Civil Engineering Reference
In-Depth Information
of CNTs used. It is observed that a similar gain (25%) in the flexural
strength of mortars nanocomposites was obtained by Li et al. (2005), using
ten times higher concentration of Cnts (0.5 wt% of cement). Comparing
the results of this study with the results obtained by Cwirzen et al. (2008)
it is observed that, despite the similar Cnts concentration used for the
preparation of cement paste nanocomposites, the flexular strength increase
for Cwirzen et al. was 10%. The extent of the flexural strength improvement
of the nanocomposites in this work was attributed to the successful nanofiber
dispersion. Effective dispersion of the CNTs in the cement matrix resulted
in the reduction of the fiber-free area in the material and in an increase in
the mechanical performance of the nanocomposite. By achieving effective
dispersion of small amounts of Cnts, the reinforcing effect of Cnts in the
matrix increases and the cost of the nanocomposite is reduced.
20.4.2 Reinforcing efficiency of CNT/CNF in
cementitious composites
The flexural strength rate of the nanocomposites reinforced with either
MWCNTs or CNFs up to the age of 28 days of hydration is shown in Fig.
20.6. The samples reinforced with nanofibers at all ages exhibit higher flexural
strength than plain cement paste. In particular, an increase up to 25% is
achieved when MWCNTs are utilized. The use of CNFs results in an increase
of the flexural strength up to 45%. Comparing the two nanocomposites, it
is observed that despite the fact that MWCNTs exhibit a higher aspect ratio
(due to their smaller diameter and larger amounts of nanotubes) it reinforces
the cement matrix since the concentration of the fibers is constant, CNFs
provide the matrix with the ability to carry higher flexural loads at lower
8
7
6
5
Plain OPC (CP)
CP + CNFs 0.048 wt%
CP + MWCNTs 0.048 wt%
4
3
0
5
10
15
20
25
30
Age (days)
20.6
Flexural strength of plain cement paste (W/C = 0.5) and cement
paste reinforced with 0.048% by weight of cement MWCNTs or CNFs.
