Self curing-concrete-

What is curing of concrete?
▪ Curing is the maintenance of a satisfactory moisture
content and temperature in concrete for a period of
time immediately following placing and finishing so
that the desired properties may develop.
▪ Curing has a strong influence on the properties of
hardened concrete ; proper curing will increase,
durability, strength, watertightness, abrasion
resistance, volume stability, and resistance to
freezing and thawing etc.

Hydration of cement:
2C3S + 6H --------> C3S2H3 + 3 Ca(OH)2
100 + 24---------> 75 + 49
2C2S + 4H --------> C3S2H3 + Ca(OH)2
100 + 21 ---------> 99 + 22
▪ C3S requires 24% and c2s requires 21% of water by weight of
cement. It has been estimated that avg. 23% is required for
complete chemical reaction.
▪ It has been also estimated that about 15% water by wt. Of cement
is requires to fill up the gel pores.
▪ So total 38% of water is requires by wt. Of cement for complete
hydration process.

▪ In all this it is assumed that hydration is taking place in sealed
container, where moisture evaporation does not take place.
▪ Excess or lack of water
may cause undesirable
Capillary cavities.

DEFINATION OF CURING;
(as per ACI-308R)
▪ The term "curing" is frequently used to describe the process
by which hydraulic-cement concrete matures and develops
hardened properties over time as a result of the continued
hydration of the cement in the presence of sufficient water
and heat.
(as per IS:456-2000 )
▪ “ curing is the process of preventing the loss of moisture
from the concrete.”

Types Of Curing
a) Water curing:
▪ immersion
▪ Ponding
▪ Spraying
▪ Wet covering
b) Steam curing
c) Self curing/ membrane curing
d) miscellaneous:

What is self curing concrete?
▪ It has been pointed out earlier that curing does not means
application of water ,it means also creation of condition for
promotion of Uninterrupted and Progressive hydration.
▪ It is also pointed out that the quantity of water, normally
mixed for making concrete is sufficient to hydrate the cement
content.

(…cntd. )
▪ Concrete in which the mixing water is restricted by means of
some chemical compounds, to go out from the concrete body
is known as “self curing concrete.”

Why self curing concrete?
▪ Some times works are carried out in
place where there is acute shortage of
water and the application of water
curing is not possible for reasons of
economy.
▪ prevention of moisture loss from the
surface of flat concrete works such as
highways and airports have been
challenging task for construction
managers.

(…cntd)
▪ If the evaporation of moisture from
concrete are not prevented properly it
may results in plastic shrinkage cracks,
poorly formed hydrated products,
finishing problems and other surface
defects.
▪ Sometimes concrete is placed in some
inaccessible , difficult or far places.
Where curing cannot be properly done
or supervised.

▪
How to find out the
rate of evaporation?
•Drying behavior of
concrete depends upon air
temperature, relative
humidity , concrete
temperature and wind
condition.
•Figure shows drying
behavior as per learch’s
investigation.
•(Based onACI:305 R-5)

How the self curing is
being done?
▪ Membrane forming curing compounds are used to
retard the loss of water from concrete during the early
age.
▪ They are used not only for curing fresh concrete but
also further curing after removal of formwork.
▪ Application of these compounds seals the concrete
surface effectively by forming monomolecular film on
the surface.
 Membrane forming curing compounds is a long chain
of hydrocarbon molecules.
 Which forms monomolecular film on the surface of
the concrete immediately after placing.

H H H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
H-C-H H-C-H H-C-H
| | |
O O O
| | |
H H H
CURINGCOMPOUNDWATERCONC.
The compound molecules is
primarily hydrophobic in nature
with hydrophilic terminal group.
 Hydrophilic terminal group
attaches it self to the film of
bleeding water.
While the long Hydrophobic
chain maintains a vertical
orientation away from the bleeding
water.
 Water molecules do not possess
sufficient energy to escape through
the hydrophobic layer.
Which results into quick
reduction in the evaporation loss.
MECHANISM:

▪ The hydrophobic effect represents the
tendency of water to exclude non-polar
molecules. The effect originates from the
disruption of highly dynamic hydrogen
bonds between molecules of liquid.
▪ A hydrophilic molecule or portion of a
molecule is one that has a tendency to
interact with or be dissolved by water.
▪ A pure hydrocarbon molecule, is incapable of
forming hydrogen bonds with water.
▪ The hydrogen bonds are partially
reconstructed by building a water "cage"
around the compound molecule.
▪ The water molecules that form the "cage“
have substantially restricted mobilities.

