Core Testing / Pyrrhotite – USA

We have established strong partnerships with Connecticut and Massachusetts firms who perform core drilling, sample identification and packaging as well as sample shipments. Typically, we will send a team of technicians to your property within 2-3 business days.

• A minimum of two (2) core samples shall be collected and submitted for analysis.
• Core samples shall be extracted from different foundation walls of the tested building.
• Core samples shall be labeled and fully documented regarding location of sample collection from concrete foundation with control number matching written report.
• Cores shall be drilled out of a 4 inch diameter cylinder.
• Coring shall be executed all the way through the wall in order to confirm presence or absence of moisture barriers.
• Resulting cavities will be filled with non-shrink grout.
• Reasonable access must be provided. Example: Moving furniture / home decor / rugs is the responsibility of the homeowner or client.
• Usual delivery time to our lab is 3 business days.

Sedexlab petrographers use stereomicroscopy and polarized light microscopy to perform the mineralogical assessment of aggregates in concrete which allows highlighting potential problems related to expansive reactions due to the oxidation of pyrrhotite and other iron-sulfide minerals in rock aggregates. Petrographic examinations are conducted in accordance with relevant guidelines outlined in ASTM C 856-17, “Standard Practice for Petrographic Examination of Hardened Concrete.”

The Analysis includes:

• Determination of percentage of coarse aggregate particles containing pyrrhotite.
• Determination of percentage of pyrrhotite per unit mass of coarse aggregate
• Determination of evidence of oxidation of pyrrhotite (presence of replacement iron oxides).
• Detailed concrete core description (concrete condition, coarse and fine aggregate description, steel reinforcement description, moisture barriers description)
• Petrographic composition of coarse aggregate and fine aggregate
• Composition of iron sulfide minerals in the coarse aggregate (pyrite, pyrrhotite, chalcopyrite, etc.).
• Petrographic photographs of concrete sections analyzed.

Since pyrrhotite is a sulfide mineral composed of iron (Fe) and sulfur (S), measuring sulfur content in concrete and coarse aggregate is an important part of the Concrete Core Analysis and supports observations made during microscopic examinations. European and Canadian standards for concrete coarse aggregate have placed a limit of 0.1% sulfur if pyrrhotite is identified in the coarse aggregate.

Total sulfur content in concrete is performed using LECO infrared combustion sulfur analysis on a portion of each core sample in the as-received condition.

The Analysis includes:

• Determination of average percentage sulfur per unit mass of concrete.
• Determination of percentage sulfur per unit mass of coarse aggregate.
• Values obtained are benchmarked against the 0.1% European  standard EN-12 620 for coarse aggregate.

Physical properties of concrete are influenced by its density as it generally reflects concrete strength and durability as well as the amount of air voids and porosity.

Concrete density and porosity measurements are conducted on a portion of the core sample in the as-received condition in accordance with the relevant guidelines outlined in ASTM C642 ‘’Standard Test Method for Density, Absorption, and Voids in Hardened Concrete’’.

The Analysis includes:

• Determination of Concrete Density (lb/ft³)
• Determination of absorption after immersion (%) and after immersion and boiling (%)
• Determination of volume of permeable voids (%)
• Values obtained are compared against values generally accepted for normal resistance concrete used in building foundations.

The written summary report comes complete with a synthesis of petrographic, sulfur and physical analysis results as well as concluding statements with professional judgement.  Test results/final reports are sent by email to the Client. A hard copy of such results and reports can be provided upon request for an additional $10.00 fee.

Pyrrhotite, a naturally occurring iron sulfide found in rock aggregate, is the suspected cause of the failing concrete foundations problem in Connecticut and Massachusetts. These foundations are experiencing a slow crack development, resulting in the eventual loss of concrete strength. The problems, sometimes developing within the first 10 years, often begin to appear after 15 to 20 years or more. According to the Geological Society of America, rock aggregate in these failing concrete foundations was largely mined from a single quarry in Willington (CT), within a stratified metamorphic unit mapped as Ordovician Brimfield Schist.

Pyrrhotite particles in coarse aggregates are unstable in oxidizing conditions. When exposed to water and oxygen, pyrrhotite oxidizes to form acidic-, iron-, and sulfate-rich by-products. One of these products is sulfuric acid which attacks the cement paste, weakening it, and generating sulfates as a by-product. These sulfates react with portlandite and hydrated aluminate phases in the paste, resulting in an expansion in the form of secondary minerals of greater volume. With more expansion and cracking occurring, more moisture is allowed in the concrete, exposing more pyrrhotite, and consequently increasing the rate of distress. At present no measure other than foundation replacement is known to reverse or eliminate pyrrhotite-Induced concrete deterioration.

According to the state Department of Housing, 42 towns and upwards of 35,000 homes in Connecticut could be potentially affected, primarily in the northeastern portion of the State. Single-family homes, home additions and detached garages, condominiums and other buildings are affected. North of the border, significant parts of central Massachusetts could also be potentially affected although no precise numbers have been issued.

The problematic concrete allegedly originated from a single Stafford Springs (CT) concrete producer during the years 1983 – 2015. The company reportedly used reactive pyrrhotite-bearing rock aggregate from a quarry located in Willington (CT) for the fabrication of concrete for building foundations.

The main tell-tale signs of premature foundation deterioration caused by pyrrhotite-induced expansive reactions in concrete are: Map/web-like cracking patterns, horizontal cracking, spalling on surface of concrete, foundation walls bowing, rust-like discoloration on surface of concrete, white efflorescence (powder) in the vicinity of cracking surface. Cracks can rapidly evolve until the eventual loss of concrete strength.

Pyrrhotite Content

Although the undesirable nature of pyrrhotite for the manufacture of concrete is recognized and although contents as low as 0.3% pyrrhotite by mass of coarse aggregate have reportedly caused significant concrete distress (e.g., in Trois-Rivières, Canada), no precise value has been issued in any U.S. State or Federal laws, as to the maximum authorized pyrrhotite content in coarse aggregates for use in concrete. More research and case history data are needed to reveal with more accuracy the minimum level at which significant concrete deterioration will occur.

Sulfur Content

The European standard for coarse aggregate NF EN 12620 (article 6.3.2), in force since 2003, has placed a limit of 0.1% sulfur if pyrrhotite is identified in the coarse aggregate. In Canada, CSA A23.1 (R2014) states that aggregate susceptible to cause excessive expansion of the concrete due to the presence of sulfides (pyrite, pyrrhotite, marcasite) should not be used in concrete. In addition, this standard recommends not using aggregates containing pyrrhotite in new concrete if these aggregates bear sulfur content higher than 0.15%. The US Army Corps of Engineers recent recommendations state that aggregate for use in new concrete should be assumed pyrrhotite-bearing and should be accepted only if its sulfur content is below 0.1%.