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Lightweight Concrete Mixture
Name: Hector E.
Status: Educator
Age: 50s
Location: N/A
Country: N/A
Date: September 2003
Question:
Could I mix concrete with polystyrene beads and bentonite and get a homogeneous
mixed compound that is lightweight?
Replies:
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 www.cae.wisc.edu/~canoe/ . As a South Carolinian, I am
proud that Clemson University (www.ces.clemson.edu/~canoe/) 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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Update: June 2012
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