Making Concrete

Cement was being made by the Romans who are thought to have made the discovery when they mixed together water, quicklime and volcanic ash. However this discovery seemed to have been forgotten about until the mid 1700s. Nowadays, concrete is a major ingredient in construction work of all types.

Aim:

To make cement and use it to make concrete.

What you need:

Bunsen, tripod and gauze, evaporating dish, beaker, 20g crushed limestone, 80g sand, 8g clay, 10g calcium oxide, 20mL water, 30-40g small stones, 2 plastic containers for your concrete eg. margarine or icecream containers.

What you do:

1. Put the limestone and clay in the evaporating dish. Mix them together and then heat them strongly for 10 minutes. Let this mixture cool.

2. Put the limestone and clay mixture into the beaker and add 10g calcium oxide and mix together. This is your cement.

3. To make concrete, mix 80g sand with your cement and add 20mL water. Stir well.

4. Pour half this mixture into one plastic container - this is the kind of concrete that is known as mortar. Leave this to set.

5.To the remaining half of concrete mix add the small stones. Pour this mixture into your second plastic container and leave this to set.

When water is added to the mixture of cement, sand and gravel, a process of crystal growth occurs, binding the components together. When this process is complete, the concrete has 'set'.

Further things to do:

1. Complete the experiment above but vary the the ratios of cement, sand, and small stones. Keep notes of each mixture. How does each 'recipe' affect the concrete produced?

2. Design a method of testing the strength of your concrete. What different tests would you need to devise to check your concrete if it was to be used for different parts of a bridge:

i. foundations and piers
ii. deck and roadway
iii. pylons of a suspension bridge
iv. guardrails and superstructure.

You may be able to use one or more of your tests on the concrete you have produced.

3. What methods could you use to make the concrete stronger? addition of other materials? different methods of production?

4. There will be a concrete - producing plant near where you live. (Concrete has a comparatively low cost in terms of its bulk, and therefore it is not economic to transport it long distances.) Contact the concrete plant and find out:

i. the source of their raw materials
ii. the different types of concrete they produce
iii. the different uses of the concrete they produce.

Questions:

1. Why is cement said to be like a glue? What chemical process is occurring as the 'glue' 'sets'?

2. Why do concrete-layers:
i. prefer that the concrete sets slowly?
ii. regularly sprinkle water over freshly laid concrete?

3. What is 'builders mix'?

You can find more 'concrete activities' for level 4 in Making Better Sense of the Material World, Learning Media, 1998, page 63

For concrete ideas online seethe educational activities on the Milburn site at www.milburn.co.nz

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