CGA has seen an upturn in work related to non-destructive hammer testing of concrete slabs-on-grade, which documents the presence or absence of voids beneath the slab. (This can be due to either localized settlement or slab curling.) An article on this was published by several staff members in the July 2009 issue of Concrete International, and a more extensive paper is in peer review at the ACI Structures Journal (American Concrete Institute).