“Since the mining industry has long used dry-mix gunite for covering underground mine surfaces and constructing ventilation structures, Strata examined the issues and identified detriments to this traditional method and determined ways to resolve these with the use of wet-mix shotcrete,” Strata Mine Services’ Chuck Pulver said.

“From there, [we] worked to develop and formulate [our] own concrete mix, and the first-ever wet-mix shotcrete that can be pumped from the surface.”

Dry-mix solutions often, by nature of design, create significant dust. This, in turn, can create issues for workers downwind and in the vicinity and can have an overall negative impact on miner health and safety once the mixture makes its way into vent circuits.

With the wet-mix solution, dust exposure is reduced, plus crews no longer have to earmark labour time for the placement and loading of large, heavy gunite bags and no supplies need to be kept underground. Instead, Strata crews perform all of the work at the pump and nozzle with minimal interference to or effect on mining crews.

Wet-mix shotcrete is also about twice as fast in the rate of application than the traditional dry-mix solution, the company says, and is more reliable and consistent in its application and the risk of nozzleman error is eliminated with Strata staff performing the work.

Finally, the design of pumping the wet-mix from the surface also eliminates the need for an intrinsically-safe and permissible wet pump, equipment that is rather scarce in North America; traditional shotcrete pumps are not permitted underground under federal regulations.

“In discussion with various people in the shotcrete and concrete industries, it was decided that with the proper mix design, the concrete could be pumped a considerable distance to the nozzle,” Pulver said.

“So working with our ready mix supplier and an admixture supplier, we came up with an initial mix design and tweaked it a few times to get a mix that looked acceptable for long distance pumping.”

Strata first tested the application at a coal operation in West Virginia last October. Crews made note of the positives of the application method versus the issues to be rectified during that test.

“As the horizontal component of the material pumping lengthens, this operation will become more challenging,” he said.

“It is expected [however] that if success with this method continues, we may be pumping wet-mix shotcrete mixes as far as 1,500 feet (458m) horizontally after 1,000ft (305m) down the shaft within the next year.”