Workability of cement suspensions

Using power ultrasound to improve cement suspension workability

Photo: www.hielscher.com

Fig. 1 Ultrasonic processor.Abb. 1 Ultraschall-Gerät.

Photo: www.hielscher.com

Fig. 2 Air void ratios of cement suspensions 20 minutes after water addition depending on w/c ratio and power ultrasound application.
Abb. 2 Luftporengehalte von Zementsuspensionen 20 Minuten nach Wasserzugabe in Abhängigkeit vom w/z-Wert und der Leistungs-Ultraschall-Applikation.

Fig. 3 a+b Air void distribution in hardened cement paste samples (w/c = 0.40; 7-day hydration).
Abb. 3 a+b Luftporenverteilung in erhärteten Zementsteinproben (w/z = 0,40; 7 d Hydratation).

Fig. 4 Slump flow of cement suspensions 15 minutes after water addition depending on w/c ratio and power ultrasound application.Abb. 4 Setzfließmaße von Zementsuspensionen 15 Minuten nach Wasserzugabe in Abhängigkeit vom w/z-Wert und der Leistungs-Ultraschall-Applikation.

Fig. 7 a+b Determination of the dispersing effect of power ultrasound by a sedimentation test.
Abb. 7 a+b Bestimmung der dispergierenden Wirkung von Leistungs-Ultraschall mittels
Sedimentationstest.

 In the field of concrete technology, the concept of workability describes that property of concrete that determines the ease and homogeneity with which it can be mixed, placed, consolidated and finished (cf. ACI 116R-90). Workability is thus a generic term used to refer to individual „stages“ of the process of producing fresh concrete. Consistency is crucial in this regard because it influences, for instance, mixing times, the degree of pumpability or required compacting work. The results outlined in this article demonstrate that power ultrasound (PUS) is not only an attractive method for accelerating setting and hardening processes but can also positively influence properties relevant to workability.

Acoustic vibration in the range from 20 to 100 kHz is termed ultrasound [1]. The term power ultrasound is used if the energy density of these sound waves exceeds the intensity threshold of 1 W/cm². As a result of this high energy density, items subjected to ultrasound may be destroyed or altered in a targeted fashion [2]. In a fluid, the application of PUS causes cavitation, which is the formation and implosion of voids in fluids due to pressure variations. This phenomenon is considered the most important effect caused by ultrasound [3]. It is assumed that the vigorous implosion of the...