Background chloride content of concrete
Background chloride content of concrete
(OP)
Tests of water soluble chloride ion, on a sample taken from a core slice 85 mm from the interior face of a perimeter basement wall gave 0.023% water soluble chloride ion by mass of concrete. The result from a core slice taken 85 mm below the top surface of the parking garage floor gave 0.026% water soluble chloride ion by mass of concrete. Both slices were taken from an area that had no signs of leakage and no cracks. The building is in Toronto and was constructed in 1957.
The concrete specialist at the lab is saying this shows the concrete was made with chloride added to the mix. I cannot see how that could be, because if chloride is added to the concrete mix as an accelerator, then the chloride ion content would be much higher than 0.026%. When chloride is added it is at the usual dosages of either 1% or 2% by weight of cement, then my calculation is as follows:
2% "calcium chloride" by weight of "cement" is
1% "chloride ion" by weight of "cement", which is approximately
0.17% "chloride ion" by weight of "concrete".
If added at only 1% "calcium chloride" by weight of "cement" that works out to be 0.085% "chloride ion" by weight of "concrete".
Both of these percentage are well above the 0.026% from the test.
From this I conclude that the 0.026% is indeed the background water soluble chloride ion content of the concrete. This seems not surprising to me because it is known that aggregates from the Niagara escarpment are high in chloride content. Of course I do not know where the aggregates came from in this particular concrete in 1957.
However the concrete specialist does not agree with me, and says that it indicates chlorides were added to the concrete mix. I always ask myself "what if I am wrong"? So I would like to get comment from anyone on this system with relevant knowledge on this issue.
The concrete specialist at the lab is saying this shows the concrete was made with chloride added to the mix. I cannot see how that could be, because if chloride is added to the concrete mix as an accelerator, then the chloride ion content would be much higher than 0.026%. When chloride is added it is at the usual dosages of either 1% or 2% by weight of cement, then my calculation is as follows:
2% "calcium chloride" by weight of "cement" is
1% "chloride ion" by weight of "cement", which is approximately
0.17% "chloride ion" by weight of "concrete".
If added at only 1% "calcium chloride" by weight of "cement" that works out to be 0.085% "chloride ion" by weight of "concrete".
Both of these percentage are well above the 0.026% from the test.
From this I conclude that the 0.026% is indeed the background water soluble chloride ion content of the concrete. This seems not surprising to me because it is known that aggregates from the Niagara escarpment are high in chloride content. Of course I do not know where the aggregates came from in this particular concrete in 1957.
However the concrete specialist does not agree with me, and says that it indicates chlorides were added to the concrete mix. I always ask myself "what if I am wrong"? So I would like to get comment from anyone on this system with relevant knowledge on this issue.






RE: Background chloride content of concrete
RE: Background chloride content of concrete