Hands-on Activity Obi-Wan Adobe:
Engineering for Strength

Learning Objectives

After this activity, students should be able to:

• Describe the steps in the engineering design process.
• Explain how engineers use experiments to develop strong construction materials.
• Explain the difference between a mixture and a solution.
• Explain the difference between an independent and dependent variable.
• Graph the result of a simple experiment.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• 1 adobe mold and extruder (see below)
• 10 paper Dixie cups (5 oz or ~150 ml) of clayey soil (potting soil will not work)
• 10 paper Dixie cups (5 oz or ~150 ml) of playground sand
• 1/2 gallon (2.2 l) container of fibrous material, loosely packed (dead grass, straw, pine needles, etc.)
• 3 one-gallon (4.4 l) plastic bags, to separately hold the soil, sand, and fibrous material
• 1 large (24 oz or ~700 ml) container (bowl, re-usable plastic, or gallon jug with the top cut off)
• 1 piece of cardboard, 16-in x 16-in (~ 40 cm x 40 cm)
• 1 container of water, ~16 oz (500 ml)
• 1 paper Dixie cup (5 oz or ~150 ml) for measuring
• 1 permanent marker
• Design Worksheet, one per student
• (optional) Pre/Post Quiz, two per student

For teacher to make adobe molds and extruders (one set per group):

• wooden board, 16-in x 1-in x 2-in (41 cm x 2.5 cm x 5 cm), to make an adobe mold (cut into 4 boards that are 4-in [10 cm] long)
• foam core board, 4-in x 6-in (10 cm x 16 cm), for the extruder
• foam core board scrap, to make a handle for the extruder
• eight 2-in nails per mold
• hammer
• hand saw
• hot glue gun and glue sticks

For the entire class to share:

• meter or yard stick
• projector to show two Microsoft PowerPoint presentations to the class
• (optional) disposable gloves
• (optional) newspaper or butcher paper to cover work surfaces
• (optional) box or desk fan, to aid in brick drying
• (optional) small step ladder, for standing on when drop testing bricks

Worksheets and Attachments

Introduction/Motivation

(To conduct the pre/post quiz assessment, administer the attached nine-question Pre/Post Quiz to the students before beginning this section. See the Assessment section for details.)

Can you list a few of the different materials used in the construction of buildings? (Take ideas from students. Possible answers: wood, bricks, concrete, steel.) Did any of you know that mud is also a building material? It may sound strange, but mud mixed with straw was one of the earliest building materials ever used and it is still in use today because it works! This special mixture is called adobe. Many people, especially those who live in developing countries, use adobe to build houses and other buildings. Some of the oldest buildings in the world are made with adobe. If adobe is carefully mixed in the right proportions, it can last hundreds and thousands of years in very dry climates.

Many construction materials are classified as mixtures. A mixture describes a combination of two or more materials in which you can still see each of the different ingredients. It is different from a pure substance or a solution because the individual parts are still visible and can be separated from one another relatively easily. The amount of each of the different ingredients compared to the total mixture is called the concentration. When the concentration of an ingredient in a mixture is changed, it can have a huge impact on how the mixture behaves. For instance, in both concrete and adobe, the concentration of water in the mixture can drastically change how strong the mixture is when it dries.

Today, we will be doing some experiments to figure out the best concentration of each ingredient in order to maximize the strength of an adobe brick.

Because the concentration of each of the ingredients in a construction material has such a large impact on how the material behaves, civil and material engineers perform experiments to figure out what concentration of each ingredient creates the best results. Once the right mixture is determined, engineers make sure that every time that material is used its ingredient concentrations are close to the ones determined during the experiment. On most construction projects, a technician runs tests on all the concrete used to make sure that the engineer-specified mixture was actually used on the project.

