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Setting is the stiffening of
the cement paste after water is mixed. Broadly it refers to change from
fluid to solid state.
Although during setting the
cement paste acquires some strength, for practical purposes it is convenient to
distinguish setting from hardening, which refers to the gain of strength of a
set cement mortar.
In practice, the terms Initial
Set & Final Set are used to describe arbitrarily chosen stages of setting.
What are initial & final setting points?
When water is mixed with
cement, the paste so formed remains pliable and plastic for a short time.
During this period it is possible to disturb the paste and remix it without any
deleterious effects. As the reaction between water and cement continues, the
paste loses its plasticity. This early period in the hardening of cement is
referred to as ‘setting’ of cement. Initial set is when the cement paste loses
its plasticity and stiffens considerably. Final set is the point when the paste
hardens and can sustain some minor load.
Both the Initial & Final
setting points are arbitrary points and these are determined by Vicat needle
penetration resistance.
Initial setting time can be
understood as the time elapsed between the moment the water is added to the
cement, to the time that the paste starts losing its plasticity. This is the
time interval for which the cement products remain in plastic conditions. As
such, activities such as mixing, transporting, placing, compacting &
finishing should be completed within this time period.
Final setting time can be
understood as the time elapsed between the moment the water is added to the
cement, to the time when the paste has completely lost its plasticity. After
placement, compaction & finishing of concrete, it is desirable that the
concrete loses its plasticity in earliest possible time so that it becomes less
vulnerable to damages from external agencies.
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Initial Set
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Final Set
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Setting time can be measured
by following methods:
1. Vicat
Needle/Apparatus Method
2. Gillmore
Needle Method
Attempts to develop Some other
reliable methods have so far not been very successful.
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