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Building with Chocrete

Roger Faires of Mott Macdonald, discusses an innovative education project that challenges schoolchildren to make beams from “Chocrete” – a mix of chocolate and cereals.

In January a colleague, Bonnie Leung, and I volunteered an event which saw 50 pupils from Cambridge schools compete in organised STEM activity.

We devised a task that saw students create a structural beam out of “Chocrete” - a mix of cereals and chocolate, using bamboo sticks as reinforcement.

The idea

The idea for Chocrete originally came from my previous participation in a Queen’s jubilee competition to build the tallest possible edible cake - Chocrete was first tested in that competition and it was a huge success.

We decided it could be a great way to explain to students how concrete is reinforced, modifying the original ‘recipe’ into “reinforced” Chocrete by providing the bamboo sticks as reinforcement.

The challenge

Following guidance from Master "Choclatier" Paul Wayne Gregory, the teams made moulds from cereal boxes for a beam to span 20cm.

They then selected the ratios of cereal to chocolate, and the amount of bamboo sticks to place at the bottom of the beam as tensile reinforcement.

The “contractor” (Mott MacDonald staff) then used a microwave to temper the chocolate and complete the pour.

The challenge had a cost element and it was highlighted that “cheap” rice crispy aggregate (which occupies large volume with relatively low weight) was a good to combine with chocolate “cement”, when compared with options like shredded wheat or porridge oats.

A rig was then erected, with a rope and a bag set-up at mid-span of the reinforced Chocrete. Timber blocks were added to the bag until the Chocrete beam failed.

We were pleasantly surprised that the beams ended up stronger than initially thought - the load carrying capacity of these beams was much greater than we had allowed, with some beams carrying almost 10kg over the 20cm span! We certainly learned that as a building material it beats the brittle gingerbread house!

Why it works

The teams, each formed by Year 6 students, were really interested in the project - especially when they had the chance to get their hands dirty!

It’s a great exercise because it reflects the engineering sector’s emphasis on teamwork, respect for others and innovative thinking. It was also lovely to see a good balance between boys and girls in the project.

STEM workshops like this are also useful as they help young people think about the sort of skills they’ll need as an engineer, and the opportunities engineering careers provide to contribute to society through developing new building technologies that will improve our quality of life and promote more sustainable lifestyles.

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