The Impact-Echo(IE) method has been used to evaluate the integrity of concrete structures. In this method, the P-wave speed of concrete is a crucial parameter in determining the thickness of concrete lining, the location of cracks or other defects. In many field applications of the IE method, the P-wave speed is determined from cores or by performing a test on a portion of the structure having known dimensions and no flaws. Occasionally, however, cores can not be obtained in specific structures as like tunnel linings, and the P-wave speed determined from core testing may not be a representative value of the structure. Another method for determining P-wave speeds in concrete is by obtaining the travel time between two points along the surface of a structure. The measured P-wave speed, however, is the P-wave speed of concrete not in the whole thickness of a structure but along the surface of a structure and this method also needs a very accurate data-acquisition equipment.
Spectral Analysis of Surface Wave (SASW) method which is nondestructive and nonintrusive was used for determining P-wave speed of concrete. This method is based on the dispersive characteristic of surface waves. The variation in surface wave speeds along the whole thickness of a concrete structure is determined and the P-wave speeds can be converted from the surface wave speeds with the Poissons ratio of the concrete.
In this paper, the feasibility of IE-SASW method, which combined two nondestructive testing methods, was investigated. IE method was used for the detailed nondestructive evaluation of concrete whereas SASW method was employed for the measurement of the average P-wave speed and for the status evaluation of concrete. Numerical analyses were carried out to investigate the effectiveness and the limitations of the proposed IE-SASW method. Several model slabs of known dimensions, which contain various types of defects or inclusions, were constructed and IE-SASW tests were performed to evaluate the feasibility of the proposed method. Based on both experimental and numerical studies, the feasibility of the proposed method was verified, showing a great potential in the nondestructive evaluation of concrete.
