Prevention and Management of Road Surface Damage

Lead Research Organisation: University of Nottingham
Department Name: Faculty of Engineering


The UK's road network totals around 250,000 miles of paved roads providing a means for efficient distribution of goods and services, supporting UK economic security and social prosperity, and this support will continue to be needed whatever the future of automated vehicle technology. The entire road network has been valued at £750 billion and as the UK's main transport infrastructure provides a vital service to road users, commerce and industry. However, road surface damage, particularly potholes, has become a serious safety and performance concern for all network users. The need to improve the quality, longevity and accessibility of the highway network is a vital concern of government, industry and the travelling public. It is highlighted by the recent dramatic increase in the number of cars taken in for repair of pothole-induced damage (up from 6.3M to 8.2M in two years according to a Kwik Fit survey, at an estimated annual cost to motorists of about £900M) and the maintenance backlog for local highway authorities, costed at £9.8B by the Asphalt Industry Alliance earlier this year. Episodes of severe weather in recent years (record-breaking rainfall, extreme cold-weather events), combined with tight financial constraints on highway authorities, have also led to a much publicised 'pothole epidemic', and the situation is made worse by the lack of longevity sometimes achieved in defect repairs.

Against this background, this proposal has twin interrelated ambitions to (1) enable the design/construction of roads so as to minimise surface damage (i.e. prevention); and (2) induce a step change in the science of road repair (i.e. management). These ambitions can only be realised by establishing a level of understanding that does not currently exist within the pavement engineering community. This involves isolating, by both experimental studies and theoretical modelling, the real root causes of road surface damage - although it is well known that water and ice play vital roles. This knowledge has then to be combined with evaluation of actual road data in order to produce a robust and validated design and analysis tool and to generate appropriate construction and maintenance guidance. The research needed to successfully deliver these twin ambitions will require the combined effort and expertise of pavement engineers, materials scientists and computational fluid dynamics experts, expertise found at the University of Nottingham and Brunel University. In addition, the project will only be possible through the assistance of industrial partners with specific capabilities that will complement the academic input from Nottingham and Brunel. These comprise: three highway authorities (Highways England, Transport for London and Nottinghamshire County Council), giving access to data resources as well as direct field investigation opportunities; two umbrella organisations (ADEPT - representing local authority highways departments, RSTA - representing suppliers and contractors concerned with road surface treatments); and, finally, one producer of highway material test equipment (Cooper Technology), giving specialist input into test development.

Planned Impact

This project will generate an understanding of the mechanisms behind pavement surface damage and skills gained from this project, especially those relating to environmental attack (rain, frost), will be applicable to both pavement engineering and the engineering of other exposed structures. In particular, the project will have significant implication for both specification of surface course materials and damage repair strategies. Specifically, impact will be felt in the following ways:

1) Road authorities (Highways England and local highway authorities) will benefit in the short term by taking advantage of the outcomes of this project to optimise repair design, material selection and repair techniques. They will also benefit in the longer term from the recommendations made for surface course specification, leading to more durable pavement structures. The current £150+ Million cost of UK pothole repairs should fall progressively as changes are implemented, and the durability of both new and repaired road surfaces improves.

2) There will be direct benefit to asphalt material developers, allowing them to target the most effective mixture properties.

3) Improved design capability will also impact on the competitiveness of UK consultants, potentially allowing them to keep one step ahead of the rest of the world.

4) Immediate impact will also be felt by test equipment manufacturers, with the introduction of new and improved testing recommendations.

5) Reducing road surface damage will lead directly to a reduction in operating costs. The proposers' view is that a 1% fuel efficiency gain is realistic in the long term and, since 47.2 billion litres of fuel were consumed by UK road transport in 2017, the saving for the economy would be about £250M per annum (considering only true cost, i.e. excluding tax).

6) It will also lead to fewer injuries and accidents, particularly to cyclists and motorcyclists.

7) The current annual cost of pothole related vehicle repair, currently estimated to be £900M, would be expected to fall dramatically - by over £200M based on recent rates of increase.

