Rare 10-year study shows benefits of apshalt reinforcement

10/11/2020
Richard Carr

Richard Carr of ABG - a leader in high performance geosynthetic systems -  discusses a 10-year trial showing geosynthetic asphalt reinforcement can save on maintenance costs.

More than just a bump in the road

Increasing traffic volumes, heavier loadings and the frequency of flooding events all place an excessive strain on the UK’s road infrastructure, resulting in defects from reflective cracking and potholes.

Asphalt Industry Alliance (AIA) put an astronomical price tag of almost £11bn to repair every pothole in England and Wales.

Highway repairs in England cost anywhere between £6,500 to £120,000 per mile depending on the extent of the damage, making more cost-effective, long-term fixes to road renovations paramount.

Why reinforce asphalt?

In civil engineering, the principle of adding a tensile element into a weaker material to make it stronger is well established, with the most obvious example being steel reinforced concrete.

Asphalt reinforcement utilises the same principle, low strain elements absorbing load pressures, reducing movement and preventing the development of cracks.

Many laboratory tests and anecdotal evidence show reinforced pavements last significantly longer, or can be constructed at a reduced thickness to achieve the same design life. However, it has always been very hard to prove on an actual heavily trafficked road due to accessibility issues and the difficulty of monitoring, plus the ad hoc maintenance by utility companies obscuring results, especially over a long period such as 10 years.

Normally councils do not have the resources or budget to continually monitor a road over that time period.

Meltham Mills road trial of long-term reinforcement

An ideal opportunity arose in 2009 when Meltham Mills Road, which acts as a bypass to the town of Meltham in West Yorkshire, needed to be fully resurfaced.

A machine installing the geosynthetic system

The road happens to run alongside an estate of industrial units serving a number of factories including ABG Geosynthetics Ltd.

ABG approached Kirklees Council with a proposed trial of their asphalt reinforcement material placed along a proportion of the road, including across the entrance to their factory where the heaviest traffic occurred.

The whole of Meltham Mills Road was planed 100mm and the trial area of geosynthetic installed and overlain with a binder and surface course.

Typical asphalt reinforcement installation build up

Monitoring of the site was easy since the firm’s engineers walk along the road each workday to access the site entrance and could note any changes in condition over the whole 10-year period.

A time lapse camera was fixed to the wall of the entrance to the ABG factory to record vehicle movements throughout the day and night to give a record of the type and frequency of traffic along Meltham Mills Road.

This gave the opportunity to record a vehicle movement count and intensity, with peak flows reaching eight vehicle movements per minute. In addition to the car and van movements, there were 189 HGV vehicle movements per day. This is three times the average traffic for a minor urban road in the Yorkshire region. The entrance to ABG factory saw vehicles turning and manoeuvring, placing high stress on this area.

SCANNER Survey

After 10 years of heavy trafficking the surface showed distinct signs of distress in the non-reinforced areas. SCANNER (Surface Condition Assessment of the National Network of Roads) results from Kirklees Council provided a dataset of road surface cracking for the longitudinal profile of the road for each lane.

The reinforcement installation area (blue) and highly trafficked area (pink) show a correlation with SCANNER results. There are obvious deformations in the unreinforced and heavily trafficked zone (pink) but no notable defects in the heavily trafficked reinforced zone (blue/pink stripes). See figure 1 below.

Figure 1 – SCANNER crack survey mapped to geosynthetic installation. The heavily trafficked/ reinforced sections (blue and pink stripes) show no sign of cracking, whereas adjacent to this heavy cracking occurs.

The benefit of geosynthetic asphalt reinforcement

After the 10 year period Kirklees agreed that the trial had been a success, providing the much needed evidence that asphalt reinforcement extends the life of a road. Kirklees had used similar treatments on other roads in the borough, which, while not monitored as closely, showed the same increase in performance.

Graham Mallory, who was the group engineer, highways and operations at Kirklees Council at the time of the trial, said: 'The trial enabled evidence and comparison of road surface performance at a single site with and without the use of the reinforcement layer.

'As a consequence of using the reinforcement layer we can clearly see the effectiveness in reducing reflective cracking, a longer service life, reduced reactive maintenance works, financial savings over time, and reduced disruption to businesses and the travelling public.'

Based on this long term study it is clear that asphalt reinforcement can provide a significant cost benefit. The initial £5 per m2 cost to install the geosynthetic is recouped by year six owing to the reduction in maintenance required. Comparing a 22-year lifecycle for an unreinforced maintained road with a 26-year lifecycle, the reinforced road saves 21% in maintenance costs alone and it is estimated the overall cost savings will be over 50%.

Long-term asphalt reinforcement trial key findings

  • Unique 10 year repair monitoring period
  • Busy road with high HGV loadings servicing local industrial estate. Three times the average traffic volume for a minor road in West Yorkshire
  • SCANNER results show crack formation correlation between reinforced and unreinforced sections
  • Maintenance saving of 21% and total cost saving of 50% extrapolated over 26-year road life
  • Proven by SCANNER graph, no cracks within geosynthetic reinforced area
  • Reduction in CO2 emissions owing to extended maintenance and resurfacing cycles

You can find out more about asphalt reinforcement geosynthetics at an upcoming seminar from LCRIG

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