ETL 1110-2-365
31 Aug 94
(2) Mechanical properties.
at or near the anticipated project maximum placement
temperature. If experience does not allow for
(a) Modulus of elasticity. The modulus of elas-
reasonably accurate estimation of the maximum plac-
ticity is defined as the ratio of normal stress to corre-
ing temperature, tests should be conducted at a lower
sponding strain below the proportional limit. For
and upper temperature to bracket the temperature rise.
practical purposes, only the deformation which occurs
Typical values for adiabatic temperature rise for mass
concrete range from 20 to 35 F at 5 days to 30 to
during loading is considered to contribute to the strain
45 F at 28 days. A curve of temperature rise versus
in calculating the modulus of elasticity. Subsequent
time will be input into the ABAQUS program
increases in strain due to sustained loading are
through the user subroutine DFLUX or HETVAL as
referred to as creep. The modulus of elasticity is a
function of the degree of hydration and therefore is
discussed in paragraph A-5a(2).
time dependent. It is also temperature dependent;
however, the effect within the range of temperatures
(b) Specific heat. Specific heat is the amount of
involved in a NISA is negligible and therefore is not
heat required per unit mass to cause a unit rise of
modeled in ABAQUS. The modulus of elasticity is
temperature. Specific heat is also referred to as heat
determined according to CRD-C 19 (USAEWES
capacity. It is affected by temperature changes, but
1949e). To adequately model the time dependency of
for the range of temperatures expected in a NISA, it
the modulus of elasticity, tests should be conducted at
should be assumed to be constant. The specific heat
ages of 1, 3, 7, 14, 28, 56, and 90 days, as well as
is determined according to CRD-C 124 (USAEWES
the design age. Typical values for the modulus for
1949b). The test should be conducted at an age of at
mass concrete are about 1 106 psi at 1 day and
least 7 but not more than 28 days. Typical values for
about 5 106 psi at 90 days. A curve of modulus
specific heat of mass concrete range from 0.18 to
versus time will be input into ABAQUS through the
0.28 Btu/lb-F.
UMAT subroutine.
(c) Thermal diffusivity. Thermal diffusivity is a
(b) Poisson's Ratio. Poisson's Ratio is defined
measure of the rate at which temperature change can
as the ratio of the lateral to the longitudinal strain
occur in a material. It is determined according to
resulting from a uniformly distributed axial stress. It
CRD-C 36 (USAEWES 1949c) for conventional
is determined according to CRD-C 19. Typical val-
concrete and CRD-C 37 (USAEWES 1949d) for mass
ues for Poisson's Ratio for mass concrete range from
concrete. The test should be conducted at an age of
0.15 to 0.20. The value input into ABAQUS should
at least 7 but not more than 28 days. Typical values
be based on test data at ages greater than 7 days and
for thermal diffusivity of mass concrete range from
0.03 to 0.06 ft2/hr. The value of thermal diffusivity
on engineering judgement.
is not input into ABAQUS but is used to calculate the
(c) Creep. Creep is defined as time-dependent
thermal conductivity of the concrete.
deformation due to sustained load. Creep results in a
progressive increase in strain under a state of constant
(d) Thermal conductivity. Thermal conductivity
stress. Creep is closely related to the modulus of
is defined as the quantity of heat flowing through a
elasticity and compressive strength of the concrete
unit thickness over a unit area of the material sub-
and is thus a function of the age of the concrete at
jected to a unit temperature difference between the
loading. Creep is determined according to CRD-C 54
two faces. This parameter is most sensitive to the
(USAEWES 1949g). For purposes of a NISA, at
proportion of cement paste, free water, and aggregate.
least three ages of loading should be conducted:
It is calculated from the thermal diffusivity and
1 day, 3 days, and 14 days. Typical values for creep
specific heat according to CRD-C 44 (USAEWES
of mass concrete are about 1 10-6 microns/psi at a
1949f). Thermal conductivity of mass concrete is not
test age of 60 days for a specimen loaded at 1 day
significantly affected by changes in temperature over
age and about 0.2 10-6 microns/psi at a test age of
typical ambient temperature ranges. Typical values
60 days for a specimen loaded at 14 days age. A
for thermal conductivity of mass concrete range from
curve of creep which is a function of the modulus
1 to 2 Btu/ft-hr-F.
A-12
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