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Name: Hector E.
Status: Educator
Age: 50s
Location: N/A
Country: N/A
Date: September 2003

Could I mix concrete with polystyrene beads and bentonite and get a homogeneous mixed compound that is lightweight?

It is possible to make very lightweight concrete with polystyrene beads, but I am not familiar with any mixes that use bentonite for that purpose. (That does not mean it will not work, necessarily, I have just never heard of it.) Normal concrete uses stone, sand, Portland cement, and water. For simple lightweight concrete, I would suggest a combination of polystyrene beads, vermiculite, Portland cement, and water. As a civil engineering college student, I participated in the making of several winning, though fragile, concrete canoes out of this type of mixture back in the 1980's.

Most people think that concrete has to "dry" to get hard, when, in fact, it actually must be kept moist for at least 3 and preferably 7 to 10 days to allow the cement in the concrete to chemically react and harden. (This is known as curing.) So, you should keep your lightweight concrete moist initially to ensure that it reaches its potential for strength. No moisture equals no hardening.

Concrete canoes have become vastly more sophisticated since I was a student 15+ years ago. The University of Wisconsin at Madison has a very good web page detailing their defending 2003 national championship canoe at . As a South Carolinian, I am proud that Clemson University ( has been the most successful concrete canoe competitor in recent years. (But, as a University of South Carolina graduate, I'd also like to point out that we used to whip them consistently back in my day...:-)

Andy Johnson

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