Civil Engineering Reference
In-Depth Information
Table 20.1
Viscosities (Pa s) at low shear stress condition
Surfactant CNTs weight ratio
1.5
4.0
5.0
CP + SF
0.86
0.27
0.20
CP + SF + CNTs
0.94
0.39
0.26
CP + SF + CNTs sonicated
0.89
0.29
0.20
P
a
0
= 6 mm
L
= 75 mm
t
=
20
mm
20.4
Three-point bending test set-up and configuration.
20.4 Mechanical properties
the mechanical performance of the MWCnt cementitious nanocomposites
was evaluated by fracture mechanics tests. Beam specimens of 20 ¥ 20 ¥
80 mm, prepared using the mixing protocol described previously, were tested
by three-point bending at the age of 3, 7 and 28 days, as illustrated in Fig.
20.4. three replications were made for each nanocomposite tested. Before
testing, a 6 mm notch was introduced to the specimens using a water-cooled
diamond saw. the test was performed using an 89 kn, MtS servo-hydraulic,
closed-loop testing machine. a clip gauge was used to measure the crack
mouth opening displacement (CMod). the CMod was used as a feedback
to produce a stable fracture at a rate of 0.012 mm/min. the load and the
CMod were recorded during the test. the aStM C348 was followed to
determine the average values of the flexural strength and Young's modulus.
the specimens that result in strengths differing by more than 10% from the
average value of all test specimens made from the same sample and tested
at the same period were not considered in determining the flexural strength.
after discarding the strength values, if fewer than two strength values were
left for determining the flexural strength at any given period a retest was
made. Following the above-mentioned procedure ensures that the variations
of the test results are not significant and do not affect the conclusions. The
Young's modulus was calculated from the load versus CMod results using
the two-parameter fracture model by Jenq and Shah (Shah et al. 1995).
