Pyrrhotite and Crumbling Foundations
Pyrrhotite, and its close cousin pyrite are two naturally occurring iron sulfide minerals present in many concrete aggregates that have caused havoc in concrete foundations, dams, houses made using masonry blocks, and many other structures across the world from Norway to Ireland, Spain, Wales, Canada, to eastern USA. For past two decades, CMC has done extensive testing and research on pyrrhotite and related deterioration of concrete from eastern USA to Ireland. Following are two research publications of our work from eastern US, followed by an authoritative treatise on state-of-the-art review of worldwide occurrences of pyrrhotite-related deterioration in concrete published in a book "Pyrite and Pyrrhotite." Also presented are some of our ongoing work from Ireland where pyrrhotite and pyrite in phyllite aggregates have caused severe cracking and crumbling of houses made with concrete masonry blocks. Our extensive laboratory facilities with specialties in petrographic examinations and associated investigative techniques have provided us an aided advantage of conducting a full range of materials testing to determine the presence and abundance of pyrrhotite, pyrite, and other sulfide minerals in aggregates and concrete and their potentially deleterious actions. A fee schedule is also provided to test quarried aggregates and cores from existing foundations.
Are you concerned of having
Pyrrhotite or Pyrite in your Concrete?
Concerns you may have...
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Does your concrete foundation contain pyrrhotite, or pyrite?
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If so, how much? Do you needed to be worried?
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Did it cause cracking and crumbling of your concrete?
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Do you see parallel horizontal cracks or spider web-like closed polygonal-shaped map cracking, discoloration, or other telltale signs of distress to suspect deleterious actions of pyrite or pyrrhotite?
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What is the extent of distress - is it a few fine cracks, or major visible cracks, or, perhaps, to the point of spalling of concrete, or may even crumbling to such an extent that you can break it down just by finger pressure?
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Can you expect a long-term performance of your foundation if there is no visible sign of distress?
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Can an aggregate quarry, or quarried crushed stone be used safely in a new construction without another future wave of pyrrhotite-related epidemic?
How we investigate...
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Do a series of chemical, X-ray, microscopical (petrographic), and physical tests on aggregates for potential distress in future, and existing concrete for the evidence and extent of damage.
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Determine the total sulfur content of aggregate or concrete by chemical analysis.
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Detect the presence (or absence) of pyrrhotite and pyrite by petrographic examinations and other laboratory tests.
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Detect amount of pyrite and/or pyrrhotite by various laboratory tests, e.g., from X-ray diffraction to chemical tests (sulfide content from total sulfur minus sulfate sulfur) to wavelength-dispersive X-ray fluorescence (WD-XRF).
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Detect microstructural evidence of distress in concrete and if it is related to pyrite or pyrrhotite.
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Evaluate quarried aggregate for new construction for the presence of pyrite and pyrrhotite from total sulfur content to petrographic examinations of aggregates.
We ask you to ...
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Collect 4 in. (100 mm) diameter concrete cores drilled from over visible cracks in your foundation, or saw-cut sections, or even 4-in. size chunks of crumbled concrete, and send your samples with some field photos by wrapping in bubble wraps in a secured shipping box. Many local core drilling companies can extract a core from your foundation, which you can ship us for testing. We recommend testing two (2) cores from two different walls of foundation.
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For aggregate suppliers, provide a representative 5-pound mass of your aggregate to test for the presence and abundance of pyrite and pyrrhotite. See our pyrrhotite testing fee schedule at the end of this page to decide which tests you want to do. Three most common short-term tests are chemical (for total sulfur), XRD (for pyrrhotite and other iron sulfides in aggregate), and petrography (for aggregate type, soundness, durability, and potential distress from oxidation of pyrrhotite).
What we will provide...
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Most important - our years of experience from numerous projects on concrete distress from oxidation of iron sulfide minerals in concrete.
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A detailed professional report of comprehensive investigation of your concrete, a few samples of which you can download from our prior studies in the 'case studies' section of this webpage.
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Competitive price, unparalleled depth of investigation, most comprehensive report in the industry, rapid turnaround, and professional expertise to understand the findings.
Why consider us...
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We have the most advanced in-house state-of-the-art laboratories from petrography to SEM-EDS, X-ray diffraction, X-ray fluorescence spectroscopy, ion chromatography, and various gravimetric and instrumental chemical analysis techniques to conduct a thorough investigation of pyrrhotite in aggregates, and pyrrhotite-related distress in concrete. We urge you to see our laboratory facilities under the 'laboratories' page in our website along with various publications and case studies presented here to see our unparalleled expertise on this issue.
