Ultrasonic Testing for Evaluation of Stabilized Mixtures

Tests were conducted to evaluate the feasibility of using ultrasonic testing for stabilization applications. The ultrasonic testing consisted of determining primary-wave (P-wave) velocities of stabilized mixtures. The ultrasonic method involves a simple and fast test procedure that allows for repeated assessment of a sample over time. For the testing program, tests were conducted on a high plasticity clay stabilized with lime, cement, and fly ash and a Type F fly ash stabilized with lime and cement. Compaction characteristics of the mixtures were determined using modified Proctor tests. Unconfined compression tests were used to determine compressive strength and modulus of the mixtures immediately after sample preparation and after 7-day and 28-day curing periods. Ultrasonic tests were conducted on the compaction and compression test samples, and the test results were correlated. Variation of velocity with water content demonstrated a similar trend to the variation of dry density with water content for the soil. The velocity increased with increasing density for both soil and fly ash. For compression characteristics, velocity increased with increasing modulus for both soil and fly ash. The velocity correlated well with the unconfined compressive strength of fly ash samples. However, this trend was not as well defined for the soil. Overall, the test program demonstrated that ultrasonic testing can be used effectively to evaluate stabilized materials. P-wave velocity correlations can be used to verify the quality of field placement of stabilized mixtures and to improve mixture design procedures.