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Iron suffide pyrrhotite cracks in a Connecticut Founation  (C) CCAB & Inspectapedia.comFoundation Damage Due to Composition or Inclusions
Foundation Cracks, Spalling, Stains caused by composition, iron sulfide pyrrhotite inclusions, steel, rust

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Foundation cracks or spalling due to choice of materials, contents, or inclusions:

Defects in concrete mix (too much water, for example), or defects in placement of steel or iron reinforcement (too close to surface, for example), as well as use of problem materials in concrete such as excessive levels of coal ash, cinders, or pyrrhotite an cause horizontal, vertical, or varied-pattern or "wandering" cracks in masonry or masonry block foundations.

Andrson & Cobb (2008) have reported similar serious structural damage occurring in structures built on top of shale containing pyrite and sulfates, producing severly-cracked foundation walls and floor slabs.

Page top photo of foundation cracks attributed to concrete that included iron sulfide (pyrrhotite), provided courtesy of CCACB - Connecticut Coalition Against Crumbling Basements. This article includes contact information for the CCAB as well as ctiations of authoritative research on the effects of iron sulfide in concrete. Click to enlarged this image and you'll also observe some spalling of the concrete surface.

Experts may refer to random pattern concrete cracks as damage caused by inclusions, iron, Other foundation damage such as rust heaving or staining, frost damage, or spalling may also be due to the specific component mix of the foundation material or for masonry or stone foundations damage may be due to composition, inclusions, or placement of reinforcement in the mortar joints.



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Foundation or Wall Cracking or Spalling Due to Foundation Materials or Contents

 Pyrrhotite ore from the Santa Eulalia Mine, Wikipedia retrieved 2016/11/15

Iron sulfide mineral (pyrrhotite) cracking

Iron sulfide mineral (pyrrhotite) cracking may appear as variegated, "random pattern" cracking in concrete slabs, walls, and foundations whose concrete contains high levels of pyrrhotite. Moisture as well as oxygen react with this iron sulfide material, causing it to swell with tremendous force, causing varied-pattern cracking in the concrete.

Bryant in his thesis describes iron sulfide pyrrhotite cracking damage in several U.S. states including in Canada: Ottawa, in the U.K. in Derbyshire, and in the U.S. in Kentucky, Mississippi, Montana, Pennsylvania, Tennessee, Texas, Virginia, and more generally in the U.S. Great Plains area and in the Mississippian and Pennsylvanian shale beds. Bryant notes that cases of "... heave due to oxidation of pyritic shale have been reported and continue to be reported worldwide. " (Bryant 2003).

[Click to enlarge any image] Photo: Pyrrhotite from the Santa Eulalia mine in Chihuahua, at Wikipedia - retrieved 2016/11/15, original source https://en.wikipedia.org/wiki/Pyrrhotite

The presence and nature of iron sulfides in mineral ores were discussed in North America as early as 1889 (Bailey), but as a factor in concrete and foundation damage iron sulfides and pyrrhotite were not discussed until there was more widespread of placed or poured concrete in building construction.

Foundation damage from the effects of iron sulfide inclusions has been discussed for more than half a century. Foundation and other concrete damage attributed to unstable iron sulfide was reported in Oslo in 1959 (Moum 1959)

Guillott warned about concrete problems ensuing from properties of some of the aggregates being used back in 1980 (Guillott 1980). Rodrigues and others discussed advanced testing methods to check concrete for mixtures that were at risk of harmful sulphur-bearing aggregates in concrete in 2015, and by 2016 those experts had specified a testing protocol to detect and avoid this trouble (Rodrigues and Ramos 2016).

Most recently pyrrhotite crack-damaged concrete foundations were reported by the New York Times in 2016 in explaining foundation damage in hundreds of U.S. homes in Connecticut.

Iron suffide pyrrhotite cracks in a Connecticut Founation  (C) CCAB & Inspectapedia.com

Above: photo of foundation cracks attributed to concrete that included iron sulfide (pyrrhotite), provided courtesy of CCACB - Connecticut Coalition Against Crumbling Basements.

[Click to enlarge any image]

Concern with the effects of iron sulfide in concrete has been discussed by experts around the world including Australia, Britain, Canada, Ireland, Norway, Russia, the United States (in several states), and other countries.

All of the Connecticut homes affected by iron sulfide inclusion cracking were constructed using concrete provided by the Becker quarry in Willington CT. Becker quarry stone aggregate used in concrete contains high levels of pyrrhotite (iron sulfide). According to the Times article similar damage has been reported in 4000 foundations of buildings in Quebec.

Iron suffide pyrrhotite cracks in a Connecticut Founation  (C) CCAB & Inspectapedia.com

Above: another photograph of foundation cracks attributed to concrete that included iron sulfide (pyrrhotite), provided courtesy of CCACB - Connecticut Coalition Against Crumbling Basements.

