ETL 1110-2-343
31 May 93
values for joint cohesion and tensile strength must
RCC mixture proportioning procedures are similar
be based on a laboratory test program that includes
to conventional concrete; however, RCC mixtures
evaluation of joint strength using core samples from
will normally contain less water and paste and more
test placements constructed under anticipated field
sand to limit segregation.
conditions. A comprehensive laboratory test pro-
4. Structures Suited to RCC Construction
gram will assure a greater degree of certainty and,
in some cases, may eliminate overly conservative or
redundant design assumptions.
RCC has gained worldwide acceptance as an alter-
native to conventional concrete in dams as well as
c. RCC permeability. The permeability or
other types of structures. It may be used for any
watertightness of concrete may be of more concern
application that allows access of placing, spreading,
than the strength, especially with respect to hydrau-
and compacting equipment and can be considered
lic structures. The ease with which water migrates
for use in new construction as well as rehabilitation
through the concrete mass may ultimately affect the
work. Application of RCC should be considered
performance of the concrete over time. The factors
when it is economically competitive with other
affecting the permeability of RCC are essentially
construction methods. It may be considered in lieu
the same as those that affect the permeability of
of gabions or riprap for bank protection, especially
conventional concrete. Historically, high perme-
in those areas where riprap is scarce. It may be
ability in RCC structures has been the result of
considered for large work pads, massive open foun-
segregation and lack of consolidation at lift joint
dations, base slabs, cofferdams, massive backfill,
surfaces.
emergency repairs, and overtopping protection for
embankment dams. It may be used in lieu of con-
d. RCC durability. Air-entraining admixtures
ventionally placed concrete in concrete gravity
are available and have been used to successfully
dams. RCC may be considered for use in levees
entrain air in RCC mixes in the laboratory. Howev-
where foundations are adequate and may also be
er, most RCC placed to date has not been air-en-
used in caps for jetties to reduce the amount of
trained and as a result, has performed poorly when
required rock. For many dam projects, it may
subjected to repeated cycles of freezing and thawing
prove that the use of RCC will allow a more
in a critically saturated state. When not critically
economical layout of project features such as an
saturated, RCC has been found to have adequate
over-the-crest spillway as opposed to a side channel
resistance to freeze-thaw damage. Currently, re-
spillway (Reference 12c). Figures 1-2 and 1-3
search is in progress to determine the most effective
show a portable pugmill continuous mixing plant,
type of air-entraining admixtures and type of air
which is often used in RCC construction.
void systems that may be achieved with RCC.
3. Conventional Mass Concrete versus RCC
RCC is designed to meet the material strength and
durability requirements established by the structural
engineer. The factors that affect the properties of
conventional mass concrete such as water-cement
ratio, quality of mixing ingredients, and degree of
consolidation and curing, also affect the material
properties of RCC. The principal difference in the
two is the mixture consistency and the method of
consolidation. Internal consolidation using immer-
sion-type vibrators is used for conventional con-
Figure 1-2.
Portable pugmill continuous
crete, while external consolidation with spreading
mixing plant. Pugmill mixers are often used in
equipment and vibratory rollers is used for RCC.
RCC construction for maximum efficiency and
The controls placed on mixture ingredient selection
production
for conventional mass concrete will apply to RCC.
1-2
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