TYPES OF COMPOUNDS:
a) Synthetic resin
b) Wax
c) Acrylic
d) chlorinated rubber

TYPE OF COMPOUND DESCRIPTION
resin and wax based curing
compound
•They seals the concrete effectively.
• with the time their efficiency will get
reduced.
• if plastering is required to be done the
surface can be washed off with hot
water.
• it gives an average efficiency of about
80%.

TYPE OF COMPOUND DESCRIPTION
Acrylic based membrane
forming curing compound
•They seals the concrete effectively.
• additional advantage of having better
adhesion of subsequent plaster. It does
not need to be washed with hot water.
• better bonding for plaster.
Chlorinated rubber type
compound
• it does not only protect concrete from
drying out but also fill the minute pores
in the surface of concrete.
• the surface film will wear out
eventually.

APPLICATION PROCEDURE
• It is applied by brushing or by spraying while the concrete is
wet.
• In the case of beam and column the application is done after removal
of formwork
• In case of road and pavements the curing compound is applied after
texturing.
• in case the concrete surface has dried, the surface should be sprayed
with water and thoroughly wetted and made fully damp before curing
compound is applied.
• the container of curing compound should be well stirred before use.

Liquid membrane forming
compound:
▪ Following types of compounds are included in it;
a) clear or translucent without dye
b) clear translucent with fugitive dye
c) White pigmented
• The main performance specification for curing compounds:
ASTM C-309 Liquid Membrane – Forming Compounds for Curing
Concrete.The curing compound shall not allow the concrete
specimen to lose more than 0.55kg /m² of water in 72 hours

White-pigmented concrete curing
compounds
▪ White-pigmented concrete curing compounds are wax-
based dispersions with selected white pigments.
▪ When properly applied, which optimizes water
retention.The white pigment reflects the sun's rays and
helps to keep the concrete surface cooler and prevent
excessive heat buildup.
▪ It is ideal for application on exterior, horizontal surfaces,
such as highways, airports pavements.

Advantages
▪ When properly applied, provides a premium-grade
film, which optimizes water retention.
▪ Protects by reflecting the sun's rays to keep the
concrete surface cooler and prevent excessive heat
buildup, which can cause thermal cracking.
▪ Furnished as a ready-to-use, true water-based
compound. Produces hard, dense concrete ...
minimizes hair checking, thermal cracking, dusting
and other defects.
▪ Offers a compressive strength significantly greater
than improperly or uncured concrete.
▪ Improves resistance to the abrasion and corrosive
actions of salts and chemicals ... minimizes

Application method
▪ Spray on in one even coat with a hand or power sprayer
as soon as the surface water disappears from concrete
surface.
Precautions
▪ Keep from freezing. Do not apply when the temperature
of the air and/or the concrete is less than 40º F (4º C).
▪ Do not mix or dilute with any other products or liquids.
▪ Do not use on surfaces that are later to be painted, tiled,
hardened, sealed or treated in any manner. Not
recommended for use on residential applications.
▪ It is applied in two coats. If needed more coat may be
applied.

Resin-Based, Water-Based
Concrete Curing Compound:
Uses
▪ Used on both interior and exterior applications where paint,
resilient tile or resilient flooring may be applied later.
▪ Because of the wide variety of coatings, paints, adhesives, and
toppings available, contact the manufacturer of the flooring
system for application approval over resin-based curing
compounds.
▪ A small test application is always recommended.
Technical data
▪ Drying time: typically dries in 1-2 hours, depending on jobsite
conditions (temperature, wind, etc.)

General Tips For Application Of Liquid-
Membrane Curing Compounds:
▪ Always apply the curing compound uniformly at the specified
application rate (typically 200 ft²/gallon, 4.9 m²/L).
▪ A major problem on most jobsites is the spraying of the curing
compounds at extremely high application rates, i.e.,The
material is applied at 300-400 ft²/gallon, rather that 200
ft²/gallon. As a result, the quality of the concrete goes down
dramatically!
▪ A good rule of thumb on flatwork is to apply the curing
compound heavy enough to create a slight flood of material
on the concrete surface or, as another option, apply the curing
compound in two applications, one at right angles to the
other.

Conclusion
▪ In short, discussed all above curing compounds are
effective tool to avoid the occurrence of plastic
shrinkage cracks in a windy, low humid and
exposed to sun condition.
▪ Contractor can benefit by able to expedite the
work schedule and placing more concrete while
client benefits by obtaining concrete free of plastic
shrinkage crack and having greater durability
value.

▪ REFERANCES:
▪ ACI 308 R
▪ Text book of concrete technology by M.S.shetty
▪ article on evaporation reducer for pavement concrete, NBM &
CW, april 2007
▪ www.wikipedia.com
▪ www.google.com
▪ Web site ofW. R. MEADOWS, 2002

Thank you
For more…. Mail to aglaiaconnect2018@gmail.com

Self curing-concrete-

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