WOODS ON CORROSIONOF EMBEDDEDMATERIALS 231
teed, other conditions being favorable, aluminum. Wright [3] has described a
at 90 per cent relative humidity and case of corrosion of sufficient severity to
probably at 75 per cent relative humidity, cause collapse of aluminum conduit in
though at a lower rate. reinforced concrete containing calcium
Concrete made with lightweight aggre- chloride, and an instance of extensive
gates dries more slowly than that made
with normal weight aggregates, and
thicker sections, such as beams and
columns, will dry more slowly than thin
sections, such as walls, or floor slabs not
on the ground.
Alw. vinutt;:
Aluminum reacts in fresh concrete
principally with alkali hydroxides from
TABLE l—RATES OF DRYING 6 X 36
X 36 IN. (15 X 90 X SO CM) SLABS OF
NORMAL WEIGHT CONCRETE.”
DryingT]meto ReachVarious
Environmental RelativeHumiditiesin the
RH ConcreteSlabat Middepth,days
90%RH 75%RH 5070RH
10. ..,.. 18 80 620
35 . . . . . . 30 110 840
50...... 36 240
75...... 36 .
From Abrams and Orals [1].
CI
cement. One reaction product is hy-
drogen gas, and for this reason alumi-
num powder is sometimes used in con-
crete to form cellular or “gas” concrete,
or in smaller amounts to provide a slight
expansion of grout in bedding machinery
base plates. Aluminum in rod, sheet, or
pipe form will react much less vigorously
than will the powdered metal, because
FIG. l—Concrete spalledby corrodingalumi-
of its lesser exposed area. num conduit (from Ref. .5).
Tests carried out by Jones and Tarle-
ton [2] indicate that the corrosion of concrete spalling over aluminum conduit
aluminum embedded in plain concrete in Washington Stadium has been pub-
can crack the concrete under unfavorable lished [4]. Some nine additional cases of
circumstances. However, it has been concrete cracking over aluminum con-
shown that the situation can be worse duit in reinforced concrete have come to
if the concrete contains calcium chloride the attention of Portland Cement Assn.
and much worse if it also contains steel, (PCA), and in every case calcium chloride
such as reinforcing steel which is con- was used as an admixture. An example is
nected (coupled) metallically to the shown in Fig. 1.
232 SIGNIFICANCE OF THE PROPERTIES OF CONCRETE
The results of laboratory investigation aluminum conduit embedded + in. from
by PCA have been given by Monfore one face. Various numbers of C-shaped
and Ost [5]. Parts of that investigation sheets of mild steel were also embedded
will be summarized here, as they bring in the cubes, externally connected for
out the effects of concentration of cal- some tests and not connected for others.
TABLE 2—CORROSION OF 6063 ALUMINUM CONDUIT EMBEDDED IN 6-IN.
CONCRETE CUBES STORED AT 50 PER CENT RELATIVE HUMIDITY FOR
28 DAYS.G
Cement Ratio of Loss in
Cement Alkalies CaCl,;H,O, SteelArea Electrodes Days to Surface
as NazO, to A~;inum Cracking Thi#&css,
%
c. .,. 0.24 0 28 coupled no crack 0.16
2 14 coupled 5 0.92
2 28 coupled 4 1.2
4 7 coupled 3 1.6
4 14 coupled 3 2.3
4 28 coupled 3
0 28 uncoupled no crack ;::9
2 14 uncoupled no crack 0.07
2 28 uncoupled no crack 0.10
4 7 uncoupled no crack 0.07
4 14 uncoupled no crack 0.07
4 28 uncoupled no crack 0.04
0 0 .,, no crack 0.09
4 0 . . no crack 0.04
D ... . 0,89 0 28 coupled no crack 0.12
1 3.5 coupled no crack 0.54
1 7 coupled no crack 0.77
1 14 coupled no crack
1 28 coupled no crack :::5
2 3.5 coupled 3 1.0
2 7 coupled 3 1.4
2 14 coupled 4 1.4
2 28 coupled 4 1.6
4 3.5 coupled 2 1.5
4 7 coupled 2 1.7
4 14 coupled 2.2
4 28 coupled ; 3.3
0 28 uncoupled no crack 0.33
2 14 uncoupled no crack 0.06
2 28 uncoupled no crack 0,06
4 uncoupled no crack 0.07
4 li uncoupled no crack 0.09
4 28 uncoupled no crack 0.08
0 .. no crack 0.17
: 0 ... no crack 0.05
~ From Ref. 6.
