Quantitative analyses of ageing status of dam concrete for a 25-year-old dam

In order to evaluate the aging status of the dam concrete for a 25-years-old concrete dam, the internal concrete and surface layer of the dam were tested by elastic wave computerized tomography (CT) and spectral analysis of surface wave (SASW). Also mechanical strength and elastic wave velocity were tested for the concrete cores from the dam. The CT results show that the elastic wave velocities of the three dam sections are basically around 4400~4500m/s and no obvious low-speed zone could be detected, indicating the quality of the internal concrete is good without aging signs. The SASW results show that the Rayleigh wave velocity of the surface layer (deeper than 25cm) is about 2500 m/s (the corresponding P wave velocity is 4500 m/s) which is basically consistent with the CT results. The average compressive strength of the concrete cores is over 40 MPa (higher than the design values) while the elastic wave velocities are between 3600 and 4400 m/s. Microstructural analysis results show that the a few microcracks could be observed in all the 16 cores from the upstream, the downstream, the gallery and the spillway. The overall results indicate that the dam concrete is of good quality and no obvious aging signs could be found.