Slurry Explosives
A slurry explosive is a mixture of AN or other nitrates and a fuel sensitizer, which can either be a hydrocarbon, or hydrocarbons and aluminum. In some cases, explosive sensitizers, such as TNT or nitrocellulose are used, along with varying amounts of water (Figure 19). There are two general classes of water-based slurries; watergels and emulsions. An emulsion is somewhat different from a water gel slurry in characteristics, but the composition contains similar ingredients and functions similarly in the blasthole. In general, emulsions have a somewhat higher detonation velocity and, in some cases, may tend to be wet or adhere to the blasthole causing difficulties in bulk loading. For discussion purposes, emulsions, and water gels will be treated under the generic family of slurries.
Cartridge slurries come in both large and small diameters. In general, cartridges less than 2 in. in diameter are made cap sensitive so that they can be substituted for dynamite. The temperature sensitivity of watergel slurries and their lower sensitivity can cause problems when substituted for some dynamite applications. The blaster(s) must be aware of some of the limitations before trying a one-for-one substitution. The larger diameter cartridge slurries may not be cap sensitive and must be primed with cap sensitive explosives. In general, large diameter slurries are the least sensitive. Cartridge slurries are normally sensitized with monometholamine nitrate or aluminum and are also air sensitized. Air sensitizing is accomplished by the addition of microspheres, chemical gassing, entrapping air, or gas during the mixing process itself.
Bulk slurries are sensitized by one of three methods: air sensitizing, addition of aluminum and addition of nitrocellulose or TNT. Air sensitizing can be accomplished by the addition of gassing agents, which after being pumped into the blasthole, produce small gas bubbles throughout the mixture. Slurries containing neither aluminum nor explosive sensitizers are the cheapest, however, they are often the least dense and the least powerful. In wet conditions where dewatering is not used or where it is not practical, low cost slurries offer competition to ANFO. Table 1, below, is a comparison of the properties of water gels and emulsions.
It should be noted out that these slurries have less energy than ANFO on a by weight basis. Higher cost aluminized slurries and those containing significant amounts of other high explosive sensitizers produce significantly more energy because of their density and are used for blasting wet blastholes. An alternative to using high energy slurries is dewatering blastholes, where possible, with submersible blasthole pumps and using polyethylene blasthole liners within the hole with AN as the explosive. Another option is to use the cartridge ANFO products. In most applications, the use of pumping for water removal with sleeves and AN, or the use of cartridge ANFO products, will produce blasting costs that are significantly less than would result from using higher priced slurries. These supplies are available from many explosive distributors (Figure 20).
