unique microstructures in the specimens
Table 10. Corrosion rates with various admixtures.
containing the antifreeze admixtures, as
Initial
2-year corrosion
Corrosion
compared to paste structures observed in
rate A/cm2
Sample
potential
control specimens. However, the speci-
no.
Admixture
(kohms/cm)
(mV vs. SCE)
(relative)
mens containing DP at 6%, and those con-
1A
Control
5.4
249
0.23
taining DPTC at 6% and at 8%, exhibited
1B
"
5.3
564
0.70
abnormally high concentrations of cal-
1C
"
5.5
536
0.28
cium hydroxide on exterior surfaces and
1D
"
6.1
91
0.05
1E
"
5.7
211
0.11
interior aggregate sockets. The abundance
1F
"
5.5
131
0.08
of calcium hydroxide suggests that sig-
Average
"
5.6
297
0.24
nificant bleeding may have occurred. The
2A
PolarSet*
3.4
86
0.06
control specimens, which contained only
2B
"
3.8
94
0.07
water reducer and air entraining admix-
2C
"
3.2
65
0.06
2D
"
3.2
76
0.06
tures, exhibited heavy concentrations of
2E
"
3.8
80
0.09
air-void clusters along the paste/aggre-
2F
"
4.0
75
0.05
gate bond interface. The mix design pa-
Average
"
3.6
79
0.07
rameters (such as water/cementitious
3A
DP*
5.2
108
0.07
material ratio, aggregates quantities and
3B
"
4.6
86
0.02
3C
"
4.5
121
0.05
qualities, and cement factor) were kept
3D
"
4.8
136
0.07
constant for all mixes. The admixtures
3E
"
4.3
97
0.06
used are listed in Table 11. Other than the
3F
"
4.8
73
0.05
differences noted above, the cement
Average
"
4.8
104
0.05
paste/aggregate bond interface did not
4A
DPTC*
4.4
114
0.06
4B
"
5.1
119
0.12
show any difference in composition or
4C
"
5.3
127
0.08
structure from those of the control speci-
4D
"
4.5
146
0.18
mens.
4E
"
4.6
113
0.19
Task 4: Alkali-silica reaction. The selected
4F
"
4.6
118
0.17
admixtures do not add sodium or potas-
Average
"
4.8
123
0.13
sium (the potentially harmful alkalis) to
*The given admixture was dosed at 6% of solids by weight of the water in
the concrete mix. Therefore, testing for
the solution.
alkali-silica reaction as planned was
found to be unnecessary, and was cut from the
ity and curing temperature, and 4) the type and
testing program.
amount of admixtures. A detailed microscopic ex-
Task 5: Air-void analysis. The air content and the
amination of concrete specimens containing se-
spacing factor are the main parameters that deter-
lected admixtures can provide insight into the ef-
mine to a large degree the freezethaw durability
fects that such admixtures can have on the
of concrete. In this task, the total air content of
compressive strength and long-term durability of
each mixture series was measured in both the fresh
hardened concrete.
and hardened states. The spacing factor, the aver-
The evaluation and characterization of the con-
age chord length, the number of voids per inch,
crete microstructure included both conventional
the specific surface, and the paste content were
and advanced imaging techniques. Preliminary
determined on hardened concrete specimens rep-
observations were conducted at relatively low
magnifications (< 75) on both fractured and pol-
resenting each of four mixtures. An air entraining
agent, Daravair, was dosed to produce an air con-
ished surfaces, using a stereomicroscope. More
tent of 57%. Also, a super plasticizer, WRDA-19
detailed and advanced imaging involved the use
of high magnification (1001000) reflected and
(Daracem 19), was dosed to produce a target slump
between 13 and 17 cm. The water/cementitious
transmitted light microscopy. The latter technique
was augmented by the use of ultrathin (< 30 m)
material ratio was 0.417. The air-void structure in
the hardened concrete was analyzed after 28 days
sections of the hardened concrete. Finally, scan-
of curing. The control specimens were cured at
ning electron microscopy (SEM) and energy dis-
normal room temperature, while all of the anti-
persive X-ray spectroscopy (EDXS) were used to
freeze test specimens were cured at 7C. The
analyze the hydration products in each specimen.
specimens were polished slabs cut from concrete
The results of a detailed microscopic examina-
cylinders.
tion did not reveal any evidence of unusual or
9
Previous Page
