Curing definition and its importance in Concrete

2.  What do the family members do when a baby is
born in the family? The baby is pampered and
protected from the aggressive environment. In
the similar fashion, newly cast concrete is a new
born baby in the world of structures and it needs
the protection in the form of curing.
 What is the important aspect for strength and
durability of concrete? Some may answer that
production of concrete, while some other may
answer that testing of concrete is important.
They all are important, but the important aspect
what many people at project sites neglect is,
curing. Either it be of concrete cubes or of the
concrete elements. Curing plays very important
role on strength of concrete.

3.  As per IS 456:2000 definition, “Curing is the
process of preventing the loss of moisture from the
concrete whilst maintaining a satisfactory
temperature.
 We all know that to achieve strength of concrete,
cement is the key ingredient and concrete by virtue
of cement gains strength by hydration process. After
adding water in concrete hydration process
immediately starts and strength is gained gradually.
To achieve this, necessary water in form of moisture
is required to be maintained in concrete. To avoid
loss of moisture, curing is require
 Curing is also a key player in mitigating cracks in
the concrete, which severely impacts durability

4. The important reasons to cure concrete are:
o Gain of strength in concrete
o Improved durability of concrete
o Improved serviceability
o Improvement in microstructure of concrete

5. If the surface area is very large (large slab or
raft foundation etc.), it is necessary to prevent it
drying out. Hence, after finishing of concrete,
curing should be started immediately using
hessian cloth or plastic sheet etc. after final
setting takes place.
After final setting, meticulous curing is required
as per selected practice.

6. Curing of concrete cube samples
AsperIS516:1959,concretecubessamplesarestored
onthe site at a place free fromvibration, under damp
hessian cloth for 24 hours ± ½ hour from the time of
adding the water. The temperature of the place of
storageshallbewithinthe range of22°to32°C. After
removing the cubes from the moulds, the samples to
be stored in curing tank until they are tested. The
temperature of the curing tank should be kept in
range of 27° ± 2° C.
Curing tanks must be prepared at stores in
transmission line projects and for railway, pipeline
and substation projects they can be prepared near
office/store.

7.  Based on experiment
conducted by
“Cement, Concrete &
Aggregates,
Australia”, it is
evident that strength
of concrete if cured
not at all, is only
40% against the
concrete kept under
continuous curing.
Effect of duration of water curing
on strength of concrete

8.  IS 456:2000 suggests that, in normal conditions, curing
should be continued at least for seven days from the day of
placing concrete in case of OPC. If mineral admixtures or
blended cements like PPC or slag cement is used, curing
should be continued at least for ten days
 If the concrete is exposed to dry and hot weather conditions,
the limits mentioned in b) above may be extended for ten
days and fourteen days respectively.
 As a good practice, date of casting should be mentioned on
concrete surface, so that number of days of curing can be
easily identified and maintained.

9.  As a good practice,
date of casting
should be
mentioned on
concrete surface, so
that number of days
of curing can be
easily identified and
maintained.
Writing of date of casting

10. Evaporation of water
from concrete soon
after placing depends on
the temperature and
relative humidity of the
surrounding air and on
the velocity of the wind.
The difference between
the temperatures of
concrete and of
surrounding air also
affects the loss of water.

11. TYPES OF CURING

12.  Concrete for flat
surfaces such as
pavements, sidewalks,
and slabs can be cured by
Ponding.
 Ponding is undesirable if
the concrete will be
exposed to early
freezing.

13.  Sprinkling is an excellent method of curing. If
it is done at intervals, care must be taken to
prevent the concrete from drying the
applications of water.
 When a fine spray of water is continuously
applied, the possibility of "crazing" or
cracking due to alternate cycles of wetting
and drying can be minimized.

15.  Wet coverings such as burlaps, cotton mats, or
other moisture-retaining fabrics are extensively
used for curing.
 Wet coverings of earth or sand are effective for
curing, too.
Moist earth or sand  ~ 5cm (on previously moistened
surface)
Moist hay or straw  ~ 15 cm (keep continuously wet)

16. Burlaps Treated burlaps

17.  Sealing the concrete surface may be done by
means of waterproof papers, plastic sheets, liquid
membrane-forming compounds, and forms left in
place.
 One important advantage of this group of methods
is that periodic additions of water are not
required.
 These methods assure the hydration of cement by
preventing loss of water from the concrete. They
should be applied as soon as the concrete has
hardened sufficiently to prevent surface damage,
and after concrete has been thoroughly
moistened.

18. Liquid membrane-
forming compounds
sprayed onto the
surface
Polyethylene
sheet
It is used at the place where finishing activities are not required after
concrete.

20. Steam curing can be used to advantage where
early strength gain in concrete is important or
where additional heat is required to accomplish
hydration, as in cold-weather concreting. There
are two methods of steam curing:
(1) curing in live steam at atmospheric pressure
(for enclosed cast in place structures and
manufactured precast units)
(2) curing in high pressure steam autoclaves (for
small manufactured units)

21. A steam curing cycle
consists of
(1) an initial delay prior to
steaming;
(2) a period for increasing
temperature;
(3) a period for holding
the maximum
temperature constant;
(4) a period for decreasing
temperature.

22.  Water-base concrete curing compound is
formulated from hydrocarbon resins and may be
used on interior, exterior, vertical and horizontal
concrete surfaces. Once applied, it forms a
liquid membrane that retains an optimum
amount of water present in freshly placed
concrete to allow complete hydration of the
cement. NOTE: After approximately four weeks,
the membrane begins to chemically break down.
When the curing cycle is complete, the
membrane will eventually wear off the surface.
This process usually takes another three to five
weeks under normal traffic and weathering
conditions

23. It is used at the place where finishing activities are
required after concrete.

24. In extreme cold condition, i.e. below 4° C, some
problems like freezing of concrete before
adequate strength, slow strength development,
induction of thermal stresses etc. are associated.
They can be prevented by providing heated
enclosures, insulated blankets, curing compound
etc. Temperature of fresh concrete must be kept
above 10° C. Curing must be continued for longer
period or time till the concrete gains the desired
strength.
Cold weather condition