DYNAMIC TESTING AT THE AASHO ROAD TEST

The road vibration machine was recently employed to measure pavement properties of the AASHO road test in northern Illinois. Dynamic measurements were made on pavement sections ranging in thickness from 11 to 19 inches, over a frequency range from 8 to 2500 cycles/second. These measurements showed that: the stiffness of asphalt pavements is greatly influenced by seasonal changes; softening of the subsoil is the main factor influencing the reduction of stiffness during spring breakup; when the quality of base anda subbase is impaired, pavement failure is imminent; the critical stiffness level for satisfactory performance is approximately 100 ton/cm; and seasonal recovery seems to take place, but its magnitude needs further investigation.