We estimate that these phrrhotite cracks range from 1/8 to 3/16" in width. But cracking ascribed to pyrrhotite or iron sulfide includsions in the concrete mix are sometimes as much as 1/2" in width according to the CCAB. See the photogarph just below, also provided provided courtesy of CCACB.

How to Diagnose Foundation Damage Attributed to Pyrrhotite Cracking

Iron suffide pyrrhotite cracks in a Connecticut Founation  (C) CCAB & Inspectapedia.com

A spokesperson for the Connecticut Coalition Against Crumbling Basements (CCACB) who contributed photographs to this article commented by email that the owner of the home whose large foundation crack is shown above ..." is not aware of specific rebar or other matters that might affect the damage to that degree. ... the home [was] featured on NBC Nightly News , some homes have reached that degree of separation."

Really? OPINION: it seems likely that there will be differences between the fine cracks in concrete that are manifestations of generally weak concrete attributed to Iron sulfide mineral (pyrrhotite) inclusions ascribed to inclusions and the very large cracks and foundation displacement shown in the photograph.

Where there are big cracks there are additional forces at work such as footing or fill settlement, frost push, frost heaving, expansive clay heaving, construction on fill, inadequate footings, or even SHALE FILL / HEAVE SETTLEMENT that involves significant settlement or heaving damage to foundations of buildings built on shale containing containing pyrite and sulfates.

Diagnosis of iron sulfide or phrrhotite concrete inclusion damage identification in the field would be aided by a catalog of indicators that could be confirmed visual inspection of the concrete, cracks in the concrete, the crack interior, or by concrete sampletesting. Such indicators could allow homeownes, contractors, and engineers to look at specific building cracks and damage to understand the cause of damage and the extent to which large cracks or foundation movement can be assigned in part or in whole to the inclusions.

For example, if you look inside the cracks with a good light, do we see concentrations of the problem material? Are there characteristivc stains like those identifiedf at SHALE FILL / HEAVE SETTLEMENT ?

Watch out: Iron sulfide (pyrrhotite) crack pattern is often rather distinctive: look for a somewhat random cracking pattern, with concrete cracks that are wider and more continuous than SHRINKAGE CRACKS at FOUNDATION WALLS.

Bérard (1975) and more recently Duchesne (2013) and Rodrigues (2012) offer clear explanations of how and why this pyrrhotite cracking damage occurs. We include summaries of the failure mechanism provided by abstracts to or excerpts from these and other articles cited below.

Rodrigues (2012) discusses mineralogical and chemical assessment of concrfete damaged by the oxidation of sulfied-bearing aggregates. But their analysis does not provide a field guide to damage assessment nor a guide to separating distinct causes of large foundation cracks such as the combination

Photos & field damage reports wanted: random foundation crack patterns, Pyrrhotite crack-damaged concrete foundations in Connecticut or Quebec or elsewhere. CONTACT us by email.

Foundation & Structural Damage to Buildings Constructed on Shale Containing Pyrite & Sulfates

Examining how pyrite and sulfites in shale can cause building problems may give added insight to how fragments of these materials may cause trouble when mixed right into concrete as aggregate. Shale formations in at least 20 U.S. states containing various clay and iron sulfide minerals (pyrite) react to water and form mild sulfuric acid causing unstable shale and clay formations.

Structural problems develope as a result of expansive clay soils and heaving. Some heaving damage is traced to pyrite oxidation and sulfate formation while other expansive soil damage is commonly traced to expanding clay soils or expanding clay in shale.
Also see FOUNDATION FAILURES in CLAY SOIL

Andrson & Cobb (2008) have reported serious structural damage occurring in structures built on top of shale containing pyrite and sulfates, producing severly-cracked foundation walls and floor slabs.

Pyrite oxidation in the Chattanooga Shale has caused serious foundation problems in numerous buildings and structures in Estill County, Ky. Pyrite oxidizes and various secondary sulfates form when excavated shale or shale fill are used in foundations. These secondary sulfates are water- and humidity-sensitive and can form when only minor amounts of water are present in foundation materials.

These sulfates form by crystal growth and expand by volume change, which causes subsequent soil expansion and heaving of any foundation materials when the materials are confined. Several structures have undergone expensive remediation to repair damaged sidewalks, floors, walls, and foundations. Zones of high concentrations of pyrite occur in the Chattanooga Shale across the state, and these mineral zones may be responsible for the high pyrite content in Estill County. - Anderson & Cobb (2008)

Anderson describes significant foundation and structural damage to three large buildings buit north of Irvine in Estill County, Kentucky in the U.S.: The Carhartt factgory, the Estill County Middle School, and the Marcum and Wallace Hospital auxiliary building. These buildings are constructed on top of the Devonian Chattanooga Shale formation. Similar swelling/heaving damage to a state highway, KY 499, built over the Crab Orchard Formation (underlying the Chattanooga Shale) was also reported.

The Chattanooga Shale in this area has a high pyrite content, which oxidizes into various efflorescent (powder-like) sulfate minerals.

