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Sand Grain Size and Brick Strength
Name: Derrick
Status: Student
Grade: 4-5
Location: IN
Country: United States
Date: February 2008
Question:
I did the science experiment of which brick will be
stronger depending on the size of the sand grains. I used very fine
sand, fine sand, and pebbles. My results were kind of strange. The
pebbles seemed to be stronger, then the medium grain, and the least
strongest was the finest grain of sand. In my experiment I mixed the
sand with Elmer's glue. My hypothesis was that the finest sand would
be the strongest. My hypothesis was wrong. Did I do something wrong
or are these results right?
Replies:
I would not give up on your hypothesis yet. You only know the results for one
specific recipe -- what is true for one mix may not be true for the
majority. Also, you may find different results if you use different kinds of
materials.
You are exploring the properties of a "composite" material. A "composite"
material is made of two or more materials that act as one. In a composite,
you typically have some kind of binder or matrix material (such as glue,
mortar, or resin) and one or more reinforcing materials (such as your sand,
rocks, or glass fibers). How much of each material makes it the strongest
depends on the materials. In your case, it is possible that each 'brick'
could be made stronger by increasing or decreasing the amount of glue or
sand/pebbles used. A good experiment would be to make a series of bricks
from each set of materials, varying the amount of each material. You would
then be able to determine which ratio gives the strong strongest brick for
each set of materials. Another possibility is that the glue you used does not
bind to the sand/pebbles very well. Elmer's glue is not very strong on
non-porous materials (like rocks or sand). You might have better luck
testing with porous materials like paper or wood. A third possibility is
that you simply did not mix the materials well enough (if they are not
well-mixed, you could get anomalous results). This seems unlikely, but
mixing is important.
Overall, I think there are more experiments to run. If you try a few more
'recipes', you might be able to make a better assessment if your hypothesis
is true or not. I would also look for a better binder-reinforcement pairing.
Hope this helps,
Burr Zimmerman
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Update: June 2012
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