Another Basement Quality/Structural Integrity Question

[Groesbeck Hurricane]

One more question concerning basements and their integrity.

We have seen a house that appears otherwise nice but I have a question concerning the basement and structural integrity. There is one corner of this home where there is a concrete retaining wall coming off the basement, It is in the corner of the home. The interior of that corner, the part inside the basement, appears as though the concrete has "peeled away" from the corner a bit. This would be from the same plane as the retaining wall. There does not appear to be any shifting in the home, the bricks above the section have no indication of cracking or separation. There is absolutely no indication of dirt in or around the separation point and there is no track of water flow on the floor. In fact, the floor is dirty from the tractor, atvs, etc and shows years of wear on the floor that water would have disturbed. There are no disturbances on the floor.

Is the wall structurally sound? Should this be run away from or looked at deeper? Our realtor seems to think this is not a big issue as there is alot of rebar in the corners. I want to know what PPOT thinks.

Thank you!!

[ckissick]

I can't quite picture the problem, so can't give a good answer. But I can say this:

The normal mode of failure for a basement retaining wall would be for the wall to bow (rhymes with low) out, with the maximum deflection about a third of the way up the wall. This is because the top of the wall is restrained from movement.

This mode of failure occurs in clayey soil and can take years to progress to an unstable condition. This can happen with no movement of the house at first, and with no seepage.

Anyway, never rely on a Real Estate agent's opinion. You should have a soils engineer look at it and get a reliable opinion. I'd help, but it's a bit of a drive for me.

[911Rob]

Sounds OK to me David and I'm both an engineer and a Realtor; ha.

Make an offer subject to the seller providing a structural engineers evaluation with a professional seal that the basement is structurally sound.

[Groesbeck Hurricane]

The photos did not turn out so that you can see what I am talking about. I will try and 'splain better:

Starting at the top of the basement wall, under the floor of the home, part of the basement wall is peeling away from the outside of the wall. Clay type soil, limestone rock abundant. The best way I can think of to explain is to use the analogy of a flaky biscuit. Part of the concrete is pulling away like a flaky biscuit starting at the top. Cannot tell if the rebar is involved or holding. The rebar is "supposedly" very concentrated and "correctly" connected in the corners. One cannot verify without x-ray and I left my Superman glasses at home...

Anyway, the more I talk about this, the more I am unhappy with the situation. The home is large, well laid out, tonnes of closets, three car garage on one level, one car garage below, geo-thermal, all brick, swimming pool....

Anyway, thoughts for the future????

[ckissick]

So the concrete is splitting apart? That's different.

A possibility is that the concrete may be deteriorating due to a process called alkali-silica reaction. This is when alkaline soil (limestone is very alkaline) attacks the silica in the aggregate of the concrete. Aggregate that is rich in microcrystalline quartz is prone to this. This process makes the concrete expand and spall, or split apart, as you describe.

A way to check for it is to get a core sample of the concrete and make thin sections to look at the silica with a petrographic microscope.

The only solution is to replace the concrete. As we say in the scientific community, this is not a trivial task.

Not having seen it first hand, I could be wrong. But if this were a test question on an exam, I'd probably get full marks for my answer.

[911Rob]

There are different classifications of concrete; type 10 and type 50.
Type 50 is sulphate resistant for those soil conditions.
Type 10 is normal.

It could be the wrong type of concrete was originally used, thus the concrete is deteriorating.

Once again, you should have the Seller produce a structural engineers report under seal. This will provide you with a better understanding and protection.

Cheers,

[Groesbeck Hurricane]

Thanks all!! Yep, seller provide a report if we go that route. I would agree on the spalling.

I'm too close to this to see the forest.... Not too many homes on the market with enough acreage for us and we are sifting through the bottom of the barrel. The ones that have enough acreage are either mobile homes (zero value in our minds and they want money for them) or the homes have serious issues and we will not get involved.