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The Nest, Wellington Zoo

03 Sep 2009

In order for Allied Concrete to advance Recycled Crushed Concrete (RCC) to a stage where it was capable of meeting structural requirements research was carried out using partial funding from FRST, together with a Masters Student from Auckland University.

In an attempt to determine the upper limits of this material, all mixes reported in the project were based upon 100% RCC as a coarse aggregate rather than the more common replacement level of 30%.

20, 40 and 60 MPa concretes were used to cast three tests slabs, which were subsequently crushed to give us recycled aggregates of known strength.  These three aggregate sources were then used to produce concretes ranging in strength from 20 to 60 MPa using these RCC materials.  A total of 9 combinations were tested.

Tests were carried out on fresh concrete to measure slump loss, bleed, air content and wet density on a wide range of mixes, from 20 MPa to 60 MPa, using 20, 40 and 60 MPa RCC for each strength grade.  Compressive and flexural strengths, drying shrinkage, creep, chloride diffusion, porosity and oxygen permeability were also tested.

The use of RCC aggregate has been shown to be practical without the need for modifications to existing procedures especially when allowing for the fact that the test results were on total replacement of coarse aggregate.

For the first time in New Zealand RCC was used in structural applications, at a 30% replacement rate, in structural elements of the Wellington Zoo’s new hospital complex (The Nest).  Around 60m3 (40% of the total cast on site) of 25MPa RCC was supplied. This project has enabled a better understanding of the properties of RCC, which when used at conventional replacement levels, performs well within accepted limits.

Bob Officer of Allied Concrete accepts the Excellence in Concrete Innovation Award from CCANZ CEO Rob Gaimster