Abstract:
The New Zealand vibrating hammer compaction test procedure has been proven to provide inconsistent results. As supported by the Opus investigation, repeatability and reproducibility values of the New Zealand Standard for the vibrating hammer compaction test method are higher than those values found in standards both in America and the United Kingdom. The research examined the variability in the vibrating hammer compaction test results. Two approaches were implemented to achieve a sound and scientific understanding of the variability associated with the test results. Firstly, repeated testing of the vibrating hammer compaction test was conducted under constant conditions to determine the natural variability of the test. Secondly, X-ray diffraction tests were conducted to verify the homogeneity of the source aggregate being used for testing. Results have confirmed that the variability is significantly large considering the tests have been conducted under constant test conditions. Under these conditions, factors that could possibly affect the reliability of the test results have been kept the same throughout testing. The natural variability in the source aggregate explains approximately 30% of the observed variation in the Opus Interlaboratory study. As evident in the results, the amount of compactive effort applied to the sample during compaction determines the degree of Dry Density achieved. X-ray diffraction results have shown that there are some differences within the aggregate in terms of physical properties and mineral constituents. However, it is unknown to what extent, if any, these differences contributed to the variation in the vibrating hammer compaction test results. Future research is recommended in areas such as the amount of contribution that segregation and degradation has on the variation of the results. Additional testing should be done on aggregates passing the 19 mm sieve to observe whether oversized particles have the effect of interlocking and interfering with compaction.
