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.

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

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

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-

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

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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