I came up with this one while walking past a crew installing new utilities for a dormitory at the college for which I work. They were sitting there using a diamond saw and wheeling away to damage as little pavement as possible (as opposed to, say, a jackhammer).

Just like a plate, if you heat up concrete, cement, asphalt, or any of the other pavers, and then quickly cool it, it will crack. By focusing the heating and coling on a particular spot, you can select the area for breakage.

This saw would basically consist of a laser beam focused on some spot or line, followed shortly by a coolant. Think of a drafter's compass - one point represents the laser beam, and one represents the coolant being applied. Move in a straight line so that one follows the other, and *crack!* The beam and coolant applicator could be independently turned off to do things like start the line or finish a corner.

Pressing/dropping a backhoe bucket onto the section of concrete should create a dent in the desired dimensions, which would then be easy to scoop up.

Due to the power/storage needs, this would have to be wielded from the back of a truck. But then, so are many cement saws.
-- shapu, Dec 28 2004

I expect that when concrete is rapidly heated it will explode violently as the water content vaporizes and rapidly expands. This happens when molten metals drip onto concrete. If the laser or torch is hot enough, the cooling step would be unnecessary.
-- Laughs Last, Dec 29 2004


Sort of like a controlled spalling process. Rapid heating or cooling cracks the concrete due to differential expansion. The same happens with dry refractory brick - normally it must be preheated slowly before use, but if not, then it will tend to spall.
Maybe liquid Nitrogen could work as well, but it would tend to float over the surface of the concrete and not give a good heat transfer. It might have advantages in that it leaves no residue, and it would attack the concrete in an easier way - with strain instead of compression.
-- Ling, Dec 29 2004


Liquid aluminum in contact with cement creates high temperatures. That was the 9-11 scenario, molten airplane aluminum, combining with concrete and dripping throught the vent systems caused fires on other floors.
-- mensmaximus, Dec 29 2004


I really just wanted an excuse to combine carbon dioxide lasers and liquid nitrogen. What can I say?

Anyway, I'm aware of rebar. I was merely suggesting this for controlled scoring of smaller areas.
-- shapu, Dec 29 2004


Those diamond saws are water cooled, I think. I wonder if you could use liquid nitrogen for this same purpose?
-- bungston, Dec 30 2004



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