Concrete Degradation

[JJPellin]

I live in a very old house in Minnesota. The driveway was concrete and was badly cracked. I suspect that it was as old as the garage which was built in 1965. I decided to replace the old driveway. I got three quotes from three reputable contractors. In the end, I chose the highest bid. This contractor seemed to have a better focus on quality. He proposed more Class 5 base, more steel reinforcement and the use of granite aggregate. I was sure I was choosing quality over price.

He seemed to do an excellent job. The driveway looked great. I was concerned about the harsh winters here in Minnesota for my new drive. I did not allow the use of salt. I kept it shoveled and used sand when needed for stubborn ice.

Now that eight months have passed and the snow is starting to melt, I stopped to examine my nice new driveway a little bit closer. I am very disappointed with what I found. There are pop-outs all over it. There are pieces cracking out into the joints. There are large areas that are almost covered in pits from the pop-outs. I have attached a picture of some of the typical damage.

As I recall, the driveway had to be poured in two sections. It is over 80 feet long. All of the damage seems to be confined to the first section. I didn't find any damage at all in the second section.

I have contacted the contractor to inform him of the problem. I am waiting for a reply. While I wait, I would appreciate some expert advice about the likely cause. I would like to be able to hold up my end of the conversation when he comes back with a response. Any help would be greatly appreciated.



Johnny Pellin

 

[hokie66]

Some information on popouts. Although your contractor proposed using granite aggregate, there may have been different aggregates used in the two sections. Was the concrete air-entrained?

http://www.nrmca.org/aboutconcrete/cips/40p.pdf

 

[JJPellin]

Thanks a lot hokie66. That is exactly the sort of information I needed. Tonight, I plan to remove a few of these pop-outs and examine the holes more carefully to see if I can indentify the aggregate underneath. I should be able to tell if it is granite.

I don't know anything about air-entraining. I don't recall any mention of this in the quote or the discussion I had with the contractor. I will look back over the quote.

Thanks again.

Johnny Pellin

 

[Ron]

JJ...yup. You got popouts! Agree with hokie66 on the air entrainment. If not used, would certainly contribute to similar issues.

The pattern of these popouts seems to be more like a coarse aggregate issue. Carefully lift one of the popouts and see if there is a powdery or gel-like substance at the apex of the cone. If so, you have a reactive aggregate issue.

 

[JJPellin]

I have had to change my plans again. The driveway is buried under fresh snow again. Before the snow fell, the contractor came and inspected it. He agreed that it is unacceptable. He is going back to his supplier to see what can be done. But, in any case, he has offered to chip it out and re-pour it at no cost to me.

Once the snow is gone, I will still examine more closely to learn for certain what happened. When he chips it out, I may ask to save a few pieces to examine for root cause.


Johnny Pellin

 

[Ron]

JJ...make sure that what he puts back in has adequate air entrainment (4% to 6% by volume). Preferably use 4000 psi concrete for durability considerations.

 

[Ron]

JJ...also, ask for aggregate certification of non-reactivity along with the concrete mix design.

 

[JJPellin]

Ron,

Thanks for the advice. I will be sure that all of these details are included.

Johnny Pellin

 

[MintJulep]

But, in any case, he has offered to chip it out and re-pour it at no cost to me.

What alternate universe do you live in where a contractor will do that with no argument at all?

 

[hokie66]

That is called the world of responsible contractors. This contractor values his reputation, knows that he (probably his concrete supplier) has provided an unacceptable result, and he is doing the right thing. Plenty of those kind of people around...still.

 

[JJPellin]

I chose this contractor, in part because he had straight A's on Angie's List. His price was high, but he seemed committed to quality. The extra cost I paid got me this sort of response. He offered to replace it. I didn't even have to ask.

Johnny Pellin

 

[JJPellin]

Update: Tomorrow the contractor is coming back to replace the bad section of my driveway. I will follow up with the outcome.







Johnny Pellin