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Newsletter 18                                                              August 1997

Testing of flexible road pavements with the 20 kg

CLEGG Impact Soil Tester

Recent testing of flexible pavements with the 20 kg CIST (or Clegg Hammer) produced encouraging results that support its application to the problem of serviceability assessment based on deflection. These tests were carried out in conjunction with Falling Weight Deflectometer (FWD) tests on a wide range of pavement types at Sutherland, New South Wales and Kalgoorlie, Western Australia.

The results of preliminary analysis of the data are reported in Technical Note 3 which shows useful correlations between the CIV of the 20 kg "Heavy" Clegg Hammer (CIV/H or CIV₂₀) and deflection.

Previous test results as reported in Newsletter 15 (Feb. ‘95) and Technical Notes 1 (May ‘94) and 2 (Feb. ‘95) indicated that the 20 kg Clegg Hammer with its 13 cm strike face and 30 cm prescribed drop height provided a suitable CIV scale for pavement basecourse testing while at the same time it is of a mass and drop height combination which is not too heavy for manual operation. Newsletter 15 suggested that based on a field correlation with Benkelman Beam tests a CIV₂₀ of 44 corresponded to 10⁶ repetitions of Equivalent Standard Axles in the design life.

Based on the latest and previous sets of tests it is considered reasonable to group flexible pavements according to stiffness as follows when considering 1) average deflection as between 0.5 mm and 1.0 mm, 2) average curvature between 0.1 mm and 0.3 mm and 3) modulus from about 300 MPa (43.5 x 10³ psi) to about 800 MPa (116 x 10³ psi) as measured on the surface:

Below 30 CIV/H: lower than average stiffness

Between 30 and 60 CIV/H: average stiffness

Over 60 CIV/H: higher than average stiffness

The following possible applications for the 20 kg Clegg Impact Soil Tester have been identified based on the collected test data together with observations of test convenience:-

* Used in conjunction with such tests as FWD and Benkelman Beam it would enable transverse variations in pavement stiffness to be observed, particularly along the edges or in locations not accessible by the other test methods be they on curves, in small areas or in remote locations;

* Determination of general variability on a statistical basis.

The portability of the CIST makes it easy to move from site to site as it is of a size that allows it to be transported in the back of a car. It has the distinct advantage of not requiring any particular technical skill to operate - though a strong arm is essential with the 20 kg Hammer! Other advantages are the comparatively low initial and testing costs.

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