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3.1 Concrete Test Data

The fresh concrete measurements are summarized in Table 2. The flow curves obtained from truck measurements are shown in Figs. 4 and 5, while the flow curves obtained from the ICAR rheometer are shown in Figs. 6 and 7. The values of the yield stress and plastic viscosity are deduced from these flow curves, as described by the Bingham model, by calculating the intercept of the linear fit for the yield stress and the slope as the plastic viscosity.

Fig. 5. Flow curves obtained with the truck mixer (C20 to C23 mixtures).

 

Table 2. Fresh concrete measurements

Truck Measurements ICAR Rheometer
Mixture Slump Yield Plastic Yield Plastic Stress
designation stress viscosity stress viscosity growth
value value value value Max torque
(mm) (kPa) (kPa·s) (N·m) (N·m·s) (N·m)
Empty 2131 1397
truck
C10 70 8074 2034 4.38 0.321 24.26
C11 110 7651 1595 3.04 0.155 9.98
C12 170 6250 1848 2.65 0.115 9.26
C13 240 4115 2374 1.42 0.086 4.18
C14 150 6074 1901 1.97 0.151 9.42
C20 60 8472 3334 4.66 0.154 13.69
C21 120 6939 3282 2.73 0.105 8.77
C22 60 6080 3278 2.33 0.126 12.30
C23 40 7792 3177 4.11 0.121 20.77

Fig. 6. Flow curves obtained with ICAR rheometer for Series 1 (C10 to C14 mixtures).

Fig. 7. Flow curves obtained with ICAR rheometer for Series 2 (C20 to C23 mixtures).

In general, the linear fit of the data for the ICAR rheometer is excellent, as indicated by an average R2 value of 0.965 for the nine flow curves. Typical stress growth test plots of torque versus time from the ICAR rheometer are shown in Fig. 8 for four selected concrete mixtures. The plots are characterized by an initial linear, elastic response followed by a nonlinear, viscoelastic response up to the peak torque (see Refs. [15, 16, 17] for more discussion of stress growth tests). After the peak torque is reached, viscous flow occurs and the torque begins to decay gradually. The variation in torque readings is typical for stress growth tests of concrete due to the wide range of aggregate sizes present.

Fig. 8. Typical ICAR rheometer stress growth test results for selected mixtures.
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