Concrete top exposed to rain for 2 years 1

[upk]

(or see

http://www.pbase.com/image/161555922

if no image above)

This column top was exposed to rain for the past 2 years.. assume water can get inside the concrete.. it won't displace the cement at all.. would it.. because cement doesn't evaporate.. what is the negative effect of such exposure on the concrete itself?? I know some water may pass through the micro pores of the concrete and reach the rebars.. but with no oxygen.. the rebars may not rust...).. so I want to know effect on concrete.. would it make it softer, how?

 

[hokie66]

You worry too much. Looks fine to me. A small around of rust on the anchor bolts. Clean the up and lubricate them.

 

[upk]

The 16mm A307 bolts have been epoxied primer and also red oxide primered 2 years ago. Now we can't insert the nut (even if we force it.. we can't turn the nut). Any idea how to remove the epoxy? We can't use saw because it may cut it.. knife would take too long. Any chemical that can dissolve both the epoxy primer and red oxide primer?

 

[hokie66]

I have never tried to remove epoxy, so don't have any suggestion as to a solvent. I think there are some, but the right solvent would depend on the type of epoxy.

Have you tried to rethread the bolts with a steel die? If you can find the right type die, it may work to cut the epoxy out mechanically.

 

[Ingenuity]

If the thread-cutting die that Hokie66 suggests does not work, maybe try a knotted wire-wheel attached to an electric angle grinder. Be careful - keep all clothing and body parts away from the wheel - one hit and it hurts!

 

[Ron]

Methyl Ethyl Ketone (MEK) is a solvent that will usually removed such coatings. Since the red oxide primer is below the epoxy primer, the MEK will immediately attack the red oxide and will also soften the epoxy.

I would take hokie66's excellent suggestion of running a threading die over the threads even if you are able to remove most of the paint. Use plenty of lubricant and then lubricate the bolts afterward....should allow a nut to properly engage the bolt. Make sure you use the proper size die.

 

[upk]

Oh. We already removed both epoxy primer and red oxide by using hacksaw blade.. the worker slowly work thru every turn of the thread and flake them off.. of course not cutting it...

 

[upk]

When the base plate was put on the column top screwed.. there is some slits (or voids) between the base plate and column top. The designer was not familiar with using non-shrink grout underneath it. I tested to ask him if one can first put the grout then base plate on top.. he said yes.. I said what if weight of base plate press down on grout. He got silent. He said he was not familiar how to do it.

If I put spacing between base plate and column top with spacers.. but the heavy rafters would be put on it the next day.. is one supposed to first put grout between base plate and column top before putting the rafter load.. but contractor doesn't have time to wait for days because they said they are only on limited time in the contract because the men need to work elsewhere afterwards.

Reviewing the threads here. Many also don't put grout between base plate and column top. So perhaps just praying the compression of the base plate on the concrete won't even out. Do you guys put them or not too?

 

[jayrod12]

Not to sound condescending but your questions are very basic, and your designer's inability to answer them also worries me.

That being said, the typical construction techniques around here use a thickness of grout. The baseplate is installed with steel shims until the plate is level. The grout should be installed directly after that. It's likely that the baseplate and shims can handle the dead load of the rafters, but you would need your designer to check the bearing stresses and bending in the baseplate when it does not have grout provided.

 

[upk]

Thank you.

 

[BUGGAR]

I am curious: Are there ties around the embedded portions of the anchor bolts? What is the concrete cover over the steel? Is this a moment column? Are you located in a Seismic area?
Thanks.