Durable Concrete in a Low-Ash World

Jerod Gross, PE, LEED APDan King, PE

Representing the CP Tech Center

What’s Coming Up…

A Virtual Better Concrete Conference

Noon webinars

Nov. 4 ACI 301 – Specifications for Concrete ConstructionMichelle Wilson, PCA

Nov. 18 Wet Weather Strategies for Handling Concrete PlacementsRon Kozikowski, North Starr Concrete Consulting

Dec. 2 The Future of Fly Ash: Dystopia or HysteriaLarry Sutter, Michigan Tech University

Dec. 16 Project Bluejay & Krause Gateway Center Dan Goldsworth, Mark Stinocher, Jordan Stokes, Nick Aldrich

https://register.gotowebinar.com/register/6780190539906386191

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https://register.gotowebinar.com/register/6780190539906386191

Special Thank you

Dr. Peter Taylor, PE, Ph. D

Director, National Concrete Pavement Technology Center

ptaylor@iastate.edu

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mailto:ptaylor@iastate.edu

Overview

• Introduction• Controlled mixtures• Other products• Impacts in Iowa• Crystal ball gazing

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PresenterPresentation NotesTo start off, we will give a background on fly ash. What is it, what is it good for, how is it used? Then we will discuss controlled mixtures, local impacts and looking to the future

Introduction

• Fly ash is amazing!• Less expensive $• More workable• Reduces permeability• ASR / sulfate / oxychloride resistant• Cooler (lower heat of hydration)

• But…• There are no fly ash factories• Utilities are changing• 2020…

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PresenterPresentation NotesThis image is from Dr. Taylors first professional conference in 1987. Fly ash is not just a waste product, it is a valuable resource.

Not cheaper… less expensive. They take the place of cement 15-30% and have similar properties of cement

More workable – sometimes challenging for tall curbs

Reduces permeability

Helps treat ASR, sulfate reaction , oxychloride resistant

Production of fly ash is slowing down

Particulates and contaminants that used to go up through the flume are captured and combined with the ash, so quality has changed over the years

Cementitious Materials

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Hydraulic cement – reacts with water, creates CH

Pozzolan – reacts with cement and water, consumes CH

Portland Cement

Slag Cement

Class C Fly Ash

Class F Fly Ash

Silica Fume

Not to scale

Cement

F Fly Ash

C Fly AshSlag

Silica fume

Metakaolin

CaO Al2O3

SiO2

PresenterPresentation NotesDefinitions!HC = Material that sets and hardens by a series of nonreversible chemical reactions withwater, a process called hydration.Portland cement = a specific type of hydraulic cement.Pozzolan = material that reacts with cement and water in ways that improve microstructure.SCM = cements and pozzolans other than portland cementSilica fume is pure pozzolanClass C is a little of both, but slightly more hydraulic

Calcium Oxide (lime), silica oxide, Aluminum are 3 main ingredients as shown in upper right figureClass C is most common in Iowa pavements…

Chart1

21.169509870370.725407975755.394417719539.15363894556.479917638183.595507726411.547005383823.094010767634.641016151446.188021535234.641016151411.547005383823.094010767646.1880215352103.923048454192.376043070380.829037686569.28203230280

103.923048454192.376043070380.829037686569.282032302869.282032302823.094010767646.188021535292.376043070392.376043070369.282032302846.188021535223.094010767657.735026919

115.4700538379

0

0

0

CaO

Al2O3

SiO2

Cement

F Fly Ash

C Fly Ash

Slag

Silica fume

Metakaolin

ca1

ca2

ca3

ca4

sa3

sa1

sa2

sa4

cs1

cs2

cs3

cs4

Frame

Cement

23.3333333333

65

47.2972972973

40.2298850575

97.8260869565

55.2083333333

20

40

60

80

60

20

40

80

20

40

60

80

0

20

40

60

80

0

0

0

0

0

0

0

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100

0

0

Sheet1

AbsoluteCalcium oxideSilicaAluminaIron oxideTotal CSA

Cement63216290

F Fly Ash552231180

C Fly Ash213518674

Slag403512187

Silica fume2900092

Metakaolin05343196

another11103

CorrectedCement70237

F Fly Ash66529

C Fly Ash284724

Slag464014

Silica fume2980

Metakaolin05545

another333333

Y axisX axis

Si1/root3*(Si-2(100-Ca))

