EN 12371 Natural Stone Test Methods - Determination of Frost Resistance

A European standard, "EN 12371 Natural stone test methods - Determination of frost resistance", describes a method used to assess the effects of freezing and thawing cycles on natural stones. In the use of this standard, the terminology is "EN 12670 Natural stone - Terminology" and the nomenclature is "EN 12440 Natural stone - Nomenclature".

Frost resistance is an important parameter for the durability of unbound natural stone in a cold environment. The resistance to freezing and thawing in a given environment depends on the porosity of the stone, its moisture content and the possible presence of dissolved salts.

The EN 12371 standard includes guidelines for both a shorter technological test (Test A) and an identification test (Test B) to assess the effect of freezing and thawing cycles on the relevant performance characteristics. As defined in the EN 12440 standard, some marbles undergo changes in their physical properties as a result of the test conditions rather than the freezing and thawing cycles. In these cases, additional tests (e.g. the standard “EN 14066 Test methods for natural stone - Determination of resistance to thermal shock ageing”) must be applied.

The frost resistance of natural stone units is determined by a test method that consists principally of cycles of freezing in air and thawing in water.

The main equipment used in these tests includes:

• A freezing tank with the capacity to hold the required number of samples and possibly an automatic control system to program the freezing and thawing cycles within the chamber with a tolerance of plus/minus 2,0 degrees. If a suitable automatic system is not available, the tests can be performed manually.
• A temperature recording system that can measure temperature to 0,1 degrees.
• A device that measures the dynamic elastic modulus in accordance with the standard “EN 14146 Natural stone testing methods - Determination of dynamic modulus of elasticity (by measuring the fundamental resonance frequency)”.
• A weighing instrument accurate to at least 0,01 percent of the mass to be weighed.
• A ventilated oven that can maintain a temperature of 70 degrees plus/minus 5 degrees.

Sampling is not the responsibility of the testing laboratory unless specifically requested. For technological tests, the number of samples must comply with the relevant standard (also included in the table provided in the standard). Two sets of samples are required, one tested after freezing and thawing cycles, the other without freezing and thawing cycles. Each set is randomly selected from the stone body to be tested. In addition, one extra sample is used to monitor the temperature of the samples. For an identification test, seven samples are selected that are considered representative of the stone body being tested. One of the seven samples is used to monitor the core temperature.

The size of the samples should be:

• Technological test (Test A): When this test is performed to determine the effect of freezing and thawing cycles on performance characteristics, the samples must comply with the relevant standard. The relevant standards are EN 12372 or EN 13161 for flexural strength, EN 13364 for dowel hole breaking load, EN 14066 for resistance to thermal shock and EN 1926 for compressive strength.
• Identification test (Test B): Specimens are rectangular prisms with dimensions of 50 mm × 50 mm × 300 mm. The long axis should be parallel to the anisotropy planes.

Initial defects and all irregularities should be marked on the samples with indelible marks. To ensure that the various dynamic elastic modulus measurements before and after the freezing and thawing cycles are made at the same points on the samples, indelible marks in the form of dots should be made on the corresponding surfaces of the samples. During the determination of the dynamic elastic modulus (in bending mode), an indelible line is drawn through the point of the axis of the two supports on which the samples will be placed.

A sample shall be equipped with a device (e.g. a thermocouple) to measure the temperature of the sample during freezing and thawing cycles. The device shall be placed in a hole drilled parallel to the long axis of the sample. The diameter of this hole shall be compatible with the diameter of the device. The centre of the hole shall be equidistant from the edges of the sample and shall be at least 50 mm deep from the top. If cubes are used, the hole shall be 25 mm plus/minus 5 mm deep. The device shall be placed in the hole, which shall then be sealed to prevent water penetration.

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 12371 Natural stone test methods - Determination of frost resistance".