huangyhg

efflorescence on concrete
i was recently sent to the task of evaluating several old structures (mostly concrete) and reporting on their conditions. in my inspection i noticed a lot of "efflorescence" deposits on beams and around cracks in walls. i always heard this to be a bad sign but after doing a little research before putting it in my report i'm not sure anymore.
pca only had reference to salt deposits on concrete (
my understanding is that effluorescence is caused by water penetrating the concrete. if this is the case at cracks in walls, i might be concerned about rust jacking (where the steel rusts, resulting in an increase in volume that causes a de-lamination of the adjacent concrete cover.
not that it is strictly a structural concern, but it can certainly turn into one.
efflorescence is salt and/or lime deposites (lime from limestone aggregates) that are left after water migrates through the concrete and evaporates on the surface, leaving the white stuff.
the concern isn't so much the deposits but rather what that represents.
strutcuraleit is correct that rusting of reinforcing steel is a concern as well as chlorides inhabiting the concrete itself and breaking down the integrity of the concrete matrix.
first job is always to find the source of water infiltration and stop it. secondly, test the concrete for chloride contamination as this would result in continued degradation of the rebar.
aci has a good concrete repair manual out that is very helpful. here's a link to it:
after what you said and doing a little more digging it seems odvious to me that there isn't a really concrete answer for this (haha). could be bad, maybe not really, there is no way to know for sure without destryoing the wall to look at and analyze it. if you have access to "ci concrete international" magazine, the august and september 2002 editions, pages 86 and 84 respectively, have a two part article discussing this topic. i could not find any good suggestions to approximate the reduced strength. probably wouldn't want to anyways. thanks!
given enough time, the concrete will be weakened by water flowing through it dissolving the minerals. this may take a long time or not depending on the water quality. concrete quality can be verified by coring a sample and sending it to the lab for analysis. we have used ctl to do this type of analysis in the past

if the concrete is quite old and there is not an exceesive amount of efflorescence, it would appear that there is not an immediate problem. generally, efflorescence is a variable cometic problem that also is an excellent indicator of a moisture problem.
obviously, as others have stated, the source of the moisture should be determined. if can be corrected and the volume appears intermittant or is minor, you could be seeing many years accumulation, which may not be a concern. eliminating the source of the moisture, should stop the process.
you cannot eliminate the source of the salts since they are probably from the free lime that exists in all concrete until it getts tied up by carbonization, which takes moisture and long exposure to carbon dioxide.
thats a good point cvg, there are analysis options available. the company i work for was hired to do a run through of some structures purchased by a utilities company. i suggested some waterproofing options and mentioned the more involved analysys to get an estimate of strength but i don't think they are interested in spending the money. i was hoping to find a general "rule of thumb" for a quick check but it seems like the situation varies a lot depending on conditions. it was build somewhere in the 1950's and we don't have any as-builts or construction documents. i attached a photo of the current conditions, i think its likely they will abandon the lift station in the near future anyways.

__________________
借用达朗贝尔的名言：前进吧，你会得到信心!
[url="http://www.dimcax.com"]几何尺寸与公差标准[/url]