EN 13161 Natural Stone Test Methods - Determination of Flexural Strength Under Constant Moment

A European standard "EN 13161 Test methods for natural stone - Determination of flexural strength under constant moment" describes a method for determining the flexural strength of natural stones under constant moment. This standard includes provisions for both a diagnostic test and a technological test.

After suitable preparation, a sample of the rock to be tested is placed between two supports and centred. The sample is then subjected to a load using two parallel rollers acting on the upper surface of the sample. These loading rollers are centred and spaced one third of the length of the span. The loads are steadily increased until failure.

The main equipment used in these tests includes:

• A balance capable of weighing a sample with a reading of up to 0,01 percent of the mass to be weighed.
• A ventilated oven that can maintain a temperature of 70 degrees plus/minus 5 degrees.
• A linear measuring device capable of reading down to 0,05 mm.
• A testing machine of appropriate force, compliant with and calibrated to the standard “EN 12390-4 Testing of hardened concrete - Part 4: Compressive strength - Specification for testing machines”.
• A device that applies a two-point load to the specimen in accordance with the standard “EN 12390-5 Testing of hardened concrete - Part 5: Flexural strength of test specimens”. This device consists of two upper rollers (load-applying rollers) and two lower rollers (support rollers). The distance between the two support rollers must be reported as required by this standard.
• A room that can be kept at a temperature of 20 degrees plus/minus 10 degrees.

Sampling is not the responsibility of the testing laboratory when preparing samples, unless specifically requested. At least 10 samples should be selected from a homogeneous batch.

As a standard reference, the surface quality of the samples should be cut, ground or polished (identification test). When testing is required on end products (technological test), the surface quality of the samples can be flame treated or sandblasted depending on the end use. Samples for technological test can be end products or cut from end products. The surface intended for use must be in contact with two support rollers. However, the type of surface quality must be stated in the report.

The dimensions of the samples are determined by their thickness:

• The thickness should be between 25 mm and 100 mm and should be greater than twice the size of the largest crystal in the stone.
• The total length should be equal to six times the thickness.
• The distance between the support rollers l should be equal to five times the thickness.
• The width must be between 50 mm and three times the thickness and in no case less than the thickness.

Limit deviations shall be plus/minus 1 mm of the nominal dimensions. In the case of identification testing, surfaces shall not deviate from perpendicularity to the axis of the specimen by more than 2 percent when measured in any direction, with a maximum difference of 2 mm.

Anisotropy is the non-isotropy, also defined as the change of physical or mechanical properties of substances depending on direction. In the identification test, if the stone shows anisotropy planes (e.g. bedding, foliation), the direction of the anisotropy planes should be marked on each sample with at least two parallel lines. If the use of the stone in terms of the position of the anisotropy planes is known, the test should be carried out with the force applied to the surface to be loaded during use. If the use of the stone is unknown but the position of the anisotropy planes is indicated on the samples, the test is carried out on each of the three arrangements shown in the figures given in the standard. The total number of samples should be three times 10.

In technological testing, samples are tested only for the relevant product direction, i.e. with the force applied to the surface to be loaded during use.

Our organization has a strong staff that closely follows the developments in the world in the field of science and technology and constantly improves itself. Among the numerous test, measurement, analysis and evaluation studies provided for businesses in various sectors, there are also test services in accordance with the standard "EN 13161 Natural stone test methods - Determination of bending strength under constant moment".