(Created and presented at the ASEE 2011 annual K-12 Workshop for Engineering Education in Vancouver, Canada, by Virginia Tech’s William N. Collins and Kacie Caple D’Alessandro, and Virginia Military Institute’s Matthew Swenty, Department of Civil and Environmental Engineering.)
Concrete for Kids is a fun, hands-on activity used to introduce students to engineering and concrete as an engineered material. Concrete can be found throughout our infrastructure (roads, bridges, buildings, stadiums, etc.), making it a familiar medium for students to work with to learn about engineering. The activities can be adapted to all age levels from K-12, and are intended to give students hands-on experience working with concrete; learning how it is made, how it is an engineered material, and how engineers use this material to make the structures we use every day, including bridges, buildings, and roads.
Grade level: K -12
Time: Two class periods. (Concrete must set and cure before it can be tested.)
After participating in the activities, students should be able to to do the following:
- Identify the individual components of concrete: water, cement, coarse aggregate (rock), fine aggregate (sand), and chemical admixtures.
- Describe how these components interact and affect the properties of concrete.
- Identify applications of concrete that influence everyday life.
- Describe the design process of mixing concrete.
- Demonstrate the ability to mix and place concrete.
- Describe the roles of engineers in concrete design.
- Additional learning objectives can be generated by incorporating supplementary activities/information with Chemistry, Environmental Science, Physics, or Industrial Technology classes.
National Science Education Standards:
Science as Inquiry; Properties of materials.
International Technology Education Association:
- F. Manufacturing systems use mechanical processes that change the form of materials through the processes of separating, forming, combining, and conditioning them. (Grades 6-8)
- F. The selection of designs for structures is based on factors such as building laws and codes, style, convenience, cost, climate, and function. (Grades 6-8) 
Illustration #1 (above): SAMPLE BEAM FORMWORK for molding concrete
- Disposable aluminum baking pans or 5-gallon buckets (1 per group) to mix concrete and test beams
- 5-gallon bucket to test beams
- 1-gallon painter’s buckets (3 per group) to measure aggregate, cement, and water
- Cement (2 lbs/0.9 kg per group) to make concrete
- Coarse (rock) aggregate, 1-inch or less (4 lbs/1.8 kg per group) to make concrete
- Fine (sand) aggregate (4 lbs/1.8 kg per group) to make concrete + 50 lbs for testing beam
- Water (2 lb/group) + extra to make concrete and clean buckets
- Spoon (1 per group) to mix concrete
- Gloves to protect hands
- Paper masks to avoid inhaling cement dust
- Protective safety goggles for beam testing
- Plastic to protect table
- Rope (optional) 25 ft/8 m for testing the beams
- Scrubbing brush (optional) to clean tools
- Large scale to measure bucket + weight when testing beams
- Small scale to measure materials
- Beam formwork (1 per group) for casting beams – see above illustration #1 for sample frame
The following steps outline the basic Concrete for Kids activities. Students will mix concrete, place concrete beams in beam molds, and break concrete beams. The activities are arranged into two days because concrete must set and cure before it can be removed from molds and tested. You may need to do a little research on your own to begin this project, but the preparation will pay off when you see your students get excited about applying engineering concepts!
- Introduce students to engineering and how engineered materials are all around them. Ask them for examples of engineered materials, and give them examples. The Virginia Tech presentation includes a slide-show and pop quiz with some surprising examples.
- Introduce students to concrete: how long it has been used, who designs and builds with concrete, steps for concrete construction (cast-in-place and precast applications), major components of concrete (coarse aggregate, fine aggregate, cement, and water), and concrete mix designs (engineering concrete). For this step, you may find some useful information at the Portland Cement Association website on Cement and Concrete Basics.
- Introduce students to the hands-on activity for the day: mixing concrete and placing concrete beams. For a basic concrete mix design, we suggest using 3 parts coarse aggregate (rock), 2 parts fine aggregate (sand), 1 part cement, and 0.5 parts water by weight.
- For younger students, pre-measure the coarse aggregate, fine aggregate, cement, and water for the students so that they are ready for mixing. You can put the dry ingredients in bags and have them ready well in advance.
- For older students, mix designs can either be pre-determined by the teacher or the students can play the role of engineer, creating their own mix designs. When allowing students to be the engineers, we suggest you still provide them with the suggested basic mix design above as guidance. Using scales, students can then weigh their own materials before mixing.
- For teachers, this activity can get messy! If you are indoors, you may want to lay plastic on tables before mixing.
- Safety Precautions: Cement is a fine powder that can be harmful if put in contact with skin or if inhaled. Cement will dry out the skin. Wear protective gloves while mixing, and apply lotion to areas of the skin that experience cement exposure. Paper masks should be used to prevent inhaling cement. Protective eye wear may also be used to protect the eyes from cement paste splash and fine cement particles. Closed toed shoes are also encouraged for this activity.
Begin the hands-on activities:
Older students – create a mix design by determining ratios of the different materials.
Older students – weigh all materials according to the given mix design ratios: rock, sand, cement, and water.
Lubricate beam forms with either WD-40, motor oil, canola oil, or a concrete form release agent before mixing concrete. This will ensure a smooth removal of the beam after it hardens, or sets.
Mix concrete in pan
- i. Using a spoon, mix the coarse aggregate and fine aggregate together, first.
- ii. Mix the cement in with the aggregates.
