falling below the standard requirements in some conventionally-designed airport AC surfaces (G. White, 2017). Since the year 1970, several design methods of flexible pavement have considered fatigue Bottom-Up Cracking (BUC) as the most critical deterioration mechanism. However, premature distresses have been observed recently close to the surface of AC pavement. Shear failure near the ACP surface is an actual dilemma caused by some factors such as: tire-pavement interaction, ACP rheological properties and environmental reasons. Topdown cracks (TDCs) have recently become a common deteriorates type and may be considered as a shear failure (Joao R.
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