Evaluation of an airport pavement after almost 8 years of overlay rehabilitation with a polyester geogrid asphalt reinforcement
Crack reflection for the new asphalt overlay have been a frequent problem in pavement mainte-nance jobs on roads and on airports. For prolonging the service life of a rehabilitated pavements, in January2002, a new overlay was executed on an originally rigid access stretch known as Taxi Golf of the SalgadoFilho International Airport in Porto Alegre, state of Rio Grande do Sul in Brazil.A polyester geogrid was used as an anti-reflective crack system and asphalt reinforcement for enlarging the service life of the restoredpavement. After almost 8 years of the work done the comparison of the benefits of the reinforced overlay with of a simple overlay is possible, once two tracks were restored, one with geogrid and other without. The trackwithout geogrid presents a severe condition of crack pattern. To evaluate the vertical and horizontal move-ments between existing crack walls a displacement measurement device called "Crack Activity Meter" was used. The adherence between asphalt layers is very important for the good behavior of the pavement. The stress distribution on the interface of asphalt layers may be deeply influenced by its adherence. A directshear equipment called "Leutner Shear Test" was used for verifying the adherence between asphalt layers and thegeogrid.
The use of the geogrid as asphalt overlay reinforce-ment on the last intervention proved to be very ef-fective. Only a few reflective cracks appeared after almost 8 years of heavy aircraft traffic on that area. In all these cases, a visual inspection leaded to the conclusion that the geogrid was responsible for keeping some "residual integrity" of the reflective cracks, avoiding important water infiltration and visual fine pumping effect. The same way, in all these cases, the surface cracks are not severe and still keep shearing resistance, what was observed by the crack activity measurements done. By analyzing the results present on Figure 7, it is clear that vertical displacements are dominant in the studied case. It is an important information at the time of studying a new maintenance project. Resid-ual shearing strength on the cracks, promoted by the geogrids, allow for a remarkable decrease of vertical displacements on the cracks on the reinforced zones, what implies on much less severe condition in terms of potential for crack reflection on those areas. It is different the situation on the non reinforced area. On these areas, reflective cracks are thick and extremely opened. A new maintenance intervention should be forecasted. At least a sealing work over these cracks for avoiding water infiltration and fines pumping effect should be done. It is also remarkable the good adherence of the geogrid on the asphalt pavement depicted from the direct shear tests performed on lab with some ex-tracted cores. The obtained results are greater than the minimum required by German regulations. The good adherence is mainly due to the bituminous coating of the geogrid used in this. It is clear that, based on the present situation of the evaluated area, a new overlay rehabilitation (simple repaving by an homogeneous thickness of asphalt concrete) would lead to different results on each track. Due to the considerably less severe con-dition of the reinforced area surface, it would be ex-pected a much longer service life of this track com-pared to the one without reinforcement. From this observation, it may be concluded that the use of a proper asphalt reinforcement material (polyester geogrid) on overlay rehabilitation works, not only prolongs the service life of the intervention in ques-tion, but also the service life of all the other future works on the same pavement.