Civil Engineering Reference
In-Depth Information
suspensions. Therefore, suspensions with larger-scale agglomerates exhibit
higher viscosity (Yang et al. 2006).
Four different CNT aqueous-surfactant dispersions were studied with a
surfactant to Cnts weight ratio of 1.5, 4.0, 5.0 and 6.25, respectively. the
Cnt content was kept constant in the solution at an amount of 0.16 wt%
of water. Two mixes were prepared for each surfactant to CNT ratio, one
with the use of ultrasonic energy and one without. then the dispersions
were mixed with cement and the rheological properties of the cementitious
composites samples were investigated using the mixing and measuring
protocol described previously.
Figure 20.3 shows the rheological behavior of the cementitious composites
(W/C = 0.5) with a surfactant to Cnts ratio of 6.25 that were treated with
and without the use of ultrasonic energy. the results are compared to the
plain cement paste containing the same amount of surfactant (CP + SF).
All samples exhibit the typical shear thinning response of cement paste. At
low shear stress the viscosity is high, while at high shear stress (>70 Pa)
the viscosity is decreasing and reaches a 'plateau' region in which the fluid
seems to have a constant viscosity. The non-sonicated dispersion exhibits
viscosity at low stress (14 Pa) of up to 0.13 Pa s while the sonicated dispersion
exhibits a viscosity of 0.09 Pa s which is very close to the viscosity of plain
cement paste (0.07 Pa s). As expected, at low stress conditions the application
of ultrasonic energy controls the dispersion of the Cnts. under high shear
stress (>70 Pa) the agglomerates can be broken down by the fluid motions
so the viscosities of the suspensions with and without sonication are similar.
analogous results, shown in table 20.1, were obtained with a surfactant to
Cnts ratio of 1.5, 4.0 and 5.0.
0.14
0.12
0.10
0.08
0.06
0.04
CP + SF
CP + SF CNTs
CP + SF + CNTs sonicated
0.02
0
0
10
20
30
40
50
60
70
80
90
100
Shear stress (Pa)
20.3
Steady shear viscosity of cement paste samples W/C = 0.5
reinforced with CNTs suspensions at a surfactant to CNTs weight
ratio of 6.25.
