Age: Grades 7-12
Skills: Comparing, similarities and
differences, description, observation
small group work
Duration: 45 minutes
Setting: Laboratory or classroom
Key Vocabulary: Aggregate, volume
Students will learn 1) About various types of aggregate 2) Why various sizes of aggregate are needed to create concrete
Make a classroom collection of aggregates to understand how they work in concrete mixes.
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.
- ceramic spheres
- expanded, clay, shale or slate
- crushed brick
- crushed limestone
- river gravel
- crushed recycled concrete
- steel or iron beebees
- steel or iron pellets
Two 1000 ml beakers, aggregate or plastic beads, water
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.”