Minimization of Leaching of Shotcrete by Admixtures

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Title: Minimization of Leaching of Shotcrete by Admixtures

Author(s): R. Breitenbucher, R. Springenschmid, and H. W. Dorner

Publication: Special Publication

Volume: 132

Issue:

Appears on pages(s): 781-794

Keywords: accelerating agents; admixtures; alkalies; drains; fly ash; leaching; moisture; shotcrete; silica fume; slag cements; tunnels; Materials Research

Date: 5/1/1992

Abstract:
In tunnels built according to the New Austrian Tunnelling Method, the shotcrete shell is often in contact with ground water. Depending on the amount and type of water, chemical compounds in the shotcrete are dissolved and transported into the drainage pipes and the main outfall. Due to precipitation of the dissolved compounds, the maintenance of the drainage systems is very expensive. Furthermore, the main outfall is loaded with water of a high pH-value. It was found that as well as Ca(OH)2, the alkalies in the shotcrete are responsible for the degree of leaching. Therefore, the accelerators needed for such shotcretes, which are based mostly on alkalies, have to be reduced as much as possible. This can be done sufficiently if silica fume is used in connection with slag cement to make the shotcrete sticky enough, so that it adheres to the rocks.