ML12153A355
| ML12153A355 | |
| Person / Time | |
|---|---|
| Issue date: | 06/01/2012 |
| From: | Office of the Chief Human Capital Officer |
| To: | |
| References | |
| Download: ML12153A355 (68) | |
Text
Concrette Tech C hnolog gy and Codes s
Curing g
Definition of Curing Curing - maintenance of a satisfactory moisture content and temperature in concrete for a period of time immediately following placing and finishing so that desired properties may develop Important for all concrete, but particularly when:
- Placing conditions result in rapid drying of fresh concrete
- Concrete exhibits little bleeding g (e.g.
( g silica fume concrete))
- Concrete develops properties slowly (e.g. fly ash concrete)
Hydration of cement Portland cement is a hydraulic cement: its components, t mainly i l calcium l i silicates, react with water to form other components called calcium silicate y
hydrates hydrates- -CSH ((hydration y )).
hydration).
Hydration stops when internal humidity is lower than 80% or temp. falls below 1414ºF
ºF
Abrams 1919
- Abrams, Still holds in 2009?
Why cure concrete?
- To allow cement hydration progress and the concrete to develop its desired properties
- To prevent moisture loss from the plastic concrete (protect against plastic shrinkage cracking)
- To o minimizee moisture o s u e loss oss from o thee concrete o eea after e
setting (drying shrinkage)
Effect of the Duration of Moist-Moist-Curing on the Strength Development for Concrete 40 Strength gain of concrete stored in fog room (or 30 immersed in lime Strength (M S MPa) water) t )
20
- i.e.
continuouslyy Continuous cured 10 curing 0
1 3 7 14 28 Age (days)
Effect of the Duration of Moist-Moist-Curing on the Strength Development for Concrete If concrete is not cured for a sufficient 40 period of time, time it will not develop its full potential in terms of 30 Strrength (MP Pa) p compressive strength g
(and other properties). 20 The pproperties p of concrete close to the Continuous surface are 10 1 day particularly sensitive t curing to i effects.
ff t Concrete at depth 0 1 3 7 14 28 will lose its moisture att a slower l rate t A (d Age (days))
when the surface is not protected.
Effect of the Duration of Moist-Moist-Curing on the Strength Development for Concrete 40 As the duration of moist i t curing i isi extended -
30 concrete achieves Strrength (MP Pa) a greater proportion of its 20 maximum potential strength p g Continuous 10 7 days 3 days 1dday 0
1 3 7 14 28 Age (days)
Curing Requirements - ACI 308R- 308R-01 Basic Curingg Period 7 days above 50oF or Time to reach 100% of specified performance, including post post-curing curing gains Additi AdditionallCCuring i R Requirements i t Based B d on Exposure
Curing Requirements - ACI 308R- 308R-01 (Continued)
St ct al Safety Structural Safet Curing period extended until 70% of specified strength is reached Reinforced Mass Concrete 7 days or until 70% of specified strength is reached Unreinforced Mass Concrete 2 weeks without SCMs SCMs, 3 weeks with SCMs
Methods of Curing
- 1. Ponding or continuous sprinkling
- 2. Absorptive mat or fabric continuously wet
- 3. Wet sand or straw 4
- 4. Spray curing compounds
- 5. Waterproof paper or plastic film
- 6. Vapor mist bath (precast)
- 7. Forms in contact with concrete surface
- 8. Others, approved by the Owner
Methods of Curing
- 1. Ponding or continuous sprinkling
- 2. Absorptive mat or fabric continuously wet
- 3. Wet sand or straw
- 4. Spray curing compounds
- 5. Waterproof paper or plastic film
- 6. Vapor mist bath (precast)
- 7. Forms in contact with concrete surface f
- 8. Others, approved by the Owner
Methods of Curing
- 1. Ponding or continuous sprinkling
