It was found that the superplasticiser (PCE) reduces the yield stress and plastic viscosity
of modified Portland cement paste more effectively than the plasticiser (LS) and the superplasticiser (MAP).
Hydration reactions tend to influence the viscosity results of ordinary and blended pastes because hydration generally increases both yield stress and plastic viscosity
. Hydration mostly increases plastic viscosity
only insofar as it increases the volume fraction of solid material .
* Corresponding Author E-mail: email@example.com Table 1: Matlab Code Input Data Parameter Value or Range Unit Mud weight, [rho] 8.5-12.5 ppg Mud plastic viscosity
, [[mu].sub.p] 15-55 Mud yield point, [Y.sub.p] 5-200 Ib/100sq.ft Well depth, h 6000-15000 ft Hole size, [d.sub.h] 7.875-9.875 inches Drillcollars-to-drillpipe ratio 0.0345-0.1538 fraction Drill pipe size (ID,OD) 3.826, 4.5 inches Drillcollars size (ID,OD) 2.813, 6.75 inches Drill string tripping speed 0-18 ft/sec Formation pore fluid pressure gradient 0.45 Psi/ft Formation fracturing pressure gradient 0.67 Psi/ft Poisson's ratio 0.25 fraction
The higher sand content increases the yield stress and plastic viscosity
of mortar due to confinement of some mixing water and enhanced interaction of sand particles, and thus destroys certain amount of the air-voids (Banfill 1994; Sa fiuddin 2008).
The intercept, Y(N * m), and the slope, V(N * m * s), of this line were considered to be related to yield stress and plastic viscosity
where [tau], shear stress, Pa; [t.sup.0], yield stress of the cement paste, Pa; [[mu].sub.pl], plastic viscosity
of the cement paste, Pa x s; [gamma], shear rate, [s.sup.-1].
The reduction in plastic viscosity
is connected, first of all, with release of the immobilized water and with the increase, in this regard, in the relative of the dispersive medium.
where T is the shear resistance of a sample measured at rotation rate N and g (N.mm) and h (N.mm.s) are constants corresponding respectively to yield value [[tau].sub.o] and plastic viscosity
Key words: concrete rheometers; dissipative particle dynamics modeling; plastic viscosity
The plastic viscosity
model has been further enhanced to extend the range of processing conditions.
For example, the yield stress ([[tau].sub.y]) and the plastic viscosity
([[eta].sub.p]) can be obtained from the measurement of the mini slump flow test :
One feasible approach to address this limitation is to indirectly estimate the pumpability through rheological properties of fresh materials, namely, yield stress and plastic viscosity
of the Bingham model (or equivalent).