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F. de Larrard
Laboratoire Central des Ponts et Chaussées (LCPC), Paris, France;
Guest researcher at National Institute of Standards and Technology (NIST),
Gaithersburg, Maryland, USA
C.F. Ferraris
NIST, Gaithersburg
T. Sedran
LCPC, Paris
Some preliminary results of an experimental program on the rheological
behavior of fresh concrete are presented. In the rheological tests, performed
with a plane-to-plane rheometer, it appears that the relationship between
torque and rotation speed is not exactly linear. The fresh concrete behavior
is better described by the Herschel-Bulkley model: 
=
'0 + a 
b
; and
are the shear stress and the strain gradient applied to the specimen,
respectively. '0, a and
b are
three material parameters describing the concrete behavior. Among other
advantages, this new description avoids the problem of negative yield stress
encountered with the Bingham model.