Ettringite formation in low C3A portland cement exposed to sodium sulfate solution

Abstract

Four low-C3A Portland cements with different C3S content (40 to 74%) were stored for two years in sodium sulfate solution. Expansion and flexural strength were monitored as mechanical properties, while the microstructural changes were studied by X-ray diffraction and scanning electron microscopy using X-ray microanalysis. For this cement type, the alteration processes can be described by three stages: induction, gypsum formation and delayed ettringite formation. The results shown that delayed ettringite is derived from ferroaluminate phases and it was found for all cements. The great expansion was measured for high C3S-content cement and the expansive formation of ettringite in this case was attributable to localized gypsum formation. © 1997 Elsevier Science Ltd.