Concrete or Cement, What is the Difference?

Ever since I worked the summer of 1972 at Brandt’s Redi-Mix in Oak Lawn Illinois I have shouted from the roof tops what the difference between cement and concrete is. Cement is the powder that you mix with sand, stone, and water to make concrete. So you don’t have a cement driveway, you have a concrete driveway.Now days you can buy premixed concrete at any home improvement, or hardware store, but you never know when you may have to mix your own.

A typical concrete mix is made up 1 part of cement, 2 parts of sand and 3 parts of aggregate, or stone. Mix these together completely and then add your water. Make sure to use water that is suitable for drinking, as impurities in the water can affect the setting of the concrete. Adding too little or too much water can also affect the ultimate setting time and the ultimate strength of the hardened concrete. The amount of water will vary but you can start with 1 gallon for the mixture above. If the sand is wet use a little less water.
There are exact measurements for the mixing of concrete but for the average homeowner doing small projects around the house the ratio above will work just fine.

Concrete does not dry it sets through a hydration process. When water and cement are mixed together it starts a chemical process and a byproduct of that process is heat. The hotter the environment the quicker it will set, within reason. There are accelerants and retarders that are commonly added to concrete when you buy it by the truckload to make the setting time more workable. They can also add a liquid air product to the concrete to help with expansion and contraction issues and plasticizers to help it flow around objects when pouring on large jobs.

Another product that has been introduced into concrete is fly ash. Basically what was a waste product of the coal industry is now a vital part of the concrete mixture, adding to its ultimate strength and workability. Its use also allows less water to be used.

If you were to look at the stone and sand particles under a microscope you would see they have jagged edges that don’t fit too well together. Introduce cement (the paste) to fill in and hold those 2 substances together. However there are still voids, places where the products have not bonded together. Introduce fly ash to the mix. Fly Ash has a smaller particulate size and manages to fill in those voids thus creating more bonding surface. Simply put the more surfaces that are in contact the stronger the finished product.

So there you are, you now have learned that cement is the powder that in part makes up concrete, and the next time someone asks you what type of driveway you have you can say concrete!


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6 Responses to “Concrete or Cement, What is the Difference?”

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