BOB HIRSHON (host):
The chemistry of cement…I’m Bob Hirshon and this is Science Update.
Today’s Why Is It question comes from Tim Pendleton’s 7th grade science class at the Chaminade College Preparatory School in St. Louis, Missouri. They wanted to know how the ingredients in cement stick together. Well, we got a ‘concrete’ answer from Michelle Wilson, manager of product development at the Portland Cement Association. She says cement is a mix of limestone, silica, aluminum, and iron that’s processed at high temperatures. When the powdered cement is mixed with water, it reacts chemically to form sticky compounds.
MICHELLE WILSON (Portland Cement Association):
And the main two products that form are a calcium silicate hydrate and a calcium hydroxide. And that’s the glue that you see in fresh concrete.
Wilson says this chemical process can be manipulated to change how fast the cement hardens. If you’ve got a science question, call us at 1-800-WHY-ISIT. I’m Bob Hirshon for AAAS, the science society.