Effect of gypsum addition on calcium sulfoaluminate cement hydration by a borated solution

Author(s): J.B. Champenois, C. Cau dit Coumes, P. Le Bescop, L. Petit, D. Damidot
Paper category: Conference
Book title: 2nd International conference on Microstructural-related Durability of Cementitious Composites
Editor(s): Guang Ye, K. Van Breugel, Wei Sun, Changwen Miao
Print ISBN: 978-2-35158-129-2
e-ISBN: 978-2-35158-123-0
Publisher: RILEM Publications SARL
Pages: 1587- 1595
Total Pages: 8
Language: English

The Early age hydration of two Calcium SulfoAluminate cements, containing respectively 0% and 10% gypsum, by a borate solution was studied using isothermal microcalorimetry. The adjunction of gypsum to the cement results in a longer induction period when the mixing solution contains borate anions. Using XRD analysis, TG analysis and pore solution pH measurements, it has been shown that the presence of gypsum buffers the pore solution pH to a low value that allows the precipitation of amorphous calcium borate C₂B₃H₈. As a result, dissolution of anhydrous phases and precipitation of hydrated phases are inhibited until the increase of the pore solution pH once gypsum is fully depleted. Without any gypsum, the pore solution pH is rapidly raised to a higher value and dissolution/precipitation of the cement phases begins just after mixing. In both cases, borate anions are incorporated in an AFt type phase, similar to ettringite, and containing simultaneously sulfates and borates in its structure.

Online publication: 2013
Publication Type: full_text
Public price (Euros): 0.00