Concrete Spalling around Access Hatch

[houselaw]

Hi everyone,

I am looking for help on how to properly assess the extend of concrete spalling around an access hatch installed on a concrete slab, and on subsequent repair methods, if deemed necessary.

Some background: the project involves the replacement of an existing aluminum access hatch in a wastewater lift station. In particular, the existing hatch is installed (built-in) on the 12" concrete roof slab of a wet vault. The replacement hatch will be ordered to have a skirt to fit the dimensions of the existing opening, the existing hatch doors will be removed and the new hatch will be dropped in the existing opening and anchored to the concrete slab. The anchors will be installed either vertically, through the perimeter frame of the new hatch, or sideways, through the skirt of the hatch (this is still undetermined).

During our inspections, we noticed surface cracking and spalling near the hatch perimeter, on all 4 sides of the hatch, and more pronounced near the middle of each side. I am attaching a few photos for reference. We also noticed some water concentrated at the top of the hatch which spilled to the sides upon opening the hatch. While water could contribute to the concrete deterioration because of the site conditions (sulfates from the wastewater etc), we have been told that the hatch is not frequently operated and that the hatch and slab are usually dry, so I am inclined to rule out prolonged exposure to moisture. On the other hand, we saw that both hatch leaves are permanently sagging and I suspect that this is likely an issue of improper hatch installation which is causing local failure.

Has anyone had a similar experience? Is this a problem that warrants further investigation in your opinion, given the two installation alternatives mentioned above? If yes, what is the recommended inspection methodology to identify the extend of the problem? And what would be a suitable repair approach?

I would greatly appreciate your input.

Thanks in advance

 

[Ron]

A couple of comments...

First, aluminum should not be installed in direct contact with concrete. Expansive reactions are common and it appears you have exactly that.

If you measure the distance from the edge of the frame to the crack, you will probably find that it is the same as the depth of the skirt angle. The angle of failure in the concrete will typically be at about 45 degrees.

Aluminum has a high coefficient of thermal expansion. It will move a lot relative to the concrete, thus causing fatigue in the concrete and resulting failure.

You likely have both of these conditions occurring.

 

[strucbells]

As Ron noted, in our spec for access hatches in similar environments we always specify a heavy bituminous coating between aluminum and concrete. Do you know how recently the hatches were installed?

 

[houselaw]

Ron and strucbells, thank you for your responses.

I am not an expert on aluminum and I have been doing some reading on it lately (another part of the project is to install aluminum railing around the hatches). I also see the hatch manufacturers typically specify bituminous coating in their drawings for the sides in contact with the concrete. All is in line with what you say.

To be more specific about the project, this is one in a series of hatches we are refurbishing, in multiple lift stations and locations. This is the only site where we saw this damage, so it could be that they missed specifying bituminous coating when they installed this particular hatch. According to the as-builts, this was 20 years ago. Unfortunately, this is all the information I have, no hatch model to verify at which depth the skirt anchors into the slab. If this is the case (bituminous coating missing) I assume 20 years would be enough time for the damage to progress that much. Ron's observation makes sense, as the distance between the edge of the frame is about the same on all sides of the hatch. That could also explain the permanent deformations on the hatch doors since the sides are more flexible.

What would you recommend in terms of concrete repairs? Does it sound reasonable to saw-cut the slab at the crack and at the depth of the skirt, remove the whole hatch, and pour new concrete before dropping in the replacement hatch? I am concerned about the pipe penetrations, but if it is done carefully at these locations I believe it could work. Thanks again for your input and looking forward to hearing your thoughts.