Measuring the change in ultrasonic p-wave energy transmitted in fresh mortar with additives to monitor the setting

Research on ultrasonic methods to monitor the setting of concrete has mainly focussed on the wave velocity as a useful quantity. To investigate the application of also the wave energy as a parameter, an experimental program was set up to apply the ultrasonic wave transmission technique on several mortar samples containing air entrainer, blast-furnace slag or fly ash causing clearly different setting behaviour. The increase of the relative energy E/Eref during setting is generally retarded if ordinary Portland cement is replaced by blast-furnace slag or fly ash. The mixtures with cement of a lower strength class or with large air content were difficult to test with the energy measurements since they were more sensitive to poor sensor contact due to shrinkage. For the other samples, the thresholds E/Eref = 0.02 and 0.13 are proposed to easily determine respectively initial and final setting based on the ultrasonic energy measurements.