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We have published the most comprehensive series of peer-reviewed research publications on pyrrhotite distress in the US, which are published by American Concrete Institute, Elsevier Publishers, and Nova Science Publishers.
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For aggregate suppliers, we have provided a comprehensive step-by-step testing protocol, which is published by ACI in our Research Publication 1.
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For past 20 years, we have been conducting laboratory tests to diagnose various concrete deteriorations by pyrite and pyrrhotite. Case studies of some of our relevant work on pyrrhotite distress in CT can be downloaded from the 'case studies' page.
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Recently, we have published the most authoritative treatise on worldwide occurrences of pyrrhotite-related distress in concrete, which can be downloaded from this page from our Research Publication 3.
Why consider us...
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Pyrrhotite or pyrite distress in concrete are inherently diagnosed by petrographic investigation, e.g., from identification of pyrite/pyrrhotite-bearing aggregates to the amounts of iron sulfide minerals, and diagnosing their deleterious roles in concrete using various optical microscopes (stereomicroscope, petrographic and metallurgical microscopes), and electron microscopes. Having the world's one of the largest collections of petrographic microscopes and sample preparation equipments in an awe-inspiring petrographic laboratory, we are more than well-equipped to examine any number of samples in a short period of time.
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Your samples will be prepared in the laboratories by a team of dedicated individuals and examined by a Professional Geologist with 30+ years of experience in petrographic examinations of concrete and aggregates.
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We do not provide just a report with results, e.g., total sulfur content or pyrrhotite content in a foundation, etc. but go well beyond to diagnose the microstructural evidence and extent of deterioration through detailed petrographic examinations so that a valid assessment can be made by a professional engineer about the anticipated service life of a foundation.
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We have extensive eperience on petrographic examinations of crushed stone and gravel according to the procedures of ASTM C 295 to evaliuate potential unsoundness, and suitability of a crushed stone or gravel for concrete aggregate without a concern on potential unsoundness from pyrite or pyrrhotite.
Due to large number of interests from homeowners and aggregate suppliers, we are offering discounted prices for core testing and aggregate evaluation for pyrrhotite.
For discounted prices, send us an email at info@cmc-concrete.com with any questions, or call us at 724-834-3551
Core Testing - Sample Report
Petrographic Atlas from a Case Study
Severity Class Codes
It is only through a detailed field inspection followed by petrographic examinations such as ours can a "severity class" (e.g., as per Connecticut Foundation Solutions Indemnity Company, CFSIC) be determined for a foundation, which has been tested 'pyrrhotite-positive':
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Severity Class Code 1 is for a foundation where only a "trace amount" of cracking is observed during petrographic examinations.
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Severity Class Code 2 is for foundations where expansive cracks and distress are apparent but still structurally sound, which are needed to be monitored and moved up to Severity Class Code 3 when walls crack expeditiously.
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Severity Class Code 3 is the worst of the worst.
Pyrrhotite - Some Facts (from Jana 2023)
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Pyrrhotite (pronounce pir-uh-tahyt, Greek pyrrhos i.e., flame-colored or redness, Deer et al., 2013) is a non-stoichiometric mineral of general formula Fe1-x S, where ‘x’ varies from 0 (FeS, troilite) to 0.125 (Fe7S8).
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Pyrrhotite is commonly associated with pyrite as minor accessory minerals in many igneous, sedimentary, and metamorphic rocks, as major phases in sulfide ore bodies, and as a secondary mineral in high temperature hydrothermal and replacement veins often after pyrite, pentlandite [(Fe,Ni)9S8], marcasite (orthorhombic FeS2), magnetite (Fe3O4) and chalcopyrite (CuFeS2).
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Pyrite (FeS2) is a cubic-structured isotropic mineral of fixed chemical composition (46.67% Fe and 53.33% S by weight) with a yellowish-white color in reflected light and a characteristic metallic luster. By contrast, pyrrhotite has variable chemical compositions and crystal structures, where Fe and S are arranged in alternating layers according to a NiAs structure, e.g., monoclinic (stable below 254°C) or hexagonal (stable above 254°C) - having various natural forms (different crystal structures, called polytypes), e.g., Type 4C (Fe7S8, most iron-deficient end member with a monoclinic crystal structure), Types 5C (Fe9S10), 6C (Fe11S12), and 11C (Fe10S11) - the last three are hexagonal but can also occur in monoclinic forms) having ideal weight percentage ranges of 60.38 to 61.49% Fe and 38.51 to 38.95% S.
