The state of technology in shotcrete materials has evolved steadily throughout the world and particularly in North America during the last 20 years. The use of supplementary cementing materials such as silica fume, fly ash and slag, the new generations of chemical admixtures, and the development of various types of fibers (steel and synthetic) significantly enhance the performance of shotcrete for a variety of applications.
These technological advancements have led the international mining industry to become a major user of shotcrete for underground support. Because the potential for instability in underground rock openings is a threat to the safety of miners, the support of permanent openings in underground mining is a critical area of shotcrete application. For over 20 years, mining companies have recog-nized the value of steel fiber reinforcement in shotcrete. It has been proven that the performance of steel fiber-reinforced shotcrete compares favorably with steel-welded wire mesh reinforced shotcrete in various ground support applications.1
The introduction of steel fibers in shotcrete increases its energy absorption or œtoughness, increases impact resistance, and provides increased ductility. Ductility is defined as the ability to continue to carry loads after the shotcrete micro-structure has cracked. These mechanical properties are considered extremely important parameters with respect to support linings designed for the underground environment.2 (The effects of addition rate, geometry, and property of fibers are beyond the scope of this article.)
Although the ability of steel fiber-reinforced shotcrete to carry loads in flexure beyond its flexural capacity can be assessed in laboratories using a variety of beam and panel test methods, the under-standing of how to relate it to ground support design guidelines for underground mine devel-opment is limited and subjective.3
Test methods evaluating the load-carrying capacity of steel fiber-reinforced shotcrete (SFRS) performed after 7 and 28 days of curing do not assess