Concrete in the Classroom
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in the Classroom>Lesson 4
Lesson
4: A Collection of Aggregates
Age: Grades 7-12
Subjects: Science
Skills: Comparing, similarities and
differences, description, observation
small group work
Duration: 45 minutes
Setting: Laboratory or classroom
Key Vocabulary: Aggregate, volume
Objective
Students will learn 1) About various types of aggregate 2) Why various
sizes of aggregate are needed to create concrete
Method
Make a classroom collection of aggregates to understand how they
work in concrete mixes.
Background
A list of aggregates is provided below. Making a classroom collection
is helpful for students to see the varieties of concrete that are
possible by varying the aggregates.
- vermiculite
- ceramic spheres
- perlite
- expanded, clay, shale or slate
- crushed brick
- crushed limestone
- sand
- river gravel
- crushed recycled concrete
- steel or iron beebees
- steel or iron pellets
Materials
Two 1000 ml beakers, aggregate or plastic beads, water
Procedure
Two different sized aggregates can be used to show that the total
volume of space between aggregates does not change when the size
of the aggregate changes. Measure the amount of water that it takes
to fill two 1000 ml beakers, each containing a different size of
aggregate. The volume of space between particles lessens only when
the different sized aggregates are mixed. This can be shown rather
dramatically if two different sizes of plastic beads are used.
Review your experience with the aggregates from the
mortar mix. The aggregates are of such a size to allow the most
efficient surface contact between the cement paste and the different
sizes of aggregates.
The amount of cement paste used must be at minimum
equal to the spaces in between the aggregate particles and a small
amount more to make the concrete mixture relatively easy to move
while pouring concrete and making the surface smooth. This is known
as “workability.”
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