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.
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:
|water||25 mL||15 mL||25 mL||20 mL|
|cement||50 g||50 g||50 g||50 g|
|aggregate||150 g sand||35 g pea gravel||4 g dry vermiculite||none|
General Safety Guidelines:
Data and Analysis:
highest density cylinder_________________
lowest density cylinder _________________
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.
The four cylinder types listed from most dense to least dense:
gravel, sand, paste, vermiculite
Answers to Questions: