The history of geogrids

The first uses of geogrids in bituminous pavements began in the late 1960s.

At the initiative of contractors, the integration of these products in the pavement bodies was to enable the traction forces, such as a wire mesh within a reinforced concrete, to be resumed.

First generation geogrids made of polyester have a modulus of elasticity of 10 to 50 GPa (which is relatively low compared to 210 GPa of steel, often taken as a reference in the construction world). Subsequent studies and experiments have shown that it is difficult to mill these geogrids.

Thus, the good idea of inserting a geogrid into the pavement body now required to be associated with more rigid materials, in order to better take up traction forces(1).

Second generation geogrids are then created: metal frames. Although technologically known and proven, metal did not enter the road reinforcement market until the 1990s. Its modulus of elasticity, sufficiently high to absorb tensile forces within a bituminous structure, as well as the low cost of this technology have led some companies to make this choice. The consequences were nevertheless felt at the end of the pavement's life: it is complex to mill a pavement reinforced with a wire mesh.

The observation of recurrent milling problems led to the successful use of geogrids whose body was rigid in the longitudinal direction, and breaking in the transverse direction. The third generation of glass fibre geogrids coated with protective resin then made a massive market entry in the late 1990s / early 2000s.

In Europe, all the stakeholders are interested in these solutions: companies are created to live only from these products, distributors are looking for products from all over the world to resell, weavers offer their own geogrids on catalog... The assault is launched. In a few years, thousands of square kilometres of pavement are reinforced with glass fibre geogrids, whose modulus of elasticity varies from 40 to 80 GPa depending on the quality of the glass used (the anti-cracking performance being proportional to this rigidity), demonstrating satisfactory efficiency.

The limits specific to the use of these geogrids are then to be found in the manufacturing technology of the 1990s: the stiffness (not to be confused with the stiffness of the materials) resulting from the presence of a fibre protection additive (resin, coating, etc.), completely or partially prevent the good mechanical indentation of the upper and lower layers of asphalt. Some projects may also have been subject to asphalt slides during the application of wearing courses, or even under heavy truck braking constraints once the construction site was completed (bus lanes among others). Some companies are starting to think about the association of a geogrid with a SAMI membrane (2), to fight against these phenomena of layer decoupling.

Thus, around 2010, construction experts specialized in the geogrid field to develop high-performance products adapted to asphalt pavement bodies and their laying methods. Flexible geogrids are then born. Standard glass (requiring a chemical protection coating) is replaced by E-CR glass (treated to resist corrosion in acidic environments), while new solutions based on carbon fibres are proposed.

Carbon fibre geogrids then prove their worth, and prove very effective, to such an extent that they are able to reinforce bituminous pavements, something that glass cannot offer.

The development process is then oriented towards the evolution of geogrid geometry. Their traditional biaxial geometry is indeed optimized for a good number of applications, but certain pavement sectors subjected to specific stresses cannot be satisfied with them.

Thus, thanks to its experience and expertise, Texum offers a solution composed of a SAMI membrane reinforced with a quadriaxial carbon fibre geogrid, to reinforce roundabouts and low radius turn zones. This solution has quickly proven itself and is now used by the largest administrations.

(1) Polyester fibre geogrids can now be used in the structural improvement of unpaved roads or in soil stabilisation, in the form of bi-directional or tridirectional grids. The manufacturers of these products are no longer in the habit of offering them for asphalt reinforcements, as these geogrids are much more efficient for other applications.

(2) SAMI diaphragms associated with geogrids have proven their effectiveness as an anti-cracking system as soon as they are put into service. These reinforced membranes now have other properties, not being associated with TEXGRID carbon fibre geogrids, to reinforce the pavement bodies most exposed to cracking phenomena and tangential forces (turning and/or braking zones).