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