curing of concrete

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CURING CONCRETE

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CURING OF CONCRETE

CURING CONCRETE

CURING CONCRETEPresented to Dr. Ayub Elahi Presented byWaqar SaleemMuhammad JahanzebMuhammad JavedMuhammad AkmalUmair Yaseen

Curing Concrete ( ASTM C31)

Curing ConcreteWhat is curing??

Process to retain and maintain for a specific time

1.Moisture(not less than 80%RH)2.Temperature(above freezing and below 176F or 80C)

Essential for cement hydration

HydrationWhat is hydration???It is a chemical process in which cement ingredients react with water.Tricalcium silicate + Water--->Calcium silicate hydrate+Calcium hydroxide + heat173.6kJDicalcium silicate + Water--->Calcium silicate hydrate + Calcium hydroxide +heat58.6KJ

Hydration (ASTM C186)

Hydration (stage I)Almost immediately on adding water some of the clinker sulphates and gypsum dissolve producing an alkaline, sulfate-rich, solution.

Stage IHydration (stage I)the (C3A) phase (the most reactive of the four main clinker minerals) reacts with the water to form an aluminate-rich gel Stage I on the heat evolution curve

Hydration (stage I)(C3A) reaction is with water is strongly exothermic but does not last long typically only a few minutes

Hydration (stage II)Stage I is followed by a period of a few hours of relatively low heat evolution. This is called the dormant, or induction period.Paste becomes stiff and not workable

Hydration (stage III)main period of hydration the alite and belite in the cement start to reactformation of calcium silicate hydrate and calcium hydroxide

Hydration (stage III)time concrete strengths increasemaximum heat evolution occurs typically between about 10 and 20 hoursafter mixing and then gradually tails off

WHAT ARE PURPOSES OR FUNCTIONS??????????

HOW TO CURE???Curing methods3 main purposes of curingMaintaining mixing water in concrete during the early hardening process2. Reducing the loss of mixing water from the surface of the concreteAccelerating strength gain using heat and additional moisture

Maintaining mixing water4 ways Ponding or immersionSpraying or foggingSaturated wet coveringsLeft in place forms

First purpose

Maintaining mixing waterFirst way

Ponding OR immersion

First purposeMaintaining mixing waterPonding or ImmersionASTM C192/C192MIdeal for preventing loss of moistureMaintain uniform temperatureDisadvantages:Requires considerable labor and supervisionImpractical for big jobs

Maintaining mixing water2nd way

Spraying and fogging

First purposeSpraying or FoggingASTM C192Excellent method when temperature is above freezing and humidity is low.Disadvantages:CostWater erosion of the newly finished concrete form.

Maintaining mixing water3rd wayASTMC84-36

Saturated wet covering

First purposeWet coveringsMoisture-retaining fabrics saturated with water i.e burlap, cotton mats, rugs.Advantage1. no discoloration2 Resistant to rot and fireDisadvantagePeriodic additions of waterUse of polythylene film over wet covering will eliminate continuous wateringASTM C171(MATERIAL)Maintaining mixing water4th way

Left in place forms

First purposeMaintaining mixing waterLeft in place formsAdvantages No extra cost or labourEasy DisadvantagesRisky Extra care in hot weatherAnd wood formsReducing loss of water3 waysImpervious paper plastic sheetsMembrane-forming compounds

2nd purposeReducing loss of water1st wayASTMC 309. (AASHTO M 148Covering concrete with impervious paper or plastic sheets

2nd purposeImpervious paperTwo sheets of kraft paper cemented tegether by a bitumious adhesive with fiber reinforcment.AdvantagesVery efficient for curing horizontal surfacesPeriodic addition of water are not requiredAssures suitable hydration by preventing loss of moistureReusableTears and holes can easily be repaired with patchesDisadvantageMarginal costASRM C171Reducing loss of waterReducing loss of water2nd way

Plastic sheets

Plastic sheetsPolyethylene films, 4-mil thicknessAdvantagesLightweightEffective moisture barrierEasily applied to complex as well as simple shapesDisadvantagesCan cause patchy discolorationMore pronounced when film is wrinkledPeriodic additions of water may be necessary to prevent discolorationASTM C 171 Reducing loss of waterApplying membrane-forming curing compounds

2nd purposeMembrane-forming compoundLiquid membrane-forming compounds use to retard or reduce evaporation of waterWaxes, resins, chlorinated rubberAdvantages hand-operated or power-driven spray equipmentOne coat 150-200 sft per gallonDisadvantages Extra costSkilled labourASTM C309Efficiency check ASTM ASTM C156 - 09a

Accelerating strength gain4 ways

Curing steam Heating coilsElectrical heated forms or padsConcrete blanket

3nd purpose

Accelerating strength gain1st waySteam CuringAdvantageous where early strength gain is required, orAdditional heat is required to accomplish hydration, ex. cold weather.Two Methods:Live steam (atmospheric pressure)Autoclave (high pressure)

3nd purpose

Steam curing

Accelerating strength gain2nd wayHeating coilsEmbedded near surface of concrete elementsPrevention from freezing in cold weather3nd purpose

Accelerating strength gain3rd wayElectrical heated forms or padsPrimarily used by precast concrete producersNow used in some sensitive projects

3nd purposeAccelerating strength gain4th wayASTM C167 Concrete blanketInsulate the surfaces in cold temperatures4300psi9hours

3nd purpose

Accelerating strength gainWinter Concrete Curing BlanketsPrevents freezing, rapid drying, & cracking all winterThaw frozen groundprior to pouringHeat spreading technologycures concretefastRoll it out, Plug it in, the blanket does the restAccelerate yourconstructionjobs all winterProduces ROCK-HARD concrete every timeMaintain optimal curing temperatures year-roundOnly pennies a day to operate

MethodAdvantageDisadvantageSprinkling with Water or covering with BurlapExcellent results if constantly kept wetLikelihood of drying between sprinklings; difficult on vertical wallsStrawInsulator in winterCan dry out, blow away, burnMoist earthCheap but messyStains concrete, can dry out, removal problemPonding on flat surfacesExcellent results, maintain uniform temperatureRequires considerable labor, undesirable in freezing weatherCuring compoundsEasy to apply and inexpensiveSprayer needed; inadequate coverage allows dry out; film can be broken or tracked out before curing is completed; unless pigmented allows concrete to get too hotWater proof paperExcellent protection prevents dryingHeavy cost can be excessive; must be kept in rolls; storage and handling problemPlastic filmAbsolutely watertight, excellent protection. Light and easy to handle

Should be pigmented for heatprotection; requires reasonable care and tears must be patched; must be weighed down to prevent blowing awayEffects on hardened concreteIncreasedStrengthWatertightnessAbrasion resistanceFreeze-thaw resistanceVolume stability

Curing tipsample waterdo not let it drydry concrete = dead concrete, all reactions stopcan not revitalize concrete after it drieskeep temperature at a moderate levelconcrete with flyash requires longer curing

Temperature effects on curingThe higher the temperature the faster the curingbest temperature is room temperaturestrongest concrete is made at temperature around 40 F.(not practical)If concrete freezes during the first 24 hrs., it may never be able to attain its original properties.

Temperature effects

Temperature effects

Temperature effects on curingreal high temperatures above 120 F can cause serious damage since cement may set too fast.accelerated curing procedures produce strong concrete, but durability might suffer.autoclave curing.

Moisture testsPolythene sheet test(ASTM D 4263)Mat TestTest StripMoisture MetersGravimetricThank you