Interlayer Working Conditions Classification and Treatment Measures of Airport Asphalt Pavement Overlay

The bonding strength between the overlays of an airport asphalt pavement directly affects its service life. In this study, a finite element model of asphalt overlay on airport pavement of Juba Airport in South Sudan was established, and the elastic modulus of overlay, thickness of overlay, running state of aircraft, variation trend of interlayer shear stress under the action of load and temperature were obtained. The AHP-entropy method was used to calculate the combined weight of each influencing factor. The climate in hot and humid areas was further zoned, and a comprehensive classification of airport asphalt pavement overlay between hot and humid tropics was obtained. Four interlayer treatment measures (asphalt precoating, two oils and one aggregate, geotextile, and geogrid) and three interlayer materials (SBS-modified asphalt, ordinary hot asphalt, and SBS-modified emulsified asphalt) were designed and tested. Through shear test, wheel-load fatigue test, and pressurized seepage test, the variation trends of interlayer shear, crack resistance, and waterproofing under different combination schemes were obtained. Finally, the matching relationship between different working conditions and interlayer treatment measures was established. The results show that the actual working conditions of an airport asphalt pavement can be divided into three levels. Combined with the performance ranking of different materials and interlayer treatment measures, the recommended interlayer treatment measures for comprehensive classifications I, II, and III are two oils and one material + SBS-modified asphalt, asphalt precoating, or geogrid + SBS-modified emulsified asphalt or ordinary hot asphalt, and geotextile + ordinary hot asphalt, respectively. The working conditions in Juba Airport in South Sudan can be classified as comprehensive classification II, the recommended treatment measures for geogrid + ordinary hot asphalt.

Pavement Overlay Design using Falling Weight Deflectometer

Pavement evaluation is a technique of assessing the condition of a pavement, both structurally and surface characteristics. Pavements which have been subjected to traffic, deform elastically under load which depends on type subgrade soil and its compaction level, pavement thickness and its composition, drainage conditions, pavement surface temperature and wheel load. There are number of different types of pavement deflection testing equipment which are being used all over the world. The most common types are Benkelman Beam Deflection (BBD), Falling Weight Deflectometer (FWD) and Dynamic Cone Penetrometer. BBD test widely used method in which rebound deflection is measured on static loading and there by evaluating strength of the pavement. However with limitations and practical difficulties of BBD, FWD was chosen for the study. The deflections of the pavement are recorded due to the dynamic loading and studied for further strength determination. A 4-lane National Highway has been selected and tested for residual strength and it is designed for overlay as per IRC:115-2014 & IRC:37-2012 using FWD equipment and with the assistance of KGPBACK and IIT PAVE software’s. An overlay of 50 mm on one direction and 100 mm on opposite direction was recommended to meet the functional and structural requirement respectively.