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Roger Weller, geology instructor

by Tory Norton
Physical Geology
Fall 2012

                  Concrete, as Hard as the Rocks itís Made Out of

Have you ever wondered what concrete is made out of? Concrete is composed entirely of sedimentary rocks and minerals, such as limestone, sand, decomposed granite, and gravel.   Cement is the crushed granite that is added with the limestone, gravel, and sand which when added with water makes concrete. What gives concrete its strength is the amount of cement within the mix.  The more cement added to the sand and gravel gives the concrete more strength. For example, seven 94 pound sacks of cement added to one yard of sand and gravel gives the concrete the compressive strength of 5000 psi.   Concrete is pressure tested to determine the amount of pressure it can withstand before it cracks.   For instance, concrete with a 3000 psi rating is used for sidewalks while a 5000 psi rating is used for structural support.

Description: Bar graph showing percent of different components in concrete

Ingredients in concrete (Photo courtesy of


Hereís the steps used to making concrete:

Step 1) First you need to determine what strength of concrete is needed for the job.

Step 2) Next add the sand, gravel, and limestone to a cement mixer.

Step 3) You will add dry cement to the sand and gravel. The more cement you add to the mixture the stronger the concrete will be.

Step 4) Depending on how thick you want the concrete to be will determine how much water needs to be added. For example, the more water added will make the mixture more fluid. After water has been added the chemical reactions will begin right away.

Step 5) The more revolutions inside the mixer the longer concrete will take to harden. The concrete will begin to lose its strength the more revolutions it has been turned.

Step 6) The concrete will begin to set up and harden now that water has been added. Depending on the outside temperature, how many revolutions it has been turned, and the amount of water added will determine how fast the concrete takes to set up.

Step 7) There are many different factors that determine the rate that the concrete cures. It can cure as fast as a couple of hours in high temperatures or it can take more than a whole day to be strong enough to walk on and not be damaged. The concrete will never stop curing over its lifetime, it just appears that itís finished.

Step 8) The finished product is a solid, grey, dense rock hard object in the shape that it was set up in.


Concrete curing (Photo courtesy of Google images)


Concrete has many different uses.  Concrete is used in building structures because of its strength and resistance to fires.  It is used as foundations for buildings, sidewalks around town, and driveways at your house. Concrete bricks are used for homes, block walls and patio pavers. The energy efficient concrete walls keep heat inside the building and are more airtight making it lose less energy than a wood or steel frame building.  As you have learned concrete offers a variety of uses.


 Finished concrete building (Photo courtesy of Google images)

Works cited

"HO    HOW TO MIX CONCRETE." How To Mix Concrete., 1999. Web. 26 Nov. 2012.
"Concrete Properties." Concrete Properties. SimScience, n.d. Web. 26 Nov. 2012.
Waverly, Jack S. "How Is Concrete Made?" EHow. Demand Media, 02 Apr. 2009. Web. 26 Nov. 2012.
"Concrete Basics | Portland Cement Association (PCA)."
Concrete Basics | Portland Cement Association (PCA). Portland Cement Association, n.d. Web. 26 Nov. 2012.