# Concrete: Experiment 2

## Experiment 2

### How Dense Is It?

An Introduction to Concrete Density and Aggregates

Objective: The objective of this experiment is to determine the density of a concrete sample and to learn the effect of various types of aggregates on concrete's density.

Scientific Principles:

Density is the physical property of matter that measures the quantity of a substance per unit of space. Density is recorded in units of grams per cubic centimeter (g/cm3) for solids, grams per milliliter (g/mL) for liquids, and grams per liter (g/L) for gases. Density is a way of determining how compact one substance is compared to another. Density is also the property that enables one object to be buoyant or another to sink. The object that is less dense will float in a more dense substance. The density of a typical concrete is 2.3 g/cm3.

Time: 45-50 minutes

Materials and Supplies:

• cured 1/2" x 2" cylinders of concrete samples (each consisting of a different aggregate)
• sample concrete recipes

• water25 mL15 mL25 mL20 mL
cement50 g50 g50 g50 g
aggregate150 g sand35 g pea gravel4 g dry vermiculitenone
• 100 ml graduated cylinder
• water
• balance

General Safety Guidelines:

• To avoid cracking the graduated cylinder, gently slide the concrete cylinder down the side.
• Wear goggles.
• Concrete can be caustic. Wash hands after direct contact.

Procedure:

1. Estimate which sample will have the highest and which will have the lowest density. Record your ideas on the data chart.
2. Mass each cured cylinder on the balance. Record in data table.
3. Half-fill a graduated cylinder with water. Record the initial volume of water.
4. Gently slide the concrete cylinder into the graduated cylinder so as to not splash out any water or break the glass bottom.
5. Record the final volume of water with the concrete cylinder in it. Subtract the final volume from the initial volume of water to obtain the volume of the cylinder.
6. Remove the concrete cylinder from the water.
7. Repeat steps 1-6 for all other cylinders.
8. Calculate the density of each cylinder by dividing cylinder's mass by its volume.

### Video Clip

Data and Analysis:

Estimates

highest density cylinder_________________

lowest density cylinder _________________

Data Table

Questions

1. a. What type of cylinder was the least dense?
2. b. What type of cylinder was the most dense?

3. Give a use for the cylinder in question 1a.
4. Give a use for the cylinder in question 1b.
5. Were your estimates correct? Did any of the results surprise you? Why?
6. How do your values compare to the typical density of concrete (2.3 g/cm3) ?

Notes for Teacher:

Many science courses already have a density experiment as part of the course. The use of concrete cylinders will add a new touch to these experiments. It is assumed the concrete cylinders were previously prepared by the teacher.

This experiment could be performed as an investigation in which students prepare concrete mixtures of different ingredient proportions to study their effect on density. These cylinders of varying composition could later be used in the Stress and Strain experiment. This could also be done with different kinds of aggregates. Aggregate densities could be determined, as well as the density of hardened paste. Lightweight aggregates are usually available from a ready mix company. Horticultural vermiculite or perlite can be used. The density of aggregates could be measured and correlated with the density of concrete. (A good project for advanced students.) When measuring the density of aggregates, it is advisable to measure the density of saturated aggregates (soak in water for at least one hour or overnight). Otherwise the aggregates will absorb water during the displacement measurement and give erroneous results. Remember, aggregates in concrete become fully saturated.

This could be turned into a materials science competition in which the students must make a cylinder with the greatest or least density.

Expected Results:

The four cylinder types listed from most dense to least dense:

gravel, sand, paste, vermiculite