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Microstructural Origins of Cement Paste Degradation by External Sulfate Attack
Pan Feng1, Edward J Garboczi2, Changwen Miao3
1Southeast University, Nanjing, Jiangsu 210096, China ; National Institute of Standards and Technology, Gaithersburg, MD 20899, United States.
Construction and Building Materials
|January 2, 2016
Summary
This study models portland cement paste degradation in sodium sulfate solutions. The model predicts damage from ettringite formation and suggests chemical or microstructural changes to mitigate expansion.
Area of Science:
- Materials Science
- Civil Engineering
- Geochemistry
Background:
- Portland cement paste is susceptible to sulfate attack, a major cause of concrete degradation.
- Understanding the microstructural mechanisms of sulfate attack is crucial for durable infrastructure.
Purpose of the Study:
- To develop and apply a microstructure model simulating near-surface degradation of portland cement paste exposed to sodium sulfate.
- To predict the localized deformation and damage initiation caused by sulfate-induced expansive reactions.
Main Methods:
- Utilized thermodynamic equilibrium calculations to guide compositional and microstructural evolution.
- Coupled confined ettringite growth with linear thermoelastic finite element analysis to model stress and strain fields.
- Investigated the role of secondary phase formation on material integrity.
Main Results:
- The model predicts ettringite formation primarily consumes calcium monosulfoaluminate and carboaluminate.
- Localized expansion and damage initiation were simulated due to constrained ettringite growth.
- Identified key chemical and microstructural factors influencing sulfate attack progression.
Conclusions:
- Thermodynamic and finite element modeling provide insights into sulfate attack mechanisms.
- Chemical mitigation strategies include increasing carbonate and magnesium concentrations.
- Microstructural modifications, such as finer monosulfate dispersion, can reduce expansion and damage.
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