Sprayed Concrete Methods for the Mining Industry | South Africa
The dry-mix method was the established method for constructing sprayed concrete linings until the mid 1990s, when the wet-mix method began to be used more widely. Due to the benefits of the wet-mix method, many contractors who were involved in underground or ground-support projects with large volumes of sprayed concrete made the change from dry-mix to wet-mix spraying.
Present estimates of sprayed concrete usage worldwide show that about 90 % of sprayed concrete is being applied by means of the wetmix method, with an increasing tendency. In some countries, the wet-mix method has been dominant for over 25 years, e.g. Scandinavian countries, Italy, and Switzerland, with almost 100 % usage of wet-mix sprayed concrete. These countries have exported this technology worldwide.
Particularly in Scandinavia, early development in the wet-mix method between 1971 and 1980 turned the sprayed concrete market upside down. During this period, the Norwegian sprayed concrete market changed from 100 % dry-mix spraying to 100 % wet-mix spraying. A similar change happened in Sweden, Finland and Japan. After that, a dramatic change from mesh reinforcement to steel-fiber reinforcement occurred. During the same period, a similar change from manual spraying techniques to robotic application with a manipulator arm took place in the Scandinavian countries. Silica fume and steel fibers have been added to wet-mix sprayed concrete in rapidly increasing volumes since about 1978, particularly in Norway.
All these changes have influenced other countries such as Australia, Korea, Brazil, Italy, Switzerland, France, the UK, Spain, Greece and some other European countries, where the wetmix method has become the dominant sprayed concrete technique
Austria and Germany were traditionally very strong dry-mix areas. The dry-mix technology was widely used and significantly developed in these countries. New systems within the dry-mix method were developed, using extremely fast-setting cement types (without gypsum). However, these countries have also changed to the wet-mix method. Many largescale projects have been completed successfully with this method.
The first large-scale projects using wet-mix sprayed concrete were Königshainer Berge, Ditschhardt Tunnel, TLM (Irlahüll, Schellenberg, Euerwang), a part of the Highspeed Railway Link Nuremberg–Ingolstadt (650,000 m3), Sieberg Tunnel and Blisadona Tunnel, both in Austria. In these countries, the shift from dry-mix to wet-mix spraying took longer than in Switzerland, where it happened in less than two years.
In Australia, the mining industry led the civil construction industry in moving from dry-mix to wet-mix application, and also partly to the use of steel-fiber reinforcement. This development has led to a substantial increase of the market share for wet-mix to almost 100 % in both mining and civil construction works in Australia (e.g. Paseminco mine, Melbourne City Link, Parramatta Rail Link).
Due to the increasing move from dry-mix to wet-mix sprayed concrete
, it is reasonable to assume that future developments within this industry will concentrate on the wet-mix method, particularly on high-performance admixtures and more mechanized spraying technologies, as well as on the appropriate design and specification of sprayed concrete
for permanent tunnel linings.