Griptop proves its 'staying power' with real road testing

Iron technology market leader Saint-Gobain PAM UK, part of leading international materials company Saint-Gobain, has returned to its original pilot project to undertake independent testing of its GripTop® high friction anti-skid access cover range. The results further highlight the product’s superior road safety performance and durability credentials, particularly when compared with those using other, non-ductile iron materials.

When the GripTop® ductile iron access cover was first launched, a comprehensive field trial was organised in conjunction with Bristol City Council as part of its initiative to provide safer roads for users. Positioned at various points around the road system of Bristol city centre, the access covers have now been in situ for approximately five years and the testing was undertaken to determine how the slip resistant characteristics of the surface had changed, if at all, as a result of exposure to weather and wear and tear from traffic.

Four locations were selected as they offered worst case scenarios for testing due to their high volume of traffic and because the covers were positioned in the wheel track of the roads. Each cover was tested in an ‘as found’ condition and the results produced an average pendulum test value (PRAV) of 80, giving an overall slip potential rating of ‘low’ for all four sites.

Mike Brewer of Bristol City Council said: “The GripTop® covers have performed in an exemplary manner and we’re delighted to learn that they’ve maintained such good skid resistance. The new covers continue to provide a safer environment for road users in Bristol and we are pleased to have been able to support this highly successful trial.”

Paul Thompson of Saint-Gobain PAM UK said: “GripTop® was originally developed and launched to improve safety for road users and at the time we ran our pilot project in conjunction with Bristol City Council, so we were keen to return to these original test sites to see how it had stood up to real road use over the years. We’re delighted with the results that show how the covers have stood the test of time and are providing virtually the same level of skid resistance they gave on the day they were installed.

“What is particularly exciting for us is that the weather was extremely wet on the test day and we were unable to undertake dry testing. However, it is widely acknowledged that wet and contaminated surfaces offer the worst case scenario and those that give good readings in the wet will at least perform as well and usually better when the conditions are dry.”

Carried out by independent NAMAS accredited provider Ceram of Stoke-on-Trent, the tests involved the use of specialised pendulum apparatus and the method was based on that outlined in BS 7976:2002 and BS EN 13036-4:2011, which is recommended by the Health & Safety Executive.

The GripTop® range has been designed and engineered to bring together the benefits of ductile iron, high performance bonding agents and resins and bauxite aggregate. The result being a durable, high friction, anti-skid surface which, as the testing has shown, maintains a high PSRV and ultimately prolonged grip over time. Ductile iron has a proven track record as the material of choice for carriageway access cover applications giving many years of service. In areas of high traffic volume, it is not uncommon for standard access covers of whatever material to become polished over time through the abrasive action of vehicle tyres, potentially resulting in poor skid resistance for road users.

Paul Thompson continued: “Since we launched this product, it has been specified and installed by a number of the UK’s largest local authorities and utilities as well as making its mark in the private sector. This recent round of testing undoubtedly further highlights the level of its performance and suitability for making our roads safer for all types of users.

“These real life results support those gained from of our other recent testing project, where polished access covers were compared to other materials, and further demonstrates how GripTop® significantly outperforms even the best non-ductile iron products by more than 20 per cent. Those specifying our aggregate-coated cover can be reassured and confident in the quality and performance when selecting GripTop®.”

Method of Measurement
The test results are obtained from averaging five values at a given point. Three points on the surface are measured (horizontally, vertically and diagonally) this is to ensure that the slip values are not influenced by the effects of any directional surface characteristics. The measurements are normally conducted in both the wet and dry conditions but due to inclement weather it was impossible to obtain a true dry reading. It is widely acknowledged that wet and contaminated surfaces give the worst case scenario and surfaces that give good values in the wet will at least perform as well and usually better in the dry conditions. The measurements were undertaken used Ceram pendulum number 669 Calibration Certificate CN16 and Rubber Sliders number 121, 122 and 21.

The four locations tested were as follows:

-Area 1 – Eastbound Carriage Way Junction with Bond Street and York Street
-Area 2 – Eastbound Carriage Way Bond Street (Bupa Building)
-Area 3 – Eastbound Carriage Way Junction with Bond Street and Pritchard Street
-Area 4 – Eastbound Carriage Way Bond Street South (Phoenix House)

The areas were tested using two rubber sliders, test slider 55 which is a softer rubber and a slightly harder rubber slider 96. The rubber sliders were pre-condition as described in BS 7976-2:2002 Section 5.2.2.2. The covers were measured in the ‘as found condition’ with no pre-preparation prior to rest.

It is normal during testing to take surface roughness measurements using a surtronic duo roughness meter, however on this occasion, the surface roughness was found to be very high and outside the measuring parameters of the machine.

A Skid Resistance Value of 55 is recommended by the Design Manual for Roads and Bridges (DMRB) as a minimum for high risk situations.

The minimum level of slip resistance value, measured on the pendulum that is deemed to be safe for pedestrians as set by the HAS, is 36 in the worst foreseeably contaminated condition.

Furthermore, the UK Slip Resistance Group, a body set up in 1986 and made up of flooring manufacturers, representatives of the Health and Safety Executive (HSE), test houses, forensic engineers who all have long experience of slip resistance testing, identifying the following categories of slip.

Slipping Potential SRV
High 0 - 24
Moderate 25 - 355
Low 36+

Reference: Modified from UKSRG Guidelines Issue 3 2005, page 20, Table 5.


About HA104/09
Document HA 104/09, entitled ‘Chamber tops and gully tops for road drainage and services: installation and maintenance’ is the latest Advice Note from the Highways Agency and forms part of the ‘Design Manual for Roads and Bridges’ which is the accepted industry ‘bible’ for highways specifiers.

The document states that ‘where chamber tops are likely to be subject to trafficking, including vehicles, cyclists, pedestrians or equestrians, covers proven to provide an adequate level of skid resistance shall be selected.’

It also recommends that products to be used at potentially high risk* sites on trunk roads and motorways should offer a minimum PSRV (Polished Skid Resistance Value) of 60.

* Potentially high risk sites include those containing traffic signals, pedestrian crossings, railway level crossings, roundabouts, bends, and gradients.