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    HOW TO CARRY OUT UNCONFINED COMPRESSION STRENGTH TEST (UCS)


    UNCONFINED COMPRESSION STRENGTH TEST (UCS)


    How to carry out unconfined compressive test (UCS)


    Aim: To determine the compressive strength of specimen.
    Apparatus: 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.
    The unconfined compression test continues until the load on the sample peaks and falls slightly.
    The unit strain Ɛ is computed from mechanics of materials as follow:
    Strain Ɛ = ∆L/L0
    Where:
    ∆L = Total specimen deformation,
    L0 = Original/initial length of specimen.
    The instantaneous stress test 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
    A’ = Corrected area of 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.
    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.
    3.   Carefully de-mould sample such that too 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).
    6.   Carefully align the sample in the 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)
    8.   After failure, remove the sample and dry 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.


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