Development of Procedures for Nondestructive Testing of Concrete Structures. Report 2. Feasibility of Sonic Pulse-Echo Technique

摘要

A sonic pulse-echo system has been developed that will measure the length of long, thin concrete members such as piles and detect discontinuities within the members. A longitudinal pulse is introduced into the concrete at a surface by mechanical impact, and the echo time is measured using the time base of an oscilloscope. The velocity of the longitudinal wave is determined initially on a known length of similar concrete. In situ pile lengths up to 70 ft have been measured successfully in soil with low damping characteristics. The system successfully measured the lengths of three drilled piers and detected the location of flaws in the piers incorporated by design at the University of Texas at Austin. Measurements of thin slabs were found to be more difficult than measurements of piles. Because reflections of echoes in thin sections are of much higher frequency, elastic pulses containing higher frequencies must be introduced into the concrete. Research should continue in an effort to provide a pulse-echo system that will be capable of nondestructive evaluation of all geometries of Civil Works structures. An ultrasonic unit of low frequency and high energy level should be designed to improve resolution above that of a sonic system for thin sections.