ML12153A355
| ML12153A355 | |
| Person / Time | |
|---|---|
| Issue date: | 06/01/2012 |
| From: | Office of the Chief Human Capital Officer |
| To: | |
| References | |
| Download: ML12153A355 (68) | |
Text
s s Curin g Curin g Code s Code s g g g y and g y and h nolo g h nolo g te Tec h te Tec h C oncre t C oncre t C C Definition of Curing Curing-maintenance of a satisfactory moisture content andtemperatureinconcreteforaperiodoftime and temperature in concrete for a period of time immediately following placing and finishing so that desired properties may developImportant for all concrete, but particularly when:*Placing conditions result in rapid drying of fresh concrete*Concrete exhibits little bleedin g (e.g. silica fume concrete
)g(g)*Concrete develops properties slowly (e.g. fly ash concrete)
Hydration Hydration of of c c e e ment ment Hydration Hydration of of c c e e ment ment P Portland ortland cement is a cement is a hydraulic cement: its hydraulic cement: its tilli tilli componen t s, ma i n l y ca l c i um componen t s, ma i n l y ca l c i um silicates, silicates, react with water
react with water to to formothercomponents formothercomponents form other components form other components called calcium silicate called calcium silicate h y drates h y drates--CSH (CSH (h y dration h y dration). ). y y (
(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
Abrams1919 Abrams , 1919Still holds in 2009?
Why cure concrete?Why cure concrete?
- Toallowcementhydrationprogressandthe
- To allow cement hydration progress and the concrete to develop its desired properties
- Topreventmoisturelossfromtheplasticconcrete To prevent moisture loss from the plastic concrete (protect against plastic shrinkage cracking)
- To minimiz e m o i s t u r e l oss fr o m th e c o ncr e t e a ft e r oeosueossoeoeeaesetting (drying shrinkage)
Effect of the Duration of MoistEffect of the Duration of Moist--Curing on the Curing on theStrengthDevelopmentforConcrete StrengthDevelopmentforConcrete 40Strength Development for ConcreteStrength Development for ConcreteStrength gain of concretestored 30 M Pa)concrete stored in fog room (or immersed in lime t)20 Strength (M Continuous wa t er)-i.e.
continuousl y 10 S Continuous curing ycured 0 Age (days)1371428 Effect of the Duration of MoistEffect of the Duration of Moist--Curing on the Curing on theStrengthDevelopmentforConcrete StrengthDevelopmentforConcrete 40Strength Development for ConcreteStrength Development for ConcreteIf concrete is not cured for a sufficient periodoftimeitwill 30 P a)period of time , it will not develop its full potential in terms of
com pressive stren g th 20 r ength (M P pg (and other
properties).
T he p ro p erties of 10 St r Continuous 1 day ppconcrete close to the surface are particularly sensitive tifft 0A(d)1371428 t o cur i n g e ff ec t s.Concrete at depth will lose its moisture tlt Ag e (d a y s)a t a s lower ra t e when the surface is
not protected.
Effect of the Duration of MoistEffect of the Duration of Moist--Curing on the Curing on theStrengthDevelopmentforConcrete StrengthDevelopmentforConcrete 40Strength Development for ConcreteStrength Development for ConcreteAs the duration of itii 30 P a)mo i s t cur i ng i s extended -
concrete achieves agreater 20 rength (M P a greater proportion of its
maximum potential stren g th 10 St r Continuous 7 days 3 days 1d pg 0Age(days)1 d a y1371428Age (days)
Curing Requirements Curing Requirements --ACI 308RACI 308R--01 01 Basic Curin g Period g7 days above 50 o F or orTime to reach 100% of specified performance, includingpost
-curinggains including post curing gainsAdditilCiRitBd Additi ona l C ur i ng R equ i remen t s B ase d on Exposure Curing Requirements Curing Requirements --ACI 308RACI 308R--01 01 (Continued)
(Continued)StctalSafet St ru ct ur al Safet yCuring period extended until 70% of specified strength is reachedReinforced Mass Concrete7 days or until 70% of specified strength is reachedUnreinforced Mass Concrete2weekswithoutSCMs3weekswithSCMs 2 weeks without SCMs , 3 weeks with SCMs Methods of Curing Methods of Curing1.Ponding or continuous sprinkling2.Absorptive mat or fabric continuously wet3.Wet sand or straw 4Spraycuringcompounds 4.Spray curing compounds5.Waterproof paper or plastic film 6.Vapor mist bath (precast)7.Forms in contact with concrete surface 8.Others,approvedbytheOwner 8.Others, approved by the Owner Methods of Curing Methods of Curing1.Ponding or continuous sprinkling 2.Absorptive mat or fabric continuously wet3.Wet sand or straw4.Spray curing compounds 5.Waterproof paper or plastic film film6.Vapor mist bath (precast) 7.Forms in contact with concrete f sur f ace8.Others, approved by the Owner Methods of Curing Methods of Curing1.Ponding or continuous sprinkling2.Absorptive mat or fabric continuously wet3.Wet sand or straw 4Spraycuringcompounds 4.Spray curing compounds5.Waterproof paper or plastic film 6.Vapor mist bath (precast)7.Forms in contact with concrete surface 8.Others,approvedbytheOwner 8.Others, approved by the Owner
Methods of Curing Methods of Curing1.Ponding or continuous sprinkling2.Absorptive mat or fabric continuously wet3.Wet sand or straw 4Spraycuringcompounds 4.Spray curing compounds5.Waterproof paper or plastic film 6.Vapor mist bath (precast)7.Forms in contact with concrete surface 8.Others,approvedbytheOwner 8.Others, approved by the Owner Methods of Curing Methods of Curing1.Ponding or continuous sprinkling 2.Absorptive mat or fabric continuously wet3.Wet sand or straw4.Spray curing compounds 5.Waterproof paper or plastic film film6.Vapor mist bath (precast) 7.Forms in contact with fconcrete sur f ace8.Others, approved by the Owner Methods of Curing Methods of Curing1.Ponding or continuous sprinkling 2.Absorptive mat or fabric continuously wet3.Wet sand or straw4.Spray curing compounds 5.Waterproof paper or plastic film film6.Vapor mist bath (precast) 7.Forms in contact with fconcrete sur f ace8.Others, approved by the Owner Methods of Curing Methods of Curing 1.
