MASS CONCRETING TEMPERATURE CONTROL FOR LARGE FOUNDATIONS FOR WIND FARM AND THE USE OF RECYCLED CONCRETE AGGREGATES (RCA) FOR GREEN BUILDING POINTS
- A Case Study:
Construction of an experimental wind farm at Horseshoe Bend in Page, Arizona, United States
Approximately 180m3 of concrete was required for a single pour at each of the three wind turbine bases.
Large pour sizes required a new mix formula and the remote location stretched trucking capacity.
An unusually large pour size for the three bases required 12 extra trucks from Dunedin, Gore, Alexandra, Wanaka and Queenstown. From Alexandra, it was an 80-minute haul time to the remote site.
In addition to the logistics, it was a challenge to reduce the heat of hydration that would naturally occur with such a large single pour job.
The solution was achieved by reducing the volume of cement in the mix. This avoided the risk of structural distortions and cracking that are likely with high mix temperatures.
A decision to enter into commercial production of recycled concrete aggregate will contribute to reducing both the demolition waste stream and the embodied energy in new projects using the recycled aggregate.
Environmental responsibility should not be driven by cost alone.
In many countries the demolition process is carefully regulated and a higher dumping cost is added incentive to find more creative and sustainable ways of disposing of demolition waste.
Recycled Concrete Aggregate (RCA) can be used as aggregate replacement in concrete for applications ranging from driveways to office blocks. The recycling process is streamlined by separating all the components of a structure during demolition.
After crushing the concrete, steel reinforcing is removed and the concrete is then washed, screened and graded to produce clean aggregate. By predetermining the percentage of RCA aggregate replacement, a reliable concrete can be produced. Different ratios have been compared to gauge losses in strength and changes in workability. Repeated testing has shown that one can manufacture an RCA concrete that can overcome these hurdles.
There is an opportunity for developers, architects and specifiers to earn Green Building Index points by specifying an amount of RCA in their concrete.
The solution was to specify a 40mm aggregate, to replace the volume normally taken by the cement.
All three bases were cast without problems and achieved the structural performance demanded.
The wind farm bases certainly stretched the capacity of the concrete batching plants, but with great input from all stakeholders they were completed with an excellent result.
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