Civil Engineering Reference
In-Depth Information
20.4.1 Effect of surfactant
The average values of maximum fracture load for cement paste samples
containing MWCnts with different surfactant-to-MWCnt ratios for 28 days
are plotted in Fig. 20.5. It is observed that samples treated with different
amounts of surfactant exhibit higher fracture load than the sample with no
surfactant. the samples with surfactant to MWCnt ratio of 4.0 give a higher
average load increase at all ages. Surfactant-to-MWCnt ratios either lower
or higher than 4.0 produce specimens with less load increase. a possible
explanation could be that at lower surfactant-to-MWCNT ratios, fewer
surfactant molecules are absorbed to the carbon surface and the protection
from agglomeration is reduced. at higher surfactant-to-MWCnt ratios,
bridging flocculation can occur between the surfactant molecules. Too much
surfactant in the aqueous solution causes the reduction of the electrostatic
repulsion forces between the MWCnts (Yu et al. 2007). the results indicate
that for effective dispersion, there exists an optimum weight ratio of surfactant
to MWCnts close to 4.0.
Table 20.2 compares the flexural strength increase of cement paste
nanocomposites achieved in this study with results of mortars and cement
paste nanocomposites reported in the literature, relative to the concentration
250
230
210
190
170
0
1
2
3
4
5
6
7
8
Surfactant/MWCNT weight ratio
20.5
Fracture load of 28-day W/C = 0.5 cement paste reinforced with
MWCNTs 0.08 wt%.
Table 20.2
Comparison of flexural strength increase in cementitious
nanocomposites reinforced with CNTs
Researchers
Nanocomposites
Amount of CNTs
Flexural strength
(wt% of cement)
increase (%)
Li et al. (2005)
Mortars
0.50
25
Cwirzen et al. (2008)
Cement paste
0.042
10
Konsta-Gdoutos
Cement paste
0.08 and 0.048
25
[present work]
