5.1 Impact Value, as determined using the standard 4.5 kg (10 lbm) hammer, has direct application to design and construction of pavements and a general application to earthworks compaction control and evaluation of strength characteristics of a wide range of materials, such as soils, soil aggregates, stabilized soil and recreational turf. Impact Value is one of the properties used to evaluate the strength of a layer of soil up to about 150 mm (6 in.) in thickness and by inference to indicate the compaction condition of this layer. Impact Value reflects and responds to changes in physical characteristics that influence strength. It is a dynamic force penetration property and may be used to set a strength parameter.
5.2 This test method provides immediate results in terms of IV and may be used for the process control of pavement or earthfill activities where the avoidance of delays is important and where there is a need to determine variability when statistically based quality assurance procedures are being used.
5.3 This test method does not provide results directly as a percentage of compaction but rather as a strength index value from which compaction may be inferred for the particular moisture conditions. From observations, strength either remains constant along the dry side of the compaction curve or else reaches a peak and declines rapidly with increase in water content slightly dry of optimum water content. This is generally between 95 and 988201;% maximum dry density (see Fig. 1 and Fig. 2). An as-compacted target strength in terms of IV may be designated from laboratory testing or field trials as a strength to achieve in the field as the result of a compaction process for a desired density and water content. If testing is performed after compaction when conditions are such that the water content has changed from the critical value, determination of the actual water content by laboratory testing enables the field density to be inferred from regression equations using IV, density and water content.
5.7 Impact Value may be correlated with an unsoaked CBR.
5.8 Impact Value may be expressed as a hammer modulus, analogous with elastic modulus or deformation modulus.
5.9 The light hammer uses the same accelerometer and instrumentation as the standard hammer. The smaller mass of 0.5 kg (1.1 lbm) results in more sensitivity for lower strength materials compared to the standard mass; that is, the zero to 100 IV scale is expanded with this lighter hammer mass and provides more definition on softer materials. To avoid confusion, the IV of the light hammer is notated as IV/L.
5.10 Light Impact Value has applications for recreation turf hardness evaluation, where the condition of the surface affects ball bounce characteristics, the performance or injury potential to participants, and where more sensitivity compared to the standard hammer is required or an imprint left by the 4.5 kg (10 lbm) hammer or other test methods is undesirable, such as on a golf putting green.
5.11 The medium hammer uses the same acceler......