Chocolate Asphalt

Joanna Ambroz from SWE magazine, Nov/Dec 1995
posted and edited by: Kristen Byrnes
8th Kingston Guides, Kingston, ON

- a unique and fun hands-on parallels the procedures used to produce asphalt pavement while introducing students to basic engineering principles

Introduction:

Pained by potholes? Frustrated by miles of road construction? Gain a new appreciation for road construction through a unique engineering presentation. Asphalt cookies are chocolate no-bake cookies. The process of making these cookies parallels the procedures used to produce asphalt pavements. Asphalt is a black sticky substance used in road construction to hold rocks together. When heated asphalt liquifies; as it cools, it hardens and becomes solid. A mixture of asphalt and rocks makes good roadway material after it hardens. The similarities between making cookies and preparing pavement include using a hot liquid added to a variety of dry ingredients and mixed together, which when cooled hardens and gains strength.

Objectives:

• - introduce the civil engineering area of paving and materials to students in grades 4 - 7
  - create a hands-on activity for groups of 5 to 10 students that lasts approximately 15 minutes
  - explain the physical properties of asphalt and discuss road construction techniques
  - use an easy-to-prepare cookie recipe as an analog for making asphalt
  - illustrate how engineering affects our daily lives, but often goes unnoticed
  

Basic Supplies:

• - large container to prepare the chocolate "asphalt" liquid binder on the stove before the presentation
  - crockpot or other heating unit to keep the liquid warm
  - large spoon for stirring
  - steep sided bowls, one per student
  - sturdy stirring spoons, one per student
  - 16 oz. sealed cans to use as rollers, one per student
  - 1/4 cup measuring cups
  - 1/8 cup measuring cups
  - tablespoon measure
  - extension cord
  - wax paper, cut into squares
  - water and paper towels for cleaning up
  

Construction Materials:

• - chopped walnuts
  - flaked or shredded coconut
  - old fashioned and quick oats
  

Asphalt Recipe:

Prepare in advance. In a large container combine the following ingredients:

• - 1/3 cup cocoa powder
  -1/2 cup milk
  - 1/4 lb. butter
  - 2 cups sugar
  

Heat, stirring frequently until mixture boils for 2 minutes .Pour into crockpot with temperature at highest setting. A single batch yields approximately 2 cups or 8 portions. Double or triple as needed.

Presentation Outline:

A large poster with photos of an asphalt plant (drum mixer type), laboratory mixing and compacting equipment, a paver/screed and a compaction roller helps to illustrate the field processes. Different textured rocks and samples of loose and or compacted pavement samples or photos of actual construction materials also help to illustrate the concepts. Bowls, spoons, and measuring cups should be set up prior to the presentation and can be reused for each group of students.

1. A variety of materials is used in the preparation of paving materials. Discuss the different sizes and textures of the rocks used.
   
   
2. Engineers select and calculate the correct quantities of each rock size needed to produce a strong asphalt pavement. Calculated percentages of the different sizes of rocks are combined to determine the appropriate blend of rocks to use in a certain climate.
   
   
3. Explain that different measuring techniques are used in the field than in the laboratory. I the field engineers use huge quantities of each rock size and weigh them on scales as large as a garage. In the lab, much smaller quantities of each material are needed and ordinary measuring utensils are used.
   
   
4. Discuss the properties of the edible construction materials to be used in the demonstration and compare with original materials. Encourage each student to measure the recommended quantities of all construction materials (ingredients) into their missing bowl: 1/8 cup old fashioned oats --- 1/8 cup quick oats --- 1 tablespoon walnuts --- 1 tablespoon coconut
   
   
5. Point out that the drum mixer at the asphalt plant tumbles all of the ingredients until they are well coated with the asphalt binder. The tumbler works like a clothes dryer. Mixing the ingredients in he bowls is a similar process.
   
   
6. Show the liquid form of the chocolate asphalt in the crock pot to the students and explain that when asphalt is heated to 300 deg F, it is also a liquid.
   
   
7. Measure and pour 1/4 cup chocolate asphalt into the materials mixture. Students should stir the combination until all of the particles are well coated. Notice that as the mixture cools while it is being stirred, it becomes stiffer and starts to stick together. Asphalt behaves in the same manner.
   
   
8. When the materials are thoroughly mixed, each student should pour and mound the mixture on to a square of wax paper. Cover with a second piece of wax paper.
   
   
9. In the field, the pavement is spread with the paver and then rolled in a thin mat with a roller. The roller is very heavy and smashes all of the air out of the pavement which helps to make the asphalt very strong. Each student should now use a can to roll their cookie to 1/4" to 1/3" thick cookie
   
   
10. When the cookies are flat, show the students that they can still identify the different materials they put in their cookies. The oatmeal, walnuts and coconut are visible through the wax paper.
    
    
11. Have each student feel the heat coming off the tope of the cookies. Immediately after pavement is rolled out it is still very hot. Just like the asphalt, the cookies will harden when the cool.
    
    
12. Congratulations! You made it through the demonstration and the students may take their asphalt cookies with them. When the cookies have cooled, they can be peeled off the wax paper and eaten.
    
    

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