Concrete Composites Lab

Engineers must determine what the best material is to use for a given design. Many materials we use are composites of materials, meaning they are made up of more than one type of material (wood, glass, metal, etc.), and the percentages of the materials affect its performance. Material engineering is all about experimenting with and creating new types of materials that we can use to improve functionality of the things around us. In this lab just like the material engineers, students will be able to create composites of their own and go through the engineering process of testing their concrete composites and analyzing their data to see what improvements can be made.

After this activity, students should be able to:

• Describe the difference between pure substances and mixtures.
• Discuss what makes a change physical and chemical.
• Test a material for density, wettability, and strength.
• Think and outline a design for improving composite compositions.

Students should be familiar with vocabulary words such as solid, liquid, gas, element, compound, homogenous mixture, heterogenous mixture, intensive, and extensive. They should also be able to calculate density.

Why are certain materials better suited to different tasks? Why are pencils made of wood? Why are chairs made of plastic? Why are windows made of glass? Material engineering is at work all around us. Material scientists create new materials and materials engineers improve upon and use on the ones currently available in an ongoing effort to make the material better suited to the job at hand.

To start this activity, choose an item from around the classroom. For that item, I want you to name the different types of materials that compose that item. Notice how all the materials work together to make everyday items function. I want you to think about why these materials are the best suited for the job and what would be the downsides of using a different type of material in its stead. Or explain why you think a different type of material would do a better job.

[Example responses: The body of a pencil is made of wood, the eraser made of rubber, the ferrule made of metal, and the lead made from graphite. If the pencil was made of glass, you wouldn’t be able to sharpen it to get the lead out when it dulls and there is a risk of breaking while using it. Plastic might do a better job because it doesn’t break as easily as glass or wood.]

Now that we understand the types of materials that make certain objects, let’s apply our knowledge to a common type of material often used in engineering: concrete. We will explore how to make a composite, which is a combination of two or more different types of materials which often have very different properties together. Within the finished structure of a composite, the individual elements remain separate and distinct, but their properties are merged creating a material that is unlike the starting materials. Can you make a composite of concrete that stands up to the rigors of testing for engineering design? Let’s get started!

Background

A composite is a combination of two or more different types of materials which often have very different properties together. Within the finished structure of a composite, the individual elements remain separate and distinct, but their properties are merged creating a material that is unlike the starting materials. This makes it distinctly different from mixtures and solutions. Concrete on its own and carbon black on its own are going to have distinct properties that are unlike a composite made of concrete and carbon black combined. The hope is that the changes in the properties of the composite will be graphable and easy to see when comparing the different composites that each student group makes.

Before the Activity

• Teacher should assign each group a particular composite to make so that no two groups in the same class period are making the same composite. For example:

Group 1: 100% concrete

Group 2: 95% concrete 5% carbon black

Group 3: 90% concrete 10% carbon black

Group 4: 85% concrete 15% carbon black

Group 5: 80% concrete 20% carbon black

• Gather materials for the lab stations.
• Make copies of the Lab Station Directions (PPTX) and the Concrete Composites Lab Worksheet (PDF).
• Set up the Concrete Lab stations so students can test different physical and chemical properties of their cement samples at each station. Feel free to exclude some stations if the materials are not readily available in your classroom.

With the Students

Part 1: Making Concrete Composites

1. Each group is assigned a cement or Quikrete Composite to make. Have students check the list to see which composition their group is assigned.
2. Using the Scale, measure out the correct number of grams of concrete or Quikrete and carbon black for the composite assigned to your group.

Example: 100% concrete = 100g concrete + 0g carbon black

                95% concrete = 95g concrete + 5g carbon black

                90% concrete = 90g concrete + 10g carbon black

3.  To your powder mixture, add 100 mL of water if assigned pure cement or 50mL of water if assigned Quikrete and Mix.
4. Divide your mixture into two and pour into the silicone molds. This should give your group 2 concrete samples to test. Make sure to flatten the top of your sample as best as possible to make testing the sample easier. Each group makes two concrete samples in silicone ice molds. Once the sample has cured they can be easily removed from the molds.CopyrightCopyright 2022 Aerielle Rodriguez, University of Houston RET
5. Leave the molds in an undisturbed location to set for 2 days minimum.