- iii. Continue mixing while adding the water slowly.
- iv. Mix until all materials are moist for about 3 minutes.
- v. Allow the concrete to rest for 1 minute.
- vi. Mix again for 2 minutes.
Place concrete beams:
- i. Transfer the mixed concrete to the beam forms, carefully.
- ii. Use the spoon to pack the concrete into the corners and edges of the form.
- iii. Once the concrete is packed into the form, remove excess material and smooth the top of the beam using the spoon.
- i. Clean the spoon, mixing pan, and any other tools covered in wet concrete before it hardens.
- ii. Do not clean these in a sink, because cement can harden in pipes. Rather, use a water hose outside or a 5-gallon bucket of water to rinse and scrub tools clean.
Store concrete for curing.
Either leave concrete beams out in open air or cover with moist paper towels before placing in a safe place for curing.
Allow the concrete to cure before continuing to Day 2.
Beams can be removed from molds after 1 to 2 days. Preferably, it is best to wait one week between placement on Day 1 and testing on Day 2; however, THREE days should be the minimal amount of time between Day 1 and Day 2.
For pictures of Day 1 activities, see the Virginia Tech ASCE Student Chapter website page on Concrete for Kids.
- Review previous Concrete for Kids activities, leading them to test the beams.
- Test concrete beams:
- Remove beams from forms, if not already done.
- Place two desks or tables 18 in. apart.
- With the 5-gallon bucket hung from the middle point of the beam, place the beam so that it spans across the tables with even amounts on either end. The beam now acts as a bridge between the tables, and the bucket will hold the weight as we load the bridge at midspan, the center point. Provide at least 6 in. of clearance between the bottom of the bucket and the floor.
- With the beam and bucket in place, slowly pour sand or gravel into the bucket until the beam fails. The beam will fail suddenly and without warning! This part should be done by the teacher, because the beam will fail suddenly and students should remain out of the way of the beam. Wear closed toed shoes. A mask and protective eye wear should be worn when using sand because small particles can be harmful if inhaled or exposed to the eyes. Protective eye wear should be worn, regardless, for safety against broken concrete pieces.
Illustration 2: Possible beam-testing setup.
- Once the beam has broken, weigh the 5-gallon bucket before removing the materials to determine the failure load of the beam. Record this load for each beam to determine which group had the strongest beam.
- Analyze test results:
- If all mixes are the same – create a bar graph to show the failure load of each beam. You should see that even if all the mixes are the same, the beams will fail at different loads. This is because concrete is highly variable, depending on exact measurements of materials, the mixing methods, and the placement methods. See if you can see any physical differences in the beams – perhaps one group didn’t compact their material as well in the form as another group.
- If mixes are different – you can compare failure load with the amount of cement and the amount of water in a mix. Engineers use the water-to-cement ratio as a quick comparison between mixes. Have students divide their amount of water by the amount of cement, and graph the water to cement ratio (x-axis) by the failure load (y-axis). Generally, as the water-to-cement ratio decreases the stronger the concrete will be, causing the failure load to increase. The downside is that as the water-to-cement ratio decreases, the workability of the concrete also decreases, making it harder to mix and to place into forms.
- Further analysis can be done to determine the cost compared to strength. Contact local concrete companies/distributors to determine a cost per item in the concrete mix. Then, have students compare their mix design cost with the concrete strength, determining which mix was most cost-effective.
- Engineers are constantly analyzing what they have done in order to make improvements in the future. Knowing what they know now, ask students how they could improve their concrete mix designs.
- Ask students to look at their broken concrete beams and determine whether or not construction methods could have weakened their beams. If a beam has holes in one area (often known as honeycombing), it can create a weak spot in the beam in that area. Concrete is a brittle material, and the concrete beams in this activity should have failed suddenly and without warning.
- Ask students to describe the failure type of their beams: was it sudden or did they have warning? Discuss the differences between brittle and ductile failures. Ask students how they would classify the beam failure: ductile or brittle?
- Reinforcing concrete can make it more ductile. Ask students if they know how they can make concrete more ductile? Ask them if they have ever seen reinforcing bars (or rebars) in concrete? Discuss how reinforcement (often steel reinforcement) can be placed in concrete to create “reinforced concrete”. Other types of reinforcement include discrete fiber reinforcement, prestressing steel, and fiber-reinforced polymers.
Beyond introducing your students to engineering and concrete, the above activities can be adapted to incorporate more specific classroom objectives. For instance, with additional information on material-science aspects of concrete, structural engineering principles, or the construction practices for concrete, these modules can be adapted specifically for Chemistry, Environmental Science, Physics, or Industrial Technology classrooms.
For questions or more information on Concrete for Kids, see the slideshow presented at the 2011 ASEE Workshop for K-12 Engineering Education or contact:
- Kacie D’Alessandro – Graduate Student, Virginia Tech (firstname.lastname@example.org)
- William Collins – Graduate Student, Virginia Tech (email@example.com)
- Dr. Matthew Swenty – Assistant Professor, Virginia Military Institute (firstname.lastname@example.org)
Special acknowledgments to Dr. Carin Roberts-Wollmann and Dr. Richard Weyers for their years of dedication as faculty coordinators for the Concrete for Kids Program at Virginia Tech.
Credits: Photos from ASEE’s 2011 K-12 Workshop by Stacie Harrison; formwork illustration by William Collins; testing set-up illustration by Kacie D’Alessandro.