Improving the Performance of Geogrids in Asphalt Layers
Improving the Performance of Geogrids in Asphalt Layers: Full-Scale Evaluation

In the first part of this blog series, we explored the importance of asphalt overlay geogrids in improving the durability and strength of pavement structures by reinforcing and controlling crack reflection. Now, we will delve into the characterization aspects, focusing on two fundamental concepts: the selection of the raw material and the evaluation of the real performance under cyclic loading conditions.
Raw Material Characterization: Polyester vs. Fiberglass

Before discussing the mechanical parameters of geogrids for asphalt layers, it is essential to understand how the raw material influences its behavior. Selecting the right material is crucial to determine its strength and durability. In the case of polyester, it is a polymer resin derived from the petrochemical industry, inherently elastic, with high resistance to cyclic loading and high temperatures, where properties such as viscosity, molecular weight and carboxylic group coefficient, They classify it as having high tenacity and high modulus.
The spinning process transforms the raw material into polyester multifilaments, with which geogrids are manufactured. These multifilaments also have high elasticity, which gives them a notable capacity for elastic recovery and low susceptibility to plastic deformations. These properties are essential to resist cyclic stresses and fatigue in asphalt layers.
In contrast, fiberglass is made up of thin strands made from silica or special glass formulations, extruded as filaments of tiny diameter and suitable for weaving processes [1], characterized by high tensile strength. and low elongation, but with low resistance to compression and bending, in fact there is a relationship of proportionality between the bending diameter of the filament, to the diameter of the filament [2], which limits its performance during the service stage due to its high damage during installation and in its behavior against cyclical tension loading
Actual Performance Evaluation: Geogrid Efficiency Factor

Since the asphalt layers are subjected to cyclic loading and stress changes in tension/compression, geogrids for asphalt layers must be evaluated under this concept. To evaluate its performance, laboratory tests were carried out on specimens reinforced and not reinforced with geogrid in their central plane, measuring the number of cycles until failure in both conditions. The failure condition is defined by the propagation of a pre-existing crack through the thickness of the specimens.
The efficiency factor is calculated by comparing the number of load cycles that the reinforced specimens withstand with the number of load cycles of the unreinforced specimens. This factor provides a realistic measure of the benefit that geogrids offer in terms of fatigue resistance of asphalt layers.
The results reveal that all geogrids provide some level of benefit in the performance of asphalt layers. However, despite having similar ultimate strengths, fiberglass and polyester geogrids show significant differences in their actual performance under cyclic loading conditions, showing that the level of benefit cannot be evaluated based on the ultimate strength of the geogrids. which is done under monotonic loading conditions.
For example, a fiberglass geogrid with an ultimate strength of 100 kN/m has an efficiency factor of 1.37, while a polyester geogrid of the same strength has an efficiency factor of 7.0. This demonstrates that, under cyclic loading conditions, lower strength polyester geogrids can outperform or equal the performance of high tensile strength fiberglass geogrids.
Conclusions and Final Considerations
In summary, accurate characterization of geogrids goes beyond simply evaluating their ultimate strength. It is essential to consider their actual performance under cyclic loading conditions, as this more accurately reflects their ability to resist fatigue in asphalt layers. Engineers and construction professionals roads They should take these factors into account when selecting the most suitable geogrids for their projects. In the next blog in this series, we will explore specific case studies and practical applications of geogrids in road infrastructure projects.
References
[1] Loewenstein, K. L. (1973). The Manufacturing Technology of Continuous Glass Fibers (in English). Elsevier Scientific. pp. 2-94. ISBN 0-444-41109-7.
[2] Hillermeier KH, Melliand Textilberichte 1/1969, Dortmund-Mengede, pp. 26-28, "Glass fiber-its properties related to the filament fiber diameter".