TM 5-809-3/NAVFAC DM-2.9/AFM 88-3, Chap. 3
the standard 12 inch truncated cone test, is typically
Ss, by:
from 8 inches to 10 inches, depending upon the
0.707P
fluidity required.
Ss '
(eq 3-1)
A
(3) Consolidating grout. Consolidation is es-
sential to obtaining grout in-place without voids or
debonding due to shrinkage. Poor consolidation
may cause reduced masonry compressive strength
Where:
and poor bond of grout to masonry unit. Mechani-
A = The average of the gross areas (solid-unit
cal vibration is greatly superior to puddling and
masonry) or net areas (hollow unit masonry) of the
should be used for consolidating all grout pours
two contiguous upper sides of the specimen.
(b) The racking test described in ASTM
greater than one masonry course in height. Con-
solidation should be done by vibrating soon after
E 72 (Section 14) has been used to measure
grout placement and by re-vibrating when the
diagonal tensile strength of eight foot by eight foot
excess water has been absorbed from the grout by
wall specimens. However, hold-down forces
the masonry units. Mechanical vibration must be
induced by the test fixture complicate the state of
done before the grout has stiffened to prevent a
stress.
(2) Sliding shear strength. The sliding shear
void in the grout caused by the vibrator.
strength is the strength in bond between the mortar
3-6. Reinforcement. Masonry is reinforced with
and the units which resists relative movement of
steel bars or joint reinforcement. Joint reinforce-
adjacent units in a direction parallel to the mortar
ment, placed in mortar beds, is unique to masonry
joint between them. In case of shear walls, where
and is primarily used to resist internal forces due to
shear is normally considered to be a horizontal
shrinkage or thermally-induced movement.
force parallel to the bed joints, sufficient bond
between mortar and units must exist in order for
diagonal tension strength to be developed.
3-7. Standard tests.
a. Compression. The compressive strengths of
Otherwise failure occurs in step-wise fashion along
masonry assemblages may be established by testing
a diagonal in the plane of the wall. It has been
small masonry assemblages referred to as "prisms",
shown experimentally that joint shear strength is
in accordance with ASTM E 447. To establish the
increased by compression across the joint. Results
compressive strength of a given unit-mortar
obtained by testing small specimens under
assemblage, a minimum of three prisms must be
controlled conditions reflect a friction coefficient of
tested. Prisms may be constructed in stack-bond or
approximately 1.0.
c. Flexure test. The standard test to establish
in a bonding arrangement which simulates the
bonding pattern to be used in the structure, except
flexural strength in masonry is given in ASTM E
no structural reinforcement is used in the prisms.
518, which provides requirements for materials,
Masonry prisms should be constructed with the
specimen preparation and configuration, testing,
same materials, joint thickness, and workmanship
and calculations. The test establishes flexural tensile
used in the structure.
bond strength in a direction perpendicular to the
b. Shear. In reinforced masonry, shear loads
bed joint by third-point or uniform loading of
may be carried either by the masonry or, if the
stack-bond specimens. Extreme care is required in
masonry is not adequate, by the reinforcing steel.
handling flexural bond test specimens. Flexural
Masonry is an assemblage of discrete units and
tensile bond strength may also be determined by the
mortar, so when the shear force is carried by the
"bond wrench" test. The test is based upon "prying
masonry, two forms of shear strength exist. These
off" one masonry unit at a time from a multi-unit
strengths are diagonal tension strength and sliding
stack-bond prism (or beam). Flexural tensile stress
shear strength along the mortar joint. The standard
is calculated based upon an assumption of a linear
tests used to determine the shear strength in
flexural stress distribution across the unit width.
masonry are as follows:
Equations provided in ASTM C 1072 account for
(1) Diagonal tension tests.
the effects of compression due to the load and its
(a) The standard diagonal tension test;
eccentricity. The test apparatus is detailed in the
presented in ASTM E 519, Diagonal Tension
standard. Whereas flexural beam tests provide one
(Shear) in Masonry Assemblages; establishes the
data point, that is the beams fail at one joint, the
diagonal tension of masonry panels by loading 4-
bond wrench method provides as many data points
foot by 4-foot panels in compression along one
as there are joints in the specimens.
diagonal. Failure occurs in tension perpendicular to
(1) The flexural capacity of unreinforced ma-
the diagonal. The value of the compression load, P,
sonry walls depends either upon the tensile bond
at failure is converted to an equivalent shear stress,
between units, as shown in figure 3-4a, or upon the
3-7
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