WORLD FOR CIVIL

Experiment 6

Make and Take

A Take-home Project

Objective: Students will develop an understanding of concrete as a construction material. A concrete product will be designed and constructed.

Scientific Principles:

Concrete is everywhere. Take a moment and think about all the concrete encounters you have had in the last 24 hours. All of these applications of concrete are created from a material that is a mixture formed from the chemical reaction of cement and water (hydration) with added aggregate. It important to distinguish between cement and concrete as they are not the same. Cement is used to make concrete.

Water is a key reactant. Water and cement initially form a cement paste that begins to react through the chemical process of hydration. In the hydration of cement, chemical changes occur slowly, eventually creating new crystalline products, heat evolution, and other measurable signs. The hydration process hardens (sets) the paste which binds the aggregate particles together.

The aggregate is the solid particles that are bound together by the cement paste to create the synthetic rock known as concrete. Aggregates can be both fine, such as sand, and/or coarse, such as gravel. The relative amounts of each type and the sizes of each type of aggregate determines the physical properties of the concrete.

Time: 1 Class period for each object made. (45 min.)

Materials and Supplies for groups of 2-3:

• cement
• pea gravel
• water
• 2 flower pots or suitable plastic containers
• wire mesh
• mixing bowl or wheelbarrow
• finishing tools
• damp sand
• 1" greased dowel rod

Procedure:

1. Prepare enough concrete to fill the space between your two containers when they are stacked with a 1" separation.
2. Coat the inside of the bottom container and the outside of the top container with plastic wrap.
3. Place a 1" lubricated dowel (future drain hole) that is 1" long, in the bottom center of the first mold for a round based flower pot or four dowels if you are making a rectangular flower pot. This will serve as a spacer now and a drain in the hardened pot.
4. Surround the dowels with concrete mix, place the top mold on the mix being sure to allow for about 1" wall thickness. Add concrete mix between the forms until the bottom form is filled. Tamp concrete to remove air pockets. Allow to harden for 15- 20 minutes. If decorations are desired on the outside of the pot, remove outer mold and add glass beads, colored stones, etc. Allow to harden 24 hours.
5. Remove molds and place in water for three days to harden. Be cautious of this step if your pot is decorated.

Video Clip

Notes for Teacher:

• Use larger sized aggregates to create a nice appearance.
• Use as a money making project.
• Many different shapes can be made and may be a great way to inspire some creativity.