Civil Engineering Reference
In-Depth Information
Load
0.15 m
0.3 m specimen
Failure plane
FIGURE 7.32
Split-tension test.
Typical indirect tensile strength of concrete varies from 2.5 MPa to 3.1 MPa
(360 psi to 450 psi) (Neville 1981). The tensile strength of concrete is about
10% of its compressive strength.
■
7.5.3
Flexure Strength Test
The flexure strength test (ASTM C78) is important for design and construc-
tion of road and airport concrete pavements. The specimen is prepared either
in the lab or in the field in accordance with ASTM C192 or C31, respectively.
Several specimen sizes can be used. However, the sample must have a
square cross section and a span of three times the specimen depth. Typical
dimensions are 0.15-m by 0.15-m (6-in. by 6-in.) cross section and 0.30-m
(18-in.) span. After molding, specimens are kept in the mold for the first
then removed from the mold and cured at
either in saturated-lime water or in a moist cabinet with a rela-
tive humidity of 95% or higher until testing. The specimen is then turned on
its side and centered in the third-point loading apparatus, as illustrated in
Figure 7.33. The load is continuously applied at a specified rate until rupture.
If fracture initiates in the tension surface within the middle third of the span
length, the flexure strength (modulus of rupture) is calculated as
24
;
8 hours,
23
;
1.7°C
1
73.4
;
3°F
2
,
Mc
I
PL
bd
2
R
=
=
(7.5)
where
R
=
flexure
strength, MPa (psi),
bending
M
=
maximum
moment
=
PL/6,
N.mm (lb.in.),
c
=
d/2,
mm (in.),
of
bh
3
/12, mm
4
in.
4
I
=
moment
inertia
=
1
2
,
P
=
maximum
applied load, which is distributed evenly (1/2 to each)
over the two loading points, N (lb),
length, mm (in.),
width of specimen, mm (in.), and
depth of specimen, mm (in.).
L
=
span
b
=
average
d
=
average
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