Testing of industrial products - Aggregates for construction

The Percentage of Crushed and Broken Surfaces test method

The principle of the method

A sub-sample of coarse aggregate is dried at 110 ± 5 ° C, and sieved, and any particles retained on the 63.0 mm sieve or passing the 4.00 mm sieve are discarded. The sub-sample is reduced, if necessary, to produce a test portion with a mass not less than the minimum value specified in the method for the size of the aggregate. Aggregates for which D > 2d are separated into size fractions for which Di <= 2di .

For aggregates for which D <= 2d , the test portion is spread out on a flat surface and separated by hand into two groups, which are weighed to give:

Mc = mass of crushed or broken particles (including totally crushed or broken particles);

Mr = mass of rounded particles (including totally rounded particles).

The totally crushed or broken particles are then separated from the crushed or broken particles, and weighed, to give:

Mtc = mass of totally crushed or broken particles;

and the totally rounded particles are separated from the rounded particles and weighed to give:

Mtr = mass of totally rounded particles.

These four masses are used to calculate the test results as percentages of the mass of the test portion.

For aggregates for which D > 2d , each size fraction is sorted into groups in the same way, and the method gives procedures for treating size fractions with either a large number of particles or a small number of particles, and formulae for calculating the test results.

The proposed CEN method

The CEN test method has been developed from methods used in Germany and some other central European countries where crushed gravel is a major source of construction material. In Germany, the DIN method is used to measure the percentages of crushed particles and totally rounded particles, but not the percentage of totally crushed particles.

Participants in the cross-testing experiment were sent copies of the method that was prepared in December 1996 for formal voting by CEN members. Some laboratories may have used the version prepared in their own language, and may have been given additional information by their National Co-ordinator.