Michael Sharpin and Angus Macdonald
Concrete Samples
Balclutha Technology Education Centre
Year 7 Technology: 5/6 weeks (including curing time)
Teachers: Simon Kay and Christine Elder
While watching their new school being built mainly from concrete, Michael and Angus became fascinated by this material. As a Year 7 project, they decided to research various concrete mixtures, and to match those results to a test sample from the site.
Michael and Angus made four different concrete mixtures in samples the size of a 1.25lt bottle. One used only 200mls of water; a second used more water; a third had a cup of sugar added to the second mixture; and a fourth had six steel reinforcing rods inserted into the second mixture. The samples were allowed to cure for 28 days before testing.
The first sample made a dry, thick, mixture that was hard to stir and resulted in a sample full of air pockets and gaps. The second mixture was more successful – "nice and smooth" says Michael – and most resembled the sample from their new school. This sugared third sample was lighter coloured, dusty, and more brittle – "you wouldn't use that as your concrete panels!" says Angus.
Engineering and construction firm Fulton Hogan volunteered to pressure test the samples and record the breaking point. Unfortunately, only the fourth, reinforced, sample could be tested – it was the only one with the flat top required for the test. Put under strain, the fourth sample finally broke at 250kN with an "exciting crack".
They presented their findings to guests at a Technology Education Expo in the Balclutha War Memorial Hall which included a a visual display, recipes for samples produced, photos of testing conditions and a movie clip of the pressure testing.
Teacher comment
Michael and Angus took full ownership of this project and worked well together. From observing a real process in the building of their new concrete tilt panel school, through to their own research and application, they now have a greater understanding of concrete as a material and what makes 'good' concrete. They also learned more about why testing is necessary for quality control and how it is done.
Above: Michael and Angus help the Education Minister, Chris Carter open their new school.
