LABORATORY VELOCITIES AND ATTENUATION OF P-WAVES IN LIMESTONES DURINGFREEZE-THAW CYCLES

The velocity and the attenuation of compressional P-waves, measured in the laboratory at ultrasonic frequencies during a series of freezing and thawing cycles, are used as a method for predicting frost damage i n a bedded limestone. Pulse transmission and spectral ratio techniques are used to determine the P-wave velocities and the attenuation value s relative to an aluminum reference sample with very low attenuation. Limestone samples were water saturated under vacuum conditions. jacket ed with rubber sleeves, and immersed in an antifreeze bath (50 percent methanol solution). They were submitted to repeated 24-hour freezing and thawing cycles simulating natural environment conditions. During t he freeze/ thaw cycles, P-wave velocities and quality factor Q diminis hed rapidly in thawed rock samples, indicating modification of the por e space. Measurements of crack porosity were conducted by hydrostatic compression tests on cubic rock samples that had been submitted to the se freeze/thaw cycles. These measurements are used as an index of crac k formation. The hydrostatic compression tests confirmed the phases of rock damage that were shown by changes in the value of Q. Furthermore , comparisons between Q values and crack porosity demonstrated that th e variations of P-wave attenuation are caused by the creation of new c racks and not by the enlargement of pre-existing cracks.