Developed in the United States in the 1920's it has become universally accepted as a measure of soil strength.  While questions are raised about the appropriateness of this test for soil in areas of the world, it has, over the years, proven to be a very useful and reliable method of pavement design.  It is defined as the ratio (expressed as a percent) of the force required to penetrate the circular piston of 1935 m2 cross section into the soil from the surface at a constant rate of 1 mm per minute, to the force required for similar penetration into a standard sample of crushed rock.  The ratio is determined at penetration of 2.5 mm and 5 mm and the highest value is used.  This test can be carried out on undisturbed or compacted samples in a mould or as a in situ test.  World Enzymes Australia in an effort to have a strength test as part of its quality control system, uses the correlation which has been established between CBR and the Clegg Impact Value (CIV).  Proven correlation's exist whereby the impact value can be used in the equation set out below to give a comparable CBR reading.
The equation is:       CBR  =  0.07 (IV) 2.
See the diagram below which illustrates the relationship as a result of field evidence.

The above diagram has been extracted from a paper titled "Design Compatibility Control of Base Course Construction"  The author is Mr B.A. Clegg, who was the Senior Lecturer in Civil Engineering in the University of Western Australia.  The paper concludes:
"correlation's have been established between the IV as obtained from the impact soil tester and the commonly used parameters CBR and TCN so that it is deduced that an IV of 37 corresponds with a CBR of 100 and a TCN of 2.  These are the present recommended minimum values for base courses to take a sealer coat." 
 

How To Uses The Above Tests

Materials are assessed for their suitability in relation to particle size distribution and plasticity index as previously stated.  Those which are deemed suitable are subsequently tested to ascertain the maximum dry density and optimum moisture content of the soil.  A further test using the impact hammer, CBR mould and the same sample is set up so that an impact value can be ascertained.  A known volume of soil is compacted into the CBR mould at optimum moisture and at a given energy input.  Equal to 2703 kjn per m2.  This is achieved by subjecting the soil in the CBR mould to 50 blows with a modified compaction hammer.  The impact value subsequently recorded on this soil sample gives a good indication of the target strengths desirable to be achieved on the day of construction.  The CIV value that results from this test can equally be cross checked on the day of construction by using the roller to compact a test strip and recording the CIV value after each pass.  The use of the impact tester is proving a useful cost effective tool that links laboratory test results with field results on the day of construction.  Coupled with moisture control tests on the day,  data can now be collected on roads and projects where previously only subjectivity was used.  By ensuring that these engineering principles are being obeyed only then can we be sure that Endurazyme is being optimised.  Remember that the use of these high clay gravel's can be extremely difficult, if not impossible without the chemical alteration that takes place with treatment.  It must also be remembered that unless basic engineering details are adhered to there are few chemicals that can compensate for significant reductions in the achieved density and therefore the strength bearing capacity of a road.  More details on field testing systems will be given further on in this manual.