1. Curing
Definition
The process of prevention of loss of moisture from fresh concrete while maintaining satisfactory temperature regime (BS 8110)
Fig: The process of curing by using sheets, watering and spraying chemicals

2. Curing Objectives Elements To stop the loss of water
Maintain the temperature
Elements
Moisture
Temperature
Time

3. Curing Advantages of curing
To avoid premature drying of concrete due to
Solar radiation
Wind
Fig: Solar radiation affecting the fresh concrete

4. Curing Advantages of curing
Avoid leaching out by rain or flowing water
Fig: Leaching of concrete

5. Curing Advantages of curing
Protection against rapid cooling in first few days
Avoid high internal thermal/temperature gradient
Fig: Thermal shock to concrete

6. Curing Advantages of curing
Protection against low temperature or frost in cold regions
Fig: Low temperature or snow

7. Curing Advantages of curing Surface zone development Strong
Impermeable
Crack free
Durable
The thickness of surface zone affected by curing is 20mm to 50mm(CIRIA 1997)

8. Curing Advantages of curing Keeping the concrete saturated
So long time that
Water filled holes/voids
Filled by products of hydration
Instead by air

9. Curing
Rate of evaporation

10. Curing Curing Mechanics When RH > 95% Hydration is adequate
Reduction in porosity adequate
When 95% > RH > 80%
Hydration is slow
No reduction in porosity
When RH < 80%
No Hydration
No reduction in porosity (Neville1995)

11. Curing Methods of Curing Form work retention Spraying with water
Ponding
Application of curing membrane
Plastic sheets
Tenting against dry winds

12. Curing Covering with wet sand
Periodically wetted cotton or Hessian mat
Water absorbant cover

13. Curing Formwork Retention Cost will increase Very good in cold weather
Prevent the thermal cracking
4.Construction time may delay

14. Curing Impermeable covering Polyethylene sheet in contact with surface
It should be suspended a few centimeter above
Sides must be sealed
Effective high relative humidity chamber must be maintained
White sheets are preferable
Surface spraying with water before to maintain any small loss of water

15. Curing Absorbent cover Wet sand and Hessian mat
keep the concrete wet until wet
Takes the moisture of concrete when dry
Not recommended for large sections

16. Ponding and spraying Possible on flat surfaces Spraying requires
Continues water supply
Clean nozzles
Wind direction and velocity
Drainage way

17. Curing Ponding and spraying Risk of thermal shock
ACI_308_92 The temperature of water should not be more than 11oC cooler than concrete temperature
Avoid in below freezing temperatures
Water should be same as drinking water

18. Curing membranes Natural / Synethic Resins Waxes Solvents
Hand/ sprayed applied sealing compounds
Applied in liquid form after free water disappear
Natural / Synethic
Resins
Waxes
Solvents

19. Curing Membrane mechanics Greatly reduce the evaporation
When rate of evaporation> rate of bleed
Wetting of surface is necessary
They can be removed if finishing operation is necessary

20. Curing Duration It is a function of Plastic shrinkage
Temperature control
Durability
Strength
Size of structural element
Type of concrete
Environment condition
Specification requirement

21. Curing
Duration

22. Curing
Duration

23. Curing
Duration

24. Curing
Duration

25. Maturity of Concrete
Definition: It is the sum of product of temperature (above datum level -11oC at which hydration stops) and time over which this temperature occurs
M= Sum (T.▲t)
It is used to predict the rate of strength development

26. Strength Development of Concrete
Effect of temperature
Low temperature decreases early strength development
High temperature at early age,
Increases the early strength
Decreases ultimate strength

27. Strength Development of Concrete
Effect of Curing
Strength development requires hydration
Hydration requires water
Loss of water due to evaporation affects hydration

28. Monitoring the strength development
Standard Procedure
Casting cubes or cylinders along with structural members
Strength of sample is different from actual structural member
Due to difference in maturity
Difference in compaction
Difference in curing

29. Monitoring the strength development
Standard Procedure
Significant temperature gradient across the section
Upper surface zone is weak due to water migration
Generally 10% higher strength in slab soffits as compared to top when tested by pull out test
In flexural members upper zone carries compressive stresses

30. Monitoring the strength development
Maturity measurement
Cubes cured along with the structure
Temperature matched curing
Measurement by Coma probes
Measurement by Windsor probe
Break out test TNS test
Pull out test or LOK test
Rebound hammer
Coring
Tables of formwork striking times

31. Monitoring the strength development
Maturity measurement
Cubes cured along with the structure Cubes generally gives lower strength
Cubes follow environment temperatures
Concrete inside structural member is hot
Strength inside is higher
In large sections difference is bigger

32. Monitoring the strength development
Maturity measurement
Tables of formwork striking times
They are conservative
They are based on lowest rate of strength gain
They can be un economical

33. Monitoring the strength development
Temperature matched curing
Procedure
A sensor is put in freshly made concrete section
A water filled tank having cubes, stirrer and heater
And control system
Control system detects temperature difference
It heats the water to same temperature as in section
Cubes have same maturity as section

34. Monitoring the strength development
Maturity measurement
Measurement by Coma probes