What is the the setting time of concrete ? how we find it ? What is the difference between the setting time of cement and concrete?
It is the time at which hydration process or gel formation begins (hardening of concrete).
Setting time of concrete is usually differentiated as initial setting time and final setting time. a known method of test for determining setting time of concrete by penetration resistance. Setting time of concrete is affected by some variables: cement type, cement content, aggregate, temperature, ....etc.
There are so many literature on this subject. Also, specifications and codes are identifying it.
Division on setting time of cement is based on Initial setting time of cement and Final setting time of cement.
Generally Initial setting is the time elapsed between the moment water is added to the cement to the time at which paste starts losing its plasticity.
Final setting time of cement is the time elapsed between the moment the water is added to the cement to the time at which paste has completely lost its plasticity and attained sufficient firmness to resist certain definite pressure.
Initial setting time of cement is 30 min and 10hrs which is referred as Final setting time of cement.
and it is find out by time period elapsing between the time, water is added to the cement and the time, the needle fails to pierce the test block by 5.0 ± 0.5 mm measured from the bottom of the mould, is the initial setting time.
SETTING TIME OF CONCRETE IS NOT SAME AS SETTING TIME OF CEMENT.
APPARATUS USED FOR CEMENT SETTING IS VICAT'S APPARATUS, FOR CONCRETE IT IS PENTROMETER.
CODE
FOR CEMENT-IS 269
FOR CONCRETE IS 8142-1976, ASTM C-803
FOR SETTING TIME OF CONCRETE
USING PENTROMETER WITH PROPER NEEDLE SELECTION,RECORDING PENETRATION RESISTANCE(MPa)(Y-AXIS)
ELAPSED TIME (MINUTES)(X-AXIS)
PLOTTING SMOOTH CURVE AND FINDING FOR PENETRATION RESISTANCE 3.5 MPa ELAPSED TIME - IT IS INITIAL SET
FOR PENETRATION RESISTANCE 27.6 MPa ELAPSED TIME IN MINUTES FROM CURVE PLOTTED IS FINAL SET.
SETTING TIME OF CONCRETE DEPENDS ON
TEMPERATURE CONDITIONS]
CEMENT TYPE
WATER CEMENT RATIO
MINERAL ADMIXTURE IF ANY USED
PLASTICIZER -ITS DOSE USED IF ANY
The action of changing mixed cement from a fluid state to a solid state is called setting of cement and time required for it to set is called setting time of cement. ... When water is mixed with cement to form a paste, reaction starts. In its pure form, the finely ground cement is extremely sensitive to water.
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