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Author Topic: Bulb log 26 2011 Concrete blocks.  (Read 1179 times)


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Bulb log 26 2011 Concrete blocks.
« on: July 06, 2011, 09:06:41 AM »
Concrete based on portland cement has a very high pH. This is what prevents rusting of inbedded steel rods. This high pH will decrease by ingress of carbondioxide from the air. Normally this is a very slow process and goes from the surface inwards. A 5cm covering will keep the steel intact during half a century or more. This longevity of the protection means that the high pH will not leak out quickly unless the concrete is crushed to gravel or "sand". The high pH is a deterrent to the life of any plant so they will only grow on the surface or in cracks where carbon dioxide has diffused in. I suggest that anybody contemplating to use crushed concrete in composts should check the pH before planting. Large pieces are of course "safe" as is shown in the photo. The pH of water reaching the surface from below by capillary might have too high pH to be congenial. I would try the surface using an indicator paper before planting.
Anyway it is a most interesting experiment since broken concrete is everywhere.
Good Luck
Göte Svanholm


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