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As Britain’s concrete roads increasingly suffer the effects of ageing, Highways England has set aside £400m for a renewals and repair programme in the latest Road Investment Strategy. As part of this, Roadgrip is offering an innovative solution that’s already delivering impressive results in UK trials. Richard Powell from Roadgrip Ltd explains the benefits of longitudinal diamond grinding (LDG).


How long has LDG been around and why was it invented?


Initially developed in the United States, LDG has been used extensively throughout the US. It came to the UK for trials in early 2009.

Mounting maintenance cost concerns and environmental noise on concrete roads meant that the Highways Agency and then Highways England needed to find a way to provide a cost-effective method of restoring the skid resistance to structurally sound concrete pavements without reconstruction.

They had looked at applying asphalt overlays, but the problem has always been that concrete expands and contracts in a different way to asphalt, which affects the joints underneath. A traditional overlay also means you have to raise barriers, drains, kerbs, which has an impact on cost and duration of works.

LDG is a treatment carried out on the concrete surface itself and doesn’t involve raising the height of the surface. This makes it a straightforward long-term treatment that you can do many times over.


How does it work?


If a pavement is structurally sound but suffers from undesirable surface characteristics, such as poor skid resistance and excessive noise, LDG provides an adequate restoration technique.

LDG removes a thin layer from the entire surface of the concrete to expose fresh aggregate. This results in several measurable improvements to the concrete’s surface safety and longevity and negates the need for expensive remedial work or replacement.

It works by passing a rotating 1.2m wide bank of closely spaced, circular diamond-coated blades on a 10-metre rolling straight edge drum. The blades cut a macrotexture into the pavement surface while removing a thin layer.

As well as cutting the improved texture into the surface this also takes out any level differences on the surface particularly differences between slab height. This improves the ride quality for users and reduces the noise created by tyres running over the joints.

During the grinding process, the revolving drum is forced onto the pavement surface under a vertical load and driven along at a constant speed in the direction of traffic, creating a corduroy texture and levelling the surface as it goes.

To reduce the temperature at the drum/pavement interface, and to control any dust created during the process, water is continually applied through the machine onto the blades from a support water tanker. The waste concrete slurry is collected and transferred to a separate tanker using an on-board vacuum before being taken to a recycling plant.



When did Roadgrip get involved with LDG?


Roadgrip has been involved in retexturing highways and runways for the past 15 years using a fleet of runway groovers. Through our involvement with the IGGA (International Grooving and Grinding Association), we became involved with the Highways Agency and Highways England.

The Highways Agency and the Transport Research Laboratory (TRL) started looking at the LDG process in more depth around 14 years ago, as they considered the whole lifecycle renewal for concrete roads. At the time LDG methodology came back as one of the most technically viable options but lost a little momentum due to the lack of equipment in the UK.

Alongside the LDG trials, fine milling was also trialled using planers. While the friction improvement was satisfactory with fine milling, what became more obvious over the years was the damage it was causing to the joints on the motorways. The joints had to be cut deeper and wider, which made the surface even noisier. It was the increased noise problems that led Highways England to revisit the use of LDG.

We were subsequently approached in early 2018 regarding the trial of various surface treatments on a heavily trafficked concrete section of the M25 DBFO [Design Build Finance and Operate] network.

We were well known for grooving runways and retexturing roads with our cutting-edge hydroblasting equipment, so they asked if our existing grooving equipment could be used to carry out grinding trials on the M1.

 In conjunction with Diamond Products and Tyrolit, Roadgrip imported and invested in the latest PC4504 LDG machinery to undertake the grinding trial. We also went through extensive, in-depth training on the process itself and the machine operation.



Where did the more recent UK trials take place?


As documented in a TRL report, the early trials, a 500m length of the A12 Chelmsford bypass at Boreham, was treated in March 2009. The second was on the A12 at Kelvedon, during October and November 2009 and the third (approximately 6 km), took place on the A14 during March and April 2010.

In December 2018, Connect Plus commissioned the LDG trial on the M1 Southbound between Junctions 6 and 5 (along with fine milling, and shot blasting and overlay treatments). The LDG works were carried out by Roadgrip, sub-contracted to Skanska the framework contractor for Connect Plus. This exercise, which aimed to compare the performance of the different treatments for enhancing surface characteristics of exposed PQC pavements, led to the subsequent approval of LDG.


How did LDG perform in the trials?


As part of the M1 trials, Connect Plus commissioned an extensive testing programme to monitor the performance of the various treatments in respect of SCRIM, skid resistance, noise and structural integrity.

Early data from the trials has revealed that:

  • LDG performed well with respect to safety, service, public and third parties, environment and relevant project road objectives
  • The LDG section of the trial is producing substantially higher peak friction values than other treatments
  • 3D laser measurements after installation found that the LDG section showed the greatest improvement in the average texture depth for the retextured concrete sections
  • Of the concrete re-texturing treatments the LDG section noise level was significantly lower than other treatments.

While further results of the M1 trial will come in due course, data published by the IGGA (International Grooving & Grinding Association) suggest that:

  • Longitudinal diamond grooved roads achieved a skid resistance improvement of 54%
  • Longitudinal grooving has excellent acoustic properties, which results in quieter pass-by traffic noise for neighbouring residents. Noise levels went down by 33%, reduced by up to 4.8dB under high-speed conditions and 6dB at 50 mph
  • The cost of longitudinal grinding is nearly half that of resurfacing the same length of road with tarmac
  • A diamond ground surface decreases accident levels by 42% in both dry and wet conditions
  • Longitudinal grooving removes pavement conditions such as warp and curl for improved ride quality
  • Evidence shows that the improvement benefits from diamond grinding retextured concrete last up to 10 years and, where pavement structure is sound, can be re-machined two more times to extend life further.


Will LDG make an impact on the local road network as well?


Our focus is currently on the high-speed network where the benefits of improved friction, ride quality and reduced noise are greater but the benefits of LDG and particularly the environmental benefits are proving of increasing interest to Local Authorities.


Is LDG best put together with any other treatments?


LDG is a standalone process that doesn’t require any other treatments, although some clients have used the road space bookings to undertake minor repairs and re-lining while we have been on site.


How would you measure the cost effectiveness compared with asphalt overlaying or resurfacing?


From a cost point of view, the cost per square meter is similar to a thin overlay but there are no additional costs in joint treatment or the raising of barriers and ironwork.

Environmentally, it has far less impact than asphalt resurfacing. It doesn’t use virgin aggregates or require movement of materials across the country. No fossil fuels are used to heat materials. Even the water used in the LDG process can be recycled on the grinding plant to reduce water consumption.


How many times can LDG be done on the same road?


As LDG only removes 3-4mm of the original pavement surface there is the potential for the surface to be treated several times. Provided that the concrete is structurally sound, the effect of the treatment could extend the life potentially up to 50 years.


This article was originally featured in Highways Magazine. See the Highways Presents video with Richard Powell here: ldg-an-interview-with-richard-powell-for-highways-magazine


To find out more about LDG, contact us for a free factsheet or quote.