29
CHAPTER Ii, SECTION 1
Variations in the physical properties of
coral rock, as noted above, required the preparation of 14 design mixes for concrete in Eniwetok Atoll and 27 design mixes in Bikini Atoll.
Concrete cylinders were carefully packed
in wet sawdust for a period of 48 hours, which
allowed the required initial period after casting
before they could be shipped to the Test Laboratory. [t was found that wax-paper cylinder
molds could not be easily stripped from concrete
cylinders and, therefore, the one-use sheet metal
cylinder molds were used. The use of these sheet
metal molds was justified by the amount of
time saved and the uniformity achieved in the
quality
of
concrete
cylinders.
A_
total
of
1,450 cylinders was taken from approximately
28,500 cubic yards of concrete placed during 1
July 1955 to 1 July 1956, amounting to one
control cylinder for every 20 cubic yards of con-
crete placed. The average results obtained from
these tests as shown below.
Specified 28-Day
Breaking Strength
Average 28-Day
Bikini Atoll
Average 28-Day
Eniwetok Atoll
2000 psi
2500 psi
3166 psi
3177 psi
2984 psi
2718 psi
3000 psi
4145 psi
The average concrete mix as used at Job-
site contained approximately the following:
1800 lbs. course aggregate
1200 lbs. fines
6 sacks of cement
42 gallons of water
The above average mix was varied to conform
to the characteristics of the aggregate used at
the place and time of the concrete pour.
The high values obtained in the average
strengths were primarily due to the large amount
of concrete poured in water because, as a safety
factor, additional cement was added to mixes
that were poured in water and the actual
strengths of the concrete were therefore much
higher than specified in such cases. The coral
aggregate obtained at Bikini was characteristically more consistent; this was due to a denser
coral thus resulting in a more uniform ratio
between coarse and fine aggregate producing
a concrete mix of higher strength.
3914 psi
Included in a variety of other activities of
the Test Section was the making of CBRtests,
Bitumen content tests, moisture tests of various
mixes, strain gage tests on tower cable, tension
tests on marine rigging and paint durability
tests.
The Inspection Department was organized
with individual site Inspectors assigned to each
major site, working under a Chief Inspector at
each Atoll. This department inspected all phases
of construction work from the first clearing and
grading stage until final completion and acceptance. Preliminary work consisted of studying
plans, specifications, bills of material, and any
special conditions. Materials were then checked
for conformance with specifications. With the
commencement of work, inspection was continuous. Excavations and foundations were checked
for location, dimensions, and orientation; forms
were checked for adequacy and alignment; re-
inforcing rods were checked for size, bends,
spacing, ties and rigidity of support; embedded
fixtures were checked for location and size. Con-
A total of 15 tests of cement (Ideal, Santa
Clara, and Santa Cruz) were made for normal
consistency and time of set. Normal consistencies were about 25 per cent and the time of
set varied from one to four hours, which con-
crete was inspected during placement to ensure
that it was well-compacted and bonded, and
various cements observed in the field.
cal items followed.
firmed the difference in set qualities of the
of proper mix. Inspection after placement for
the removal of forms and backfilling was likewise continuous. With the structure formed,
inspection on electrical, sanitary, and mechani-
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