Cracked asphalt is one of the most widespread scourges of pavement engineering. Unwanted pavement cracks develop on roads, in parking areas, at airports and even on the factory floor. Once cracks begin, they are quickly propagated by trafficking and climatic temperature changes, resulting in escalating repair bills and reduced usability.
Fiberglass geogrid has made a major in-road into the asphalt overlay industry. It does not replace the asphalt pavement; rather, it acts as a stress reliever and reinforcement between the asphalt and a substrait base comprised of smaller aggregates. Fiberglass geogrid controls crack reflection and pavement performance. In this article we explain how fiberglass geogrid works, what makes asphalt crack and how fiberglass geogrid makes highway last longer.
What is Fiberglass Geogrid in Asphalt Reinforcement?
Fiberglass geogrid is a reinforcement manufactured from woven, continuous glass fiber filaments. The fiberglass filaments are woven to a dimensionally stable grid, finished with a protective layer of polymer or bitumen coating.
The sintered grid is high strength and thankfully low elongation. This is the critical characteristic that keeps the grid from stretching too much under load, deforming its own shape.
Beside the highway or elsewhere, fiberglass geogrid is laid in pavement applications between the existing pavement and the new asphalt overlay as the reinforcement layer interface. It is used in road rehabilitation, highway engineering, and heavy load pavements.
How Does the Fiberglass Geogrid Work?To appreciate this we must look at what causes cracks in an asphalt pavement in the first place.Fatigue Cracking
What we would otherwise call traffic ‘wear-and-tear’ causes repeated bending stress in the innermost layers of the pavement. Heavy traffic due to trucks makes this action worse. Starting small at the bottom, the cracks work their way up to the top; lazily at times.
Reflection Cracking
When an old road is simply overlaid with new material, reflection cracking can be one of the worst problems of the whole operation. Cracks from the older pavement reflect themselves in the new layer of asphalt. And even though a new surface is laid one is not long waiting for the old cracks to re-appear.
Structural Weakness
A weak base/sub-base, or even bad soil of any kind underneath can led to uneven stress distribution and subsequently to cracking and deformation at a comparatively early stage.
With all of these in mind it can be seen why pavement on its own is not always enough to confer lasting stability.
How Fiberglass Geogrid can stop cracks spreading
Fiberglass geogrid works chiefly, and thoroughly by, a mechanical method of reinforcement and stress redistribution.
High Tensile Strength stops movement
In both machine and transverse directions of the fiberglass geogrid a very high tensile strength is present. Formed in the asphalt as a result of the strain on it, if deformation occurs at all, the grid then works to inhibit any stretching. In effect this means that horizontal movement in the pavement, and thence the development of cracks, are all nervously inhibited, as it were, and happen a lot slower than if the grid were not present.“Forms a bridge”: Stress distribution across a broader area
Not only does this function inhibit the horizontal spreading of a crack but the equally laudable effect can be noted from a stress distribution point of view. Exclude the reinforcement and stress is concentrated vertically—true above the crack or weak point.
Stress distribution undertaken by the geogrid meanwhile, spreads the area of influence due to the load being applied—a larger area, in other words.
This serves to bring down the peak effect in an area—and localized failure is often averted. This geogrid is acting as a ‘bridge’ across a crack perceived to be too great a gamble!
Crack bridging effect
This fiberglass geogrid forms a bridge over the crack already apparent. Attempting to lift itself clear of the pavement, the cracked road is met by a resisting material further ‘up’ in the layers.
Fibreglass geogrid is positive (where applicable). Even in a composite effect with the tack coat, the grid is forming a truly effective binding with the asphalt layers below….and the pavement is working in with each other rather like one large ‘pavement’ instead of bands of separate layers such as the bound and unbound and the bituminous surfacing (see also Fig. 1).
Key Performance Advantages in Road Engineering.
“Fibreglass geogrid protects and reinforces the bituminous surfacing on both asphalt and concrete pavements”
Longer Life Pavement
A reduced susceptibility to cracking of the pavement results in a life of quite definitely longer pavement. This, in turn, helps to lengthen the time to the next stage of resurfacing.
Reduced Maintenance Cycles
Fewer cracks leads to infewer repair cycles. Lengthening the time between maintenance leads to a lower cost of managing the highway for years.
Improved Bearing Strength
Fine use of the glacedover reinforcement and tighter composition of the surfacing helps provide a bituminous layer that will hold its own under the pressure of lighter and heavier loads. Especially useful when loaded with heavier traffic on the highways, logistic roads, industrial zones etc.
Improved Temperature Performance
Glaced over fibreglass grid on the top of the bituminous surfacing is particularly resilient no matter the climate found. Works well in hot or cold areas.
Early Stage Surface Failure Prevention
Most of the asphalt failures are early. Fibreglass geogrid simply delays the damage caused by the low quality of reinforcement early on in the life of the asphalt.
How Is Fibreglass Geogrid Installed Within an Asphalt Overlay System?correct installation is crucial – even the most quality firm, fibreglass geogrid installation if poorly installed will remain of little value.
Surface Cleaning and Sealing: Careful preparation of the surface is required. Dust, oil, random spurious material must all be clean prior to the fibreglass geogrids being laid. Cracks are often sealed first.- Application of Tack Coat: A tack coat of bitumen is sprayed upon the surface and ensures there’s a solid bond between this fibreglass laid upon it and the existing surface. The coat should work as a bond and a friction as it hold together, but too soft a touch and there’s no bond, yet arrestingly large up stabilizes to hold it still. This coat should be applied uniformly. It must be laid flat without wrinkles. Overlap between rolls should be managed as with geogrid.
Asphalt Overlay
After placement of the grid, hot asphalt mix is laid, and the compaction process locks the grid into the pavement structure. Upon cooling, the system is a reinforced laying.
Typical Applications of Fiberglass Geogrid
Widely used for infrastructure projects where cracking control is critical.
Highway Rehabilitation
Old highways suffering reflection cracking of joints a prime candidate for geogrid reinforcement.
Airport Runways
Loading is extreme on runways. Fiberglass geogrid helps maintain the regular surface.
Industrial and Logistics Roads
Trucks cause fatigue damage frequently. Reinforcement makes for a hardier surface.
Parking Lots
Dense lots benefit from reduction in maintenance and longer life of surface.
Municipal Roads
Urban roads subject to rampant traffic continue to be most subject to the temperature change as well, putting the system to the test.
Material Properties and Selection Considerations
Employing different specs for different projects, fiberglass geogrid is often selected for that combination of tensile strength associated with coating type and grid, itself. Common grades of reinforcement with true, rounded polygon mesh include some high-strength designs, suitable for placing under heavy traffic loads. Some systems will use products of fiberglass geogrid in conjunction with geotextile composite systems, for better separation and drainage performance. On some soil reinforces, polyester geogrid and polypropylene geogrid is used, but generally it is fiberglass geogrid preferred in asphalt overlay use since it’s low elongation and high stiffness material makes it ideal. Common names in road engineering would be products like TGSG series and high-strength blends like 80/80 kN. All used by brief design, of course.
Common Design and Installation Mistakes using Fiberglass Geogrid
Using the material of fiberglass geogrid does not simply, of course, let the operator rest on his laurels. Poor practice can reduce effectiveness of the system. One common faux pas is sparing with tack coat application. This causes conflicting layers in which geogrid content fails to bond with bottom layer, slippage. Which leads to improper alignment at installation. And isn’t that how wrinkles and folds in the pavement are created? Temperature control at time of asphalt paving is also important. If too cold, hot stuff cannot penetrate and bond with the mesh. Even grade of tensile strength picked can make the design fail in some conditions.