Cement2321

F Fly Ash6571

C Fly Ash4755

Slag4039

Silica fume9856

Metakaolin5584

another3358

Sheet1

11.547005383823.094010767634.641016151446.188021535234.641016151411.547005383823.094010767646.1880215352103.923048454192.376043070380.829037686569.28203230280

103.923048454192.376043070380.829037686569.282032302869.282032302823.094010767646.188021535292.376043070392.376043070369.282032302846.188021535223.094010767657.735026919

115.4700538379

0

0

0

CaO

Al2O3

SiO2

Cement

F Fly Ash

C Fly Ash

Slag

Silica fume

Metakaolin

ca1

ca2

ca3

ca4

sa3

sa1

sa2

sa4

cs1

cs2

cs3

cs4

Frame

Cement

20

40

60

80

60

20

40

80

20

40

60

80

0

20

40

60

80

0

0

0

0

0

0

0

0

100

0

0

Sheet2

CS

XY

CaSiAl1/root3*(Si-2(100-Ca))

1000000

802001220

604002340

406003560

Boundary208004680

000100058100

0100

00SA

00CaSiAlXY

001001150

0208010420

040609240

060408160

080206980

0100058100

CA

CaSiAlXY

1000000

80020230

60040460

40060690

20080920

001001150

Sheet3

Fly Ash Production

• By-product of combustion of pulverized coal• During combustion

• Volatiles & carbon burned off• Mineral impurities remain in

flue gas• Fused materials cool into

glass spheres

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PresenterPresentation NotesNo fly ash factories! We depend on power! We have figured out how to burn low quality coal. Grind coal very small (flour consistency), blow air into furnace with the coal and still get good efficiency. Fine powder burned at high temperatures, very fine powder melts the rock, tiny spherical balls go up the flue, captured the waste on filters or electrostatic precipitators, the waste is cooled quickly that makes it glassy. Three properties: 1) Glass, 2) calcium silica alumina, 3) very small

Fly Ash Contaminants

• Carbon (LOI)• Sucks up air entrainers

• Sulfates• Expansion

• Moisture• Handling, workability

• C3A• Can contribute to incompatibility

8 Hwang, Sun, Li

PresenterPresentation NotesContaminantsCarbon - Image is unburned carbon transported out with the fly ash. Very porous, huge surface area so it sucks up air entrainers. With low quality ash, we have harder time entraining air with high carbon content.Measuring carbon is somewhat difficult so we have the term LOI (loss of ignition.) How much mass is lost when igniting (burning carbon) now burning other materials so LOI isn’t the best measurement any more. Not a 1:1 relationship anymore

Looking for alternative ways to measure the effect of fly ash with air entrainers

Sulfates – high lime systems tend to have high sulfate.

Moisture – if there is any water left in the system, it can effect workability. mixes can get sticky

With High calcium ashes (class C ash with lots of lime) may be in the form of tri-calcium aluminate C3A. This can contribute to incompatibility and can accelerate flash set.

Specs are important ASTM C618. Need to watch for contaminants.

CH

How SCMs Work

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Cement

Water

React C-S-H

CH

https://iowadot.gov/research/reports/Year/2007/fullreports/MLR-05-02.pdf

PresenterPresentation NotesImportant – modern cements produce more CH which can be addressed with the SCM .

CH is flaky crystalline structureEasy to break a flat crystal (CH is not very strong) CH is reasonally soluable

Faster curing concrete, industry has ground into finer particles, this has increased CH

Calcium Hydroxide

• Good for raising pH and protecting steel• Bad for

• Oxychloride• Solubility• Shear strength

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CH

PresenterPresentation Notes

CH is great for raising pH 13-14 range

Calcium oxychloride is a bad thing. Forms and stable at relatively cool weather (above 32 degrees)Expands at 300%. 30 times the amount of water when it freezes

CH

How SCMs Work

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Cement

Water

React C-S-H

CHWaterSCM React C-S-H

PresenterPresentation NotesGray text in reaction arrow means slows the hydration

Introduction

• Can we go back to this?

