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Mixture Proportions and RCC structural Properties

 
  
 
ETL 1110-2-343
31 May 93
RCC must also be sufficiently stiff to support haul-
ing, spreading, and compaction equipment; and
must contain adequate paste at the appropriate con-
sistency to become distributed throughout the con-
crete mass during mixing, placing and compaction.
RCC must contain sufficient mortar to prevent
segregation and fill large voids between coarse
aggregate particles. The paste is the binder that ties
the coarse and fine aggregates together. In a plastic
state, the paste provides cohesion and workability to
the RCC. In a hardened state, the paste content and
quality will dictate the concrete strength, bonding
potential, permeability, and durability. The paste
volume is proportioned to fill the void system of the
fine aggregate. Typically, fine aggregate has a void
content ranging from approximately 35 to 40 per-
cent. The minimum paste-to-mortar volume ratio
(Vp/Vm) specified in EM 1110-2-2006 ensures that
voids in the mortar fraction are completely filled.
Guidance for typical RCC mortar contents are also
given in EM 1110-2-2006 (Reference 12c).
b. Water-cement ratio. The compressive
strength of RCC depends primarily on the water-
cement ratio and degree of compaction. For RCC
that is fully consolidated, the compressive strength
Figure 1-3. Pugmill mixing chamber. Paddles
will increase as the water-cement ratio decreases.
are mounted on horizontal shafts in the
Water-cement ratio guidance for conventional con-
pugmill mixing chamber. The paddles can be
crete is given in EM 1110-2-2000, "Standard
adjusted or replaced as required to maintain
Practice for Concrete" (Reference 12b). In this
mixing efficiency
guidance, the maximum permissible water-cement
ratio is provided for various anticipated exposure
conditions of the structures. Water-cement ratios
The Corps has used RCC for the construction of
should be selected during the laboratory mixture
gravity dams, a lock floor at New Cumberland Lock
design phase to meet all strength and durability
and Dam, in place of riprap for erosion protection
requirements.
downstream of a floodwater sill on the Chena Pro-
ject, as erosion protection for the Toutle Sediment
c. Aggregate quality and gradation. Aggre-
Retention Structure, at the Bonneville Project to
protect weak foundation rock from weathering, and
gates for RCC should meet the same high standards
as navigation lock guide/wing walls. RCC has also
for quality and grading as required for conventional
been used for emergency repairs of a check dam
concrete. Only where extraordinary circumstances
exist, such as construction during an emergency
and as a spillway through an earthen sediment
situation in which use of a poorer quality does not
retention dam on the Toutle River. RCC can and
prevent meeting design quality requirements of the
has been used for stilling basins, plunge pools,
concrete, could aggregates of a lesser quality be
spillway repair and replacement, foundation mats,
justified. Coarse aggregates for RCC are graded to
diversion walls and open channel lining.
standards identical to those for conventional mass
5. Mixture Proportions and RCC structural
concrete; however, the fine aggregate used for RCC
Properties
will normally contain a greater proportion of mater-
ial passing the No. 200 sieve in order to fulfill paste
a. Paste and mortar content. RCC mixtures
and workability requirements. RCC containing
must be workable, free of segregation, and easily
minimally processed pit run aggregate may require
a greater water content, be less durable, have a
compacted using external vibratory rollers. The
1-3


   


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