[
]
1
6.8 = 0.955 Kca5 vf + 0.005 10.5
0.5
0.
CEMENT
/
A textbook value of dielectric constant for un-
Kca/vf = 6.84.
hydrated portland cement was not found. A di-
electric constant was developed from the known
3. Individual coarse aggregate particles in a
chemical composition of a general-purpose ce-
saturated condition yields a dielectric constant
ment (Mindess and Young 1981). The primary
(Kica/wf) of
components of such a cement are, in weight per-
[
]
1
α
α
Kica/wf = VKca/vf + Va Ka
a
centage, lime, 63; silica, 22; alumina, 6; ferric oxide,
2.5; sulfur trioxide, 2. The corresponding dielectric
Kica/wf = [0.955 6.840.5 + 0.005 800.5 ]
1
0.5
constants are calcite, 8.5; quartz, 4.34; aluminum
oleate, 2.4; ferrous oxide, 14.2; sulfur, 4.0 (Handbook
Kica/wf = 7.01.
of Physics and Chemistry 1977). Weighting these
4. The dielectric constant of bulk coarse aggre-
dielectrics according to their percentages yields a
gate at saturated surface-dry (ssd) condition
dielectric of 6.9. The measured void ratio (ASTM C
(Kica/ssd) becomes
29) of the cement used in this study was 0.58.
1. Thus, the dielectric constant of bulk cement
[
]
1
Kica/ssd = VKiαa/wf + Va Ka
α
a
becomes
c
Kica/ssd = [0.54 7.01.5 + 0.46 10.5 ]
1
[
]
1
0.5
α
α
+ Va Ka
α
Kc =
Vc Kc
Kc = [0.42 6.90.5 + 0.58 10.5 ]
1
Kica/ssd = 3.57.
0.5
Kc = 2.83.
HYDRATED CEMENT
COARSE AGGREGATE
The following describes the procedure used to
The coarse aggregate used in this study was a
derive a dielectric constant for hydrated cement.
crushed ledge classified as a metamorphic, amphi-
Unless noted, Mindess and Young (1981) was ref-
bolite rock. We could not find a textbook dielectric
erenced for the facts in this section.
constant for this rock type. Measurements show
Portland cement (PC) evolves into a gel of
that this rock has bulk specific gravities (ASTM C
constant 26% porosity.
127) of 2.89 (ssd) and 2.87 (od), a moisture absorp-
PC chemically combines with water equal to
tion (ASTM C 127) of 0.5 %, and, for the large CRREL
gradation in Table 2, an interparticle void ratio
24% of its unhydrated mass.
(ASTM C 29) of 0.46.
Excess water is held in both capillary and gel
We chose dolomite, of the rock-type minerals, as
pores.
being most like amphibolite. The only justification
The total volume of gel equals 68% of the un-
for making this choice was that dolomite has an
oven-dry specific gravity of 2.85 which is quite like
hydrated cement mass.
that of amphibolite. The Handbook of Physics and
The fraction of cement that hydrates is time
Chemistry (1977) lists the dielectric constant (Kca) of
and temperature dependent.
dolomite as 6.8.
Mironov (1977) measured the degree of hy-
1. Its bulk, oven-dry dielectric constant (Kbca/od)
dration after 28 days at 20C as 0.66.
becomes
All samples were made with a 0.41 water to
Kbca/od = [VcaKca + Va Ka ]
1
α
cement ratio.
a
a
Kbca/od = [0.54 6.80.5 + 0.46 10.5 ]
1
1. Each gram of cement will hydrate into vol-
0.5
ume of
Kbca/od = 3.45.
V = 0.68δ Wc
2. Its void-free dielectric constant (Kca/vf) be-
V = 0.86 0.66 1
comes
[
]
1
α
α
Kca = VKca/vf + Va Ka
V = 0.449 cm3.
a
10
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