Dear Ms. Archibald,
Thank you for posting your request on History Hub!
We searched the National Archives Catalog and located a series titled Central Correspondence Files, 1936 - 1950 in the Records of the U.S. Maritime Commission (Record Group 178) that includes 8 file units pertaining to construction and/or contractors of concrete ships. For access to and/or copies of these file units, please contact the National Archives at College Park - Textual Reference (RDT2) via email at email@example.com.
There is additional information about concrete ships during WWII on the American Merchant Marine at War section of the U.S. Merchant Marine website.
We hope that this is helpful. Best of luck with your research!