Posted by: nedpelger | July 29, 2008

Little Mistake = BIG Cost

We’re building a big parking lot with pervious paving and learned a tough lesson yesterday. If you know about pervious bituminous paving, you’re familiar with the deep layer of crushed stone that needs to be placed below the paving. In our case it’s a 3′ to 4′ deep layer of #3 stones that will provide storage volume for the stormwater until it seeps through the geotextile and  into the subsoil.

We had lots of meetings with the Township officials, inspecting Engineers, Design Engineers and Geotechnical Engineers to make sure we had the right materials and were doing the work in an acceptable way. Everything seemed to be going well. My old boss Ed Abel always said, “If you  think everything is going well, you obviously don’t know what’s going on.”

Yesterday morning I got a call that the quarry delivering the stone didn’t work Saturdays, so they hauled from another quarry last weekend. That stone was called #3s but had lots of fines, including some soil. They hauled and placed over a thousand cubic yards of stone.

As we met on site with all the players mentioned above, it slowly turned into one of those “Oh crap” moments. The amount of fines in the stones was apparent and anyone with experience in construction knows that stone dust does a good job of stopping water infiltration. We discussed all sorts of possible solutions, but couldn’t do better than the obvious one: take the wrong stone out and put the right stone back.

So a simple call to the quarry, asking for “#3 stone”, not “clean and washed #3 stone” is a Little Mistake that equals a BIG Cost. There are so many opportunities in Construction Supervision to make these kinds of mistakes, I sometimes wonder why any of us even do the job. We make so many decisions in a day, in which any one could be a huge mistake. Yet we go on making the decisions and doing our best. Why?

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Responses

  1. #3 stone usually refers to the screen size of the material. For example locally there is AASHTO #3 stone or clean 3’s and then there is 3A modified. Both stone types are sized with the largest size of the material being 3″. There is a big difference though in these stone types in both appearance as well as cost. From a cost perspective clean #3’s are generally more expensive.

    AASHTO #3’s or clean 3’s are manufactured by screening off 3″ size material only utilizing at least 2 screens in the process. This allows only this size material to be segregated to make the product.

    3A modified is typically manufactured by having the material only pass through 1 screen which would be sized at 3″. When making this product any material that is 3″ and smaller will pass through the screen.

    A good and experienced site superintendent should have known the difference between the materials as well as there intended uses and applications.

    I would think that when the first few loads of this material were delivered to the site, someone would have realized this was not the proper product regardless of what the quarry may have told them and stopped. Not waiting till there was 1,000 cubic yards deleivered.

  2. I can respond more succinctly: way to go bonehead!


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