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Two main properties of cementitious mortar and concrete are most important, i.e. rheology and setting and hardening. Rheology determines workability and compaction ability. Setting determines the end of workability and hardening is responsible for strength gain and stiffness development. Rheology and setting are measured in practice by rather conventional methods, which do not lead to a continuous monitoring of properties as a function of age. A testing device was developed which utilizes the velocity of ultrasound (US)-waves in order to continuously monitor the setting and hardening of cementitious materials. Two development steps are emphasised, i.e. the design of the container and the exact determination of the transmitted US-pulse. It was shown that the method leads to very reproducible results. While the beginning of setting can be determined from the velocity vs. age of mortar curve by a mathematical …