Part 2: Testing Concrete Composites

• Follow the Lab Station Directions (PPTX) to test different physical and chemical properties of the concrete composites.
• Use the following images, to help with lab station set-up.

Measure the mass, length, width, and height of each sample to calculate the density.CopyrightCopyright 2022 Aerielle Rodriguez, University of Houston RET

Drop test station setup, which is used for testing for wettability and reactivity to water, soap, and alcohol.CopyrightCopyright 2022 Aerielle Rodriguez, University of Houston RET

Strength Test station setup. Weights are suspended off the concrete sample and increased until the sample breaks. The weight the sample breaks at is the strength of the sample.CopyrightCopyright 2022 Aerielle Rodriguez, University of Houston RET

Solubility station. Scissors can be used to shave a small amount of the concrete sample into powder.CopyrightCopyright 2022 Aerielle Rodriguez, University of Houston RET

Acid vs. Base Drop Test station setup. Testing for reactivity of the concrete sample to a strong acid (Hydrochloric acid) and a strong base (bleach)CopyrightCopyright 2022 Aerielle Rodriguez, University of Houston RET

Strength Test station setup. Weights are suspended off the concrete sample and increased until the sample breaks. The weight the sample breaks at is the strength of the sample.CopyrightCopyright 2022 Aerielle Rodriguez, University of Houston RET

Part 3: Improving Concrete Composites

• Have students remake their concrete composites but this time they will change the composition to improve one of the properties being tested based on what samples performed better in the class combined data.

Pre-Activity Assessment

Pre-Assessment: In the Concrete Composites Lab Worksheet (PDF) there are three open-ended questions that asks students to engage their prior knowledge of states of matter and types of matter. It also has students hypothesize on if they think certain processes in concrete creation are physical or chemical changes.

Activity Embedded (Formative) Assessment

Formative-Assessment: In the Concrete Composites Lab Worksheet (PDF), there are four questions that students complete as they perform the lab. It has students differentiate the properties being tested as physical or chemical, then the physical properties only into quantitative, qualitative, intensive, and extensive. This section also includes the table where the students will write their observations and measurements that they collect while performing the lab.   

Post-Activity (Summative) Assessment

Post-Assessment: In the Concrete Composites Lab Worksheet (PDF), there are two open-ended assessment questions that ask students to identify if two of the tests they performed was an observation of a physical or chemical change and how do they know.

Making Sense Assessment: In the Concrete Composites Lab Worksheet (PDF), there are five open-ended assessment questions that ask students to draw conclusions from the class data and make a claim about the relationship between the composition of the composite to the density, wettability, and strength. It also has students rethink their own composite and come up with a plan on how to improve the results for their composite during the second round of testing.

• Use eye protection while conducting the Strength Test and Reactivity to Bleach and Hydrochloric Acid Test.
• Use gloves while conducting the Reactivity to Bleach and Hydrochloric Acid Test.
• Bleach and hydrochloric acid should be washed off the composite sample thoroughly before performing any other tests on the sample.
• Excess bleach and hydrochloric acid should be disposed of in the hazard container not the drain.
• If using carbon black for composites, wear gloves and goggles when handling samples as it is an irritant.
• If using wood/plastic/metal shavings, wear gloves and goggles while creating composites as shavings can be sharp.
• After performing tests students should wash hands thoroughly with soap and water.

• For lower grades, focus on creating the concrete samples to explore the differences between states and types of matter.
• For upper grades, have students explain scientific reasons why their sample may not have performed the best. Give them multiple attempts to improve their samples. Focus on a particular property to improve on for the class and make it a competition to see which group can create the best performing sample for that property.