Internal taylor Curing Taylor

8/12/2019 Internal taylor Curing Taylor

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Internal Curing Concrete

Dr Peter Taylor

With thanks to:

John Ries, ESCSIDale Bentz, NIST

Jason Weiss, Purdue


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Internal Curing

Why?

How?

So What? Where Next?


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Internal Curing - Why

Curing is:

Provision of moisture and temperature

to allow hydration and minimizedimensional change

Keep it wetKeep it warm

Start early

stay late


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Without curing we will increase risk of

Cracking

Scaling

A soft surface

What about strength?



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Time

Pro

perty

Continuous cure

Curing stops

Elevated temperature curing


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Water

Unhydratedcement

Capillarypores

HCP

W/C = 0.40 W/C = 0.75 W/C = 0.25


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Material should

Hold sufficient water

Hold the water until needed and not

effect w/c

Give up water at high RH (desorption)Not adversely effect

the concrete quality

Internal Curing - How


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Super Absorbent Polymers


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Desorption

- Virtually all moisture available at 94% RH

Castro 2011


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Water Moving From Aggregate

Paste

LWA

Interface

0.0 mm 0.5 mm0.0 mm 0.5 mm

Detector

X-ray Source

Cement Paste

LWA

Water Can Move ~2 mm after sometime

Schlitter(2010)


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Its All About the Distribution

Henkensiefken (2008)

Coarse

LWAFine LWA


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How Much?

LWA

f

LWAS

CSCM

*

**max

where

MLWA

= mass of (dry) LWA needed per unit volume of concrete (kg/m3

or lb/yd3);Cf= cement factor (content) for concrete mixture (kg/m3 or lb/yd3);

CS= chemical shrinkage of cement (mass of water/mass of cement);

max = maximum expected degree of hydration of cement (0 to 1);

For ordinary Portland cement, the maximum expected degree of

hydration of cement can be assumed to be 1 forw/c0.36 and tobe given by [(w/c)/0.36] forw/c< 0.36.

S= degree of saturation of aggregate (0 to 1);

LWA

= desorption of lightweight aggregate from saturation down to

93 % RH (mass water/mass dry LWA).

Bentz & Snyder (1999), Bentz, Lura, & Roberts (2005):


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Simple IC Mixture Design

Need 7 lbs of IC water per 100 lbs of

cementitious

600 lbs cementitious = 42 lbs of IC water

Assume 18% LWA absorption in the field Assume LWA at 55 lbs/cf

55 x .18 = 9.9 lb/cf water at 90% desorption 8.9

Need 42 lbs IC water / 8.9 = 4.7 cf of LWA 4.7 cf x 55 lb/cf = 259 lbs of LWA aggregate


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NY State DOT Specifications

Proper amount of water

30% replacement of fine aggregate Minimum 15% absorbed

moisture

Place under sprinklerfor minimum of 48 hours

Allow stockpiles to drain

for 12 to 15 hoursimmediately prior to use


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Can we do without this?

Nope

Still have tokeep the

surface

hydrating

Thats where

the abusehappens


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Internal Curing - So What

Benefits

Better hydration & SCM reaction

Improved durability Less cement

Less shrinkage, warping, cracking

Extended service life Improved economics

Increased

sustainability


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More Hydration

0.40 0.425 0.45 0.475 0.50

Degreeofhyd

ration(%)

Mixture with

internal curing

Mixture without

internal curing

0%

20%

40%

60%

80%

Water / cement ratio

Espinoza-Hajazin (2010)

Degree of hydration of cement @ 90 days, cured @ 50% RH


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Internal Curing So What

Less Shrinkage (Sealed)



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Less Shrinkage; Less Cracking

0 20 40 60 80

Time to Cracking, hours

Control IC Byard (2010)


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Reduced Warping

Wei (2008)


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Lower Absorption



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Reduced Conductivity

Castro (2011)


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Lower Chloride Permeability (90 days)

0.40 0.425 0.45 0.475 0.50

Chargepassed(cou

lombs)

Mixture with

internal curing

Mixture

without

internal curing

0

water / cement ratio

1200

2400

3600

Espinoza-Hajazin (2010)


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Higher Compressive Strength

- Portland Cement Mortar

0.30 & 0.50 w/c50% RH Curing

Golias (2010)


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Looks too easy

Need an extra stockpile

It has to be wet Not produced in IA


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Service Life Prediction

Cusson (2010)


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Initial & Life Cycle Cost

Cusson (2010)


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Paving in Texas, Bridges in New York & Indiana

UPRRIntermodalFacilityConstructed2005

NY: 9 built or under construction, 7

in design

IN: 33 bridges

Examples


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Buchanan County - Bridge

Three span bridge at Pine Creek

One half conventional (both lanes) Other half using Internal Curing Concrete

About 20% of fine aggregate replaced withlight weight aggregate

Other mix proportions unchanged

Internal Curing Whats Next


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176 feet long, 40 wide

Three spans

Instrument two external spans


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Similar mixtures Control Test

Unit weight 143 138

Slump 4.25 5.00 Air 6.5 6.8

Set time 276 272

7-day strength 4,760 4,820 28-day strength 5,910 7,070

28-day flex 660 715

Shrinkage 0.028 0.023



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Task 1 - Test aggregate and mixture in ISU

lab and during construction

Fresh properties Mechanical properties over time

Cracking potential

Permeability

Hydration rates Moisture contents

Corrosion in the deck



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Task 2 - Live Load Testing

After construction Prior to traffic

One year post-construction

Strain transducers installed on the bottom of thedeck and the girders

Loaded with a fully loaded tandem axle dump

truck to evaluate the live load performance of the

structure



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Concrete overlay

40-ft panels!

Hoping to monitor Warping

Cracking

Buchanan County - Pavement


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Fundamental concept makes sense

Lab data is promising

Field data looking good

Closing

Internal taylor Curing Taylor

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