| Popis: |
A variety of studies were performed using existing and newly proposed techniques and instrumentation to further the understanding of nondestructive testing of concrete. A new combined stress wave propagation method was developed that combined the existing methods of the spectral analysis of surface waves, impact echo, and free-free resonant column experimental and analysis techniques. The method was used to determine the stiffness profile and location of embedded voids in a concrete tunnel lining modeled as a three layer concrete slab. A new equation was proposed that predicted the level of damage of concrete samples based on the functions of the change in first mode longitudinal frequency and the absorption of energy during cyclic loading to failure. During this study, new instrumentation was developed that aided in the dynamic stiffness measurements during the cyclic loading. A comparison of the static and dynamic Young’s modulus was performed. It was found that the ratio of these two moduli depend on a concrete’s strength and damping properties as well as the age of the specimen. A new equation was proposed using these three properties to determine the ratio of static to dynamic Young’s modulus. An experimental program was performed on samples of high performance self-consolidating concrete (HPSCC). The HPSCC exceeded expected values of strength and stiffness over that of regular high performance concrete. Finally, a comparison of prestress losses in prestressed bridge girders fabricated using the HPSCC was conducted. Prestress losses were measured and calculated using the American Association of State Highway and Transportation Officials (AASHTO) LRFD 2004 and 2007 Specifications. It was determined that the AASHTO LRFD 2007 Specifications most accurately predict the measured prestress losses. |
