The personal meeting and after this the contact with personalities such as G. Dawance, R. H. Elvery, I. Facaoaru, R. L'Hermite, R. Jones, E. Pohl, etc. exercised a very significant influence on the author and his activity! At the boundary of two centuries, the author takes the opportunity to strike the balance of his activity. Out of consideration remain his contributions to the execution of the first bridges in prestressed concrete abroad, and with that, closely connected innovations. Not mentioned are the limitations/corrections he has brought for the use of some well known structural calculation methods (e. g. Säger: Schiefe Biegung mit Normalkraft, Homburg/Marx: Schiefe Stabe).

The author was the first establishing the influence of curing conditions of concrete on the relations between nondesctructively measured values, ultrasonic pulse velocity or attenuation are rebound indices (V, A, R) and its compressive strength. Since 1969 he has been behind a new approach for simultaneous use of NDT (V, A, R) to determine the compressive strength of concrete. The advantages of this multiple correlation concept (an off- spring of an original method for statistical quality analysis for the control of concrete quality) have been already well documented.

The author established also a new criterium for the frost resistance of concrete, based on the variation of the logarithmic decrement of the vibrations (both, free or forced) for the concrete subject to freezing. His main conclusion is that if the aggregate is not resistant to freezing, neither cement quality or increasing the amount of cement not the air entraining agents can prevent destruction of the concrete by frost action.

On the Fotokina Exhibition in Cologne, October 3-10, 1990, the author and his collaborators presented an original"pressure-chamber". With a video camera and a monitor, it was possible for the first time to follow the process of crystallization in cement suspensions at high temperatures (ca. 200° C).