SA UTFC certified - The Civil Engineering Contractor , October 2008
A contractor has received the first stamp of approval for a brand of ultra-thin frictional course. This could change the status quo, writes David Poggiolini
Novachip has received the Agrément South Africa Certificate of Technical Approval. This is the first ultra-thin frictional course (UTFC) in South Africa to be certified as requested by major client bodies, such as the South African National Roads Authority Limited (SANRAL), in line with concerns about some of the mixes they encountered on their road networks.
Civil Engineering Contractor has learned there is a possibility SANRAL will eventually specify UTFC in an open tender when more contractors certify their products. This gives the Roads & Earthworks division of Concor a major competitive advantage in terms of bidding for road-maintenance contracts. Bear in mind the company was also the first to launch UTFC locally in 1999.
Concor learned about the French Colas pavement methodology from its then subsidiary, Colas South Africa, in the early 1990s. Its array of advantages, including significant cost reduction in road-maintenance programmes, whet the appetites of South African client bodies. With the first major step taken, it was time to formulate a mix suitable for South Africa with its different road-construction materials and warm climate. The final step entailed the purchase of two UTFC pavers and the application of the Novachip on two trial projects for SANRAL. And, in 2001, SANRAL began specifying UTFC from time to time in open tenders. It was only much later that SANRAL expressed concerns about some UTFC mixes used in its projects, and told contractors to seek an independent professional body in order to certify its product fit-for-purpose.
Paul Kruger, from the Roads & Earthworks division of Concor, is extremely bullish about the development. “We have tested Novachip extensively and it has met all our expectations,” he enthuses.
Ultra-thin layers
UTFC is a layer of open-graded hot-mix asphalt applied to a modified-binder tack coat laid in a single pass with a special paver – commonly referred to as the Novachip paver by representatives of Concor Roads & Earthworks.
Since the first project in 1999 on four busy interchanges across the N1 near Pretoria, Gauteng, 13 other highly-successful contracts have been undertaken countrywide by Concor Roads & Earthworks.
Novachip has been used on projects where the UTFC is placed over the existing surfacing with very little preparation similar to that carried out for seals, such as crack sealing, isolated patching and edge-breaking repairs. Texturing of the existing surfacing is not required when applying Novachip; one aspect that has to be considered when comparing costs to conventional seal treatments.
Consulting engineering company Jeffares & Green has acted as a consultant in all of these projects: overseeing the plant and on–site mixes, paying special attention to the voids, bitumen content and, most importantly, grading of the mix. It was also involved in the accreditation of Novachip by Agrément South Africa.
Why UTFC?
Jaco van der Bijl, contracts director of Concor Roads & Earthworks, points out some of the advantages of UTFC. Firstly, the Novachip paving – something between a seal and an asphalt layer – is only applied up to 18 mm thick. This is much thinner than a conventional asphalt layer; offering up to 50% cost reduction in road-construction materials. However the use of this “paved seal” has to be investigated regarding its applicability on a rehabilitation project. Typically, its use is recommended when the remaining life of the existing pavement is of the order of 10 years. In addition, because of its open grade, water dissipates through the mix immediately during heavy rainfalls and thus eliminates the spray factor. Noise also dissipates into the voids of the surface, resulting in a more environment-friendly road.
Add to this an extremely high skid-resistance and the ability to open the road to traffic within an hour or two after the mix has cooled down, and there is no loss of stone associated with conventional chip-and-spray techniques.
Van der Bijl tells Civil Engineering Contractor the company is working with Colas France to develop another product for client bodies with different binders that will provide the mix with enhanced performance. It is, however, still very early days. “Obviously, from a risk point of view, we need to ensure we have the right product before putting it on the road,” states Van der Bijl.
Eye on the road
Nelson Galé of Jeffares & Green notes there is still a second phase to the accreditation of the NOVACHIP. The performance of a road needs to be assessed every six months over the next two years. Factors taken into consideration include skid-resistance, visual deterioration and texture depth.
The UTFC placed in South Africa is too young to know what the typical “end-of-life” signs will be as is the case internationally. However the failure mode expected is ravelling. The expected life of UTFC is between eight and 12 years depending on traffic.
Skid-resistance, texture depth and visual condition
The reseal of the N2 Section 18 between Ibika and Tetyana is being used as the test site for Phase B of the accreditation programme. The Novachip section was constructed in June 2008 on behalf of SANRAL by Concor Roads & Earthworks.
CSIR Built Environment is monitoring the road network on behalf of Agrément South Africa.
Focus will be placed on skid-resistance and texture depth, as well as visual condition of the road network.
Erik Denneman of CSIR Built Environment first visited the site in June 2008 – about a week after construction was actually completed.
He found the road to be in a good condition with no obvious defects. Micro texture was measured by means of the Pendulum tester, which is relevant only when applied at slow vehicle speeds.
Denneman points out: “It would be of interest for low-speed applications to continue performing Pendulum test measurements over the trial period to determine the development of micro texture. However it will also be necessary to monitor macro texture as this determines skid-resistance at high speeds. This would cover the typical application of Novachip. It is deemed acceptable if the measurement of macro texture with a suitable device will first be performed after six months. However it is stressed that the measurement of macro texture will have to form part of the performance trial.” Meanwhile the texture depth results obtained to date, as measured by the sand patch test, satisfy the criteria in the guideline document. Time will tell what transpires at the test site but, for now, Civil Engineering Contractor can give Concor Roads & Earthworks and Jeffares & Green a thumbs up for ongoing work in pavement techniques, and can reveal there are a few more exciting developments up their sleeves.
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