ABSTRACT
This chapter describes the original invention by Carl Akeley in 1907 of the so-called gunite (dry-mix shotcrete) double pressure chamber gun. In the 1950s, new types of dry-mix guns were developed such as rotary barrel and rotary bowl guns. Also in the 1950s, wet-mix pumped shotcrete started to find use, but it was not until the 1970s with the development of swing valve pumps, that the wet-mix shotcrete process took off. Other equipment advances include the development of remote-control manipulator arms for underground shotcrete application in the 1980s. Major materials innovations that have advanced the state-of-the-art of shotcrete technology include the following: development of steel fibre reinforced shotcrete in the 1970s and synthetic fibre reinforced shotcrete in the 1990s; and the incorporation in shotcrete mixtures of supplementary cementing materials such as fly ash, silica fume, slag and calcined metakaolins to improve the rheology and durability of shotcrete. Advances in chemical admixture technology have also had a pronounced effect on what is now possible with the shotcrete process, including high range water-reducing admixtures to control water demand; hydration-controlling admixture to extend workability and delay setting time; and alkali-free shotcrete accelerators, for addition at the shotcrete nozzle to provide instantaneous stiffening, with thick build-up and rapid setting and hardening and resistance to sloughing and fall-out in tunnelling and mining operations.
