Pyrite in masonry blocks: ACEI publish advice

ACEI Guidance note

The Association of Consulting Engineers Ireland (ACEI) have published, on 15th May 2014, an interim advice note stating

“It has come to the attention of the ACE that there have been recent instances of apparent pyrite content in concrete blocks provided by block manufacturers.

In cases reported the affected blocks were noted to have a brown discoloration. The physical strength characteristics diminished over short period of time, particularly when exposed to moisture.

The ACEI are concerned about these occurrences and recommend all member firms request assurance from suppliers that materials are free of deleterious materials and that a representative sample of blocks be tested for pyrite content by chemical analysis.”

RIAI Guidance issued

An email sent to members of the The Royal Institute of The Architects of Ireland (RIAI) on the 29th May 2014 was posted on the Pyrite Action Facebook group and adds more detail to the pyrite problem

“A number of RIAI Practices have brought to the attention of the RIAI problems encountered on projects in the Leinster region with conrete blocks that contain pyrite.

The problem, as identified, where concrete blocks containing pyrite are used structurally, is likely that the structural integrity of the block-work will need to be investigated, in particular where it is in contact with moisture/water.

RIAI Practices or Members, who have specified concrete block-work in recent months, and have used it in construction on site, may need to be prudent and establish the identification of sources of masonry and specific testing that has been carried on them. If a Consulting Structural Engineer was involved, they should be consulted, together with the main contractor.

It is early days as yet for more complete information to be made available, however, the RIAI will be seeking
to consult with various bodies to ascertain a better picture, and advise on how to deal with the problem.”

According to comments on the Pyrite Action Facebook group, problems related to pyrite in concrete blocks had been identified “as a significant problem” in Donegal. It is of note that a “Mica problem” has been identified in Donegal and these two problems may be unrelated.

pyrite in concrete blocks – previous cases

Whilst perhaps only recently appreciated in Ireland (pyrite in concrete blocks was not deemed a serious concern in Ireland at the time of the 2012 Pyrite Symposium), pyrite within the aggregates of concrete blocks is not a new civil engineering problem. The presence of sulfides (pyrite, pyrrhotite, chalcopyrite etc) in concrete aggregates is partly responsible for the major issues termed the “Mundic Problem” in South West England relating to concrete produced pre-1950 (Bromley and Pettifer, 1997).

Deterioration of concrete blocks due to pyrite was also noted by Gallias (2003) in the outside walls of private houses coated with cement. Gallias (2003) reported the nature of the damage as cracks exposing rust-like staining, six years after construction. Detailed testing of the aggregate revealed pyrite whilst gypsum and iron hydroxides were found in contact with the concrete.

More recently, oxidation of sulfides in aggregate for concrete foundations in the Trois-Rivieres area of Canada has led to a widespread “pyrrhotite problem“, with as many as 1400 homes requiring repair. Several recent papers have been published on this area of Canada, which provide excellent detail of the problem (Duchesne and Fournier, 2011; 2013, Rodrigues et al., 2012).

In March this year, RTE News reported on pyrite found to have caused damage to external blockwork in 15-20 houses in the Erris area of Co. Mayo. The Department of the Environment stated that home owners were not eligible for remediation as pyrite was not found in the under-floor fill. RTE News (23.03.14).

The European Standard for aggregates used in concrete, EN 12620:2002+A1:2008 states that aggregates other than air-cooled blastfurnace slag must have < 1 % S (total sulfur) by mass. Additionally, it states that the total sulfur must not exceed 0.1 % S if pyrrhotite is present.

Pyrite panel comments

The Pyrite Panel report (published in 2012) states

“The panel was not informed of any failures of concrete or concrete products, due to aggregates containing reactive pyrite being used as a constituent of the concrete, at the same time or in the locality where the problems with hardcore occurred.

The standards for concrete and its constituents (e.g. aggregates) are well established and there is full acceptance of the testing regime in place. However, there did not appear to be the same level of awareness of the necessity for testing aggregates for use as hardcore under floors in buildings.”

Could it now be the case that there was not full acceptance of the testing regime in place?

PDF acei advice note

ACEI-Pyrite-in-Concrete-Blocks-Advice-Note-2014-05-13

References

Duchesne, J., and Fournier, B. (2011). Petrography of concrete deteriorated by weathering of sulphide minerals. Proposed Paper for the 33rd International Conference on Cement Microscopy, Omni San Francisco Hotel, San Francisco, California, U.S.A. April 17 – 20.

Duchesne, J., and Fournier, B. (2013). Deterioration of concrete by the oxidation of sulphide minerals in the aggregate. Jnl. Civ. Eng. Arch. 7 (8), 922-931.

Gallias, J.L. (2003). Deterioration of outside walls made with concrete blocks containing pyrite. International Concrete Abstracts Special Publication. 212, 607-620.

Rodrigues, A., Duchesne, J., Fournier, B., Durand, B., Rivard, P., and Shehata, M. (2012). Mineralogical and chemical assessment of concrete damaged by the oxidation of sulfide-bearing aggregates: Importance of thaumasite formation on reaction mechanisms. Cement and Concrete Research. 42, 1336, 1347.

 

 

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