*3.1.4 Brick freeze resistance tests for 25 cycles*

According to ČSN 722609 technology of brickmaking, the samples selected for frost resistance tests were first saturated with boiling. Then the resonant oscillation frequencies were measured again. This was followed by alternating freezing and thawing for 25 cycles in an automatic freezing device including the calculation of the so-called relative dynamic modulus of elasticity.

From the results, it is evident that practically all samples passed on frost resistance after 25 cycles, only in sample N 3 found anomalies in the longitudinal resonance frequency. It was a sample that resulted in a greater decrease in resonance frequencies in the saturated state, which can predict a certain disorder in the internal structure. In addition, the samples were dried and subjected to a tensile strength test for bending and strength in pressure.
