No tags yet.
Efflorescence on concrete is a result of leaching of calcium hydroxide and subsequent carbonation and evaporation. It is soluble salts. The main problem is that it is unsightly especially when it is trapped under a sealer. It can be seen as a white blush on sealed floors. On unsealed concrete surfaces it is normally worn off. Efflorescence does not affect the structural integrity of the concrete but merely the aesthetics of it.
Efflorescence is caused by water leaking through cracks or through poorly compacted concrete. This water dissolves some of the calcium hydroxide and after evaporation leaves calcium carbonate as white deposit on the surface.
It can also be caused by unwashed seashore aggregates, gypsum and alkaline aggregates.
It is cheaper to prevent it than to rectify it. Many finishing contractors and building owners can testify to the cost and inconvenience of such remedies.
This is where fly ash replacement can help. A replacement of 15% to 20% of Portland cement contributes significantly to lessening efflorescence. There are three benefits of doing this:
1. Fly ash reduces the amount of Portland cement required.
2. Fly ash binds up a portion of the free lime and salts that caused efflorescence.
2. Fly ash requires less water again resulting in a denser paste which aids in keeping moisture from traveling up from the bottom and from the top down.
