Rheology and vibration of fresh concrete: Predicting the radius of action of poker vibrators from wave propagation

• Published in: Cement and concrete research 2011-09, Vol.41 (9), p.932-941
• Main Authors: Banfill, P.F.G., Teixeira, M.A.O.M., Craik, R.J.M.
• Format: Article
• Language: English
• Subjects: Applied sciences; Bingham model; Buildings. Public works; Concretes; Concretes. Mortars. Grouts; Effectiveness; Exact sciences and technology; Fresh concrete (A); Liquefied; Materials; Mathematical models; Properties and performance of fresh concrete; Rheology (A); Shear; Vibration; Vibration (A); Vibrators; Wave propagation
• ISSN: 0008-8846; 1873-3948
• DOI: 10.1016/j.cemconres.2011.04.011

The compaction of fresh concrete by an internal poker vibrator has been analysed using closed-form solutions for the propagation of the shear and compressive waveforms, assuming that concrete conforms to the Bingham model. In the inner liquefied zone around the vibrator the flow is due to shear whereas in the outer unsheared zone propagation is due to compressive waves. The analysis gives a method of predicting the radial position at which the flow changes, which coincides with the radius of action of the vibrator. Theory and experiment agree well and confirm that the peak velocity of the vibration governs its efficacy, with radius of action increasing with increasing velocity. The radius of action increases with decreasing yield stress and with increasing plastic viscosity. The work offers the potential to optimise the design and use of vibrators.