Composite grid reinforcement for long-term pothole prevention
Geogrid composites provide crack control and pavement reinforcement for a long-term solution to road repairs
More than just a bump in the road
The bill to UK taxpayers for repairing potholes has risen to more than £1billion, with the number of potholes being filled up by about a fifth on last year according to research published in March by car servicers Kwik Fit.
Despite spending on road maintenance increasing, with an extra £420million pledged to deal with the problem in the last budget, the Asphalt Industry Alliance (AIA) – whose members supply much of the materials used for repairing holes – claims one in five local roads in England and Wales is in a poor condition and £8bn is needed to carry out a one-time, thorough fix of potholes in England. More than 24,400 miles of road is identified as needing essential maintenance in the next year.
What Causes potholes to form?
Road surface damage and instability is usually a result of a combination of factors including poor soil conditions, poor drainage, weathering effects, increased weight of traffic and the age of the surface.
High vehicle weight and axle loads of traffic can cause load associated cracking with shear and bending forces exceeding the fracture strengths of the existing asphalt (see figure 1).
Figure 1: Water weakens the underlying ground, and the weight of traffic then fatigues and breaks the poorly supported asphalt surface, with aggregate moving both laterally and vertically under loading.
How potholes are typically repaired
The most common repair solution is to construct asphalt inlays (see figure 2). Inlays are economically practical and convenient, however old cracks under the new overlay can rapidly propagate back through to the new surface causing repeated failures. This phenomenon is called reflective cracking (see figure 3).
Because asphalt inlays are otherwise the most practical pothole repair option, research and development has focused on how to prevent reflective cracking.
Figure 2: Asphalt inlay
Solving the problem with Geogrids
Unsurprisingly in light of the road safety and cost issues caused by the UK pothole problem, cracking in asphalt pavements is now recognised as one of the biggest problems faced by highway maintenance engineers and focus has turned to finding a longer-term, more effective repair including using geosynthetics such as reinforced geogrids.
High-strength glass fibre or steel reinforced grids are backed with a polyester geotextile. The benefits of installing the geosynthetic interlayer between the old pavement and new overlay include:
- Waterproofing the pavement
- Delaying the appearance of reflective cracks
- Lengthening the useful life of the overlay
- Added resistance to fatigue cracking
- Saving thickness
Asphalt is confined and compacted within and above the geogrid reducing both vertical and lateral movement. Having a composite sandwich layer with reinforcement grid enables a more efficient means by which to transfer load onto underlying layers.
This approach has resulted in significant whole life cost savings:
- Maintenance cost reduction
- Significant extension of road life over conventional surfacing
- Reduction in asphalt thickness, in some circumstances, saving on material costs, tipping & planing
- Reduced environmental impact associated with longer maintenance intervals
- Reduced hidden costs to businesses and the general public through delays caused by road closure and traffic restrictions.
It is strongly advised that a competent specialist contractor is employed to undertake the installation. Installation by the asphalt surfacing contractor is not usually satisfactory because the operatives will be unfamiliar with the process and they are unlikely to have the necessary skills or qualifications or the correct equipment to ensure correct installation. Installation of the geogrid will usually be scheduled to take place immediately prior to the asphalt surfacing.