Efflorescence on car park wall 2

[Settingsun]

A residential single-level car park has ongoing appearance of efflorescence at most of the wall segments that are retaining ground (up to 3-4m retained height). The wall is 25-30 year old concrete masonry which I assume is reinforced, and also gets some water penetration during rain. The water penetration isn't an issue by itself as the amount is literally a trickle and the car park has a drainage system, although in recent heavy rain the water pressure was sufficient to create a half-dozen or so small fountains at small voids in the mortar joints in additional to the trickle over larger areas of wall.

Does ongoing efflorescence eventually cause structural issues? The Cement & Concrete Aggregates Australia datasheet says it's mostly cosmetic while Dulux Protective Coatings says is will weaken the cement matrix.

 

[dik]

Catch the link:

http://canadamasonrydesigncentre.com/download/9th_symposium/CLAYMS01.pdf

The growth of the salt can exert pressure that over a period of time may cause cracking to enlarge.


Dik

 

[Ron]

Efflorescence is a result of primarily calcium constituents in cement (both concrete and mortar)that are dissolved into solution as water migrates into and out of cementitious materials (concrete and mortar). CaO (calcium oxide) is one of the primary and most abundant of the cement constituents. As water passes through the material, some of the CaO reacts with water and becomes Ca(OH)₂ (calcium hydroxide). When the calcium hydroxide gets exposed to the outside air, it reacts with CO₂ and produces CaCO₃(calcium carbonate) and the water evaporates. This is the white residue you see as efflorescence. In actuality it is a little more chemically complicated as there are alumina compounds, magnesium compounds and other constituents of the reactivity (as dik described...the "salts"), but calcium is the more prominent one.

Does this affect the strength of concrete and mortar? Yes....over time. As more and more calcium is consumed in this reactivity process, calcium that is a part of the hydration of portland cement is depleted thus causing an ultimate reduction in the cement binder. This generally takes many, many years unless the influx of moisture is relatively constant. Even then, it takes a long time.

The solution to the issue is to waterproof the concrete on both sides, particularly the side exposed to greater moisture.

 

[Settingsun]

Thanks both. What sort of strength reduction can occur considering the composite reinforced structure (as opposed to looking at the masonry and mortar in isolation)? I'm thinking along the lines that bending strength might be relatively insensitive to the strength of the masonry/grout if it's a lightly-reinforced wall, with shear not being critical unless the strength loss is particularly severe.

 

[hokie66]

steve,

I think the answer to your questions depends to a large degree on the quality of the masonry units. I have seen some which, in the condition you described, have suffered almost complete disintegration of the inside shell. On the other hand, I have seen some very leaky walls without noticeable deterioration of the blocks.