This bulletin focuses on the investigation, sampling, and testing of in-place wearing surface materials, in-place base materials, and in-place subgrade materials in advance of paving. This is especially important the first time the road is to be blacktopped. However, the investigation and testing methods suggested herein are equally applicable to existing blacktop pavements needing reconstruction. The test methods focus on two quick field tests that have been developed through research to measure equivalent CBR values. CBR is a measure of the load-carrying capacity of base or subgrade materials.

The methods and procedures set forth in this bulletin should go far in helping county road officials plan for a better, more efficient use of county highway construction funds.


road base, road subgrade, base, subgrade

Date of this Version


Tech Report Number

County Highway Series—No. 14