GB/T 9966.12-2021Test methods for natural stone—Part 12:Determination of static elastic modulus (English PDF)

5.1 Number of Samples

Prepare at least 6 specified test specimens in the same batch of test samples.

5.2 Sample Size

The sample dimensions are a cuboid of 50 mm × 50 mm × 100 mm or a cylinder with a diameter of 50 mm and a height of 100 mm.

Deviation ±1.0 mm. If the largest crystalline particle size in the sample is greater than 5 mm, the side length or diameter of the sample should be adjusted to the largest particle size.

The sample height is 10 times the side length or diameter, and the sample height is twice the side length or diameter.

5.3 Length Deformation Test Dimensions

The test length should be the side length or diameter of the sample, as shown in Figure 1.

5.4 Sample Surface

The flatness of the stress-bearing surface of the specimen should be less than 0.1 mm, and the deviation from the perpendicular axis of the specimen should be less than 0.01 rad or not exceeding 0.01 mm per 100 mm.

The sample should be less than 1 mm thick. The sides of the sample should be smooth, without any irregular protrusions, and the straightness deviation should be within 0.3 mm.

To meet the above requirements, the samples may be machined using a lathe or surface grinding. Only when machining is insufficient will a method be used that conforms to the specifications.

The cement grout of 52.5R as specified in GB 175 should be used to smooth the sample and allowed to harden sufficiently, and this should be clearly stated in the test report.

If the specimen has anisotropic surfaces, the specimen axis should be perpendicular to the principal anisotropic surface. Further testing should be conducted on the directions of the remaining anisotropic surfaces.

For testing, a set of specimens of the same size and surface should be prepared as required and noted in the test report. Two [test specimens] should be applied to the specimen. Parallel lines clearly indicate the direction of anisotropic surfaces.

5.5 Sample preparation

The sample was dried in a drying oven at (65±5)°C for 48 hours, and then placed in a desiccator to cool to room temperature.

One of the samples was selected as the prediction sample, and at least two length deformation test sensors were attached to each of the other five samples.

Parallel to the sample axis, the installation position is the center of the sample side (see Figure 1).

6.1 Determination of Specimen Dimensions

Use vernier calipers to measure the dimensions of the top and bottom surfaces of each sample. For square surfaces, measure the side length along the center line; for circular surfaces, measure the side length along the center line.

Two diameters, accurate to 0.1 mm. The area of each specimen's cross-section is calculated using the average of four measurements. The axis of each specimen is measured. The height of the line is accurate to 0.1 mm.

6.2 Determination of High and Low Pressures in the Test

According to the test method of GB/T 9966.1, the predicted maximum failure pressure of the specimen was tested, and the results were obtained at 2% and 33% of the maximum failure pressure, respectively.

The low and high pressure values will be used as the basis for the following tests.

6.3 Cyclic Load

Place the sample in the center of the material testing machine, ensuring full contact between the upper and lower trays and the sample. Connect the length deformation sensor to the measuring system.

The system was debugged and tested to reach its optimal testing state.

The sample was loaded at a pressurization rate of (0.5 ± 0.2) MPa/s, and when the specified high pressure value was reached, it was then loaded at a further pressurization rate of (0.5 ± 0.2) MPa/s.

The pressure is reduced by unloading the sample at a certain rate. When the specified low pressure value is reached, the sample is then loaded again at the same rate until the high pressure value is reached. Then, the pressure is reduced by a certain rate.

The pressure reduction rate is reduced to a low pressure value.

6.4 Deformation Measurement

Keep the low pressure value constant and let it stand for 30 seconds (point A in Figure 2). Record the deformation coefficient (epsilonu) and low pressure (sigmau) at this time. Apply pressure to the sample at a rate of (0.5 ± 0.2) MPa/s until the high pressure value is reached, maintain the high pressure value, and let it stand for 30 seconds (point B in Figure 2). Record this value. The deformation coefficient (epsilono) and high pressure (sigmao) at that time.

After completing the test at point B, apply pressure according to GB/T 9966.1 until the specimen fails, and record the maximum failure pressure. If the specimen... If the deviation between the compressive strength and the predicted compressive strength of the specimen is greater than 20%, it should be stated in the test report.