Stop of Reflective Crack Propagation with the Use of PET Geogrid as Asphalt Overlay reinforcement
Asphalt concrete overlays placed over cracked pavements suffer large stresses at the interface under the passage of traffic loads, leading to the reflection-cracking phenomenon. This paper presents a laboratory study for evaluation of the effect of apolyester geogrid as an interlayer reinforcement between a cracked asphalt concrete layer and a non cracked one. The quantitative and qualitative evaluation of the effects of reinforcement system in relation to the traditional rehabilitation technique of asphalt concrete overlay was performed using dynamic fatigue tests were conducted on prismatic beams resting on an elastic foundation that were conceived to simulate a cracked pavement after rehabilitation, with the load applied at the two critical positions: on bending and on shearing. The beams with dimensions of 460 x 150 x 75 mm, had a pre-crack with an opening of 3, 6 and 9 mm. The geogrid was placed on the crack tip. Increases on the fatigue life were observed. The cracking mechanism was changed from a process controlled by a single dominating crack to another one where several micro cracks were formed. These micro cracks were of lower severity, leading to a better performance for the asphalt concrete overlay. The presence of the polyester geogrid had the effect of drastically reducing the opening of the reflective crack and reducing of the plastic deformation on the fatigue life. Simulation using Finite Element Model (FEM) explains the mechanism observed in laboratory.
The laboratory investigation and FE simulation lead to the following conclusions:
• It was observed in laboratory that the inclusion of a polyester geogrid in an asphalt overlay modifies the pattern of reflective cracking propagation. At first, the beginning of crack propagation is delayed. The reflective cracking propagates to a certain length, then it stops. Additional microcrackings arise because of the asphaltic mass fatigue. Such microcrackings are spread over a greater volume within the layer, with a random propagation pattern and a very slow increment. The level of the stress transference along the walls of each microcracking is high, which helps on the reduction of the growth speed for mitigating the stress concentration in its extremity. The random direction of the microcrackings also acts in this way, leading to the occurrence of microcrackings with a geometric shape capable of blocking its subsequent growing.
• For the tested beams, Factors of Effectivness of Geogrid ranging from 4.45 up to 6.14 were obatined.
• In FE simulation, the observations done in laboratory were justified. It was seen that as the crack propagates, the tensile stresses in the tip of the crack decreases up to such a small value that the propagation stops. On the other hand, the tensile stresses in the geogrid increases as the cracks propagates.