Precast Concrete Column "Deformity"

[StructuresDesign]

Hi Structural Sleuths,

Do you have any good suggestions as to what is going on with this column:

For reference, the column is approx. 7" in diameter and is one of three interconnected columns with shared bases and caps. The "tumor" is hard to the touch, so it is not just paint blisters. The wet sheen is from water pushed out of a paint blister above. The rust stain seems to indicate that the reinforcement is failing, but I have never seen concrete bulge out like this. I am used to seeing concrete spall off due to swelling rebar.

 

[OldBldgGuy]

You know that it's concrete? Moisture is pretty well certainly the immediate cause, but what it's reacting with is the question. The appearance is more along the line of a softer, lime-based material that has been constrained by the coatings. It could be a lime binder in a sand or sand & stone matrix, or it could be a chemical reaction of the aggregate in a portland-based mix with poor aggregate. I have a materials expert that I do a lot of work with; old masonry and concrete are his thing. I will forward the photo to him & get an opinion. In the mean time, finding & stopping the source of the water is imperative regardless of what comes next.

 

[SlideRuleEra]

May be corrosion on a 19^th or early 20^th century cast iron column that was coated with with some type of cementitious coating. The detail at the top of the column is typical of what would have been used on a cast iron column. If water gets trapped between the column and the coating, cast iron corrosion can form bulging tubercles. A strong magnet is an easy way to see if cast iron is a possibility.

http://www.SlideRuleEra.net

http://www.VacuumTubeEra.net

 

[OldBldgGuy]

I have to wonder if you aren't right, SlideRuleEra. In my previous post I asked if the OP was sure it was concrete, but it didn't occur to me that it looks exactly like cast iron (how many bad drainage pipes have I seen in basements & crawlspaces?). My concrete guy said it doesn't look like concrete to him. I think a bit of destructive investigation is in order.

 

[StructuresDesign]

I think OldBldGuy may be on to something. It may be that swelling of the rusting reinforcement caused the concrete to spall off, and they then tried to patch it with a grout that subsequently reacted with water and bulged out.

However, when I have a chance to get on site again, I will use a magnet to see if the cast iron with cementitious coating hypothesis "holds water" - pun intended.

 

[bridgebuster]

The "tumor" - shiny, yellow area looks like typical concrete effloresence. I agree with SRE

 

[StructuresDesign]

I have been able to dig up the undated architectural drawings, and the columns are precast concrete with a single 3/4" square reinforcing rod at the center of each trefoil section. From what I can gather, square reinforcement was commonly used in the 1920's-1940's.

 

[Lomarandil]

Yes, absolutely -- at least the 20s and 30s, and some mixed use into the 40s.

 

[OldBldgGuy]

If they are early 20th century concrete the repair should be fairly straightforward. Chip off everything bad & clean the surface (including the steel) well, then use a pre-packaged repair mortar matched to the properties of the original concrete. I know, that sounds really dumb & "pass the buck", but manufacturers are in the business of doing this; get a rep there & they'll be only too happy to help. I don't know where you are, but presumably in the States. I'm in Ontario & there are a couple of guys I know who want to be spec'd on every job so they are more than helpful when I need a test or some minor analysis; I'm sure you can find them too. There are pre-packaged repair mortars for everything from cheese to granite, so the one you want is out there.