Investigation on characteristics of internal structure of early-age concrete by non-destructive testing

Non-destructive methods such as ultrasonic wave, impact echo, and ground penetrating radar were used to study the internal structure of early-age concrete. The results indicate that the ultrasonic, stress, and electromagnetic wave velocity can reflect well the variation of the internal structure in concrete. With the influence of cement hydration, it is obvious that the three wave velocity increases and the dielectric constant decreases in the first 28 days. However, the changing of these characteristics tends to slow down with cement hydration. Results of compressive strength tests show that the combination of the three methods can accurately probe changes in the internal concrete structure at early ages. In addition, structural defects and the above steel bars in reinforced concrete were also investigated using ground penetrating radar together with the impact echo method.