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Pyrrhotite has a pink-cream or skin color in reflected light that has a metallic luster and bronze brown, yellow, or reddish color. Pyrrhotite is distinguished by its bronze rather than brass color of pyrite, its lower hardness, decomposition in HCl with the evolution of H2S, lower S/Fe atomic ratios (1 to 1.25 for unoxidized forms, as opposed to 2 in pyrite), and its weakly magnetic nature (monoclinic pyrrhotite Fe7S8, Type 4C is magnetic at room temperature, whereas hexagonal Types 5C, 6C, and 11C are non-magnetic, troilite is non-magnetic, magnetism decreases with increasing iron content).
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Upon heating, the magnetic monoclinic pyrrhotite 4C shows a characteristic drop of magnetic susceptibility across its Curie temperature (e.g., 310 to 325°C), which can be used to determine the pyrrhotite content. Hexagonal pyrrhotite 5C (Fe9S10) usually undergoes a reordering of Fe vacancies when heated above 200°C to become ferrimagnetic between 210°C and at another phase transition at 265°C.
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Pyrrhotite rarely exists as a pure phase mineral but usually consists of mixtures of hexagonal and monoclinic phases, which means that non-magnetic and magnetic varieties can occur simultaneously, forming complex intergrowth textures.
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Pyrrhotite has four times higher solubility and a much faster rate of oxidation (especially the magnetic hexagonal form 4C) in the presence of oxygen and moisture than pyrite, which makes pyrrhotite a more serious candidate for oxidation-related distress than pyrite when present in aggregates used for concrete and exposed to moisture during service. The proportion of ferric ions in the structure of pyrrhotite indicates the oxidation reactivity of the given pyrrhotite. The ferric ions act as internal oxidizing agents, which explains why 4C pyrrhotite is more prone to oxidation than the 5C type. Consequently, the proportion of ferric ions relative to total iron is positively correlated with the oxidation rate.
Brimfield Schist Formation
The Source of Pyrrhotite-Bearing Rocks in CT and MA
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The source of pyrrhotite-bearing aggregates quarried in CT are from the Brimfield Schist geologic formation of Ordovician age, which was formed more than 500 million years ago.
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Brimfield Schist formation consists of gray, often rusty-brown weathered, medium- to coarse-grained, metamorphic rocks of interlayered schist and gneiss that show characteristic parallel and layered arrangements of quartzo-feldspathic and micaceous minerals. Minerals in these rocks are feldspar (oligoclase, K-feldspar), quartz, and biotite mica, along with garnet, sillimanite, graphite, and pyrrhotite.
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The following geological maps show potential areas across CT and MA where pyrrhotite-bearing rocks of Brimfield Schist formation are present.
Connecticut Crumbling Foundations
Background of Crumbling Foundation Distress in CT
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Pyrrhotite-bearing aggregates used in the concrete for homes in Connecticut and Massachusetts were quarried from Becker’s Quarry in Willington, Connecticut, which is a rectangular-shaped quarry sits on the Brimfield Schist formation that has formed extensive pyrrhotite deposits by hydrothermal alterations. Becker’s quarry stopped supplying aggregates for residential foundations under an agreement of voluntary compliance between the State of Connecticut and Becker’s Quarry.
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Pyrrhotite-bearing concrete was originated from J.J. Mottes Concrete Company in Stafford Springs, Connecticut, which was delivered to several thousands of residential and commercial foundations in an area extending as far as 40 miles from the quarry, including many towns in central Massachusetts. The impacts of the use of this concrete have been most significant in the state of Connecticut with many homes in MA are facing similar problems.
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Since the early 1980’s, Becker’s Quarry was the primary source of the aggregate used by J.J. Mottes to produce concrete, and they have been the only company identified that produced material connected to the deteriorating foundations. No foundations produced outside of this timeframe have been reported to have deteriorating concrete as of 2019.
