Civil Engineering Reference
In-Depth Information
ultrasonic processor with a cylindrical tip and temperature controller. the
sonicator was operated at an amplitude of 50% so as to deliver an energy
of 1900-2100 J/min at cycles of 20 s in order to prevent overheating of the
suspensions.
20.3.2 Effect of ultrasonication energy on the
rheological characteristics
The influence of MWCNT dispersion on the rheological properties of
cement paste samples was investigated. the rheological characteristics of
the samples with the sonicated dispersions were measured using a Haake
Rheostress 150 rheometer with a 20 mm concentric cylinder measurement
system. a steady stress protocol similar to the one proposed by Yang et al.
(2006) was applied to determine the viscosity dependence on stress. Cement
paste was placed in the rheometer immediately after mixing. Each sample
was presheared at 100 s
-1
for 200 s, and then allowed to rest for 200 s. a
low stress of 4.5 Pa was applied to the sample, and the stress was increased
stepwise using the protocol shown in Fig. 20.2. Initial stresses were chosen
to be higher than the yield stress of the material. the samples were held at
each stress condition for 40 s. the holding time was necessary to ensure that
an equilibrium flow had been reached. Apparent viscosity (h) as a function
of time was monitored and recorded during the test. the viscosity at each
shear stress was obtained by averaging the values at the last 10 seconds that
corresponded to the equilibrium region.
the effect of ultrasonic energy on the dispersion of the Cnts was
investigated by measuring the rheological properties of cement paste samples
reinforced with MWCnts under steady shear stress. Rheology is a method
commonly used to study the microstructure in nanotube dispersions. under
low shear stress, Cnt agglomerates control the viscosity of cement nanotube
1000
100 Pa
140 Pa
200 Pa
70 Pa
100
45 Pa
30 Pa
20 Pa
16 Pa
14 Pa
10 Pa
7 Pa
10
4.5 Pa
1
0
40
80
120
160
200
240
280
320
360
400
440
480
Time (s)
20.2
Rheology measuring protocol.
