Civil Engineering Reference
In-Depth Information
0.4
Low stiffness
C-S-H
High stiffness
C-S-H
Porous phase
CH (Ca(OH)
2
)
0.3
CH w/c = 0.5
CP + 0.08 wt% short CNTs
0.2
0.1
0
0-5
5-10
10-15
15-20
20-25
25-30
30-35
35-40
40-45
45-50
Young's modulus (GPa)
20.9
Probability plots of the Young's modulus of 28-day cement paste
and cement paste reinforced with 0.08 wt% short CNTs with w/c =
0.5.
of the Young's modulus of plain cement paste and cement paste reinforced
with MWCNTs (w/c = 0.5). Similar experiments, using the same type of
cement and testing procedure, were carried out by Mondal (2008) on 28-day
cement paste specimens (w/c = 0.5), who used a peak analyzing protocol to
fit four normal distributions to the probability plot of the Young's modulus
corresponding to the porous phase, low stiffness C-S-H, high stiffness
C-S-H and calcium hydroxide. The same analyzing protocol was used by
Constantinides and ulm (2007) on the nanoindentation results of 5 months
white cement paste specimens (w/c = 0.5).
the probability plot of Young's modulus of cement paste reinforced
with MWCnts is in agreement with the probability plot of Mondal and
the frequency plot of Constantinides and Ulm. However, while the peak
of the distribution of the nanoindentation modulus of both Mondal and
Constantinides and ulm and the plain cement paste falls in the area of 15-
20 GPa and represents the low stiffness C-S-H, the peak of the probability
plot of the Young's modulus of the MWCnts nanocomposite was found to
be in the area of 20-25 GPa which represents the high stiffness C-S-H. This
result suggests that the incorporation of Cnts increased the amount of high
stiffness C-S-H.
Similar results were obtained with nanosilica cement composites by Gaitero
(Gaitero 2008). Furthermore, the area between 0 and 15 GPa is attributed to
a material region for which the indentation response is dominated by high
porosity. Comparing the probability plot of the Young's modulus of the
MWCnts nanocomposite with the plain cement paste it is observed that
the probability of Young's modulus below 10 GPa is reduced from 0.10
to 0.03 in the case of the samples with MWCnts. these results suggest
that MWCNTs reduce the nanoporosity of cement paste by filling the gaps
