UNCONFINED
COMPRESSION STRENGTH TEST (UCS)
Aim:
To
determine the compressive strength of specimen.
To
determine the compressive strength of specimen.
Apparatus:
mallet,
mould, rod, screw driver, extruder, cutting edge.
mallet,
mould, rod, screw driver, extruder, cutting edge.
Theory: The
unconfined compressive strength test consists of trimming a sample of some
diameter to an adequate L/d ratio, placing it in a compression device, and
measuring load and corresponding displacement intervals.
unconfined compressive strength test consists of trimming a sample of some
diameter to an adequate L/d ratio, placing it in a compression device, and
measuring load and corresponding displacement intervals.
The unconfined compression
test continues until the load on the sample peaks and falls slightly.
test continues until the load on the sample peaks and falls slightly.
The unit strain Ɛ is computed
from mechanics of materials as follow:
from mechanics of materials as follow:
Strain Ɛ = ∆L/L0
Where:
∆L = Total specimen
deformation,
deformation,
L0 =
Original/initial length of specimen.
Original/initial length of specimen.
The instantaneous stress test
σ, on the sample is computed as follows:
σ, on the sample is computed as follows:
Stress = σ1 = P/A’
Where:
P = Load on specimen at any
instance for a corresponding value of ∆L
instance for a corresponding value of ∆L
A’ = Corrected area of
specimen for the corresponding load P (mm^2)
specimen for the corresponding load P (mm^2)
But A’ = A0/(1-Ɛ)
Procedure:
1. Weigh a given amount of your sample and
mix with an amount of water determined from the compaction of that sample.
mix with an amount of water determined from the compaction of that sample.
2. If you are using a mould to prepare your
sample, compact the sample in the mould in three layers and compact each layer
with 10 blows of the rammer.
sample, compact the sample in the mould in three layers and compact each layer
with 10 blows of the rammer.
3. Carefully de-mould sample such that too
much degradation of sample is not observed.
much degradation of sample is not observed.
4. Weigh sample before test.
5. Prevent sample from losing its moisture,
this could be by covering it with a poly ethylene bag (or whatever method is
suitable and can efficiently prevent moisture loss).
this could be by covering it with a poly ethylene bag (or whatever method is
suitable and can efficiently prevent moisture loss).
6. Carefully align the sample in the
compression machine and ensure the two ends of the sample are exactly
perpendicular to the machine.
compression machine and ensure the two ends of the sample are exactly
perpendicular to the machine.
7. After a final check for equipment
clearance, start the test and take load and deformation dial readings as follows:
(for a 0.01mm/div dial gauge), 50, 100, 150, …… 450)
clearance, start the test and take load and deformation dial readings as follows:
(for a 0.01mm/div dial gauge), 50, 100, 150, …… 450)
8. After failure, remove the sample and dry
in the oven for 24 hours to determine moisture content.
in the oven for 24 hours to determine moisture content.
Conclusion:
Show
sample calculations and show results in a tabular form; plot a graph of stress
against strain.
sample calculations and show results in a tabular form; plot a graph of stress
against strain.