Today, we are going to help a village in Peru make the best adobe bricks possible by doing experiments just like civil engineers. To do this, we must first choose a variable. A variable is something that you allow to change in an experiment. The opposite of a variable is a control. A control is something that you are very careful to keep exactly the same during the experiment. In this experiment, we select a variable that relates to the concentration of ingredients in each brick. For instance, we may change the amount of water that we put in several different bricks to see how it changes the strength of each brick. In this case, the amount of water is the independent variable because we intentionally changed it. The strength of the brick is called the dependent variable because it changes as a result of the changes we made to the dependent variable (the amount of water). Once we've chosen our variables, we must be very careful to control everything else so that we get really good results. Let's get started!

Procedure

Before the Activity

• Use the hammer, nails, wood and hand saw to make one small adobe mold for each group. A finished mold should have an opening that is approximately 3½-in x 1½-in x 1½-in (8.9 cm x 3.8 cm x 3.8 cm), with no top or bottom, as shown in Figure 1.
• Use foam core board to make a "brick extruder" for each group. The extruder is used to push each individual brick out of its mold. Make sure it fits almost perfectly inside the mold opening and has a small handle.

  

• Measure each group's supply of soil, sand and fibrous material and place each into the three plastic bags for each team.
• Make copies of the Design Worksheet, one per student. Do not staple the pages so they can be handed out at different times.
• On Day 1 and Day 2, set up a projector to show a PowerPoint presentation to the class.

With the Students: Day 1

1. (optional) Administer the Pre/Post Quiz. See the Assessment section for details.
2. After the Introduction/Motivation section, introduce the activity using the Day 1 Presentation.
3. Divide the class into groups of three students each.
4. Hand out to each student a copy of worksheet page 1.
5. Assign each group a different variable to test (water content, straw content, sand content). Have the students circle on their worksheet the variable they are testing.
6. Make an example brick in front of the class to show students how adobes are made. (Steps: Carefully mix the ingredients in a bowl with your hands, wet the mold, place the mixed ingredients inside the mold, gently pack the ingredients into the mold, scrape the top flat, use the extruder to push the completed brick onto a piece of cardboard.)
7. Distribute the materials and molds to each group, along with a piece of cardboard.
8. Have students begin mixing and forming their own bricks. When a brick is complete, have them label it on the piece of cardboard with the marker (A, B or C).
9. When all three bricks are complete, have each group write their names at the top of the pieces of cardboard with the marker and store the bricks in a sunny place to dry. The bricks need at least 3–4 days to dry completely. Drying them in front of a blowing fan takes about two days.

With the Students: Day 2

1. Hand out to each student a copy of worksheet pages 2-5.
2. Have students carry their labeled bricks to a designated test area, such as a level concrete surface outside.
3. Test the bricks by dropping them from progressively higher heights until they show substantial failure. You may need a small step ladder to get high enough so they break when dropped. Do this either as a class activity in which each group tests their own bricks, or as an observation time in which the entire class watches you test each brick. Make sure students record their test information on their worksheets.
4. If the testing is done as an observation time, have each student record the data of at least three other groups (two of which tested separate independent variables) on their worksheets. If each group tests their own bricks, have students gather information from several other groups after testing is complete.
5. Return to the classroom and show the Day 2 Presentation.
6. Have each student graph test results for each of the three variables on pages 3-4 of the worksheet.
7. Spend a few minutes leading a class discussion to analyze experimental results so far (as described in the Assessment section). Why might team results be different from each other? What other variables might be affecting brick strength? How can make our manufacturing process more uniform to reduce some of these differences among teams?
8. Challenge each group to develop an ideal adobe brick design based on analysis of the test results and graphs.
9. Give teams time to each make one brick following their own "recipe," using a procedure similar to Day 1. Make sure each group labels its brick. Have them fill in the "model brick recipe" information on worksheet page 5. Store the bricks in a sunny place to dry.

With the Students: Day 3

1. Make sure students still have worksheet page 5 (which was handed out on Day 2).
2. Test each group's brick in a manner similar to that on Day 2.
3. Have each student keep track on their worksheets of the "recipes" and drop heights for all groups.
4. Lead a class discussion to explore what was discovered during these testing experiments. (See a list of suggested post-activity questions and topics in the Assessment section.)
5. (optional) Administer the Pre/Post Quiz. See the Assessment section for details.

