In Los Angeles, existing roads are being ground up and replaced with ‘plastic asphalt’, reducing the need for new asphalt to be produced and improving the overall durability and quality of the ground. A similar process has been undertaken in Australia, where recycled glass is being processed into asphalt, while in the UK, a section of the M25 has been laid using 50 per cent recycled content, making it the highest level of recycled content used on a UK strategic road network to date.
In the UK, there are a number of initiatives in use that have been designed to increase the amount of recycled asphalt (RA) used on the motorway and truck road networks, as well as a means of delivering innovative techniques and additives. Recycled plastic has been trialled as a bitumen modifier and as an aggregate replacement, while recycled crushed glass was used for several years as an aggregate replacement by one producer. Both local authority highways teams and government-run bodies are keen to improve the environmental profile of road materials.
- What is the Managing Reclaimed Asphalt Guidance?
- What has changed with Managing Reclaimed Asphalt Guidance?
- What else does reclaimed asphalt guidance include?
- Road Tar
- The Excavation Process
- Coal Tar Hazards
- The Environmental Agency Position on Reclaimed Asphalt
- Coal Tar Sample Preparation
- Determinants of Coal Tar
- Screening for PAH for PAK Marker Spray
- Leachate Testing
- Asphalt and Planings Road Testing
- Site Investigation/Design
- Asphalt Treatment Options
- Health & Safety Considerations
- Environmental Considerations
- How can SOCOTEC help?
What is the Managing Reclaimed Asphalt Guidance?
The Managing Reclaimed Asphalt – Highways and Pavements ADEPT Guidance note is intended as an aid to classifying and reusing arisings from bituminous bound road materials. The main aim of the document is to reduce the amount of hazardous or non-hazardous waste being sent to landfill or for incineration, allowing the industry to reuse as much of this valuable material as possible. The document also outlines the requirements and recommendations for sampling and testing strategies in order to correctly identify the arisings as product wherever possible.
The Guidance is not intended as a complete guide to managing waste materials and should be read in conjunction with the regulations and guidance issued by the relevant regulator – this information should take precedence over the Guidance note.
What has changed with Managing Reclaimed Asphalt Guidance?
As of August 2019, the Managing Reclaimed Asphalt – Highways and Pavements ADEPT Guidance version 2019, revision 1 has been updated to bring it in line with technical information on in-situ stabilisation, as well as detailing the responsibility of those who hold a Duty of Care in relation to arisings from roadworks. This now supersedes the January 2016 version of the document, which has officially been withdrawn.
What else does reclaimed asphalt guidance include?
The guidance covers a large amount of detail around classifying and reusing arisings from bituminous bound road materials. The main points are summarised below:
Road tar is defined as ‘a product prepared by treating high temperature coal tar in such a manner that the product conforms to a specification’. It contains a complex mixture of hydrocarbons; some of these have been shown to be carcinogenic, others are toxic to aquatic life, while some are both.
Road tar is processed from coal tar but does not contain all of the chemicals contained in unrefined coal tar. However, as coal tar and many tar-derived products are classed as carcinogens, road tar must also be considered a carcinogen, despite it potentially containing fewer hazardous compounds than untreated coal tar.
The Excavation Process
Road materials require occasional replacement for a variety of reasons, such as the breakdown of the integrity of the material; a deficit of structural strength in the lower layers of the material, or a loss of surface property. In the removal process, the existing material is milled out using a powered device and the arisings are collected for disposal, or, ideally, re-use.
The removal is a construction process similar in nature to demolishing a building; this cannot be an exact process, as tar and bitumen are often found in close proximity to one another within UK roads.
Coal Tar Hazards
The hazardous nature of coal tar has been assessed through a study of workers in the coal tar industry who have had long and high exposure to coal tar products. The most likely human pathways of exposure are inhalation and ingestion of dust at ambient temperatures. Dermal exposure is also a pathway for tar products, and therefore personnel should avoid handling road planings.
The Environment Agency Position on Reclaimed Asphalt
In the UK, the four environmental regulators generally take the view that all arisings from construction processes should be classed as waste. Anyone carrying, recycling or reprocessing these materials must possess all of the appropriate permits and licences.
