Shotcrete is ideal for early ground support after blasting or excavating in mining, providing early strength development. Putzmeister´s mobile shotcrete equipment applies concrete in mines and tunnels all over the world, with concrete output rates of up to 30 m3/h and spraying ranges of up to 17m. The common denominator of all Putzmeister machinery is its high performance and reliability in rough working conditions above and underground.

Putzmeister’s most advanced model for concrete spraying in mining is the Sika-PM 4210, a further development of the well-known Sika-PM 4207. The first machine of this new series has been allocated to the German Sachtleben Bergbau GMBH & Co. KG, which owns and runs the Clara mine (“Grube Clara”) in Oberwolfach,  in the Black Forest of Baden-Württemberg, Germany.

Under the highest technical standards, this mining operation has been continuously extracting barium sulphate for over 100 years, as well as fluorspar for over 25. The sulphates are further processed into high-quality products at the near-by preparation plant. The annual output of raw material amounts to approximately 140,000 t, resulting in a salable production of 50,000 tons of barite and 25,000 tons of concentrated fluorite.

The Sika-PM 4210 concrete spraying equipment will be used in all of the three main fissures of the mine for structural support in roadway heading as well as special operations in critical situations. According to Sachtleben, the biggest challenges the machine faces are the frequently changing geological conditions of the rock, varying significantly in composition, strength and stability. Therefore, the machine operator needs to be flexible during the concrete spraying process as far as concrete output and additive dosage are concerned, depending on the early-strength and drying time requirements of each situation.

The new proportional remote control of the Sika-PM 4210 needs  to this customer’s need exactly, as it allows the complete regulation of the concrete output as well as fine-tuning of the preset additive dosage. All other functions of the machine are also available via remote control, including the automatic start of the spraying sequence (air, concrete and additive).

In addition to this, the range of the spraying arm is 1.4 m longer than the standard model, achieving a maximum vertical spraying range of 10.5 m. The spraying arm is also more agile, with an increase of 25% in the spraying speed at the tip of the arm. The cylinders of all arm extensions are covered for protection, but are can still be easily accessed for maintenance. Lastly, new high intensity xenon working lights have been fitted on the spraying arm.

Other improvements of the Sika-PM 4210 to cope with the rough working conditions at the Clara mine are:

• the inclusion of state-of-the-art heavy duty axles with mining tires
• a manually-released automatic fire-extinguishing system which comes into action at 6 critical spots of the machine at once
• a heavy-duty stainless steel switchboard
• a special low-profile concrete hopper with a discharging height of only 1150 mm
• a strong stainless steel additive tank with a capacity of 450 litres