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The Story of Concrete – or is it Cement?
So you’ve decided to do a little home improvement project on your concrete (or is it cement?) driveway, and you need a cement mixer (or is it a concrete mixer?)
What’s the difference between concrete and cement anyway? Is there a difference? Or is this one of those “You say concrete and I say cement” cases?
The answer is that there is definitely a difference between concrete and cement, even though the two are often used interchangeably. Cement is one of the ingredients that are used to make concrete. Concrete is a mixture of aggregates, which are usually sand and gravel or crushed stone, and paste, which is made of water and cement. The cement usually comprises only 10 to 15 percent of the concrete mix, by volume.
Concrete is the most often used man-made material on Earth. Water is the only substance that man uses more than concrete. Throughout the centuries, various materials have been used to make concrete. The Assyrians and Babylonians used clay as cement. The Egyptians used lime and gypsum cement.
Today, most of the cement used to make concrete is portland cement. Portland cement doesn’t come from Portland, and it isn’t a brand name; it’s a generic name, like stainless steel or sterling silver. By some accounts, British engineer John Smeaton pioneered the use of portland cement in 1756. By other accounts, portland cement was first made by Joseph Aspdin, a bricklayer in Leeds, England, who made it by burning powdered limestone and clay in his kitchen stove and patented it in 1824.
Today’s portland cement is a carefully controlled chemical combination of calcium, silicon, aluminum, iron and small amounts of other ingredients to which gypsum is added in the final grinding process to regulate the setting time of the concrete.
Concrete is used to make buildings, roads, bridges, walls, posts, bases for posts, fences and gates, and any number of other things. One of the most notorious uses of concrete is for “concrete shoes,” a slang word for gang-related murder. The term is derived from the real or Hollywood-inspired use of concrete for weighting down a victim and throwing him or her into the water to drown.
Concrete makes such a good building material because it actually gets stronger as it gets older. This is because the process by which it hardens continues for years. Instead of just solidifying as it dries, the cement has a chemical reaction with the water, causing the sand and gravel to stick together and form a material similar to stone. This is also why concrete should be “cured” or kept moist for at least six days after it is poured.
. In the modern day, the use of recycled/reused materials as concrete ingredients is gaining popularity due to increasingly stringent environmental legislation. The most conspicuous of these is pulverized fuel ash, recycled from the ash by-products of coal power plants. This has a significant impact in reducing the amount of quarrying and the ever-attenuating landfill space.
About the Author: Independent Author in Thailand