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Changes in cement paste during accelerated mortar bar testing for pyrrhotite containing aggregate

Abstract

The accelerated mortar bar test (AMBT) for pyrrhotite (Fe1-xS) containing aggregates accelerates expansion using two regimes: Phase I, during which Fe1-xS oxidation to iron hydroxide is accelerated by bleach and storage at 80 °C; Phase II that promotes thaumasite formation with continued bleach soaking and storage at 4 °C. Two bleach concentrations and one aggregate containing 0.5 wt% Fe1-xS are tested. SEM-EDX data indicate that the oxidized iron precipitates as iron hydroxide at the place of the Fe1-xS, leading to significant expansion (0.22%) during Phase I. The released S distributes in the cement paste but leads only to limited amount of additional ettringite and thaumasite and thus only to limited expansion (0.07%). The NaOCl bleach reduced during the test resulting in chloride and thus to Friedel's salt formation and ettringite stabilization at 80 °C. Only during the prolongation of Phase II, the formation of thaumasite and additional expansion was observed.
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Category

Academic article

Language

English

Author(s)

Affiliation

  • SINTEF Community / Infrastructure
  • SINTEF Community / Architecture, Materials and Structures
  • Swiss Federal Laboratories for Materials Testing and Research
  • Norwegian University of Science and Technology
  • Laval University
  • Diverse norske bedrifter og organisasjoner

Year

2024

Published in

Cement and Concrete Research

ISSN

0008-8846

Volume

188

View this publication at Norwegian Research Information Repository