During the compression test, what is the size of the square that is isolated for tapping?

• A. 30 x 30 cm
• B. 20 x 20 cm
• C. 40 x 40 cm
• D. 10 x 10 cm

Answer: (A)

In a compression test, you isolate a square area to tap so you can verify the specimen is seated evenly and the load will be transmitted through a uniform contact surface. The 30 x 30 cm size is chosen because it’s large enough to give a clear tapping signal and to cover small surface irregularities, yet small enough to stay within the central region of the platen and avoid edge effects. A much smaller area might miss misalignment or defects, while a larger area could reach towards the edges and introduce edge effects that distort the reading. So 30 x 30 cm is the practical, standard choice.