ETL 1110-2-343
31 May 93
coefficient of thermal expansion. The range of
strength, the strength at lift surfaces will govern the
values for each of these RCC properties is pre-
design. Cohesion varies a great deal from lift sur-
sented in the following paragraphs. It should be
face to lift surface, while the angle of internal fric-
noted that the rapid construction time of RCC struc-
tion is usually quite consistent. The factors that
tures, and the general practice of specifying the
affect tensile strength at lift joint surfaces also
required RCC strength at 1 year, can lead to the
affect shear strength. Cohesion can vary from 0 to
structure being loaded prior to the RCC attaining
10 percent of the compressive strength. A prelimi-
the required design strength. It is therefore impor-
nary design value of 5 percent of the compressive
tant that the structural engineer be involved in the
strength is recommended for lift joint surfaces that
mix design process in order to assure that the
are to receive a mortar bedding; otherwise, a value
required strength gain characteristics of the mix are
of 0 should be assumed. The angle of internal
attained. All values assumed in the preliminary
friction can vary from 40 to 60 deg. A value of
design must be verified through testing as outlined
45 deg may be assumed for preliminary design
in Section 7.
studies.
b. Compressive strength. RCC with high qual-
e. Modulus of elasticity. Properly propor-
ity aggregates will produce compressive strength
tioned and consolidated RCC should provide a
equal to conventional concrete. The strength will
modulus of elasticity equal to or greater than that of
depend primarily on the water-cement ratio. The
a conventional concrete of equal compressive
relationship between water-cement ratio and
strength. The same modulus-strength relationships
strength for RCC is similar to that for conventional
used for conventional concrete may be used for
concrete. Normally, for durability reasons, the RCC
RCC. For rapid strain rate loading, such as occurs
mixture will have a minimum compressive strength
during earthquakes, the modulus of elasticity may
of 2,000 psi at 1 year. However, higher compres-
be 15 percent higher than that predicted by the
sive strengths may be required to produce RCC
usual strength modulus formula. For thermal analy-
with the desired tensile and shear strengths.
ses, where creep effects are considered, the effec-
tive modulus may be 33 percent less. Preliminary
c. Tensile strength. The tensile strength of
design studies should assume the modulus of elas-
ticity to be equal to 57,000 (f'c)1/2 psi (increased by
RCC is dependent on the method of test used (split
cylinder, flexural, direct tension). The tensile
15 percent for seismic load conditions and reduced
by one third for long-time load conditions where
strength of RCC can be expressed as a function of
creep effects are important).
the compressive strength and, in general, is lower
than for conventional concrete. The in-place tensile
f. Poisson's ratio. The normal range for
strength of RCC is sensitive to the maximum size
Poisson's ratio is between 0.17 and 0.22. A value
of aggregates, the workability of the mixture, and
of 0.20 should be used for preliminary design
the condition of the lift joint surface. With the use
studies.
of a mortar bedding on lift surfaces, direct tensile
strengths in the range of 3 to 9 percent of the com-
g. Coefficient of thermal expansion. The ther-
pressive strength can be expected. A direct tensile
mal movements in concrete are primarily dependent
strength equal to 5 percent of the compressive
on the aggregate type and content. The coefficient
strength is recommended for preliminary design
of thermal expansion, or the thermal movement per
investigations. This value can be increased by
unit temperature rise, is usually smaller for RCC
50 percent for seismic load conditions that involve
(because of higher aggregate content) than for con-
high strain rates.
ventional concrete. The coefficient of thermal
d. Shear strength. The total shear strength
expansion for conventional concrete varies between
4 and 8 x 10-6 inches per inch per degree F. A
along horizontal lift surfaces of RCC is a combina-
value of 5 x 10-6 inches per inch per degree F
tion of cohesion (bond) and frictional resistance.
should be used for preliminary RCC design studies.
The shear strength along lift surfaces is always less
than the parent concrete. Therefore, as for tensile
1-20
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