EP 1110-2-12
30 Sep 95
Chapter 3
joint surfaces in addition to the tests to determine the
tensile strength of the parent concrete.
Material Properties of RCC
a. Location of critical tensile stress. Critical
tensile stresses are located at the upstream and down-
3-1.
Similarities of RCC and Conventional
stream faces of the dam. The tensile stress distribu-
Concrete
tion within the dam mass is of interest to help
establish zone boundaries for superior, higher strength
The strength and elastic properties of RCC vary de-
RCC mixes that may be required to control cracking
pending on the mix components and mix proportions
near the faces.
in much the same manner as that for conventional
mass concrete. Aggregate quality and water-cement
(1) Usually the tensile stress in the lift joints in
ratio are the principal factors affecting strength and
the direction normal to the joint surface is critical
elastic properties. Properties important to the seismic
near the upstream face of the dam. This is because
analysis of RCC dams include compressive strength,
the direction of the principal tensile stress near the
tensile strength, shear strength, modulus of elasticity,
upstream face is very nearly normal to the joint sur-
Poisson's ratio, and unit weight. Except for unit
face, thus there is little difference between the joint
weight, all these properties are strain rate sensitive,
stress and the maximum principal stress in the parent
and the strain rates that occur during major earth-
concrete. Since tensile strength of the lift joint is
quakes are in the order of 1,000 times greater than
notably less than the parent RCC, it will control the
those used in standard laboratory testing. Guidance
design near the upstream face.
concerning the determination of RCC material proper-
ties is given in EM 1110-2-2006 and ETL 1110-2-
(2) Near the downstream face, the direction of
343.
the principal tensile stress is nearly parallel to the
face which results in significantly higher principal
tensile stresses in the parent concrete compared to the
3-2.
Compressive Strength
tensile stresses in the lift joints normal to the joint
surface. The ratio of the tensile strength of parent
The relationship between water-cement ratio and
concrete to the tensile strength of the lift joints varies
compressive strength is the same for RCC as for
according to several parameters including workability
conventional mass concrete. Normally, for durability
of the mix, joint preparation, and maximum size
reasons, the RCC mix will be designed to provide a
aggregate. Thus, it usually becomes necessary to
minimum strength of 2,000 psi; however, for seismic
investigate both the principal tensile stress and the
reasons higher compressive strengths are often
component tensile stress normal to the lift joints to
required to achieve the desired tensile and shear
determine which is critical near the downstream face.
strength. The compressive strength at seismic strain
rates will be 15 to 20 percent greater than that at the
b. Preliminary design. For preliminary design,
quasi-static rates used during laboratory testing (ACI
the tensile strength of the RCC may be obtained from
Committee-439 1969); however, compressive strength
Figures 3-1 through 3-6 for the proposed concrete
is never the governing factor in seismic design.
compressive strength (f'c). These figures show both
the tensile strength of the parent material and the
tensile strength of the lift joint based on the proposed
3-3.
Tensile Strength
consolidation and joint treatment method. These
figures were developed from Tables E2 and E3,
The tensile strength of RCC shall be based on the
Appendix E.
direct tensile strength tests of core samples. For the
final design of new dams, cores shall be taken from
c. Tensile strength tests. Splitting tensile tests
test-fill placements made with the proposed design
are easier to perform and provide more consistent
mixes, and placed with the proposed consolidation
results than direct tensile tests. However, splitting
and joint treatment methods. When an existing dam
tensile test results tends to overpredict actual tensile
is evaluated for compliance with the requirements of
strengths, and should be adjusted by a strength reduc-
this EP, cores shall be taken directly from the struc-
tion factor to reflect results that would be obtained
ture. Cores should be taken vertically so that tests
from direct tensile tests. When splitting tensile tests
can be made which reflect weaknesses inherent at lift
3-1
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