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The very first evidence of distress was noticed in a home at Tolland, CT which was built in 1985 with the concrete from J.J. Mottes Company. In April of 1993, the owners noticed some cracking on the north and east side of the basement, which, within two years, by 1995 developed extensive cracking and discoloration of foundation. Pyrrhotite was subsequently detected to be the culprit by petrographic examinations of cores. Eventually, many homes from Tolland including a school (see our Pyrrhotite Research #2 in the 'Case Studies' page) examined by our laboratories by petrographic examinations found extensive pyrrhotite grains in the crushed gneiss aggregates, often developed rust stains and extensive cracking of aggregates by oxidation in the presence of moisture and oxygen during service.
Locations of Potential Pyrrhotite-Bearing Aggregates in Massachusetts and Connecticut
Towns Identified by the Capitol Region Council of Governments (CRCOG) in CT as having been impacted by Crumbling Foundations
The Affected Zones
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Concrete poured between 1983 and 2015 from J.J. Mottes Concrete Company are within a 40-mile radius of the plant that are potentially impacted by this concrete, with the ones within 20 miles of the plant are the most at-risk.
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Within the 20-mile boundary are towns that include Wales, Holland, Southbridge, Sturbridge, Brimfield, Palmer, Monson, Hampden, Wilbraham, Springfield, Longmeadow, East Longmeadow, as well as parts of Dudley, Charlton, Brookfield, Warren, Ludlow, Ware, Belchertown, and Agawam. Within these cities and towns, a total of 20,704 residential structures were built during the aforementioned timeframe. Springfield saw the largest amount of construction, with 4,050 homes being created in this time. As many as 34,000 homes constructed in the entire northeastern Connecticut between 1983 and 2000 may have concrete foundations containing pyrrhotite and are at risk of cracking or crumbling.
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Towns within the 30-mile radius, marked at moderate risk by the Special Commission, include Southwick, Westfield, West Springfield, Holyoke, South Hadley, Granby, New Braintree, North Brookfield, Spencer, Leicester, Webster, Oxford, and Hardwick. These cities and towns saw a total of 15,846 homes created.
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Inside of 40-mile boundary are a total of 95,073 residential structures built between the years 1983-2015.
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The following map from the "Final Report of the Special Commission to Study the Financial and Economic Impacts of Crumbling Concrete Foundations due to the Presence of Pyrrhotite" published in December 2019 from Commonwealth of Massachusetts show these three zones around J.J. Mottes concrete plant.
How Pyrrhotite Causes Damage to Concrete
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Pyrrhotite causes the slow deterioration of the concrete when exposed to oxygen and water. When present in the aggregate material used to make concrete, the building material itself becomes compromised as water and air enter through small cracks and holes, allowing the iron sulfides to begin breaking down, expanding and allowing more water and air to enter.
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While the presence of pyrrhotite indicates the potential for concrete deterioration, its existence alone does not necessarily cause it unless moisture and oxygen are present to cause oxidation of pyrrhotite. Oxidation process is expansive since the iron oxide and hydroxide products occupy larger volumes than pyrrhotite, which causes cracking in concrete. Oxidation process also releases sulfate ions which causes a second wave of destruction by internal sulfate attack in concrete.
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So far, there is no minimum level of pyrrhotite that is deemed acceptable for use since homes having as low as <0.3 % pyrrhotite can still experience crumbling foundations.
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The cracking starts at micro scales and may take more than 10 years to over 30 years to appear visually at macro scales to cause structural damage. Horizontal cracks or cracks that splinter out like a spider web (map cracking) are the most concerning. Cracks may occur on the outside of the foundations or on may extent through the entire wall to become visible in the interior surfaces of walls. It may take 15 - 20 years for the pyrrhotite damage to make the foundation structurally unsound.
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A rust-colored residue or white efflorescence powder may appear on the exposed walls of foundations, and the walls often show flaking or spalling exposing soft powdery concrete inside. Cracks are often noticed when the drywalls in finished basements are removed.
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The damage, like most other concrete damage, is irreversible. Unlike many other types of distress, however, repair is usually not an option. As the concrete continues to crack to bring more moisture in and continue pyrrhotite oxidation, it often becomes crumbled and structurally unsound.
Replacement is the only option, Unfortunately!
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The repair is to fully replace the impacted foundation with a new foundation that does not contain pyrrhotite. While technological improvements may offer alternative solutions in the future, this is the only permanent fix available at this time. The cost to replace a foundation can vary greatly based on multiple factors but estimates range between $150,000 and $250,000 per home.
