Magnesium silicate hydrate formation at the surface of hydrated cements

Author(s): B. Lothenbach, E. Bernard, W. Kunther and K. de Weerdt
Paper category: Proceedings
Book title: Proceedings of the International Conference on Sustainable Materials Systems and Structures (SMSS2019) Durability, Monitoring and Repair of Structures
Editor(s): Ana Baričević, Marija Jelčić Rukavina, Domagoj Damjanović, Maurizio Guadagnini
ISBN: 978-2-35158-217-6
e-ISBN: 978-2-35158-218-3
Publisher: RILEM Publications SARL
Publication year: 2019
Pages: 31-38
Total Pages: 813
Language: English

Abstract: At the interaction zone of hydrated cements with seawater or with clayey rocks, leaching, carbonation, decalcification of C-S-H as well as the formation of magnesium silicate hydrates (M-S-H) is observed. The formation of M-S-H is related to the relatively high magnesium concentrations (3-60 mmol/L) in seawater as well as in the interstitial solution of clayey rocks and the lowering of the pH at the leached surface of the cement. Leaching and carbonation decrease the pH at the surface and destabilise C-S-H, which accelerates M-S-H formation. The direct study of the properties of M-S-H at surface of hydrated concrete in contact with seawater or clays is complicated by the very poor crystallinity of M-S-H and the presence of other minerals. Detailed studies on synthetic M-S-H indicated that M-S-H has a sheet silica structure similar to clay minerals and contains in addition to magnesium, silica, and water also some aluminium, calcium and alkalis. Thermodynamic modelling indicated that conditions which favour leaching of C-S-H ease the formation of M-S-H at the surface of mortars and concretes. Thermodynamic modelling was able to highlight the sequence of chloride, sulfate and magnesium accumulation observed at the surface of mortar exposed to seawater.

Online publication :2019
Publication type : full_text
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