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Concrete Or Cement? What’s The Difference?

Albeit small, there actually is a difference. During the course of environmental consulting, construction, or even that rare home/garden project, we often have the need for a hard, durable building material capable of withstanding the elements and ground traffic. Two such materials are concrete and cement. Quite often, we hear others use the terms concrete and cement interchangeably. Landowners, shop owners, and even some contractors will refer to "cement mixers" and "cement floors" inside buildings.

Let's see if these are the correct terms and materials. First, there is cement. Ancient civilizations experimented with producing a material capable of being used as a mortar to hold building bricks together. They used various types of clay for this purpose. The Egyptians went on to add quantities of lime and gypsum to their large construction projects such as the Great Pyramids. The Greeks followed to make improvements and the Romans ultimately "perfected" cement by adding some quantity of water to dried calcium oxide (lime) and produced "slaked" lime, then added to volcanic ash. Portland cement, the principal "earth based" cement in use around the world today, was first patented in 1824 by Joseph Aspdin in Great Britain. It was given the name Portland due to its color resemblance to stone quarried on the Isle of Portland off the British coast. Portland, is composed of varying quantities of calcium, silicon, iron, and alumina. These materials are combined, burned in kilns, and then pulverized into the gray colored powder we see at hardware stores and on construction sites. Cement, although a great binding agent, is structurally weak on its own when exposed to the elements and structural stress.

Concrete is cement's "big brother". After all, if it weren't for cement, there would be no concrete! Again, we look back to the Romans and their work with cement as a binding material. Cement was found to be very good at binding materials together, but not structurally strong enough to bear the weight and loads of structures alone. The Romans fixed this problem by applying sand, shells, and gravels down in layers and using the cement as a mortar, similar to brick laying. Today, we add aggregate (sand, gravel, crushed stone, etc.) to a 10 to 15% (by volume) Portland cement mix with water to produce typical concrete. For economic reasons and to reduce the air possibly left in concrete mix, we add the aggregate and cement at a mixing plant and truck the concrete (tumbling as it is transported) to the site. Concrete, once allowed to cure, hardens with age as the cement bond between the aggregate and cement "set".

So, the next time someone says "cement sidewalk", "cement truck", etc., remind them it's concrete (with a little help from cement)!

- Robert Mangum, Operations Manager