Testing of industrial products - Aggregates for construction

The Schlagversuch method

The principle of the method

The Schlagversuch provides a measure of the resistance of aggregates to fragmentation. The test procedure calls for a test specimen of aggregate, placed in a steel cylinder, to be subjected to ten impacts from a hammer of mass 50 kg, falling from a height of 370 mm. The mass of the specimen (in kilograms) is calculated as 0.5 times the particle density (expressed as g/cm3) of the aggregate. The amount of fragmentation caused by the ten impacts is measured by sieving the test specimen, using five test sieves of aperture size 8.00 mm, 5.00 mm, 2.00 mm, 0.63 mm and 0.20 mm.

A determination on a test specimen is calculated by summing the percentages passing these test sieves, and dividing by five. The result of the Schlagversuch, the "SZ value" is the mean of the determinations made on three test specimens. Annex D of EN 1097-2 gives a worked example for one test specimen, and an example of the calculation of an SZ value from the percentages passing for three specimens is shown in Table A, below.

Figure B, below, shows the grading curves produced by the Schlagversuch for the three aggregates used in this experiment (the curves are obtained by averaging results from all the participating laboratories). On each grading curve the symbol "X" is used to indicate the average SZ value for the aggregate. From this figure it may be observed that, for each aggregate, the SZ value is similar to the result that would be obtained by subjecting test specimens after the impact test to a determination of the percentage passing a test sieve having an aperture size of approximately 3.00 mm. In comparison, the result of a Los Angeles test is obtained by determining the percentage passing a 1.60 mm sieve.

The proposed CEN method

The CEN version of the Schlagversuch has been produced by the committee responsible for drafting test methods for determining physical properties of aggregates (CEN/TC 154/TG 7).

The Schlagversuch is the test on which the main and only physical strength requirement for aggregates in road construction in Germany is based. This applies to concrete as well as bituminous pavement constructions.

Participants in the cross-testing experiment were sent copies of the German version of the test method that was submitted to CEN Enquiry in 1994.

Table A. An example of the calculation of an SZ value.
SieveTest specimen 1
% passing
Test specimen 2
% passing
Test specimen 3
% passing
8.00 mm30.330.130.9
5.00 mm14.613.813.9
2.00 mm5.55.25.3
0.63 mm2.11.92.0
0.20 mm1.11.01.0
Sum ÷ 510.7210.4010.62
SZ value (10.72 + 10.40 + 10.62) ÷ 3 = 10.6

Figure B. The average gradings after the Schlagversuch.