Enhancement of Pilot and Automax compression machines for ACV test
Aggregates Crushing Value test according to BS 812:110
BS 812 part 110 describes a method to determine the aggregate crushing value (ACV) which gives a relative measure of the crushing resistance of aggregate under an increasing compressive load. The method is applicable to aggregates passing a 14.0 mm test sieve and retained on a 10.0 mm test sieve.
An aggregate specimen is compacted into a steel cylinder fitted with a no-friction plunger. The specimen is then loaded via the plunger. The load crushes the aggregate to an extent depending on the crushing resistance of the material. It is measured by a sieving test on the crushed specimen and it is a measure of the aggregate crushing value (ACV).
A compression testing machine of 500/600 kN capacity, a suitable steel cylinder and plunger are required to perform this type of test (see links below).
A compression machine with a higher capacity also can be used, however, extended calibration assuring Class 1 accuracy from the very beginning of the range is recommended.
The accuracy of the applied load has a strong influence on the test result: the standard states that the required force of 400 kN has to be reached in 10 min ± 30 s.
At the very beginning of the test there is significant sample deformation, which affects the loading rate. According to the standard, the compression machine control system shall automatically compensate these instabilities and complete the test in an overall time of 10 min ± 30 s.
Dividing the whole test duration of 600 seconds into 10 intervals of 60 seconds each, each 40 kN load step should be reached in 60 ± 3 seconds.
The table shows the 10 load steps and corresponding times.
Conformance to the standard is perfect, in fact the actual and standard lines are overlaid:
TEST TO AUSTRALIAN STANDARDS 1141.21 and 1141.22
The Australian Standard is more restrictive vs. BS for the tolerances. According to BS 812:110, the final load shall be achieved in 10 min ± 30 seconds; the Australian Standard requires instead that a fixed load is reached every 1 minute, with a specific tolerance of ± 1 kN. These loads depend on the sample particle size and cylinder assembly in use.
Different tests with various nominal aggregate sizes marked in the table above have been performed by Controls with a PILOT compression machine.
Results confirm that the PILOT system in use is ideal for these types of tests.
The test results (blue) are perfectly between the 2 AS limits (green and red) almost exactly overlaying the target (violet).
The 2015 enhanced PILOT and AUTOMAX machines perform ACV tests with excellent accuracy, better than the requirements of the Standards.
As is well known by our customers, PILOT and AUTOMAX can perform automatically many types of test: compression, flexure and indirect tensile tests on concrete and cement samples (cubes, cylinders, blocks, etc.) conforming to the main International Standards, depending on the spherical seat / platens assembly in use.