8) Increased road user satisfaction would also be expected due to reduced frequency of intrusive and disruptive road maintenance, with time / financial benefit to UK business and the travelling public.


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Title Simulation of asphalt cracking using FE including interface elements 
Description This tool is able to replicate the observed failure pattern in a dense asphalt mixture by assigning sensible visco-elastic properties to the bituminous mortar surrounding a crushed rock aggregate, and appropriate cohesive strength to both mortar and interface elements. The spatial distribution of aggregate is based on X-ray CT images. The mesh density has to be very high in zones at or close to contacts between aggregate particles. Although this computational tool is limited by being 2D, it's observed realism suggests that it will be suited to use for the case of road surface fragmentation under the complex combination of stresses induced by the tyre / water pressure combination under traffic in wet conditions. 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2021 
Impact Impact is expected later in the project when combined with other project elements. 
Title Simulation of moisture diffusion through bituminous mortar and into aggregate particles 
Description This software developed applies Fick's laws in 2D, taking published diffusion parameters as input. Whilst no direct validation of the findings can as yet be put forward, the results strongly suggest that diffusion is a likely mechanism contribution to weakening of the adhesive bond between mortar and aggregate. As yet, this computational tool has only been applied to an artificial geometry, and the degree of weakening that might be engendered is yet to be established. Nevertheless the tool stands ready to be applied once calibration evidence emerges from planned experiments. 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2021 
Impact Impact will occur when combined with other project elements 
Title Simulation of temperature regime in a pavement 
Description This is a relatively simple 1D application of Fick's laws. The purpose is to provide a way of predicting the frequency of occurrence of different pavement temperatures applying through a typical year. The tool has been developed and awaits use as part of a broader pavement deterioration prediction method once other elements are in place. 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2021 
Impact No independent impact. But it will contribute to overall impact when combined with other project elements. 
Title Simulation of water effects at the tyre-surface contact 
Description This is a complex computational tool that combines FE for solid elements (tyre, pavement) with CFD for water and air. It has been applied to the situation at the front part of the contact where the tyre pushes through the water in order to touch the surface. This pressurises the water locally - approximately matching the applied tyre pressure - and induces large water velocities both at the surface and within cracks in the pavement. To date this tool has been applied to the issue of stresses acting on a surface stone due to 'drag' as water flows past and over, suggesting that this would expedite stone loss from a surface. It has also been applied to flow through a crack, where predicted velocities are up to 40 m/sec, and this will inform some of the simulative bitumen erosion experiments being carried out in this project. Finally, the combined effect of water pressures at the surface and in connected voids has been translated into a stress map within an asphalt. This highlights very high stresses predicted close to contacts between aggregate particles, high enough to cause localised failure in some cases. 
Type Of Technology New/Improved Technique/Technology 
Year Produced 2022 
Impact Impact will occur when combined with other project elements. 
Description Industry workshop 
Form Of Engagement Activity A formal working group, expert panel or dialogue
Part Of Official Scheme? No
Geographic Reach National
Primary Audience Professional Practitioners
Results and Impact The primary purpose of this workshop was to provide input from road maintaining authorities, tapping into their experiences and thereby refining the priorities of the project. Specifically, the workshop was tasked with addressing the following five questions:
Q1: Based on your experience, what are the main reasons for/factors affecting pothole formation?
Q2: Based on your experience, are there any asphalt types more prone to potholes than others? And why?
Q3: What are the reasons behind premature failure of pothole patching?
Q4: Based on your experience, what are the most successful methods for treating potholes and how long do you think they last?
Q5: How do you think we can improve the survival life of pothole patches?
The following were the principal points that arose:
- There is general agreement that potholes put a serious burden on local government budgets and critically affect the safety of road users. This problem requires innovative practical solutions that can reduce the repair cost, increases the service life of the repair, and improve safety on the roads.
- Premature failure of roads can happen due to two group of factors: during construction (weak substructure, poor structural design, poor compaction, poor bond between pavement layers, and oxidisation) and after construction (oxidisation, poor water drainage, and water ingress).
- The presence of water on the pavement surface or in the pavement is one of the main factors that leads to deterioration of pavement condition and appearance of distress.
- Pore water pressure in voids in asphalt pavements can have a significant impact on the initiation and propagation of pavement distress in particular pothole formation and deterioration.
- Erosion at the road surface due to water flow under vehicle tyres is a slow process that may or may not produce noticeable damage to the pavement. It depends on vehicle speed and tyre pressure, which are the main factors affecting water velocity at the pavement surface. Therefore, the water flow damage (if any) may be more evident on motorways and Class A roads than other road categories due to the speed issue.
- Moisture remaining on a pavement surface prior to a surfacing process could be an important cause of pothole formation. This moisture would be expected to turn into steam and become entrapped under the new layer, then condensing to water again and causing damage through mechanisms such as water pressure, debonding, or freeze and thaw.
- Oxidisation of the top 10-15mm of roads is also a critical factor affecting the formation and deterioration of distress. Delaying bitumen oxidisation can prolong pavement service life and delay the appearance of distress.
- Variable compaction, variable pre-existing moisture content, and variable asphalt temperature during construction are some of the main factors that lead to variability in the appearance of potholes on the road network.
- Research efforts need to concentrate on developing a better understanding of the pavement water damage mechanisms and how to integrate them with pavement damage by other factors such as traffic and ageing to provide better pavement performance prediction methods. This should be aligned with better understanding of the relationships between air void content, air void interconnectivity, "surface" air void and water damage mechanisms such as pore water pressure and water ingress.
Year(s) Of Engagement Activity 2021
Description Press release: "Pothole project to pave way to smoother roads" 
Form Of Engagement Activity A press release, press conference or response to a media enquiry/interview
Part Of Official Scheme? No
Geographic Reach International
Primary Audience Professional Practitioners
Results and Impact This press release was put out through our research partners at Aston University. The primary purpose of the press release was to ensure that information about the project was in the public domain at an early stage, allowing interested parties to contact the research team. The following is the text to the press release:

