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Tar Testing

Nicholls Colton Analytical has been providing a tar testing service for a few years now and we found that many of our customers were unsure about what testing they required and how the results related to their schemes.  This page is intended to guide you through the options of tar testing on road materials.

History of Tar in Road Construction

The term tarmac (from tar macadam) is occasionally still used as a description of road surfacing materials. Tar was used as a binder in road materials since the 1800’s but has not been used in road construction since the mid 1970’s although it remained in use for surface dressing until the late 1980’s.

The Problem

Tar (or coal tar) is classified as a carcinogenic substance (cancer causing) due to the presence of high levels of Polyaromatic Hydrocarbons (PAHs) and other harmful components within its make-up. Due to the carcinogenic nature of tar a hazard is created whenever road materials are dug up or when the surface is planed this makes tar testing essential.

Many of our existing roads could potentially contain tar in one of the numerous unseen layers that make up the pavement construction.  There may be a layer of surface dressing that was applied before 1980 that was subsequently overlaid with a bituminous material.

When any roads are to be dug up or planed, unless records covering all of the road construction exist, there is a need for tar testing to ascertain the hazards.  This is necessary whether the material is to be recycled or destined for landfill as a waste.

The Solution

In January 2009 the County Surveyors’ Society (CSS) produced a guidance note called “Road Materials Containing Tar”. This document provides guidance that is invaluable to anyone planning works where excavation of bituminous roads is required. The CSS guidance note recommends that cores be taken prior to the design of the works so that relevant data can be gathered and informed decisions made regarding management of the hazards.

Nicholls Colton Analytical offer a full in-house tar testing service that follows the testing guidelines outlined in the CSS guidance note. Testing consists of determination of PAH levels of the supplied material to provide Total and speciated PAH figures.  The speciated figures are essential to provide Benzo (a) pyrene concentrations.  The material is also subjected to a leaching step (rolling a set mass of solid sample with a known amount of water).  The recovered water (leachate) is then subjected to a Phenol analysis.

For the material to be classified as non hazardous the guidance note suggests that:

Benzo (a) pyrene should be below 100ppm (mg/kg), the total PAHs (USEPA 16 + coronene) should be below 1000ppm (mg/kg) and the concentration of Phenol in the leachate is less than 1mg/kg.

Selection of Samples

As already mentioned it is advisable to obtain cores through the whole depth of construction before any major works commence. Some customers prefer to identify layers that appear to contain tar using a quick method e.g. a spray test and then confirm this with the full tar testing suite.  It might be useful to test all of the layers individually so that all variations of combining different layers can be considered therefore optimising the recycling options. Ultimately this is the decision of the customer but Nicholls Colton Analytical are happy to assist in the decision making process.

Method Selection

It is important that your chosen laboratory understands the nature of this type of testing to ensure that the materials are treated in the correct manner.  Many environmental labs were set up to test soils with regard to classifying them for hazards to human health and therefore without modification would produce results that would not be useful for the assessment of road materials. Nicholls Colton Analytical has developed specific methods designed for customers requiring road materials testing. We are also quite unique in being able to offer a complete in-house service including pavement coring, core logging, identification of tar by the PAK indicator test and a full tar testing suite.

If you would like more details including prices please contact us by e-mail or call 0116 2536333 and ask for James Gane or Luigi Sorrentino.