Carbonation in concrete

On April 16, 2016



Carbon dioxide present in the air will slowly penetrate the surface of concrete over time.  As it does, there is a reaction that occurs between the carbon dioxide in the air and the calcium hydroxide in the concrete.  In actual fact, this reaction also requires water.  Therefore, this process is accelerated in very wet concrete.  This reaction forms calcium carbonate and this, in turn, alters the alkalinity levels within the concrete.  Where the concrete happens to be reinforced with steel, which is almost always the case above ground, the steel will begin to corrode.  When the steel corrodes, it loses its tensile strength and ultimately ends up weakening the overall structure.  It also expands, forcing apart the concrete.  As this ‘spalling’ occurs, large sections become loose and fall away from the building (see picture).  This is obviously dangerous, as the falling sections could potentially hit someone on the ground or shatter roof windows, etc.

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