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sodium silicate

The bad news is that the release of radioactivity from the stricken reactor site continues, the Japanese authority has raised the level of the accident to level 7 on the scale. This is not due to the fact that the accident is getting worse it is more to do with the fact that the accident is still occurring.

One of the measures which is being taken is that the leak through the cracked concrete has been plugged by using sodium silicate. The sodium silicate is a water soluble and cheap chemical which reacts with any calcium hydroxide (lime) in the cement to form an insoluble calcium silicate gel. This helps to block the holes and cracks in the concrete.

It is important to understand that while the surface of a concrete object might have little free calcium hydroxide the inner part of the concrete which is isolated from the carbon dioxide of the air will often have free calcium hydroxide.

A key test for concrete buildings is to drill a hole in a wall and then paint the new surface with a solution of phenolphthalein, this will show how deeply the alkaline part of the concrete is below the surface. In the following link you can see how this test can be used.

http://www.understanding-cement.com/carbonation.html

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