'A project which will be the driving force behind the redesigning of roads and changes in road repairs could revolutionise the way potholes are repaired, and road surfaces are designed. The three-year collaboration, 'Prevention and Management of Road Surface Damage', is being led by Mujib Rahman, professor in civil engineering, Department of Civil Engineering at Aston University and Dr Nick Thom of the University of Nottingham. The project will combine the efforts and expertise of pavement engineers, material scientists and computational fluid dynamic experts from both universities. The research aims to improve the design and construction of roads to minimise surface damage caused by water freezing and thawing, and general wear and tear from traffic. It also will be looking at how to change the science behind road repairs and maintenance. Research will be looking at two main elements:
- Enable the design of roads to prevent surface damage from water and environmental factors
- Introduce a change in the management of road repair and create a more durable repair of the road surface.
Professor Rahman said that smoother roads were critical to the nation as the 250,000 miles of paved road, valued at £750 billion, which is the network for deliveries of goods and services across the UK. But he added potholes and damage to roads had become 'increasingly problematic' for all users."We want to drive out the pothole epidemic that has overcome the UK in recent years. Due to record breaking rainfall, extreme cold weather and tight financial constraints on highway authorities, this situation has become much worse. This has been combined with the lack of longevity in some repairs" he said.
Dr Nick Thom, from the Nottingham Transportation Engineering Centre Research Group, said: "The expected deliverables are material specifications and maintenance guidelines designed - like a Covid vaccine - to stop this disease of the road in its tracks. In the main this will be about doing better with currently-used resources, but, given the expected slump in future oil production with consequent loss of bitumen supplies, the search will also be on for alternative viable high-performance products."
The project has been funded by Engineering and Physical Science Research Council (EPSRC) and will be running until March 2024. Supporting it will also be ADEPT, Highways England, Transport for London, Nottinghamshire County Council, Cooper Technology and the Road Surface Treatment Association (RSTA).'
Year(s) Of Engagement Activity 2021