Some peculiar chemistry aspects of shotcrete accelerators

Title: Some peculiar chemistry aspects of shotcrete accelerators
Author(s): D. Lootens, B. Lindlar, R.J. Flatt
Paper category : conference
Book title: International Conference on Microstructure Related Durability of Cementitious Composites
Editor(s): W. Sun, K. van Breugel, C. Miao, G. Ye and H. Chen
Print-ISBN: 978-2-35158-065-3
e-ISBN: 978-2-35158-084-4
Publisher: RILEM Publications
Publication year: 2008
Pages: 1255 - 1261
Total Pages: 7
Nb references: 6
Language: English

Abstract: Tunnelling and mining job sites rely on the quality of recently sprayed shotcrete to secure freshly excavated zones. Worker safety in particular is therefore greatly dependent on the ability of this sprayed material not only to stick to the wall but also to reliably develop a true load bearing capacity.
In this paper, we demonstrate by ultrasound spectrometry that accelerators can alter both flocculation and hydration. By flocculation, we refer to the stage in which fast precipitation, mainly of ettringite, thickens the material enough for it to stick on the wall and remain there.
Apart from this the accelerators affect diversely hydration.
More specifically, we demonstrate in the case of alkali free accelerators that some additives that increase accelerator shelf life can dramatically retard hydration and strength development. These results explain that while as some shotcrete mixes may hold up perfectly well they do not develop sufficient load bearing capacity and may fail due to having to sustain load over a too long period of time or due to build up of hydrostatic pressure in cases of water infiltration. In such cases sudden collapse of shotcrete may occur after some hours, a situation that is clearly undesirable.

Online publication: 2009-06-09
Publication type : full_text
Public price (Euros): 0.00