Engineered Concrete Lesson

Engineered Concrete at a glance

Background

Concrete is everywhere, from the buildings we enter to the roads we drive on. But what makes it so strong? In this lesson, students will discover that the secret lies in the mix. The main ingredient in concrete is Portland cement, a ceramic material that, when mixed with water, forms a paste that hardens through a process called curing. This process locks the water into the cement, creating a strong, solid material.

Concrete's strength isn't just from cement and water. By adding materials like sand, rocks, or fibers—known as reinforcements—concrete becomes even stronger and more durable. These reinforcements customize the concrete for different uses, from building bridges to creating sidewalks. The right balance of ingredients is crucial; too much or too little of any component can weaken the concrete, so scientists and engineers carefully design the perfect mix through trial and error.

By the end of the lesson, students will understand that concrete is a composite material—one that combines different elements to create a material with superior properties. They’ll see how this engineered material plays a vital role in our everyday lives.

Lesson Objective

Students will explore how different mix designs affect the properties of a composite material by creating and testing Portland cement pastes. They will learn about the role of reinforcement and the design process in developing materials with specific properties.

Experiment Description

Students will mix cement with varying amounts of reinforcement and water to create cement pastes. After curing the samples, they will test their strength by dropping them from a height to observe how their mix designs performed.

Materials List

200g Portland cement per puck
Plastic measuring spoons
Disposable plastic cups
Polystyrene (styrofoam) bowls
Ruler
Popsicle sticks or plastic spoons
Plastic wrap
Permanent marker
Optional: latex or non-latex gloves

Safety Precautions

Avoid skin contact with Portland cement and prevent dust clouds when handling the powder. Wash hands immediately after working with the cement paste and consider wearing gloves.

The Experiment

1. A few days before the lab, divide students into groups of three to choose their reinforcement materials.

2. On the lab day, students prepare styrofoam bowls by marking a ¾” line from the bottom and filling the bowls with cement paste up to the line to ensure uniform puck thickness.

3. Each student measures 200g of cement powder into a cup, and groups are provided with water, measuring spoons, and different water-to-cement (w/c) ratios to evaluate how water quantity affects the paste. Students calculate the required water amounts for their w/c ratios, and then measure a specified amount of reinforcement item for their pucks.

4. Groups mix their cement paste with varying water amounts, add the reinforcement using their chosen method, and pour the mixture into bowls, making sure to fill only up to the marked line. The pucks are left to cure overnight, then removed from the bowls, labeled, and examined for differences in color or texture.

5. Finally, students drop the pucks from a height of at least 15 feet to observe and compare their performance.