I understand the committee has called this meeting because of damage caused to many houses in recent years by heaving fill and concerns about the possibility of pyrite-induced damage to the new M3 which is due to open in a few months' time. Pyrite is a mineral consisting of iron and sulphur. It is one of the most common sulphide materials and is found in a wide range of rocks and soils, coal beds, quartz bands and elsewhere. It has been mined since ancient times and is still in use for some commercial applications, for example, the production of sulphuric acid and sulphur dioxide.
The sulphur in pyrite can, in certain circumstances, oxidate, to form sulphates. These acids may combine with other materials, particularly carbonates, to form lower density materials. These lower density materials occupy more space and swelling occurs. The potential of the pyrite to produce heave-inducing sulphates is dependent on its concentration, the presence of water and oxygen, the crystallisation structure of the pyrite, the composition of the pyrite-bearing rock, the availability of other materials, especially carbonates, and so on.
Pyrite-induced heaving is a well-recognised concern for buildings where the swelling of fill under the structure may damage foundation and floor slabs and, in turn, cause other structural damage. It is a particularly prevalent risk in some parts of the world, such as Quebec in Canada as well as part of the Appalachians in the United States, and it can cause serious problems here in Ireland too, as has been seen. Aggregates can release sulphates such as sulphuric acid if the stone is coated with pyrite-bearing soil or sediment. This would typically arise when aggregate is excavated from old marine deposits or the aggregates may contain reactive pyritic mineralisation. Once the stone and sediment are exposed to air, the pyrite can oxidise and produce acid.
There have been occasional cases of swelling affecting road pavement but most of the swelling problems relate to buildings. We have had a few minor heave problems on our national roads which may have been pyrite-induced, but these were of small significance and were readily dealt with. Those involved in road construction are primarily concerned about the sulphate content of structural backfills, but not because of heave. Sulphate can, either directly or through intermediary products, damage buried concrete and steel. Research has been done in other countries that have had pyrite-related problems with road construction in recent years, such as the UK and the USA, and numerous research papers have recommended various tests. Our road construction contracts typically contain due diligence and care provisions which preclude the use of inappropriate materials. Additionally, as a precaution we specify that certain minimum tests should be carried out for aggregate used as fill near concrete.
The NRA's test requirements introduced in 2000 were based on British standards. Those requirements were updated in 2004 to comply with new European standards. We review our standards from time to time and currently, as part of the roads standards committee, we are reviewing new tests introduced by the UK Highways Agency that were last updated in November 2009. In view of the widespread use of NRA specification for roadworks, we will be consulting the Department of the Environment, Heritage and Local Government and other stakeholders before introducing any changed requirements.
Turning to the M3, the committee is probably aware that it is being built by a public private partnership concession which is fully responsible for the construction and maintenance of the motorway for the next 45 years. At the end of that time, the motorway has to be in good condition and repair before it is handed over to the State. Consequently, if there are any pyrite related problems with the motorway, and we are not aware of any, the responsibility for dealing with them rests squarely with the PPP company. There are approximately 4.2 million cu. m. of fill on the M3 scheme and materials are drawn from dozens of sources around the country. The PPP concessionaire was aware of concerns about pyrite and consequently declined to use materials from mining, which would be high risk. Additionally, when the products from a couple of other quarries were being mentioned in connection with the housing heaving problems, it checked on the use of materials from those sources. This can be done because test records identify where materials are used as well as their source. None of the stone from either sources was used as structural fill. As mentioned previously, if in fact there is any shortcoming in its quality assurance system and if any problems result, all remedial works will be up to the concessionaire.
To summarise, sulphate related problems with road constriction in Ireland have been quite limited. There is no evidence of the unacceptable use of pyrite-bearing rock on the M3, but if any problems emerge, the full cost of any repairs will lie with the PPP concessionaire.
