EN 14066 Natural Stone Test Methods - Determination of Resistance to Ageing by Thermal Shock

A European standard, “EN 14066 Natural stone test methods - Determination of resistance to ageing by thermal shock”, describes a test method used to evaluate the changes that may occur in natural stones under the influence of sudden temperature changes (thermal shock).

For the purposes of this standard, the terms and definitions given in the “EN 12670 Natural stone - Terminology” standard are valid.

When performing this test, in principle, after drying at 40 degrees plus/minus 5 degrees for one week, the samples are subjected to successive cycles, each of which is formed by drying at 70 degrees plus/minus 5 degrees and then immediately immersing in water at 20 degrees plus/minus 5 degrees. Potential strength loss is measured according to the standard "EN 12372 Natural stone test methods - Determination of flexural strength under concentrated load". The exposed samples and, where relevant, changes in other physical and mechanical properties are performed on the samples before and after the thermal cycles by one or more of the following non-destructive tests:

• Dynamic modulus of elasticity according to the standard “EN 14146 Natural stone testing methods - Determination of dynamic modulus of elasticity (by measuring the fundamental resonance frequency)”.
• Ultrasonic pulse velocity according to the standard “EN 14579 Natural stone testing methods - Determination of sound velocity propagation”.
• Open porosity according to the standard “EN 1936 Natural stone test methods - Determination of true density and apparent density and total and open porosity”.

The main equipment used in these tests includes:

• A ventilated oven that can maintain a temperature of 70 degrees plus/minus 5 degrees.
• A flat-bottomed, closed tank containing small, non-oxidizing, non-absorbent supports for samples.
• A weighing instrument that provides an accuracy of at least 0,01 percent of the mass to be weighed.

Sampling is not the responsibility of the testing laboratory unless specifically requested. At least 20 samples should be selected from a homogeneous batch: one set of 10 samples as a reference for the measurement of the flexural strength of the fresh material and another set for thermal cycles.

The dimensions of the test samples must comply with the standard “EN 12372 Natural stone test methods - Determination of bending strength under concentrated load”, that is, they must be determined according to their thickness. Namely,

• The thickness should be between 25 mm and 100 mm and should be greater than twice the size of the largest grain in the stone.
• The total length should be equal to six times the thickness.
• The distance between the support rollers 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.

To ensure that measurements of the dynamic elastic modulus or ultrasonic pulse velocity before and after the thermal shock test are made at the same points, indelible marks in the form of dots are made on the corresponding surfaces of the samples to indicate the location of the transmitter and receiver. Indelible lines are drawn to indicate the location of the axes of the two supports on which the samples will be placed during the determination of the dynamic elastic modulus and ultrasonic pulse velocity.

The samples are dried for one week in a ventilated oven at 40 degrees plus/minus 5 degrees and then cooled to ambient temperature at 20 degrees plus/minus 5 degrees before the start of the cycles.

Prior to cycling, samples subjected to cycles are measured according to one or more of the following non-destructive tests, depending on the test selected to assess the change in performance:

• Dynamic modulus of elasticity according to EN 14146 standard.
• Ultrasonic pulse velocity according to EN 14579 standard.
• Open porosity according to EN 1936 standard.

The dried samples are subjected to temperature changes according to the following procedure: 70 hours plus/minus 5 hour in a ventilated oven at 18 degrees plus/minus 1 degrees, immediately followed by 20 hours plus/minus 5 hours completely immersed in tap water whose temperature before immersion of the samples was 6 degrees plus/minus 0,5 degrees.

In both the oven and the water vessel, the samples are placed on supports at least 50 mm apart from each other and from the wall. In the water vessel, the samples are placed on supports at the bottom of the vessel filled with tap water so that the water level above the samples is 60 mm plus/minus 10 mm. The procedure described above constitutes one cycle. If the test is to be interrupted at any time other than during the test, the samples shall be immersed in water at 20 degrees plus/minus 5 degrees.

After the 20th cycle, the samples are dried at 70 degrees plus/minus 5 degrees to constant mass. Constant mass is reached when the difference between the two weighings at an interval of 24 hours plus/minus 2 hours is not greater than 0,1 percent of the first of the two masses. They are then visually inspected and compared with reference samples. All changes are recorded.

One or more non-destructive tests are performed:

• Dynamic modulus of elasticity according to EN 14146 standard.
• Ultrasonic pulse velocity according to EN 14579 standard.
• Open porosity according to EN 1936 standard.

Finally, the flexural strength test is performed on dried reference samples and samples subjected to thermal cycles according to EN 12372. This standard includes a test method for determining the flexural strength under concentrated load for natural stone.

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 14066 Natural stone test methods - Determination of resistance to aging by thermal shock".