The early setting is
usual measured with the penetrometer or the Vicat apparatus. This
kind of measurement has some disadvantages. In the early sixties some
researchers suggested to use the ultra­sonic transition time as
method for measuring the setting of mortars or fresh concrete. In
cooperation with a German dry mix company, Schleibinger developed a
special ultrasonic unit with an integrated datalogger and a special
designed setup for the mortar specimen.

Measurement Principle

Fresh mortar is
setting between two ultrasonic transducers, which are supplied with
0.25s or less pulses per second at a frequency of 54 kHz. The mortar
changes, according to the setting, the ultrasonic transition time.
From the beginning of first contact of the growing binder-stone, the
ultrasonic sound speed increases. If there is a complete crystalline
structure the change of the sound speed will be slower. Until the a
further aggregation of the cement stone it increases again.

Measurement Setup

Each measurement cell
is supplied with a pair of ultrasonic transducers. The Vikasonic
continuously measures the ultrasonic transition time and the signal
damping. The data sets are recorded digitally to a common USB stick.
Also the sound speed and the elastic modulus is calculated and
recorded. Additionally the temperature inside the specimen is
measured with a type K thermocouple.