Work

Thermomagnetic susceptibility as a quick screening measure and quantification of pyrrhotite in concrete aggregates

Year: 2025

Type: article

Abstract: Premature concrete deterioration due to internal sulfate attack (ISA) has been increasingly linked to the presence of pyrrhotite-bearing aggregates. This study investigates thermomagnetic analysis (TMA) as a rapid screening and quantification tool for detecting pyrrhotite polytypes in concrete aggregates with concentrations as low as 0.1% by weight. Pyrrhotite, particularly in its hexagonal (NC-type) and monoclinic (4C-type) forms, can cause expansive deterioration reactions in concrete when oxidized. Current quality assurance methods, such as differential thermal analysis, optical microscopy, and total sulfur measurement, lack the specificity and resolution to distinguish between pyrrhotite polytypes and concentrations, leading to either underestimation of risk or to unnecessary disposal of viable aggregate materials. Here, thermomagnetic analysis measures magnetic susceptibility changes across heating cycles to identify and quantify pyrrhotite polytypes based on their magnetic transitions. Pure NC- and 4C-type pyrrhotite reference samples were analyzed and used to develop a TMA quantification correlating magnetic susceptibility peaks with pyrrhotite concentration. Crushed aggregates from Norway and North America were tested and compared with results from electron microprobe analysis and automated mineralogy. The findings demonstrate that thermomagnetic analysis effectively differentiates between pyrrhotite polytypes and estimates their relative content, offering a fast, low-cost complement to current testing protocols. Adopting this method could significantly improve material assessment accuracy, reduce unnecessary aggregate disposal, and mitigate ISA risks in concrete infrastructure.

Source: Construction and Building Materials

DOI: 10.1016/j.conbuildmat.2025.143748

Authors: Nikolas Å. Oberhardt, Nathan S. Church, Stefanie Lode, Kurt Aasly

Institutions: Norwegian Public Roads Administration, Norwegian University of Science and Technology, Geological Survey of Norway

Language: English

Topic: Geomagnetism and Paleomagnetism Studies

Subfield: Molecular Biology

Field: Biochemistry, Genetics and Molecular Biology

Domain: Life Sciences

Open Access status: hybrid

Estimated APC paid: $4,540

Funders: Norges Forskningsråd, Statens vegvesen