Tabby Concrete (Seashell Aggregate Concrete)?

[LakeNormanTiger]

A column footing that I was inspecting yesterday was made of concrete that had visable "Seashells" on the surface. This was not an archtectural feature. The footing was under a wooden floor and was not intended to be seen. A forman called the concrete "Tabby Concrete". He said that this type of concrete mix was commonly used in construction during the late 1800's in coastal areas.

I "googled" Tabby Concrete and found: "Tabby, a type of concrete made in the seventeenth century, by burning oyster shells to extract the lime, then mixing it with a slurry of water, local sand and broken oyster shells."

I am looking for any information (literature, reports, etc.)on this type of concrete mix. Any help would be appreciated.

Thanks
LNT

 

[Ron]

You won't find much info. Tabby was common as noted from about 1700 to 1900 in the coastal southeast, and very common in the "low country" area of South Carolina and Georgia.

It was made generally as you described; however, the quality varied wildly. It has performed quite well over the years, with its most significant detriment from wetting and drying. If maintained in a dry condition it is probably as good today as when it was done.

You can encase the tabby foundations in concrete for additional protection, but if you have to maintain the historical significance of the structure, you'll have to be careful with how you remediate the tabby.

You can find some info in the Savannah area (try calling the Savannah public library).