EFFECT OF SURFACE CRACKING ON RESPONSES OF FLEXIBLE PAVEMENTS STRUCTURE

Abstract

Pavement cracking is a major factor of failure in sof pavements structure, In spit of this, seldom intention has be en considered how is the pavement structure has been affected when surface cracking a re presented and/or progressed. On the other hand, higher costs are presented for m aintenance and repair. Generaly, pavement surface conditions in terms of pavement su rface cracks, rutting, roughness and pit-holes are the main factors used to establis h criteria for pavement maintenance and repair. Structural adequacy factor of the pavem ent is usualy neglected. The accurate decision making processes for maintenance and repair works must be done not only due to functional conditions, but also due to structural conditions. Finite element analysis is used in this research p aper using the ANSYS-10 program. SOLID45, and SOLID185 elements represent u nbounded layers, and asphalt cement layers respectively to evaluate the stresses in a flexible pavement system under different conditions. These conditions were: (1) Th e vertical load of a single wheel was modeled as uniform pressure placed directly at the edge of the transverse crack. (2) The effects of seasonal differentiation of the pave ment material properties during winter and summer. and (3) Various crack depthes wh ich represent 25% , 50%, 75% and 100% of the asphalt layer thicknesses are also, considered in the analysis. The horizontal normal stresses along the top and bottom of the AC layer, and vertical stresses at selected points in the base has been in vestigated. Comparisons of stresses finally were made for all scases. It is found that the presence of crack in the AC layer significantly increases both the vertical stresses and the horizontal stresses in the AC layer which i ndicate a greater potential for tensile stresses outside the tire treads than in the middle of the treads. With the wheel load located at the edge of transverse crack there is considerable change in the values of horizontal and vertical normal stresses in the a sphalt pavement layers. Seasonal variation has significant effect on the normal stre sses values, where the maximum horizontal tension stresses (σyy ) is higher in winter than that in summer with abo ut 66% . Finally, it is recommended that at crack depth rati o (CDR) 50% pavement must be rehabilitated to prevent initiation of new crack s or rutting of asphalt pavement surface. In other side the winter season is consid ered the critical for initiation of cracking, as summer season is considered critical f or rutting occurrence.