curing of concrete

1. 1
CONCRETE
TECHNOLOGY
LECTURE NOTES-CHAPTER 8
CURING OF CONCRETE

2. 2
CURING OF CONCRETE
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.

3. 3
CURING METHODS-2
Concrete for flat surfaces
such as pavements,
sidewalks, and slabs
can be cured by
ponding. However, it is
often impractical except
for small jobs.
Furthermore, ponding is
undesirable if the
concrete will be
exposed to early
freezing.

4. 4
CURING METHODS-3
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.

5. 5

6. 6
CURING METHODS-4
Wet coverings such as burlaps, cotton mats, or other
moisture-retaining fabrics are extensively used for curing.
Treated burlaps that reflect light and are resistant to rot
and fire are available. Wet coverings of earth or sand are
effective for curing, too. However, it is expensive and may
be useful only in small jobs.
Moist earth or sand  ~ 5cm (on previously moistened
surface)
Moist hay or straw  ~ 15 cm (keep continuously wet)

7. 7
Burlaps
Treated burlaps

8. 8
CURING METHODS-5
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.

9. 9
Liquid membrane-
forming compounds
sprayed onto the
surface
Polyethylene sheet

10. 10

11. 11
CURING METHODS-6
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)

12. 12
CURING METHODS-7
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.

13. 13
CURING METHODS-8
Mostly, time lapses from casting to steam shut off is constant at
18 hrs.
Steam curing at atmospheric pressure is generally done in a
steam chamber or other enclosure to minimize moisture and
heat losses. Tarpaulins are frequently used to form
enclosure. Applications of steam to the enclosure should be
delayed at least two hours after final placement of concrete
to allow for some hardening. Maximum steam temperatures
above 80°C should be avoided because they may result in
low ultimate strength and they are uneconomical.