SPECIALIST EQUIPMENT
in to mix the resin, looser ground causes problems. If a borehole falls in as the drill bit is extracted, the cartridge cannot be inserted. If the borehole is bigger than intended due to overbreak, or even due to a worn drill bit, there won’t be enough resin in the cartridge to fill the borehole. For instance, an increase in diameter of just 2mm on a 32mm bolt hole requires 15% more grout to fill the annulus. Te speed at which the bolt is rotated into the hole is also important when using a cartridge system. Too little rotation and the two components in the cartridge won’t be sufficiently mixed; too much and it will be overmixed. Bolts that are not fully encapsulated by grout become weak points in the system.
When the rock mass moves – which often happens due to other mining activities – load on the bolt will be unevenly distributed, increasing the risk of failures. Poor encapsulation could also lead to corrosion due to groundwater reaching the bolt.
Another downside of cartridges is that they are sensitive to temperature. If they are stored or transported at too high a temperature, their reactivity and performance are affected. If the temperature is too low during installation, the resin will be more difficult to mix.
A BETTER WAY As more and more mines experienced the problems outlined above, the need to develop pumpable resins became greater.
Te idea of pumpable resins for rock bolting had been around for many years, but chemical technology has only recently developed sufficiently to allow the idea to become viable. Te goal in developing them was to combine the effectiveness of pumpable cementitious grouts with a resin that would cure much faster. Cementitious grouts must cure for between 12 and 24 hours before it is safe to re-enter an area, causing severe schedule limitations. Resins can go off in a few seconds to minutes only. For the chemists who developed systems such as the MasterRoc RBA 38X series of pumpable resins, the goal was to create a fast-setting resin that was also thixotropic to allow overhead
Because pumpable resins, such as the MasterRoc RBA 38X series, are thixotropic they can be used in overhead rock bolting without additional borehole sealing
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Cracks in the rock will be filled and consolidated, which improves the overall stability
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