The positive effects of power ultrasound on Portland cement pastes and mortars; a study of chemical shrinkage and mechanical performance

The influence of the direct application of power ultrasound (PUS) on the pore solution of Portland cement (PC) pastes was previously found by the authors to increase the aluminium concentration in the pore solution. The evidence of increasing the aluminate and carbonates in the pore solution was observed. In the present work, the effect of PUS on the rate and extent of PC hydration was followed by measuring the chemical shrinkage using an automated dilatometry method. Additionally, the compressive and flexural strength of the PC mortars were evaluated over 91 days. The results showed an increase in the rate of chemical shrinkage when both 26 and 132 kHz frequencies were applied to the cement paste for 2 min, soon after mixing. Sonicating at the higher acoustic power intensity of 26 kHz resulted in a higher rate of both compressive and flexural strength development for mortars over 91 days of curing in water. The addition of aggregates to the pre-sonicated paste was found to lead to 17% increase in the flexural strength of mortars at 28 days, indicating a possible modification of the paste-aggregate interface.