Investigation of Methods for Improved Precision of Test Method TEX-113-E (0-5135-1)

The Texas Department of Transportation (TxDOT) employs the impact hammer method of sample compaction for laboratory preparation of road base and sub grade materials for testing. Serious concerns exist about the precision of the dry density obtained from this method. This report documents findings from efforts to improve the precision of Test Method Tex-l13-E, TxDOT's impact hammer compaction method for aggregate base materials. First, a new sample finishing tool replaced the old finishing method. While data from this change indicated a slight improvement in precision, the change did not hold up to statistical tests of significance. Additionally, four unique variations of laboratory preparation with the impact hammer method were investigated. All four methods resulted in the same mean dry density of compacted test specimens. However, two of the methods clearly resulted in poorer test precision.