抄録
It is known that the ultimate strain of the concrete within some range of compressive strength is almost 2000 to 2500 micro strain. This means that if the Young's modulus of concrete at a certain strain state is given, the ultimate compressive strength can be estimated by using measured Young's modulus within some accuracy allowance. Through the theoretical consideration and field examination, it is found that the mechanical impedance of the contact surface between hammer and concrete indicates the Young's modulus of the concrete if it is taken into account during reactive phase of the hammer blow. The mechanical impedance can be calculated by dividing the maximum force, when the hammer collides the concrete surface, with the initial velocity of the hammer rebound. This fact simplifies the mechanical impedance measurement process, i.e., the maximum force and rebound velocity can be calculated by using acceleration wave form. This paper shows the theoretical background of the reactive mechanical impedance measurement and the results of laboratory and field tests on the compressive strength estimation of the concrete. The results of field tests show the accuracy of this method is within 15% for the normal concrete of fifteen to forty N/mm^2 strength range.
