Many of Britain’s urban roads were constructed prior to the 1980s and are now subject to repair/replacement. This can involve a complete new pavement construction or the planing off of the upper wearing course, and its replacement with a new surface. The volume of bound aggregate or planings generated by such works can be significant. Any road surface constructed before the 1980s, or any roads surface dressed to the end of the late 1980s could contain coal tar as a binder for the aggregate.
Planings are likely to be classed as ‘non hazardous/hazardous waste’ and may be costly to dispose of to landfill. ESP undertake assessments for clients to assess the levels of contaminants within road planings, provide guidance on re-use options and, if necessary, disposal options. It is good practice (and most cost-efficient) to re-use the planings wherever possible. Depending on the levels of PAH within the planings, re-use options could include inclusion in a hot mix, use as unbound aggregates (subject to a site-specific risk assessment), or as an aggregate in a bitumen bound material such as cold mix asphalt, cement bound material, or hydraulically bound materials.
Coal tar is rich in polyaromatic/polycyclic hydrocarbons and is a potentially hazardous material manufactured from by-products of former ‘town’ gas works and was used as a binder or as spray coating in road construction due to its good adhesive and water-proofing properties.
The US Environmental Protection Agency (EPA) designated 16 PAH compounds which were commonly found on brownfield sites, but also were the most likely to pose a risk to human health or the environment. Other authorities have selected other groups of compounds for their own purposes (e.g. 22 compounds by the UKSHS) however the US EPA 16 PAH compounds form the basis of most analyses.
Relevant guidance on the reuse of road planings includes CSS ENG/2-97 (Sustainable road maintenance – Reduce, Reuse, Recycle), WRAP (Resource efficiency in highways) and the Specification for Highways Works Series 9002/8003. Coal tar compounds and their by-products (e.g. tar oil and pitch) are potentially carcinogenic, and can include very high levels of PAH compounds, some of which have been proven to have carcinogenic effects. The levels of PAH compounds are significantly lower in bitumen and, hence, it is a less hazardous material (PAH compounds commonly pose problems on former industrial and other brownfield development sites).
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