Nottingham Transportation Engineering Centre at the University of Nottingham 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. (See Amey trials graphene-enhanced asphalt.)
Gipave is a graphene-enhanced polymeric supermodifier that involves melting pellets (containing graphene and recycled plastics) into the aggregate mix when the stone is mixed with bitumen. The resulting product has been shown to extend expected surface lifetime by approximately 2.5 times over its non-Gipave alternative – expecting to last up to 25 years.
To better estimate the longevity of Gipave when used to build or repair pavements, the University of Nottingham carried out pavement design analysis that looked to model the structural performance that Gipave could exhibit in the real world across a range of different road types and surfacing materials.
Working in collaboration with Amey’s Kent highways team and KCC, four recently resurfaced roads with different construction types were identified, core sample results provided and the University of Nottingham carried out a set of comparative pavement design analyses (PDAs) for each site. The PDAs looked at Gipave vs stone mastic asphalt (SMA), Gipave vs asphalt concrete (AC) and Gipave vs 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. It also indicated that the scale of that lifetime extension was limited by the quality of the base and binder course below the Gipave surface. However, the performance of a Gipave asphalt mix – like any asphalt layer – depends on the pavement's structural characteristics.
Professor Nick Thom from the University of Nottingham 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 to 3.”
Using the outputs from the PDA, Amey’s team has worked with Kent County Council to produce an asset lifecycle model that provides estimates for the cost and carbon saving using the Gipave product, showing that over a 65-year asset life, carbon savings of 23kg CO2/m2 could be achieved on a scheme such as East Hill, Dartford (covering 2,700 m2), as well as more than 1.5 tonnes of waste plastic that would be recycled into the asphalt surface. Although the material is more expensive to lay in the first place, modelling showed a 32% reduction in cost over its lifetime.
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.”
As a result of the research from University of Nottingham, KCC 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 over the years – reducing the need to come back after 15 years to resurface again.