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8th International Symposium on Sprayed Concrete

fibre reinforced concrete, Alum Shale, paper, Dramix
Paper

8th International Symposium on Sprayed Concrete

Modern use of wet mix sprayed concrete for underground support

Trondheim, Norway 11-14 June 2018

 

Durability of sprayed concrete for rock support a tale from the tunnels

Per Hagelia

Tunnels and Concrete Division, Norwegian Public Roads Administration, Norway

per.hagelia@vegvesen.no

 

Summary

Modern steel fiber reinforced sprayed concrete used for rock support is generally regarded as a durable construction material. However, long-term durability data are scarce. The main durability challenge in Norway is related to sulfate attack in the Alum Shale environment and a combined microbial and abiotic attack in the subsea environments.

In previous studies, we found that Alum Shale still represents a concern and that biofilm accumulations in subsea tunnels had caused localised loss of cross section and severe steel fiber corrosion after few years in service.

This paper discusses the effects of four categories of ground waters, hydrogeology and mix design (w/b-ratios 0.40-0.50) at concrete ages up to about 25 years. Sprayed concretes thinner than 80 mm suffered some degradations in aggressive environments, being accentuated in areas characterised by a poor and permeable adhesion zone.

Cement paste degradation and steel fiber corrosion were mainly unimportant in cases where sprayed concrete layers are thicker than 100 mm. It is significant that reactions causing cement paste degradations are mainly independent of fiber type. A minimum thickness of 100 mm, w/b-ratios=0.40 and low capillary porosities (<20%) is regarded as sufficient for long lifetime in aggressive grounds.