Sixth progress report of the investigation of prestressed c-oncrete for highway bridges / conducted by the Engineering -Experiment Station University of Illinois ; in cooperation -with the Division of Highways State of Illinois and the U.S-. Department of Commerce Bureau of Public Roads 

 - Urbana, Ill. : University of Illinois 
 - [83] p. 
 - Progress report ; no.6 Progress report ; no.6 .