Early in 1945 a request was made by the Bridge Division of the Kentucky Department of Highways that bond characteristics of certain reinforcing bars be analyzed by the Department's Materials Research Laboratory. Nothing extensive was contemplated, it being the intent of the Bridge Division to determine whether reinforcing steel commonly used on bridge projects at the time should develop bond stresses reasonably close to those that could be developed by the specially prepared bars; and if not, whether the special bars produced benefits commensurate with increased costs.

Five types of bars were selected, and pull-out tests in preference to beam tests were chosen, largely as a matter of expediency Variable slumps were included but subordinated since structural concrete in Kentucky specifications is limited to 2-inch to 4-inch slumps for most of the heavily reinforced sections in which bend characteristics would be of concern. Unfortunately, at that time, suitable means for vibrating the concrete were not available in the Laboratory for there again the experimental condition did not conform strictly with specification requirements.

Initially, a fairly large variety of tests were planned, but by the fall of 1945 more urgent research on matters pertaining to pavement designs for an expanded construction program made curtailment of the project necessary. Even so, the study served its primary purpose very well, and revealed new relationships and new problems that probably were more important than those originally conceived. As such, these carry a high priority on the list of subject matter for investitation when problems of immediate consequence in design construction and maintenance have been solved.

Report Date


Report Number

No. 27

Digital Object Identifier



Prepared for presentation by L. E. Gregg, Associate Research Engineer, at the 43rd Annual Convention of the American Concrete Institute, Cincinnati, February 25, 1947.