- 2. Absorptive mat or fabric continuously wet
- 3. Wet sand or straw 4
- 4. Spray curing compounds
- 5. Waterproof paper or plastic film
- 6. Vapor mist bath (precast)
- 7. Forms in contact with concrete surface
- 8. Others, approved by the Owner
Methods of Curing
- 1. Ponding or continuous sprinkling
- 2. Absorptive mat or fabric continuously wet
- 3. Wet sand or straw 4
- 4. Spray curing compounds
- 5. Waterproof paper or plastic film
- 6. Vapor mist bath (precast)
- 7. Forms in contact with concrete surface
- 8. Others, approved by the Owner
Methods of Curing
- 1. Ponding or continuous sprinkling
- 2. Absorptive mat or fabric continuously wet
- 3. Wet sand or straw
- 4. Spray curing compounds
- 5. Waterproof paper or plastic film
- 6. Vapor mist bath (precast)
- 7. Forms in contact with concrete surface f
- 8. Others, approved by the Owner
Methods of Curing
- 1. Ponding or continuous sprinkling
- 2. Absorptive mat or fabric continuously wet
- 3. Wet sand or straw
- 4. Spray curing compounds
- 5. Waterproof paper or plastic film
- 6. Vapor mist bath (precast)
- 7. Forms in contact with concrete surface f
- 8. Others, approved by the Owner
Methods of Curing
- 1. Ponding or continuous sprinkling
- 2. Absorptive mat or fabric continuously wet
- 3. Wet sand or straw
- 4. Spray curing compounds
- 5. Waterproof paper or plastic film mperature (oC Curing Tem C)
- 6. Vapor mist bath (precast)
- 7. Forms in contact with concrete surface f
- 8. Others, approved by the Owner
Methods of Curing
- 1. Ponding or continuous sprinkling
- 2. Absorptive mat or fabric continuously wet
- 3. Wet sand or straw
- 4. Spray curing compounds
- 5. Waterproof paper or plastic film
- 6. Vapor mist bath (precast)
- 7. Forms in contact with concrete surface f
- 8. Others, approved by the Owner
METHODS OF CURING Membrane Partially saturated
- SEAL IN MIXING WATER Spray curing compound Saturated Waterproof paper Polyethylene sheets
- SUPPLY ADDITIONAL WATER Water supplied from external Ponding source Soaker hose Wet sand W t burlap Wet b l S Saturated d Immersion (precast)
Steam curing (saturated air)
600 4
Tensile Strength 500 Cracking Drying y g Stress 3 400 Tension n, psi Tension,, Mpa 300 8 in. (200 mm) wall 2 73 °F (23 °C) temp.
Fully Restrained 200 Cement: 517 lb / ya 3 (307 kg / m 3 )
W / C = 0.45 1 100 3 7 Start of drying at 50% R.H.
1 28 40 60 Age, days
Timing of Operations Heat Development Heat generated H d Contact of cement and water setting 0 2 to 3 Time (hours)
Evaporation of Surface Moisture from Concrete
Precautions to Minimize Plastic Shrinkage Cracking
- Moisten aggregates
- Cool aggregates and mixing water
- Dampen subgrade
- Erect temporary windbreaks and sunshades
- Cover concrete
- Fogg slab immediately y after placing
- Add plastic fibers
Fogging Good Fogging Bad Fogging Evaporation Retarders Curing Compound Applied to Fresh Concrete Moist Curing After the C
Concrete t HHardens d
Ad Adequate t curing i isi essential ti l
Wet burlap & plastic X
Curing Membrane
X
Ensuring Adequate Curing
- Curing should be a separate pay item in the contract
- Contractor should submit a curing plan
- The various tasks - initial, intermediate &
final curing - have to made someones specific responsibility
- Adequate inspection required
- Problems with curing-membrane systems?
- Proper coverage/application
- No thermal benefit (+/-)
( /)
- Bonding of subsequent overlay materials
Field example, Iff time allowsll Examplel where h curing was criticall on thin h
low permeability shotcrete overlay:
Specification 1/2 - in. thick 6000 psi at 28 days Less then 1500 coulombs rating (low permeability)
Bond strength of 200 psi Project Climate: frequently hot and windy conditions
Questions.