b Calculated from weight losses
cium chloride, alkali content of cement, Various amounts of calcium chloride were
coupling steel to aluminum, and the used. The cubes were removed from their
ratio of steel area to aluminum area. Six molds at 24 hr, coated with a curing
inch (15 cm) concrete cubes were pre- compound, and then stored at 73 F
pared using two cements of alkali con- (23 C) and 50 per cent relative humidity
tents 0.24 and 0.89 per cent, containing for 28 days. They were observed regu-
pieces of nominally + in. (1.25 cm) larly for cracks. After 28 days the alumi-
WOODS ON CORROSION OF EMBEDDED MATERIALS 233
num pieces were removed, cleaned, and TABLE 3—EFFECT OF PROTECTIVE
COATINGS ON CORROSION OF ALUMI-
weighed. The principal results are given NUM CONDUIT EMBEDDED FOR 28
in Table 2. DAYS IN 6-IN. CONCRETE CUBES CON-
Several important findings are to be TAINING 4 PER CENT CALCIUM
CHLORIDE AND STEEL COUPLED TO
noted in these results. THE ALUMINUM.C
1. All cubes that cracked contained ProtectiveCoating Lossin
calcium chloride. Days to Surface
Material Thick- Cracklng Thi;c~
2. The cubes containing 1 per cent ness,roils
calcium chloride (as CaClz.2Hz0, by
None . . . . . . . . . . 3 2.5
weight of cement) did not crack, but Silicone . . . . . . . . 2 2.1
metal losses in these cubes were as high Lacquer B..,... “1’ no crack 0.47
as, or higher than, those in other cubes Lacquer C..,.., 2 no crack nil
Bitumen A.,... 5 no crack nil
which cracked. One may surmise that Bitumen D...,. 15 no crack nil
exposure to a damper atmosphere might
4 From Ref. 6,
have brought about sufficiently more b Calculated from weight losses.
corrosion to have caused cracking.
1. I
120“
P
>.s Steel area/oluminum oreo = 28
+3 o
~g Cement D, 0,890/0 alkalies
Zs
Q)x 7\
1
<a
w>
o 1 I
o 10 20 30
TIM E, DAYS
FKG.2—Effect of calcium chloride on galvanic currents (from Ref. .5).
3. With no calcium chloride and no Additional tests were made to de-
coupling, the corrosion was greatest with termine the effectiveness of several
the high alkali cement. coatings applied to the aluminum before
4. With 2 or 4 per cent calcium embedment in 6-in, concrete cubes
chloride present, and with metals cou- made with cement of 0.89 per cent
pled, corrosion was a little greater with alkalies and containing 4 per cent cal-
the higher alkali cement. cium chloride by weight of cement. The
5. With calcium chloride present, and results are shown in Table 3. These
with metals coupled, corrosion generally show that a silicone coating was ineffec-
increased with increasing ratio of steel tive . and that Lacquer B prevented
area to aluminum area, and invariably cracking within 28 days but permitted
increased as the amount of calcium some’ corrosion. Lacquer C and bitumi-
chloride increased. nous coatings A and D were all effective
6. The cubes that cracked did so in preventing both corrosion and crack-
within seven days. ing.
234 SIGNIFICANCE OF THE PROPERTIES OF CONCRETE
In the case of coupled metals, con- would also facilitate corrosion of alumi-
siderable galvanic currents were found num. Sodium chloride is the principal
to ilow in the circuit connecting the constituent of sea salt, and it therefore
aluminum and steel. Some measured seems prudent not to use aluminum in
currents as a function of time and cal- concrete in or near sea water.
cium chloride content are shown in Fig.
2. The effect of increasing calcium
Lead:
chloride in increasing the current flow Lead has a high resistance to certain
at all periods (up to end of test at 28 chemical actions but, in contact with
days) is evident, When the total elec- damp concrete, is attacked by the cal-
trical flow during 28 days in ampere cium hydroxide in the concrete and be-
hours per unit area of aluminum was comes converted to lead oxide or to a
plotted against the amount of corrosion mixture of lead oxides. If the dampness
as loss in thickness, straight lines were persists, the attack will continue, and a
obtained with slopes depending on lead pipe, for example, may be destroyed
amount of calcium chloride used, the in a few years. If the lead is coupled to
slope being greatest for the higher reinforcing steel in the concrete, galvanic
amounts of calcium chloride, This sup- cell action may accelerate the attack [7],
ports the conclusion that the corrosion in which case the rate of corrosion may
observed with calcium chloride and be several millimeters per year. A pro-
coupled steel and aluminum is essentially tective coating or covering should al-
galvanic corrosion, the two metals acting ways be used when lead pipe or cable
as electrodes of an electric cell and the sheaths are to be embedded in concrete.
calcium chloride acting as the electrolyte Bituminous coatings have been used
and probably in other ways. successfully. Synthetic plastic coatings
Tests somewhat similar to those re- or sleeves which are themselves un-
ported by Monfore and Ost were carried affected by damp concrete are suggested.
out on 12-in. (31 cm) concrete cubes by There appears little, if any, likelihood
Wright and Jenks [6]. With coupled of concrete itself being damaged by
steel and aluminum (area ratio 10: 1) corrosion of lead, because of the softness
the cubes did not crack when no calcium of the metal.
chloride was used, but cracked at various
Copper and Copper Alloys:
ages from 61 days with 1.1 per cent flake
calcium chloride (70 to 80 per cent In general, copper is not corroded in
CaCIJ to 8 days with 5.7 per cent. concrete, although it is reported that
The results of these various investiga- thin sheets can become perforated if
tions and field observations show that soluble chlorides are present. Copper
reinforced concrete is likely to crack and pipes are used successfully in concrete
span from corrosion of uninsulated except under the unusual circumstance
aluminum embedded therein if an appre- where ammonia is present [8]. Very small
ciable amount of calcium chloride is amounts of ammonia and possibly
present. Whether insulating coatings for nitrates can cause stress corrosion
aluminum to be used in concrete are cracking. It is reported that brass wall
commercially practical remains to be ties have failed by stress corrosion and
demonstrated. that manganese bronze bolts have
In view of chemical similarities be- sheared below their ultimate strength,
tween calcium chloride and sodium but as such phenomena can occur under
chloride, it seems evident that the latter circumstances unrelated to concrete, it is
