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55058Re: [bolger] Re: Big Dig epoxy

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  • Bruce Hallman
    Aug 10, 2007
      > Picking a "glue" for a tunnel roof? That's a tough one.

      Leave it to the lawyers to sort out the settlement here, but having
      done some tunneling professionally... I am guessing that they used
      epoxy to glue steel dowels into holes drilled in the rock. One common
      problem is that it is hard to ensure that you got epoxy injected all
      the way into the hole, it is very easy to have a trapped air bubble
      and/or dust layer in the drilled hole that impedes epoxy bonding.
      Also, very often you are working with poor or uneven quality rock, and
      the rock can crumble. I have heard that, theoretically, epoxy can
      creep, so I guess that is a possibility too, but I have never seen it.

      In the case of our boats, epoxy is applied differently, covering large
      surface areas, and wood is much less dense than even the softest rock.
      I have looked at several broken epoxy|wood glue joints, and I always
      have found that the wood fails before the epoxy, typically with a thin
      layer of wood fibers pulling loose just next to the plane of the glue.

      Telling me that for strong joints in wood you want:
      1) lots of surface area and 2) compression joints not tension joints.
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