Vocabulary/Definitions

admixtures: Ingredients other than water, aggregates, cement and fibers that are added to a concrete batch immediately before or during mixing to provide beneficial effects to concrete. Source: US Dept. of Transportation, http://www.fhwa.dot.gov/infrastructure/materialsgrp/admixture.html

adobe: A sun-dried brick composed clay mud and straw. A common building material used in countries having little rainfall.

concentration: The percent amount of one ingredient compared to the total mixture or solution.

control variable: A variable that is neither changed by the engineer/tester nor affected by the independent variable.

dependent variable: A variable that changes as a result of changing the independent variable.

engineering design process: The cycle engineers go through while creating a new device: ask; imagine; plan; build; test; improve.

independent variable: A variable that is intentionally changed by the engineer or tester.

material: A substance or substances of which a thing is made or composed.

mixture: A combination of two or more materials in which you can still see each of the different ingredients.

solution: A combination of two or more different substances in which you can no longer see the different ingredients.

variable: Something that you allow to change in an experiment, or while testing an idea, device or system.

Assessment

Pre-Activity Assessment

Pre/Post Activity Quiz: To conduct an overall pre/post assessment of the activity to gauge student learning, administer the nine-question Obi-Wan Adobe Quiz to the students before beginning any discussion on variables, mixtures and solutions, or adobe bricks. After activity completion, administer the same quiz to the same students and compare pre- to post- scores.

Class Voting: Show the class the images in the Day 1 Presentation. Have them vote on whether the substances shown are mixtures or solutions. Call on students to justify their choices.

Activity Embedded Assessment

Worksheet: Have students follow along with the activity using the Design Worksheet. Make sure they fill in the appropriate tables and graphs during the course of each day. Check their answers between days to gauge their understanding.

Experiment Analysis: After the first round of bricks have been tested, discuss as a class why different groups who made the same bricks may have come up with different results. Make a connection to the topic of variables and ask students to list all of the additional variables they can think of that may have affected the strength of the bricks. (Possible answers: How hard the material was packed in the mold, the size of fibrous material, the position when drying, bricks not fully dry, the amount of mixing, moisture content of sand, etc.). During Day 2, have students create and incorporate uniform instructions for their brick-making that eliminate as many of these variables as possible; for example, 1) Thoroughly mix all dry ingredients, 2) Add water, 3) Mix for 30 seconds, etc.

Post-Activity Assessment

Class Discussion: As a class, discuss the results of all of the experiments and graphs (refer to the attached Design Worksheet Example Answers). Ask the students:

• Looking at all the graphs, what combination of ingredients would maximize the strength of the adobe bricks? Let's decide as a class.
• What is a variable? What is a control?
• What is the difference between an independent and dependent variable?
• In our experiments, which were these variables?
• Why do we test one variable in an experiment?
• Why is it important to test and conduct experiments in engineering?

Pre/Post Activity Quiz: After activity completion, administer the Obi-Wan Adobe Quiz to compare students' pre- to post- knowledge of the subject matter.

Troubleshooting Tips

Since this activity can be messy, covering the desks with butcher paper or newspaper makes clean up much easier.

Be sure to provide a visual demonstration of brick-making since oral instructions alone can be confusing.

Activity Extensions

Writing: Challenge students to write a short paragraph based on the following scenario: You are a civil engineer who is designing a building constructed of concrete. The concrete must be as strong as possible. How would you figure out what amount of each ingredient (sand, cement, gravel, and water) to use in the concrete in order to maximize its strength?

Activity Scaling

• For lower grades, only test one variable rather than three. Varying the soil/sand ratio has the most noticeable effect on strength.
• For lower grades, eliminate some of the more complicated math activities, such as graphing, or walk through the graphing as a class, calling on individual students to plot points on a large graph created on the board.
• For upper grades, have the groups choose their own variables to test. Eliminate the values given for bricks A and C, and challenge the groups to develop their own "recipes" to test their chosen variable, using brick B as a standard brick.

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of these digital library curricula were developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.