The use of aluminun powder to make lightweight concrete is the chemical reaction between lime Calcium Hydroxide and Aluminum. This results in the release of hydrogen gas, forming bubbles....
Yes Hydrogen gas is VERY flamable.....so be careful.
To see this reaction safely, you may make a small tray of uncoated aluminum foil. Put on your safety glasses.
Fill the tray with water, and then add calcium hydroxide powder. Shortly, you will see bubbles appear. Light a match, and apply to the bubble...POP..as the hydrogen explodes. Very quickly the surface of the aluminum foil will become non-reactive as the reaction proceeds, and the bubbles stop; due to the formation of Calcium aluminate formed on the surface of the aluminum metal foil.
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