Review of potential mitigation methodologies for existing
concrete structures containing pyrrhotite-bearing aggregates
Ashley S. Carey
*
, Stephanie S. Watson
Infrastructure Materials Group, Engineering Laboratory, National Institute of Standards and Technology (NIST), 100 Bureau Drive, Gaithersburg,
MD, 20899, United States
ARTICLE INFO
Keywords:
Concrete deterioration
Mitigation
Pyrrhotite
Sulde-bearing aggregate
Transport properties
ABSTRACT
Deterioration of concrete foundations due to pyrrhotite oxidation has led to several studies to
better understand its reaction mechanisms, develop methodologies to identify potentially reactive
aggregates, and quantify the inuence of mixture formulations on potential pyrrhotite oxidation.
However, little research has evaluated the potential of sealants that mitigate oxidation of existing
foundations known to include pyrrhotite-bearing aggregate that has yet to cause severe deteri-
oration. This paper provides a comprehensive review regarding the potential use of mitigating
sealants from three perspectives. First, a general overview of pyrrhotite reaction mechanisms and
associated damage in concrete structures is provided. Second, mitigating sealants commonly used
to mitigate deleterious reactions in concrete substrates are summarized, and their potential ef-
cacy for mitigating pyrrhotite is discussed. Last, a brief overview of established methodologies
for evaluating moisture and gas transport properties of concrete is provided from the perspective
of quantifying sealant performance and their potential to be used within a performance-based
framework. The ndings of this review are envisioned to guide future research efforts toward
recommending potential mitigation strategies for existing structures known to contain pyrrhotite-
bearing aggregate.
1. – Introduction
1.1. - Background
In parts of Connecticut and Massachusetts, concrete aggregate containing pyrrhotite was unknowingly used to construct thousands
of structures from the 1980s to the 2000s. Over a period of decades, the pyrrhotite aggregate began to oxidize due to exposure to
oxygen and water, which led to an unprecedented number of crumbing foundations (Fig. 1). Currently, there are approximately 5000
homes in Connecticut that have been identied as having pyrrhotite-induced damage; however, the Connecticut Department of
Housing estimates that upwards of 35,000 homes could have been built with pyrrhotite-bearing aggregate and be susceptible to future
damage although this estimate is likely high [1,2]. Bashaw [2] notes that the quarry identied as responsible for supplying pyrrhotite
aggregate ceased operation in 2015, meaning it could be decades before the full extent of foundation damage is known. State gov-
ernments in Connecticut and Massachusetts have passed legislation to stop the use of pyrrhotite aggregate in concrete mixtures by
limiting the allowable sulfur content in concrete aggregates [3,4]. In both Connecticut and Massachusetts, aggregate with a sulfur
* Corresponding author.
E-mail address: ashley.carey@nist.gov (A.S. Carey).
Contents lists available at ScienceDirect
Journal of Building Engineering
journal homepage: www.elsevier.com/locate/jobe
https://doi.org/10.1016/j.jobe.2025.113408
Received 23 September 2024; Received in revised form 23 June 2025; Accepted 6 July 2025
Journal of Building Engineering 111 (2025) 113408
Available online 11 July 2025
2352-7102/Published by Elsevier Ltd.
