GB/T 9966.2-2020Test methods for natural stone—Part 2:Determination of dry,wet and after freezing flexural strength (English PDF)

4.1 Specifications

Method A. 350mm × 100mm × 30mm, or a sample with actual thickness (H) can be used. The sample length is 10H + 50mm, and the width is... The width is 100 mm. Method B. 250mm × 50mm × 50mm.

4.2 Deviation

The sample length deviation is ±1 mm, and the width and thickness deviations are ±0.3 mm.

4.3 Surface Treatment

The upper and lower stress surfaces of the specimen should be sawed, ground, or polished to achieve flatness and parallelism. The sides can be sawn, and the angle between the front and side surfaces should be... It is 90° ± 0.5°.

4.4 Stratification Marking

For specimens with stratification, the stratification direction should be marked on the specimen with two parallel lines, as shown in Figures 3, 4 and 5.

4.5 Surface Quality

The specimen should be free from defects such as cracks, missing edges, and missing corners that could affect the test.

4.6 Pivot Marking

Mark the positions of the support points on the top and bottom surfaces and the front and back sides of the specimen (see Figures 1 and 2). The span (L) of the lower support in Method A is... Method B has a lower support span (L) of 200 mm, with the upper support located at the center. The distance between the upper supports is 5H, and they are centrally symmetrically distributed. Location.

4.7 Number of Samples

Each test condition requires five specimens per layer for each bedding direction. Typically, the stress direction of the specimens should be aligned with the actual stress direction.

Consistent with practical applications, if the application direction of the stone is unknown, tests should be conducted simultaneously in three directions, with 15 samples prepared for each test condition. Five pieces in each direction.

5.1 Dry bending strength

5.1.1 Dry the sample in a forced-air drying oven at 65°C±5°C for 48h, and then place it in a desiccator to cool to room temperature.

5.1.2 Select the appropriate specimen support according to the test type, and adjust the distance between the supports to the specified span requirement. Follow the markings on the specimen.

The fulcrum should be positioned between the upper and lower supports, and the stress-bearing surfaces of the specimen and supports should be kept clean. The decorative surface should be placed downwards on the lower support of the bracket.

During the loading process, the decorative surface of the sample is in a state of bending and tension.

5.1.3 Apply a load to the specimen at a rate of 0.25 MPa/s ± 0.05 MPa/s until the specimen fails, and record the location and mode of specimen failure. Maximum load value (F), reading accuracy not less than 10N.

5.1.4 Measure the width (K) and thickness (H) of the fracture surface of the specimen with vernier calipers, accurate to 0.1 mm.

5.2 Water-saturated flexural strength

5.2.1 Place the samples upright in a constant temperature water bath, with a minimum spacing of 15 mm between samples, and use cylindrical supports at the bottom of the samples. Add tap water.

(20°C±10°C) Add water to half the height of the sample, let stand for 1 hour; then continue adding water to three-quarters the height of the sample, let stand for 1 hour; then continue adding water to fill the sample completely.

Water, the water level should be 25 mm ± 5 mm above the height of the sample.

5.2.2 After soaking the sample in clean water for 48 h ± 2 h, remove it, wipe off the surface moisture with a wrung-out damp towel, and immediately proceed according to 5.1.2 to 5.1.4 Conduct a bending strength test.

5.3 Bending strength after freeze-thaw cycles

5.3.1 Place the specimens upright in a constant temperature water bath, with a spacing of not less than 15 mm between specimens, and use cylindrical supports at the bottom of the specimens. Add tap water.

(20°C±10°C) Add water to half the height of the sample, let stand for 1 hour; then continue adding water to three-quarters the height of the sample, let stand for 1 hour; then continue adding water to fill the sample completely.

Water should be used, with the water level 25 mm ± 5 mm above the sample height. The sample should be soaked in clean water for 48 h ± 2 h before being removed.

5.3.2 Immediately place the samples in a freezer at -20°C±2°C for 6 hours, ensuring a distance of not less than 10 mm between samples and a distance between the sample and the freezer wall.

Not less than 20 mm. After removing it, place it in a constant temperature water bath for 6 hours to thaw. The temperature of the constant temperature water bath should be maintained at 20°C±2°C. Repeated freezing and freezing.

After 50 melting cycles, wipe the surface moisture of the sample with a wrung-out damp towel, observe and record the changes in appearance, and then immediately press... 5.1.2 to 5.1.4 Conduct bending strength tests.

5.3.3 When using an automated freeze-thaw testing machine, the sample should be flipped over every 14 cycles. (Freeze-thaw test process...)

If an abnormal interruption occurs during the process, the sample should be immersed in clean water at 20°C±5°C.

6.1 Method A

Bending strength is calculated according to formula (1).

6.2 Method B

Bending strength is calculated according to formula (2).