Pyrite in Aggregate 1

[mickmac]

Is anyone aware of any specifications, anywhere, for maximum permitted levels of pyrite in building products and in particular fill material for use below concrete slabs in house construction?

 

[Stego1]

If you're in the UK, BRE Special Digest 1 'Concrete in Aggressive Ground' covers this. See

http://www.brebookshop.co.uk

Not sure about overseas spec.

Cheers

 

[mickmac]

Thanks Stego1,
Are you aware of any European legislation or directives relating to maximum permitted levels of pyrite, or does each member country have its own?

 

[Stego1]

I've done a quick search but can't find any Euro stuff, although maybe the new Eurocodes cover it or have pointers in their reference sections. I think Eurocode 2 is for concrete structures.
Otherwise British Standards prefixed BS EN are in line with European directives. I'm not sure which ones cover concrete I'm afraid.

Cheers

 

[geomtl]

In Quebec (Montreal area) we have had extensive problems with expansion of granular materials below slab on grades. In particular, this phenomenen is extremely dangerous on lightly loaded slabs as found in homes. In many cases, the homeowner has to completely remove the offending materials and replace, in particular when selling the house as it is a known liability.

The response to this has been to develop a pertrographic test whereby the actual granular fill is inspected visually, and a value assigned various types of materials (i.e a shale with visible pyrite has a very high number (potential for expansion), while a limestone or granite would have a very low number (low potential for expansion).

The cumulative total number (IPPG) assigned to the granular fill then is given a qualitative value i.e. IPPG less than 10 is low probablility for expansion, etc....

See attached link for further info.

http://www.habitation.gouv.qc.ca/publications/M16940.pdf

 

[mickmac]

Thanyou geomtl,
I see where the problem of cracking and rising of floor slabs has occurred here in Ireland. Automatically pyritic oxidation has been blamed. The fill material below the slab was a limestone. Is it fair to automatically place the blame on the aggregate, or can other forces be at work here. Are there also different forms of pyrite and if so is there a particular type which is more susceptible to the formation of gypsum.

cheers

 

[iandig]

The Eurocodes do have maximum levels of sulfate permitted, but they generally refer back to national guidance documents, reflecting the fact that if you try and write a standard which works in the Artic Circle and southern Europe, it will only ever be 'general'
In the UK BS EN 13242 covers 'hydraulically bound and unbound materials for use in civil enineering'. This covers all earthworks materials but makes repeated reference to the Specification for Highway Works [SHW] Volume 1. Under the general guidance at the start of the SHW series 500 [dranage materials], 600 [earthworks materials] and 800 [unbound aggregates in road construction] they specify the maximum sulfate contents. In addition to this, for specific classes under these series, additional requirements may also be listed, pending the proposed end-use of the material.
There are also a whole new series of test methods as well as a new standard for aggregates for use in concrete. The new standards also include tests for sulphur containing compouds [i.e. pyrite] so this is covered for aggregates for use in concrete as well as engineering fill materials.
UK guidance can also be found in the PD 6682 [Parts 1 to 9] which although not adopted as standards are provided by BSI as 'formal' guidance in the use of the new European codes, and as a first port of call I would strongly reccomend buying these before any other standards. PD 6682 are written in English [i.e. they explain the text of the Eurocodes in the same way that English works] and not in the 'general' language contained wihtin the Eurocodes [implicit in English, implied in Europe]