1.PondingPondingor continuous sprinkling 2.Absorptive mat or fabric continuously wet3.Wet sand or straw4.Spray curing compounds 5.Waterproof paper or plastic film C)film6.Vapor mist bath (precast) 7.Forms in contact with f m perature (o Cconcrete sur f ace8.Others, approved by the OwnerCuring Te m Methods of Curing1.Ponding or continuous sprinkling 2.Absorptive mat or fabric continuously wet3.Wet sand or straw4.Spray curing compounds 5.Waterproof paper or plasticfilm plastic film6.Vapor mist bath (precast) 7.Forms in contact with fconcrete sur f ace8.Others, approved by the Owner METHODS OF CURING METHODS OF CURING Membrane*SEAL IN MIXING WATERSpraycuringcompound Saturated Partially saturated Spray curing compound Waterproof paper
Polyethylene sheets Saturated*SUPPLY ADDITIONAL WATER PondingWater supplied from external source Ponding Soaker hoseWet sandWtbl source Sd W e t b ur l ap Immersion (precast)
Steam curing (saturated air)
S aturate d
600 4Tensile Strength 500 3 Dr y in g StressCracking 400 3 yg n , p s i , M p a 200 300 2 T e n s i o n T e n s i o n ,8 in. (200 mm) wall73 °F (23 °C) temp.Fully Restrained Cement:517lb/ya 3 100 200 1Cement: 517 lb / ya(307 kg / m )W / C = 0.45 3 100 1 3 28 40 60Start of drying at 50% R.H.
7 1 28 40 60Age, days
Timing ofTiming ofOperations Operations HeatDevelopmentHeatDevelopment Heat Development Heat Development d setting Contact of cement and water nerate d setting H eat ge 0 2 to 3 HTime (hours)
Evaporation of Surface Evaporation of Surface MoisturefromConcrete MoisturefromConcrete Moisture from Concrete Moisture from Concrete Precautions to Minimize Plastic Precautions to Minimize Plastic ShrinkageCracking ShrinkageCracking Shrinkage Cracking Shrinkage Cracking*Moistenaggregates
- Moisten aggregates*Cool aggregates and mixing water*Dampen subgrade*Erect temporary windbreaks andsunshades and sunshades*Cover concrete
- Fo g slab immediatel y after gy placing*Add plastic fibers Fogging Fogging Good Fogging Good Fogging Bad Fogging Bad Fogging EvaporationEvaporationRetarders Retarders Curing Compound Applied to Fresh Concrete Curing Compound Applied to Fresh Concrete Moist Curing After the Moist Curing After the CtHd CtHd C oncre t e H ar d ens C oncre t e H ar d ens
AdtiitilAdtiitil Ad equa t e cur i n g i s essen ti a l Ad equa t e cur i n g i s essen ti a l W Wet burlap & plastic et burlap & plastic X Curing Membrane Curing Membrane X X Ensuring Adequate CuringEnsuring 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 someone's specific responsibility*Adequate inspection required*Problems with curing-membrane systems?*Proper coverage/application
- Nothermalbenefit(+/-)No thermal benefit (/)*Bonding of subsequent overlay materials Field example, Field example,fll fll I f time a ll ows-I f time a ll ows-lhlh Examp l e w here curing was critica l on t h in low permeability shotcrete overlay: Specification Specification1/2 -in. thick6000 psi at 28 daysLess then 1500 coulombs rating (low permeability)Bondstrengthof200psiBond strength of 200 psiProject Climate: frequently hot and windy
conditions
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