Damage caused by pyrites has now become a major issue particularly in Ireland where the use of pyrite laden aggregate has been widespread.
Pyrite (FeS2 Iron Sulphide) is a common mineral, of which traces are often found in sedimentary type rock used to make crushed stone for backfill. In the presence of water and oxygen the pyrite crystals expand and swell, which can cause any retaining structures such as floors and walls to crack and swell.
What causes Pyrites to swell?
In contact with water and oxygen, pyrite oxidizes and produces sulphuric acid. This acid then reacts with calcium carbonate (i.e. limestone) found in the crushed stone to produce sulphate and possibly gypsum, whose crystallization can cause the stone to burst and the backfill to swell. The whole process can be slow and can take anything up to 10 years before signs are visible.
So what are the signs of pyrite induced damage?
- Gradually spreading cracks, often star shaped in concrete slabs
- Noticeable heaving and bulging of the floor slab and or worktops
- Visible needle-like fragile white crystals mixed with the concrete near the cracks
- Cracks over and around doors and at wall junctions, when in contact with floor slab.
- Doors sticking and catching on the floor slab
- Expansive block work
It would be common for a combination of the above to be visible
The Testconsult Approach to Pyrite Testing
Testconsult Ireland offers a comprehensive approach to pyrite testing. Our qualified engineers and technicians are proficient and accredited in sampling, testing and management of situations where pyrite damage is suspected. The test is only as good as the sample taken, which has to be representative of the material under suspicion.
Depending on the investigation type, we carry out testing only relevant to the investigation in hand.
When required, we follow Insurance sampling and testing protocols, SR 21 requirements and SR 21 2004 Guidance on the use of EN 13242 2002 (Aggregates for unbound and hydraulically bound materials for use in civil engineering work and road Construction) SR21 requires utilising a 2 stage approach:
Stage 1: Grading analysis, Los Angeles Value, Water Absorption, Magnesium Sulphate Soundness, Total Sulphur and Acid Soluble Sulphate
Depending on the results obtained, it could then lead to stage 2.
Stage 2 : Petrographic Analysis using thin sections and X-ray Defraction
Our approach is unique in that :
- We will only use accredited tests and accredited test companies
- We only carry out tests if they are required
- We always take sufficient samples to enable all tests to be carried out strictly in accordance with test specifications
This approach keeps the costs to a minimum
Our clients include, home owners, quarry owners, government agencies, commercial building owners, contractors and consultants.