‘Forgotten’ asphalt additive could extend road life
MPA Lime hosting webinar to reignite interest in long-proven benefits of adding hydrated lime to asphalt
THE durability of UK highway surfaces could be radically improved by adding hydrated lime to asphalt mixes, according to European research. And now a panel of experts is being brought together for a special webinar to explain the benefits of hydrated lime in asphalt and encourage its specification on the UK’s road network.
MPA Lime, which represents UK lime producers, says that when the recent National Audit Office report and Annual Local Authority Road Maintenance (ALARM) survey are both identifying the poor state of local roads, the time is right to raise awareness of a widely available product that is known to improve the durability, longevity, and sustainability of road surfaces.
Established evidence from highway authorities and researchers in the EU and US – as well as research studies in the UK – shows how adding hydrated lime can benefit the asphalt in numerous ways, helping to improve the climate resilience of asphalt infrastructure.
Hydrated lime acts as an ‘anti-stripping’ additive, helping the bitumen binder to adhere to the aggregate; it also acts in a multi-functional way, reducing bitumen hardening with age and increasing moisture resistance, at the same time stiffening the bitumen to reduce rutting, and improving resistance to fracture growth at low temperatures.
Research suggests that typically with the addition of less than 2% of hydrated lime in the mix, the asphalt could last up to 25% longer, which means slower road deterioration and extended maintenance intervals, leading to fewer potholes and less roadworks, as well as smoother road surfaces and better journeys for road users.
Hosted by MPA Lime, which represents UK lime producers, the webinar on Tuesday 15 October 2024 from 1–2pm will bring together more than 150 years of combined technical and practical career experience in asphalt materials. The panel members are:
Prof Gordon Airey, Professor of Pavement Engineering Materials and Director of Nottingham Transportation Engineering Centre (NTEC), University of Nottingham, UK
Lyle Andrew, executive director, Institute of Asphalt technology, UK
Dr Helen Bailey, programme lead: asphalt and pavements, Centre for Mineral Products, University of Derby, and director, The Driven Consultancy, UK
Dr Didier Lesueur, chief executive officer, Western Research Institute, Wyoming, US
Andy Stevenson, associate director - road services, WDM Ltd, UK.
Hydrated lime – also known as calcium hydroxide – has been specified widely particularly in the US for many years as an anti-stripping additive and there, and elsewhere, to increase moisture resistance of asphalts. There is also proven evidence that it can reduce asphalt ageing by lowering the oxidation of the bitumen binder.
Hydrated lime has been used in the asphalts designed for UK and international airport runways for decades and it is already a permitted, multi-functional additive in the UK’s National Highways asphalt specifications and is in the register of durability improvement options towards achieving its zero-carbon target.
Across Europe and the US hydrated lime is a regularly required component in asphalt and, in some locations, it is compulsory because of the clear evidence of durability and performance improvement leading to more resilient roads.
Research by the University of Nottingham shows how hydrated lime additions absorb unwanted ‘polar compounds’ (such as carbonyls and asphaltenes) within bitumen. Adding hydrated lime means that, with ageing, there are fewer oxidative reactions that cause bitumen to become stiffer, more brittle and lead to cracking and deterioration of roads, and development of potholes.
The study compared the performance of mastics containing hydrated lime to those made with granite or limestone fillers alone, and found that in all cases the hydrated lime made the asphalt softer after ageing – or less stiff – than its counterparts with standard filler alone. Other researchers are now observing a long-term case study on asphalt that was laid on a stretch of the A38 near Burlescombe, Devon, in 2021.
According to Mike Haynes, director of MPA Lime, the case for adding hydrated lime to asphalt is so compelling that highway authorities should not wait before specifying it in the mix.
‘The condition of the UK's road network is rarely out of the headlines these days and so there’s never been a better opportunity for highway specifiers to learn or be reminded about the numerous advantages of hydrated lime as an approved and widely available asphalt additive with a proven track record in improving highway performance,’ he said. ‘It just appears to have been forgotten about and is underused in the UK.
‘I am delighted that we will be joined by such an impressive line-up of speakers for our panel discussion that is looking to reignite interest in the long-proven benefits of adding hydrated lime to asphalt, improving durability, longevity, sustainability, and climate resilience.
‘Longer-lasting road surfacing materials mean slower road deterioration and longer maintenance intervals, leading to fewer potholes, less roadworks, and smoother road surfaces and journeys for road users.’
Webinar details
Title: Hydrated Lime in Asphalt
Date: 15 October 2024
Time: 1pm – 2pm
Register now
