North Goonyella concrete pour sets two new records

Mine owners, Peabody Energy Australia, faced the daunting task of resurfacing a 1040-metre-long underground concrete roadway (drift) that had deteriorated over time.
The challenge involved replacing rough and potholed sections of the 5.2-metre-wide concrete access drift with a minimum of 150mm of new reinforced concrete as well as repairing a section where the clay base had heaved, resulting in a loss of headroom and associated safety concerns.
This would involve pumping 1300 cubic metres of concrete along a narrow opening over a one-in-seven fall, terminating 150 metres below the surface.
The difficult task was completed over 10 consecutive nights, setting new Australian records for the country’s longest concrete pour (1040 metres) and the longest distance that steel fibre reinforced concrete had been pumped (360 metres).
Apart from the engineering and technical issues involved in the complex task, Outbye Superintendent Mark Riemer insisted that the job be completed in a cost-effective, safe and timely manner so as to minimise mine production delays.
Kevin Walters of Capital Consulting Engineers, Mackay, was given the task of solving the many engineering issues involved in the project.
A team of top-flight contractors was gathered together to tackle the complex challenge.
The team included:
1 Mark Combe of Fibercon, concrete fibre specialists, based in Brisbane;
2 Paul Morris of PV and JM Morris Builders, Mackay;
3 Troy Brell of Brell Concrete Pumping, Mackay;
4 Gary Blackburn of Mansell Premix Concrete, Mackay;
5 TRM underground road maintenance experts, Mackay; and
6 Jak Kidd of BASF (concrete additive supplier).
Riemer said contractors had to take all possible steps to prevent delays to the setting of the fresh concrete during the pour to avoid blocking the pipeline.
This involved pouring at night and lowering the temperature of the concrete by adding chilled water so that the concrete could be pumped at a constant 18 degrees Celsius.
Attention was also paid to the layout of the pipeline, mix design and the level of additives to maintain concrete integrity and workability.
Communication between the pump operator and the placer proved critical as the concrete was beginning to form a solid plug under pressure during the pipe change period of 8-10 minutes per change from about 850m onwards.
Slump tests were performed for each truck and the slump adjusted gradually to avoid excessive pump pressures as there was a decrease in slump from the pump to the end of the pipe of up to 40mm. Concrete samples were taken every 50 cubic metres for strength testing.
Riemer said the concrete was reinforced with F102 mesh with additional reinforcing bars added where the broken sections occurred.
The original concrete was removed from the clay section that had heaved upwards, allowing the team to stabilise the clay with ballast and concrete binding before placing a reinforced 250mm slab over the area.
Troy Brell of Brell Concrete Pumping said his machines were able to maintain a constant pumping rate of 30 cubic metres per hour.
“Washout was by water method in the interests of the environment and to satisfy safety concerns,” he said.
“Only one blockage occurred in 100 hours of pumping and this was due to human error.”
Brell said that initially he was unsure they could reach a depth of 1000 metres, as they only had 150 bar of pump pressure available to pump the concrete.
“We knew we weren’t going to get the full 35 bar of gravitational head advantage and as it turned out, we only got about 10-15 bar advantage, but due to the superior quality of the concrete which involved slump retention, water reducer, viscosity modifier and retardants, we made it,” he said.
The level of detailed planning was so critical that Gary Blackburn, production manager of Mansell Mining and Shortcrete, changed quarries to ensure the shape of the rock was suitable for such a long pour.
“The moisture rate was critical in this job – if each stone wasn’t completely saturated with water, we would have run the risk of the concrete drying out,” said Blackburn.
With concrete at 120-130 slump being pumped over such a long distance, there was a chance that the stone could be left behind unless it was an integral part of the mix.
“The raw materials were tested prior to the commencement of the project and stockpiled separately to ensure the material gradings were uniform.
“This was a crucial step in the mix design process as we wanted to achieve little or no variation in the mix, given that we had previously dealt with a complex project such as this,” he said.
“The concrete mix we supplied was specially designed to provide high-quality concrete through careful selection of sand, stone and additives to retain slump and to retard the mix.
“We incorporated a viscosity emulsifier (Suretec) supplied by Jak Kidd of BASF to ensure the concrete did not separate under pressure and over the long pumping distances.
“With this attention to detail and great teamwork by the professionals involved in the project, we made it,” said Blackburn.

For more information contact:
Mark Combe (Fibercon) tel: +61 (0)414 647077
Kevin Walters (Capital Consulting Engineers) tel: +61 (0)427 013012