Widespread failures of concrete basement foundations in Connecticut appear to be the result of oxidation of a particular mineral found in the aggregate from a Connecticut quarry, according to a 101-page report by University of Connecticut experts to the state Attorney General. The Hartford Courant has the story here (see: "Attorney General Issues Final Report On Cause Of Crumbling Foundations," by Jordan Otero Sisson).
"The 101-page report, compiled by the UConn researchers, focuses solely on the investigation into the scientific cause of the crumbling foundations," the Courant reported. "The attorney general's final report is dated Aug. 31, 2016, but was delivered to the governor's office Nov. 3. It echoes the results, announced in July, of a first round of state testing saying pyrrhotite, present in the particular concrete aggregate that was used for the foundations, was partly to blame."
But that information won't be much help to homeowners with failing basements, the paper reported: "The attorney general's office offered little hope to homeowners seeking financial relief from the burden of replacing their foundations, based on the finding of pyrrhotite. In a cover letter to Gov. Dannel P. Malloy and Consumer Protection Commissioner Jonathan A. Harris, Attorney General George Jepsen wrote: 'consumer protection laws do not provide a viable source of broad-based relief to the homeowners affected by deteriorating concrete resulting from pyrrhotite reactions. Connecticut law has never prohibited, limited or otherwise regulated the presence of pyrrhotite in residential concrete foundation construction.'"
The UConn report, "Investigating the Deterioration of Basement Walls Made of Concrete in CT," by Kay Wille and Rui Zhong, describes a comprehensive investigation of the problem, including a visual inspection of the damage, sampling and compressive testing of concrete cores from seven problem basements, and an analysis of the concrete and aggregate samples using X-ray diffraction, X-ray fluorescence, scanning electron microscopy, and energy dispersive X-ray testing.
The report's conclusion is expressed, however, in carefully hedged academic language: "A hypothesis is established: pyrrhotite in the aggregate oxidizes at the presence of water and oxidant (oxygen or ferric ions) which lead to the formation of expansive secondary mineral product such as ferrihydrite and the release of sulfate. The released sulfate promotes the reaction with aluminum containing phases in the cement (tricalcium aluminate (3CaO∙Al2O3)) and results in the formation of expansive and thus deleterious secondary minerals such as ettringite. Furthermore, at the presence of carbon, either from the calcite in aggregate or from CO2 from environment, another deleterious mineral thaumasite can be formed. Both of these secondary minerals are expansive and might ultimately lead to the premature deterioration of the concrete foundation investigated in this research. The hypothesis is validated by the chemical, mineralogical and microstructural investigation on the pyrrhotite-bearing aggregate, sulfate containing whitish deposits found at the vicinity of the cracking surface along with the spatial association of secondary minerals with microcracks in the cement matrix."
