Technical
continues for a longer period, even after final
Following diagram depicts the process of
setting time:
hydration and formation of cement gel which
1. As the molecules of the component do not
bind the aggregate particles together.
exist in molecular form, they are connected
with other molecules of same component
with Vander Waal forces to form a cement
particle, which is visible to our eyes. When
this particle comes in contact with water,
the outer molecule first reacts and then
after sometime it provides the space for
water to percolate and react with the
interior molecules of the component. So,
due to this process, the reaction of
hydration continues for a longer period on
contrary to the theory.
2. These
reactions
components
of
of
molecules
cement
with
of
water
produce a lot of heat called heat of
hydration, this heat or energy is absorbed
by the unreacted water and it evaporates
out. Due to this evaporation of water
molecules, a shortage of water is created
and due to this the amorphous/unhydrated
molecules are unable to react instantly.
Because of this, the reaction period is
prolonged and henceforth, to complete
these reactions curing is done after the
setting of the cement.
Formation of Cement-Gel
In the above diagram, (a) shows the condition
of amorphous cement particles in a cementaggregate mix in unhydrated form. When
water is added, then the water molecules fills
the voids between the cement particles and
after laps of initial setting time the molecules
of the cement particles start reacting with
water molecules to form hydrated-cement
molecules as shown in (b). When the hydration
reaction is complete an almost uniform
porous cement-gel is formed as shown in (c),
which sets to form a solid shape.
Role of the Cement in Concrete
The
components
of
the
cement
being
amorphous and dry in nature are sticky and so
the particles of cements stick to anything
which has moisture in it. Due to this property
of
anhydrous
cement
to
stick,
when
aggregates are mixed with cement the colour
of the mixture changes and the colour of
aggregates are dispersed and a uniform colour
of cement persists after mixing.
When water is added to the mixture of cement
and aggregate, then the molecules of cement
particles reacts with water to form the
hydrated molecules of cement-gel which
enters in the pores of the aggregates and sets
inside it. These hydrated molecules are
cohesive in nature and so remains connected
to other hydrated molecules at the same time
as shown in above figure. These hydrated
molecules of cement in total are termed as
cement-gel. The molecules of cement-gel
which sets inside the pores of aggregate