108 Section 2 Construction Materials
Steel Reinforcing Bars
Compression occurs in an object when
forces push on an object. Tension occurs in an
object when forces pull on an object. Concrete is
much stronger in compression than in tension,
Figure 6-2. The tensile strength of concrete
is improved using reinforcing bars, or rebar,
Figure 6-3. Rebar is made of steel. The surface
is often deformed to make the concrete adhere
better. Additional information about rebar and
other materials used to reinforce concrete is
included in Chapter 7, Metals.
compression: Force that pushes on an object.
tensile: Force that pulls on an object.
reinforcing bars (rebar): Steel bars used to increase
the tensile strength of concrete.
Math
Volume Calculations
Mathematics is about more than just numbers. The units of measurement are also
important. If you multiply six peanuts times seven grapefruit, mathematically the answer is 42
peanut-grapefruits. Since there is no such thing as peanut-grapefruit, however, the calculation
is meaningless. When calculating volume, multiplying measurements given in inches with
measurements given in feet results in a meaningless unit of measurement such as inch-inch-
feet or inch-feet-feet.
The formula for calculating the number of cubic yards of concrete required for a
project is:
thickness (feet) × width (feet) × length (feet)
= _____ cubic yards
27 ft.3/yd.3
A concrete wall is being made that measures 6″ thick, 8′ tall, and 56′ 9″ long.
0.5′ × 8′ × 56.75′
=
227 cubic feet
= 8.4 cubic yards
27 ft.3/yd.3 27 ft.3/yd.3
It is important to check your calculations several times. This way you will be certain your
answer is correct and the correct amount of concrete will be delivered. For example, what
would happen if instead of using 6″, you mistakenly read the number as 6′?
6′ × 8′ × 56.75′
=
2724 cubic feet
= 100.1 cubic yards
27 ft.3/yd.3 27 ft3/yd3
If the concrete were ordered based on this calculation, 12 times as much concrete as
is needed would be delivered to the site! This could be a very costly error and illustrates the
importance of checking and rechecking math calculations.
Tension
Compression
Load
Figure 6-2. Concrete cracks in tension before it
crushes in compression.
STEM Connection