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Pyrrhotite Aggregate Analysis



At Durability Engineers, our experts have a comprehensive understanding of iron sulfide-bearing aggregates, such as pyrrhotite, and the deleterious impacts these aggregates can have on concrete structures. We use this knowledge to assists our clients evaluating aggregate sources, performing specialized testing, and evaluating existing structures.

Pyrrhotite Landing Page
Polished Pyrrhotite Aggregate Cross Section


pir-uh-tahyt - Fe(1-x)S (x=0 to 0.2) - is an iron sulfide mineral that occurs as a trace constituent in many igneous, sedimentary, and metamorphic rocks.  The iron sulfide reacts with water and oxygen inside concrete elements, causing staining on exposed surfaces and cracking of the concrete.

In cold regions, concrete structures containing pyrrhotite have been shown to be susceptible to more severe mechanisms of degradation due to internal sulfate attack, resulting in degradation of the cement paste and loss of structural capacity.

What is Pyrrhotite


In new construction, our team employs petrography, standardized and specialty testing of aggregates and minerals proposed for use in concrete. We develop an engineering strategy that provides mitigation approaches for each structure.  Our services include:

  • Specification Development

  • Materials Selection

  • Durability Consulting

  • Standard and Specialty Testing

Prevention & Mitigation
Concrete with Map Cracking


In existing concrete structures, we employ state of the art techniques to evaluate existing conditions, identify the cause of deterioration and determine the potential for continued deterioration.   We extract samples of the concrete and examine them in our laboratories for more in-depth characterization and testing. We augment and validate results from field investigations with petrographic and laboratory assessments. Our team provides:

  • On-site Evaluations,

  • Assessment of Existing Conditions,

  • Non-Destructive and Destructive Testing,

  • Oversight of Sample Removal,

  • Specialty Pyrrhitite Testing to Determine Diagnosis and Prognosis

  • Instrumentation and Monitoring of the Structure In-situ

  • Standard and Specialty Testing

Evaluation and Assessment
Pyrrhotite Test Methods


Durability Engineers tests materials in accordance with CSA specifications such as:

CSA A23.1:19 P2 Test Method for Detection of the Oxidation Potential of Sulphide-Bearing Aggregates by an Oxygen Consumption Test

CSA A23.1:19 P3 Test Method for Detection of Potential Reactivity of Sulphide-Bearing Aggregates by Accelerated Expansion of Mortar Bars

ASTM C295 Standard Guide for Petrographic Examination of Aggregates for Concrete

ASTM D4239 Standard Test Method for Sulfur in the Analysis of Sample of Coal and Coke using High Temperature Tube Furnace Combustion

ASTM D2492 Standard Test Method for forms of Sulfur in Coal


Is legislation ahead of science?

Principal Engineer, Dr. Anthony Bentivegna and Associate Principal Engineer, Stephen Stacey recently co-authored an article on pyrrhotite in concrete aggregates. Published in American Concrete Institute's, Concrete International (CI) journal, the article provides an overview of the pyrrhotite deterioration mechanism, manifestation of the reaction, current state of knowledge for identification and quantification, and current proposed legislation.  

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Pyrrhotite CI Article

Let's Work Together

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