Testing for Coal Tar Products.
Coal Tar Sample Preparation
It is vital that any samples presented for analysis are representative and homogenous.
Determinants of Coal Tar
When detecting tar products, two tests are usually carried out:
- Speciated PAH Analysis (PAH16)
- Phenols and cresols either by speciated analysis or by phenol index
To establish whether waste, or potential waste, is hazardous, it is only necessary to test the material in solid form.
Screening for PAH with PAK Marker Spray
It is possible to use an aerosol spray product, known as a PAK marker, which is specifically designed to detect PAH (Polycyclic Aromatic Hydrocarbons). However, PAK marker spray can give false positive results. Other screening methods, such as acrylic white paint spray, can be used, but should be calibrated against the analytical methods for PAH.
Leachate testing is required if the material is to be disposed of in landfill. The leaching properties, as required by the appropriate WAC (Waste Acceptance Criteria) testing, would then need to be established.
Leaving coal tar bound material undisturbed without testing for leachate potential is acceptable. Leaving the material in place means the material never becomes waste and is situated at the highest level in the waste hierarchy. This is the preferred methodology for testing road tar from both an economic and environmental perspective.
Asphalt and Road Planings Testing
If an investigation has not been carried out and the asphalt and road planings are not characterised, the planings must be tested instead.
Prior to any excavation operation for a highways project, it is recommended that an investigation is carried out to establish the location of any road tar contaminated material, the properties of the in-situ material and the anticipated properties of any excavated material. An investigation into existing road conditions and the assessment of the properties and quality of the arisings are essential to achieving the proper re-use of the excavated material.
Cores are recommended for investigating the bound construction, as they allow individual layers to be easily distinguished, while trial pits are useful for investigating the unbound layers.
Site Investigation Design
To assess the nature of the arisings, the variability of the source material must be considered. Cores should be nominally 150mm in diameter and be taken between a range of 25 to 50m centres. A minimum of three cores should be taken unless the site is less than 30 metres squared, when one core will be adequate.
A road core sampling plan should be made and recorded, including the details of all decisions made.
The investigation project manager should have sufficient experience of highway investigation and be familiar with the legislation and guidance referred to throughout the full Managing Reclaimed Asphalt document.
Asphalt Treatment Options
Any treatment chosen must meet the engineering demands of the specific road and the appropriate permits and licences obtained from the relevant regulators. Options include in-situ stabilisation, which can be used to repair roads containing tar, and ex-situ treatment, which involves the removal and treatment of asphalt by crushing, grinding and screening.
There are also a range of alternative solutions, including:
- Short-term prevention (leaving tar contamination in place)
- Reusing planings containing tar classed as hazardous waste (only in cold mix processes)
- Recycling (turning new waste into a new substance/product)
- Recovery processes (removing road tar from the aggregate using biological agents or via pyrolysis of the tar)
- Disposal (a last resort option – incineration and landfill may be available)
Health & Safety Considerations when Handling Asphalt Arisings
A proper assessment of all of the hazards associated with handling asphalt arisings should be carried out, including a full COSHH assessment. Testing should be performed by appropriately qualified personnel and laboratories.
Environmental Considerations – PAH in coal tar
As well as posing a risk to human health, PAH found in coal tar can affect other organisms. Transmission can be by air, surface, groundwater or direct contact. Asphalt plants and other processing areas can be monitored for PAH emissions, either as dust or vapour.
This guidance note summarised in this ‘Hot Topic’ was written by John Booth of SOCOTEC on behalf of ADEPT. Additional input to the original version was provided by Robert Gossling of Lafarge Tarmac and by the Mineral Products Association. Version 2019.2 was updated by Maxine Townsend of Skanska on behalf of ADEPT and CDWF.
How can SOCOTEC help with reclaimed asphalt management?
As one of the UK’s leading providers of bitumen, asphalt and coal tar testing, analysing and reporting, SOCOTEC can offer technical advice, support and on-site services to support your construction and maintenance projects. Get in touch with our team of specialists here.