What is commonly called pyrite swelling is actually a chemical oxidation reaction between groundwater and pyrite. Many sulfates form from this chemical reaction, but two of the most common are jarosite and copiapite. Jarosite, an iron sulfate, is a mineral salt and copiapite is a calcium-iron sulfate with a distinctive yellow color. - op. cit. 

Watch out: other more subtle damage due to settlement, heaving, or floor, wall or foundation movement may be extremely dangerous if it causes dislocations in and damage to gas piping, electrical wiring, heating systems, chimneys, or other building mechanical systems. In my [DF] opinion even a small dislocation that risks rupturing a gas line risks fire or explosion similar to hazards occurring in earthquake zones.

Visual or Historical Evidence of Building Damage Possibly Related to Construction on Shale Containing Pyrites & Sulfites

Visual evidence of buildings for damage and for evidence of pyrite and sulfites as root-cause contributors to this damage included the items listed below. Many of these inspection points of damage could have very different underlying causes.

Technical Evidence of Building Damage Possibly Related to Construction on Shale Containing Pyrites & Sulfites

Technical Explanation of Why Construction on Shale Fill High in Iron Sulfide, Phrrhotite, Pyrites Causes Damage

Anderson explains that construction on shale fill material may be a major contributor to damage, particularly if the fill is subsequently wet by roof or surface runoff. He describes three underlying causes of foundation failure for the buildings studied:

  1. Oxidation of pyrite and growth of secondary sulfates in the shale is listed by the author the primary cause of foundation problems [in this construction area]. A more mechanical explanation is that crystals form in the material, increasing its volume and producing tremendous heaving or expansion forces. The sulfates, plus water, also produces mild sulfuric acid that may contribute to foundation failiures. I think similar forces may occur within a poured concrete component high in similar materials as aggregate.
  2. Un-stable soils: shale degrades into clay and sulfate minerals to form an un-stable soil lacking in shear strength.
  3. Construction on shale fill: Anderson explains both why shale fill with these properties causes trouble and also why we may see worse heaving and damage in floor centers and in non-load-bearing partitions.

    ... [Shale fill material high in pyrite and perhaps sulphur] weathers rapidly, and causes the pyrite to oxidize to sulfates very rapidly. The primary cause of these structural failures is pyrite oxidation, also called pyrite swelling, which creates secondary sulfate growth beneath the slab foundation, causing floor heaving, wall and flooring cracking, and structural instability.

    This pyrite oxidation leads to crystal growth that can crack concrete and lift foundations. Normally, the load-bearing walls in these structures exert enough load or pressure on the expanding pyrite to balance the strength of crystal growth within the sulfate in the shale, so that the load-bearing walls do not move, but the adjacent slab flooring does move.
    - Op. Cit.

More information on iron sulfide pyrrhotite cracking damage to foundations:

Rust damage at mortar joint in brick wall, Poughkeepsie NY (C) Daniel Friedman

Foundation Cracking Due to Reinforcing Steel Placement

Rust & Frost Horizontal cracking and heaving may appear at masonry unit (brick or concrete block) mortar joints if leaks cause steel reinforcing mesh or re-bar to rust.

Exfoliating rust has tremendous lifting power as does frost that may damage masonry foundations that are already cracked and then wet. Rust damage may be severe above improperly-sealed steel window & door lintels.

Rust staining and damage may also occur to stone structures due to inclusions in the stone itself.

More information on rust & frost damage to foundations:

Spalling brick wall, Brooklyn NY (C) Daniel Friedman

Spalling Damage to Foundations

Spalling damage occurs at poorly-mixed concrete walls, floors, slabs, walls. Spalling damage also occurs on concrete block "cinder block" made from poor-quality material such as using too-little cement or too much aggregate that contains high levels of iron or other contaminants. Spalling damage occurs in brick foundations when the brick surface has become soft, damaged by sand-blasting, and when it then absorbs water, especially in freezing climates.

This article series provides a guide to identifying & evaluating different types of concrete or masonry foundation, wall or floor cracks in buildings: this article series describes how to recognize and diagnose various types of foundation failure or damage, such as foundation cracks, masonry foundation crack patterns, and moving, leaning, bulging, or bowing building foundation walls.

Foundation cracks and movement are discussed by type and location of foundation cracks, vertical foundation cracks, horizontal cracks, and diagonal foundation cracks, and shrinkage cracking.

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Continue reading at FOUNDATION CRACK DICTIONARY or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see BRICK WALL FROST & WATER CRACKS, EFFLORESENCE, SPALLING

Or see CHIMNEY SPALLING

Or see FOUNDATION DAMAGE SEVERITY

Or see FOUNDATION FAILURES by TYPE & MATERIAL

Or see SPALLING CONCRETE BLOCK WALLS & CHIMNEYS

Or see these

Concrete Crack Diagnosis & Repair Articles

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