Phase-selective degree of hydration at setting: An in situ synchrotron diffraction study. (18th April 2022)

• Record Type: Journal Article
• Authors: Morales-Cantero, Alejandro; Cuesta, Ana; Santacruz, Isabel; Aranda, Miguel A.G.; De la Torre, Angeles G.
• Is Part Of: Construction & building materials. Volume 328(2022)
• Publication Date: 2022-04-18
• Subjects: Portland cements -- Hydration kinetics -- Early age hydration measurements -- Synchrotron radiation -- Amorphous quantification; Building materials -- Periodicals; 624.18
• DOI: 10.1016/j.conbuildmat.2022.127117
• Languages: English
• ISSNs: 0950-0618

Abstract

Highlights: The leading phase contributing to setting has been quantitatively determined to be C−S−H gel for the studied neat Portland cement pastes. AFt precipitation does not contribute significantly to setting for these studied cements. Cements with similar chemical composition and texture differ in setting times due to the different hydration kinetics of alite, likely due to aluminium retardation in one case. Independently on the setting time, for grey Portland cements with w/c = 0.50, initial setting takes place when alite degree of hydration is close to 20% and the C−S−H gel content reaches approximately 6 vol%. Abstract: Setting of Portland cements is still not well understood. Previous studies used techniques that analyse the pastes as a whole to correlate setting times with degree of hydration. Here, in-situ synchrotron X-ray diffraction analysed by the Rietveld method, with internal standard methodology, is used to derive alite dissolution rate and the crystallization kinetics of ettringite and portlandite in three commercial cements. Moreover, C–S–H gel precipitation pace has also been determined. C–S–H gel precipitation is key to account for setting. For grey Portland cements with w/c = 0.5, initial setting is attained when alite degree of hydration is close to 20% and the C−S−H gel content reached approximately 6 vol%.