1. PRECAUTIONS TAKEN FOR CONCRETING IN
SUB-ZERO TEMPERATURE
•SELECTION OF SUITABLE CEMENT
•ADMIXTURES
•INSULATION
•ECONOMICAL METHOD OF HEATING
MATERIALS OF CONCRETE
•USE OF AIR ENTRAINING AGENTS
•ELECTRICAL HEATING OF MATERIALS
2. CEMENT
Cement that hydrates fast give larger
quantity of heat and develops early strength.
Prehardening period 40 to 50% of OPC.
Higher % of C3S and lower % of C2s
Eg:rapid hardening cement,high alumina
cement
3. P
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•Heating of water is the easiest method
employed
•For very low temperatures heating of water
alone is inadequate,so aggregates can also be
heated by closed steam coils or by injection of
live steam.
•To maitain prehardening temperature electrical
heating of entire concrete mass is adopted.
•Electricity is conducted through mats or
reinforcing bars
•The evaporation of mixing water should be
restricted by covering entire suface with vapour
tight membrane
4.
5.
6. •Use of accelerating ad mixtures is widely adopted
•The most commonly used material is CaCl2 when
temperature is very low,without any fear of corrosion or
strength reduction
•But it may cause increase in volume change ,lower
resistance to sulphate attack & greater tendency for AAR
•Eg:Russia use combination of Nacl and CaCl2.
•The addition of these regulate freezing point of water and
promote hydration
• But NaCl reduce 28 days strength by 12% though it
accelerates the early strength
7. AIR ENTRAINING AGENTS
•IT IS SEEN THAT WEAKER CONCRETE WITH AIR ENTRAINMENT IS
MORE DURABLE THAN STRONG CONCRETE WITHOUT AIR
ENTRAINMENT
•AIR ENTRAINMENT INCREASES DURABILITY TO 3 TO 7 TIMES THAT OF
OODINARY CONCRETE
•MODIFICATION OF PORE STRUCTURE CAUSED BY AIR ENTRAINMENT
IS THE REASON FOR BETTER FROST RESISTANCE
•THE REDUCTION OF WATER-CEMENT RATIO BECAUSE OF AIR
ENTRAINMENT IS ANOTHER REASON FOR INCREASED DURABILITY
8. •The figure reveals that with no
admixture the mean was lower
than 1, indicating the existence
of damage
•With the admixture, the mean
was clearly higher than 1
revealing a lack of damage
• Consequently, this categorical
division was highly significant,
statistically speaking, and the
presence of the air-entraining
admixture was obviously
instrumental in the existence or
otherwise of post-freezing-
thawing damage.
9. •THE HEAT GENERATED DURING HYDRATION IF
PRESERVED WITHIN THE BODY OF CONCRETE
DURING THE PRE-HARDENING PERIOD CAN
REDUCE HARMFUL EFFECTS OF LOW
TEMPERATURE
•THIS CAN BE DONE BY INSULATING CONCRETE
BY A MEMBRANE,BURLAP,SAW DUST,ETC
•IN CASE OF BEAMS AND COLUMNS IT CAN BE
DONE BY KEEPING THE FORMWORK
