The Stranges Building is the one of the first major structures to be started in the Christchurch CBD and construction started in the old red zone in late 2012.
The project originally specified self-compacting concrete with low shrinkage characteristics for the core walls due to heavy reinforcing with 40 mm diameter bars in some areas. During initial construction of the lift core section of the building a stitch joint concrete was used by Allied Concrete that is typically pumped from the bottom. This concrete was extremely sticky, which increased pumping pressure and produced a variable surface finish on the wall. Optimum flowability was achieved at higher than normal spread levels of 750 mm and this meant the concrete was vulnerable to segregation.
Before the start of the circular core structure in the atrium of the building it was decided to change the design of self-compacting concrete. Development of this new mix was done in the laboratory and on selected smaller projects around Christchurch to ensure a decent track record of performance. The lower viscosity of the new self-compacting concrete was found to be much easier to batch, was easier to pump and was able to flow right around long sections of wall. The development of this new SCC mix was able to significantly improve both productivity and performance without compromising aesthetics, in fact the surface finish achieved was significantly improved.