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For concerned homeowners, do not start panicking if you see a few cracks in your foundation, which may be quite normal (e.g., shrinkage cracks) and doesn’t necessarily indicate pyrrhotite distress. The first three things to consider after seeing a few cracks are if home is located within 50-mile radius of the J.J. Mottes Plant in Stafford Springs Connecticut, was the structure built between 1983 and 2015, and if the visible cracks are seemed more than normal in which case a home inspection is needed.
Detecting Pyrrhotite-Related Damage
Field Inspection - Core Testing
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Diagnosis of pyrrhotite damage is first done in a field survey by an experienced home inspector who is knowledgeable about pyrrhotite-related distress from which various locations are selected for drilling 4-in. (100-mm) diameter cores for core testing by a reputable lab which has the facilities, experience to conduct proper testing to detect and presence and abundance of pyrrhotite as well as the extent of damage.
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Core testing usually involves which typically involves chemical analysis of concrete for total sulfur to calculate sulfur content in aggregate, XRD analysis of aggregates in concrete to detect pyrrhotite, and detailed petrographic examinations of aggregates that not only detects pyrrhotite, but the extent of damage caused by pyrrhotite.
Massachusetts Crumbling Foundations
Map showing known affected towns in MA
Media Images of Foundation Distress
Copyrighted images reproduced for web viewing only for nonprofit educational purposes under fair use
It is time to examine quarries along the Appalachian Mountain where potentially pyrrhotite-bearing rocks may be present
Location of rock units that may contain pyrrhotite (Mauk and Horton, 2020); locations of pyrrhotite from the USGS Mineral Resources Data System database (U.S. Geological Survey, 2019); and locations of pyrrhotite from the Mindat.org database (Mindat.org, 2019). The national map shows that pyrrhotite may be distributed widely in metamorphic rock along the Appalachian Mountains and in smaller pockets in the western United States.
There are some limitations to this map. Pyrrhotite is not a particularly common mineral, so there are no maps that show where it does occur throughout the United States. USGS scientists instead used their geologic knowledge of where and how pyrrhotite forms to infer which rock formations may have it. The map, therefore, shows rock formations that may have pyrrhotite, but they are not guaranteed to have it.
Our 2020 Research in ACI Publication
Click on the images or texts to download the entire publication
Our 2022 Research in Elsevier Publication
Our 2023 Review Paper in Nova Science Publishers' Book 'Pyrite and Pyrrhotite'
From the Editor...
“For those interested in learning the current state of knowledge of pyrrhotite-induced damage in concrete, Dipayan Jana’s comprehensive review in Chapter 5 is a masterful treatise on the topic. As a specialist consultant in construction and geological materials, with a focus on concrete petrography and advanced laboratory investigation techniques, Mr. Jana is well qualified to provide this overview. To set the context, the chapter provides a detailed review of pyrrhotite and pyrite problems in aggregates around the world. He goes on to describe his recommended investigation techniques and the broad range of laboratory analytical techniques available for detailed examination of recovered samples. The author uses illustrated examples of how the findings of these detailed forensic examinations were used in the case of the northeastern United States pyrrhotite problems, to understand the causes and progression of the resulting concrete damage. The detailed annotated microscopic images provide excellent insights into the interpretation of the various techniques described. Based on his extensive experience, Mr. Jana provides a five-step laboratory testing protocol for assessment of pyrrhotite reactivity risk in concrete aggregates.”
Our 2024 Paper in
ACI Concrete International
Our Work on Crumbling Concrete Houses
in Ireland
Cracking and Crumbling of Houses Made with Concrete Masonry Blocks in Donegal, Ireland
Pyrrhotite and pyrite in phyllite aggregates used in a rather poor quality concrete block have caused the havoc from oxidation of iron sulfide minerals followed by internal sulfate attacks (from ettringite and thaumasite).
ICISR Extended Abstract 2024
A Case Study of A Sound Home
Do you want to read more?
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Then read some of our case studies on pyrrhotite-related cracking of concrete foundations in the 'case studies' section of our website. Those case studies will give you an idea about the depth of our investigation and what you would expect from our examinations.
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We will also provide 1-2 page executive summary of our work for aggregate suppliers and homeowners to follow through and find the most relevant information.
Case Studies on Pyrrhotite-related Distress
Our 5-Step Laboratory Testing Protocol for Assessment of Aggregates for Pyrrhotite
Laboratory Testing for Assessment of Pyrrhotite Oxidation and Related Distress in Existing Concrete Structures, and
Aggregates for New Construction
Fee Schedule
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Standard: 3-4 weeks
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Expedite: 3-5 business days
