Last week the U.S. Geological Survey (USGS) released a map of where the mineral pyrrhotite naturally occurs in the continental United States. My first reaction was huh?!! According to the press release: “This project was a bit unusual for us, because typically we’re trying to help people find mineral deposits that they want, not minerals that they don’t want,” said USGS scientist Jeff Mauk, who led the project.
Pyrrhotite is related to the more common and well-known mineral pyrite, Fool’s Gold. They are both worthless. Pyrrhotite differs from pyrite because it has less sulfur and is far more reactive to water than pyrite. Pyrrhotite is known to be present in Great Brittan, France, the United States and Canada. It turns out where pyrrohitite is important- to avoid using it as fill in cement mixtures. When pyrrhotite is exposed to water and oxygen, it breaks down to produce sulfuric acid and secondary minerals, including gypsum, which have larger volumes than the pyrrhotite they replace.
If pyrrhotite-bearing stone is crushed up and used as filler for the concrete it can break down over time to form secondary minerals that expand and crack concrete, causing concrete structures, like roads, bridges, aqueducts and home foundations, to fail. Thus, identifying where pyrrhotite may occur can help identify where there may be a risk of pyrrhotite being included in crushed stone production. The new 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.
The phenomenon when concrete undergoes an increase in volume and subsequently cracking under long exposure to sulfate enriched solutions, was first discovered in the early days of the 20th century. An investigation of cement failures in 1914 involving the USDA, the U.S. Bureau of Reclamation and the American Portland Cement Manufactures Association found that Secondary mineral formation is strongly dependent on the availability of sulfate which can be either natural or manmade contaminants in ground water, moisture in soils and sulfate-rich acid rain. Sulfur dioxide from the combustion of fuel and the sulfate impurities of deicing salt have been found over the years to be sources of sulfur contamination and damage to concrete structures.
It wasn’t until the last part of the 20th century when it was discovered that concrete rich in iron sulfide were also subject to premature deterioration. Pyrite (FeS2) and pyrrhotite (Fe1-xS) are the most common iron sulfide compounds in nature. The pyrrhotite was found to especially serve as an internal sources of sulfur for delayed mineral formation.. Oxidation of these sulfides over time in the presence of water and an oxidant (either oxygen or ferric ion) leads to the formation of cracking and ultimately the failure of the concrete.
Although sulfide containing aggregates induced premature deterioration of concrete, only a limited number of scientists were aware of this problem before the late 1990’s. However, as more damage appeared in highway and foundation deterioration interest in the problem increased. The first symposium on pyritic rock fills in concrete was held in May 1997 by the Montreal section of the Association of Engineering Geologists (AEG).
More recently, premature deterioration of concrete foundations were found in thousands of homes in eastern Connecticut and western Massachusetts. Pyrrhotite occurs in rocks in many areas of the United States. To help assess the national risk of pyrrhotite in aggregate, the 2019 appropriations bill for the U.S. Geological Survey (USGS) allocated funds to develop this map (below) showing the distribution of pyrrhotite across the United States in hopes of preventing the inclusion in concrete and the devastating consequences to homeowners. Slow deterioration of concrete is not a covered event under homeowners insurance.
Last summer the Associated Press reported that” hundreds of suburban homeowners in a large swath of eastern Connecticut are getting help from the state to salvage properties.” The Connecticut Foundation Solutions Indemnity Company, which is funded with $20 million a year for five years in state borrowing and an annual $12 fee on homeowners’ insurance policies is providing eligible homeowners up to $175,000 to repair their homes. The he work involves cutting back the driveway, disconnection and removing the furnace and plumbing hookups, then creating holes into the foundation walls so steel beams can be slid underneath the home. Then the house is jacked up using the steel frame. Workers then jack hammer away all the concrete, and a new foundation is poured. The grant from the Connecticut Foundation Solutions Indemnity Company often doesn’t cover the whole cost.
Pyrrhotite is related to the more common and well-known mineral pyrite, Fool’s Gold. They are both worthless. Pyrrhotite differs from pyrite because it has less sulfur and is far more reactive to water than pyrite. Pyrrhotite is known to be present in Great Brittan, France, the United States and Canada. It turns out where pyrrohitite is important- to avoid using it as fill in cement mixtures. When pyrrhotite is exposed to water and oxygen, it breaks down to produce sulfuric acid and secondary minerals, including gypsum, which have larger volumes than the pyrrhotite they replace.
If pyrrhotite-bearing stone is crushed up and used as filler for the concrete it can break down over time to form secondary minerals that expand and crack concrete, causing concrete structures, like roads, bridges, aqueducts and home foundations, to fail. Thus, identifying where pyrrhotite may occur can help identify where there may be a risk of pyrrhotite being included in crushed stone production. The new 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.
The phenomenon when concrete undergoes an increase in volume and subsequently cracking under long exposure to sulfate enriched solutions, was first discovered in the early days of the 20th century. An investigation of cement failures in 1914 involving the USDA, the U.S. Bureau of Reclamation and the American Portland Cement Manufactures Association found that Secondary mineral formation is strongly dependent on the availability of sulfate which can be either natural or manmade contaminants in ground water, moisture in soils and sulfate-rich acid rain. Sulfur dioxide from the combustion of fuel and the sulfate impurities of deicing salt have been found over the years to be sources of sulfur contamination and damage to concrete structures.
It wasn’t until the last part of the 20th century when it was discovered that concrete rich in iron sulfide were also subject to premature deterioration. Pyrite (FeS2) and pyrrhotite (Fe1-xS) are the most common iron sulfide compounds in nature. The pyrrhotite was found to especially serve as an internal sources of sulfur for delayed mineral formation.. Oxidation of these sulfides over time in the presence of water and an oxidant (either oxygen or ferric ion) leads to the formation of cracking and ultimately the failure of the concrete.
Although sulfide containing aggregates induced premature deterioration of concrete, only a limited number of scientists were aware of this problem before the late 1990’s. However, as more damage appeared in highway and foundation deterioration interest in the problem increased. The first symposium on pyritic rock fills in concrete was held in May 1997 by the Montreal section of the Association of Engineering Geologists (AEG).
More recently, premature deterioration of concrete foundations were found in thousands of homes in eastern Connecticut and western Massachusetts. Pyrrhotite occurs in rocks in many areas of the United States. To help assess the national risk of pyrrhotite in aggregate, the 2019 appropriations bill for the U.S. Geological Survey (USGS) allocated funds to develop this map (below) showing the distribution of pyrrhotite across the United States in hopes of preventing the inclusion in concrete and the devastating consequences to homeowners. Slow deterioration of concrete is not a covered event under homeowners insurance.
Last summer the Associated Press reported that” hundreds of suburban homeowners in a large swath of eastern Connecticut are getting help from the state to salvage properties.” The Connecticut Foundation Solutions Indemnity Company, which is funded with $20 million a year for five years in state borrowing and an annual $12 fee on homeowners’ insurance policies is providing eligible homeowners up to $175,000 to repair their homes. The he work involves cutting back the driveway, disconnection and removing the furnace and plumbing hookups, then creating holes into the foundation walls so steel beams can be slid underneath the home. Then the house is jacked up using the steel frame. Workers then jack hammer away all the concrete, and a new foundation is poured. The grant from the Connecticut Foundation Solutions Indemnity Company often doesn’t cover the whole cost.
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