COMPRESSIVE STRENGTH
OBJECT
To determine
the compressive strength of concrete (used in PCC. Work at site).
APPARATUS
Mould Cube
(15×15×15 cm), temping rod etc.
PREPARATION OF
SPECIMEN:-
- Before
placing the concrete in the mould, its interior surface and the base plate
should be lightly oiled.
- The
concrete mixture (1:4:8) is filled into the mould in layers of approximate
5 cm deep.
- Each layer
is uniformly compacted by the temping rod 60 cm length & 16 mm
diameter.
- For cubical
specimens, the number of strokes should not be less than 35 strokes per
layer.
- The mould
is filled again upper 5 cm depth & repeat step 3 & 4 till the
mould is fully filled.
- As the
mould is filled unto the top & the concrete is finally compacted, the
concrete should be struck off level with a trowel any mortar, which has
leaked out between the base, and mould is cleaned away.
CURING:-
a.
As
soon as molding is complete, the mould is stored in a place free from
vibration, in moist air of at least 90 % relative humidity and at a temperature
of 27 ± 2◦C for 24 hours.
b.
After
this period, the specimens are marked, removed from the moulds and immediately
submerged in clean, fresh water and kept there as upto required time period of
testing.
TEST ON COMPRESSION
TESTING MACHINE
- Test should
be done after 7 & 28 days.
- Specimens
stored in water should be tested immediately on removal from the water and
while they are in the wet condition.
- The load
should be applied without shock & increased continuously at the rate
of approximate 140 Kg/cm2/min until the resistance of the
specimen to the increasing loads breaks down and no greater load can be
sustained.
Compressive Strength = P/A
Table:-Average
of three values for 7days & 28days is taken as the compressive strength.
|
Time period
|
Load at failure
|
Cross-sectional area
|
Compressive
Strength
|
|
After
7 days
|
N
|
15x15mm2
|
N/mm2
|
|
After
28 days
|
N
|
15x15mm2
|
N/mm2
|
RESULT
The compressive strength of M 10 (1 : 4 : 8)
grade concrete occurs after 7 days is ...... N/mm2 & after 28 days
is .......N/mm2.
PRECAUTIONS
§ Safety shoes should be used at the time of testing.
§ Before testing, CTM machine should be properly checked.
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