Author(s): Johann Plank and Vipasri Kanchanason
Paper category: Proceedings
Book title: Proceedings of the 2nd International Conference on UHPC Materials and Structures (UHPC2018-China)
Editor(s): Caijun Shi and Baochun Chen
ISBN: 978-2-35158-219-0
e-ISBN: 978-2-35158-220-6
Publisher: RILEM Publications SARL
Publication year: 2018
Pages: 289-296
Total Pages: 8
Language : English

Abstract: It is known since long that the needles of calcium silicate hydrate (C-S-H) which mainly
constitute the matrix of hardened cement develop from initially formed C-S-H foils. However,
our study reveals that the C-S-H foils are in fact preceded by an amorphous, metastable
precursor with globular morphology. Experiments demonstrate that when silicate ions are
combined with calcium ions in aqueous solution, then nanoscale droplets exhibiting diameters
between 40 – 60 nm are precipitated. From there, following a non-classical nucleation
mechanism, the well-known C-S-H nanofoils develop by first growing inside the globule until
the droplet has completely dissolved. The conversion starts ~ 15 min after formation of the
droplets and is finished after ~ 45 min. When C-S-H is precipitated in the presence of
polycarboxylate (PCE) superplasticizers, then C-S-H droplets exhibiting a PCE layer (and
thus core-shell particles) are formed. From this inorganic-organic hybrid, the conversion of
the droplets to the nanofoils begins later (after ~ 2 hrs) and takes much longer, depending on
the thickness of the adsorbed polymer layer surrounding the particles. As a consequence of
the slower transformation, the resulting nanofoils are much smaller in size (length) and
therefore present excellent accelerators to achieve high early strength of concrete.

Online publication : 2018
Publication type : full_text
Public price (Euros) : 0.00

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