In order to develop a non-destructive in-situ testing for strength of concrete, Ultrasonic Contact Impedance (UCI) method was modified and verified with experimental data. The conclusions are below.
1. Because the Young's modulus of concrete is changing with age, it is necessary to measure the Young's modulus of concrete at that age in order to estimate the strength of concrete by UCI method.
2. It is possible to estimate the young's modulus by UCI method, using steel plate of 0.2 mm thickness between material and Vickers diamond.
3. There is a high correlation between measured hardness and strength of concrete.
4. This modified UCI method has some possibility of being a micro-destructive in-situ testing for strength and Young's modulus of concrete.
