What can the concrete truck driver do if he or she is hopelessly stuck in traffic with 20,000 pounds of material hardening in the twirling drum on the back? Add sugar. Really!

Very little new construction can take place without the use of concrete. It’s used all over the world. To find out how much is being used, experts track the key component of concrete, Portland cement. According to the latest statistics, nearly 2.9 billion tons of cement was produced in 2008, reports cemnet.com, publishers of the International Cement Review. Most of that cement was used in China; the United States ranked third worldwide, adds cemnet.com.   According to the Portland Cement Association, the United States used nearly 94 million metric tons worth of the stuff in 2008, worth $10 billion.

Portland cement is a careful blend of limestone and clay. The mixture is crushed to form a powder, which is then heated to about 1500ºC to convert the limestone to lime and melt the ingredients. After it cools, a lumpy gray material called clinker is left. Gypsum is then added and the clinker is ground into fine particles.

To make concrete, sand, coarse aggregate such as gravel, and water are added to the Portland cement. The ingredients are mixed, and a process called hydration turns the Portland cement into a rock-hard mass. Hydration means water is incorporated, so wet and cured concrete weigh about the same- the concrete doesn’t get lighter as it “dries”.

Other materials can be added to the Portland cement or to the final concrete mix to alter the engineering properties such as workability, strength, and curing time.

Sugar is a well-known and inexpensive concrete retarder . Concrete usually takes about two hours to begin to harden once it is mixed. Sugar is thought to interfere with hydration. About 10 pounds of sugar in a full load of concrete buys the driver an additional four hours. 

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Comments (3)

 

	Alan says: 2010-Jun-17 12:44
	Great topic! I always enjoy reading about a practical use of a common "chemical" to solve a real-world problem.  Reply     0     0     Report

   

	Tonya says: 2010-Jun-17 12:41
	Interesting story. I had no idea that sugar was a concrete retarder. Now when I see a concrete truck I'll think of this article.  Reply     0     0     Report

   

	Bobby says: 2010-Jun-17 08:36
	Great article. I wonder what is the mechanism behind the sugar interfering with the hydration of the concrete.  Reply     0     0     Report

 

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