I'm afraid I'm not going to be a great deal of help, but I'll add what little I know below: On 8/14/06, Gus S Calabrese wrote: > I want to make a machine that recycles plastic, grinds it up, heats it > and blows very thin wall bubbles to mix with concrete. > The advice I am looking for is ..... > #1 What plastics are suitable > #2 suggestions on best size for bubbles It depends on the application. I imagine that certian applications could support very large bubbles (several inches in diameter) but for most floating concrete applications you need the concrete to maintain a great degree of strength and rigidity, so very small bubbles (a few mm in diameter and smaller) are the largest you might use. If you use polymer strings to increase the strength of the concrete you can get away with bigger bubbles. I suspect very thin wall plastic bubbles will collapse during the mixing process regardless of the size. Also keep in mind that concrete heats up as it mixes and cures, and in fact can get very hot internally. Concrete canoe builders typically use glass microspheres. One such composition is shown in this page: http://www.concretecanoe.org/ (editorial - caution: ugly site!) > #3 Has anyone ever worked with a technology like this and if so, > what happened ? No, but I've followed the various concrete canoe competitions at some universities as well as the very interesting flexible concrete being developed at places like the University of Michigan. Before I saw this picture and read the article I had never considered concrete to be elastic: http://www.umich.edu/news/index.html?Releases/2005/May05/r050405 I drive over that about once a week. What's the application? -Adam -- http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist