Strata control products supplier Celtite has recently released several new products in Australia, including the GXT tensionable cable bolt, coupled bolts and the CV Hi-Grip rock bolt.

The GXT tensionable cable bolt has been designed primarily as a point anchor system. The bolt offers high load transfer and superior stiffness from long tendon support, said Neil Hunt, Celtite product development manager.

"The bolt itself is constructed from seven strand wires rather than multiple wires, which have inherent operational problems. The strand is pre-stressed during manufacture. Pre-stressing is widely used in civil engineering as an accepted way of resisting cyclic or dynamic loading, and is also used to limit structural movement due to steel elongation," Hunt said.

The GXT strand is also bulbed using the "Garford" technique, which enhances the load transfer performance. The bolt has been used successfully in underground coal mines, where it has been installed in one continuous length up to 15 meters, although it is normally used in 4, 6, and 8m lengths.

Its construction means it is easy to handle and is flexible enough to be used in even the lowest seam heights, Hunt said. Normally anchored with a resin cartridge the bolt is installed into standard 27mm diameter holes.

The use of resin rather than cementatious grout means the bolt can be installed literally at the coal face and pre-tensioned within a matter of seconds, rather than hours.

Applying 10-25 tonnes at the face can make a huge difference to certain strata types, reducing bed separation, and, in some cases, even visibly lifting failed strata back up again.

Solid rock bolts have been coupled together and used in mining and tunnelling for a number of years. However, the Product Development Dept at the Celtite laboratories has designed a new product around an old concept, Hunt said.

"Coupled bolts are traditionally joined together by means of an external sleeve, which is threaded internally, allowing two rock bolts to be screwed inside the coupler. Normally the coupler is of a much larger diameter compared to the rock bolts. This usually means the coupled bolts can only be point anchored, which reduces the performance of the system.

"Celtite has developed a new and novel system which allows the coupler to be made from the parent bars. One bolt becomes the female end the other bolt the male. The bolts are then screw together by means of a specially designed high strength thread.

"The beauty of the system is that the new coupler is substantially the same diameter as the parent bar. The advantage is that it allows the coupled bolt to be installed into a hole of one continuous diameter. Celtite have developed a range of low viscosity resins which will allow their coupled bolts to be fully encapsulated, over the entire 4-6m length. This system offers ease of handling, superior grip, and are economical to use."

The CV Hi-Grip rock bolt is the latest generation roof bolt designed and manufactured by Celtite. It is a hot rolled, solid bolt, which incorporates the latest in steel chemistry and has the ability to grip strata better than any other roof bolt of the same size and weight.

According to Hunt, it has been designed to meet the needs of primary roof support to help coal mines reduce their bolting costs and at the same time improve roof conditions.

"The concept behind the CV Hi-Grip was to produce a superior bolt which can be installed by both hand-held and mechanised bolters into standard 27mm holes. Its high load transfer design has meant that some of Celtite's customers have been able to reduce their bolting costs by modifying their support pattern and bolt density and reduce the amount of resin at the same time."

Released earlier this year at the Queensland Mining and Engineering Exhibition in Mackay, the Hi-Grip roof bolt generated a lot of interest from the mining fraternity with several trials planned.

Celtite is a leading supplier of strata control products into the underground Australian coal industry. It manufactures a wide range of mining consumables, including rock bolts and tensionable cable bolts.

It is the only Australian supplier that manufactures and markets its own chemical products. With a number of offices around Australia and its head office is in Sydney, its steel products are manufactured from a new purpose built manufacturing facility in Newcastle.