Paving the way to better asphalt

Research into the use of a graphene-enhanced asphalt ‘supermodifier’ has found that the additional upfront cost is more than compensated for by the increased lifespan of the repaired surface.

The University of Nottingham’s Transportation Engineering Centre has been working with Kent County Council (KCC) and its highways contractor Amey to assess the pros and cons of using Gipave to repair and resurface road pavements.

The research, part of the £22.9m Association of Directors of Environment, Economy, Planning & Transport (Adept) Smart Places Live Labs programme, builds on the Gipave trial KCC and Amey undertook in July 2020, where core samples from the Gipave asphalt carriageway showed improvements in many structural factors, including fracture toughness, stiffness modulus and fatigue.

Gipave is a graphene-enhanced polymeric supermodifier comprising pellets containing graphene and recycled plastics that are melted into the aggregate mix with bitumen. The resulting product has been shown to have an extended surface lifetime of up to 25 years – approximately two and a half times that of traditional asphalt.

This article was first published in the July 2022 issue of The Construction Index Magazine. Sign up online.

To better estimate the longevity of Gipave when used to build or repair pavements, the University of Nottingham carried out pavement design analyses (PDA) to model the product’s structural performance across a range of different road types and surfacing materials.

Working in collaboration with KCC and Amey’s Kent Highways team, the university analysed core samples from a number of recently-resurfaced roads of different construction types, namely stone mastic asphalt (SMA), asphalt concrete (AC) and polymer-modified bitumen (PMB).

Modelling from the PDAs concluded that all of the sites would show some improvement in lifetime extension through the use of Gipave, with one site lasting more than four times longer with Gipave than SMA before top-down cracks started appearing.

The research also indicated that any lifetime extension was limited by the quality of the base and binder course below the Gipave surface; performance of a Gipave asphalt mix, like any asphalt layer, depends on the pavement’s structural characteristics.

University of Nottingham professor Nick Thom said: “Two cases have been identified where Gipave is likely to provide significant benefit. The first is the case of SMA surface and binder course over a hydraulically-bound (e.g. cemented) or cold-mix asphalt base; the second is a thick asphalt pavement including SMA surface and binder course. In both these cases the benefit derived from Gipave additive in terms of life extension prior to significant maintenance is predicted to be a factor of 2.5 - 3.”

Using the results of Nottingham University’s analysis, Amey and KCC have produced an asset lifecycle model that estimates the cost and carbon savings achievable using the Gipave product. The model indicates that over a 65-year asset life, savings of 23kg CO₂/m² could be achieved on one particular scheme (East Hill in Dartford) covering 2,700 m². Furthermore, plastic waste in excess of 1.5 tonnes would also be recycled into the asphalt surface.

Although the material is more expensive to lay in the first place, modelling showed there would be a 32% reduction in cost over its lifetime.

This article was first published in the July 2022 issue of The Construction Index Magazine. Sign up online.

Sunita Dulai, head of business improvement for transport infrastructure at Amey, said: “Working in collaboration with the University of Nottingham we’re able to show the science behind live research trials and provide statistical evidence to our client of the benefits of introducing new, environmental products to traditional repair and maintenance works.”

KCC now plans to undertake works with Gipave on three other schemes later this year to trial the material in a wider range of locations and road types. These trials will seek to replicate test results from the 350-metre trial in East Hill, Dartford, and also test the commercial viability of Gipave.

Depending on the results of these further trials, KCC is considering using Gipave to resurface some of its busiest roads so as to minimise disruption at the most sensitive sites and reduce the need to come back after 15 years to resurface again.

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