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PresenterPresentation NotesCan we just leave out the fly ash?No, we have been there done that.

Introduction

• Review the benefits

13 Hover 2020

Workability

• Does workability matter to anybody other than the contractor?• “Add 10”

• Hurts long term performance• The right vibration

• How fast, how long• Moves air, water and aggregates

• Aesthetics• Matter to the owner

• Fly ash and admixtures help

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PresenterPresentation NotesExcess vibration moves air upwards, moves water horizontally. (not good for structural applications)Photo is from Route 5 Need uniform distribution of aggregate and uniform air min. 5%

Durability

• Durability is largely governed by permeability / transport• Most failure mechanisms involve water

• Getting low permeability• Low water/cement (MN history)• Appropriate SCM dose

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PresenterPresentation NotesMN DOT led the charge for low w/cm 0.38-0.4Far more durable concrete

SCM helps by densifying the system and tying up the CaOxy

Oxychloride

• MgCl2 and CaCl2 • React with CaOH to form calcium oxychloride• Forms when temperature >32 ºF• Expands ~300%• Unstable at higher temperatures

• Prevented by using SCMs to reduce

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CH

PresenterPresentation NotesSome researchers say we need 30-35% SCM 20% ash seems to work and is practical amount.

Review

• What do we (really) need from fly ash• ASR• Oxychloride

• Permeability• Workability• Strength• Heat

• Sustainability• Cost

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Limited alternatives to fly ash

Alternativesavailable

PresenterPresentation NotesStates like Michigan that pay attention to ASR does not have oxychloride because they use F ash

There are alternative ways to getting Perm, workability, strength, heat

1% increase in costSustainability may come into play in the future. More important to get durable pavement now.

So lets design our mixtures for what you need .. Next slide

Controlled mixtures

• Prepare the mixture for the application• Use what you need (and no more)• From what you have• Control the cementitious

content

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Controlled mixtures

• Use what you need (and no more)• Its like balancing the family checkbook

• ASR – depends on the aggregate• Oxychloride – depends on the cement

• Permeability• Workability• Strength• Heat• Sustainability

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Limited alternatives

Alternativesavailable

True or False?

• More cement = more strength• Strength is everything• Slump indicates quality• Stronger concrete is more “brittle”

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Controlled mixtures

• Control the cementitious content• With more cement you need more fly ash

• Excess has a:• Negative effect on permeability, shrinkage, cost• Small negative effect on strength

• “Optimum” depends on:• Aggregate type• Gradation

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How do we proportion to achieve design goals?

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Workability Transport Strength Cold weather

Shrinkage Aggregate stability

Aggregate System Type, gradation - - - -

Paste qualityAir, w/cm, SCM type and dose

Paste quantity Vp/Vv - - - -

PresenterPresentation NotesThis chart indicates which of the three mixture parameters affects what critical property. The yellow stripe is where the specification should reside. All else should be left to the contractor to match available materials with their equipment while still meeting spec requirements.

Controlled mixtures

• From what you have• Class C or F• Behave differently

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Cement

F Fly Ash

C Fly AshSlag

Silica fume

Metakaolin

CaO Al2O3

SiO2

Other Products

• Slag cement• Metakaolin• Other minerals like zeolite?

• Microspheres for f/t protection

• IP cements

• But…

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Sutter

But

• Do they do what we need?• They change mix properties• Cost

• Particularly shipping• Is it worth it?

• Availability• “Free market?”

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But

• Education• Every product has its own quirks

• Specifications• Have to be appropriate• AASHTO PP84• Iowa

• DOT: QM-C• SUDAS: C-SUD

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AASHTO PP84

• Require the things that matter• Transport properties (everywhere)• Aggregate stability (everywhere)• Strength (everywhere)• Cold weather resistance (cold locations)• Shrinkage (dry locations)

• Workability (everywhere)

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AASHTO PP84

• Measure them at the right time• Prequalification• Process control• Acceptance

• A buffet of approaches• Prescriptive: w/cm, paste volume• Performance: Formation factor

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AASHTO PP84

• Allow contractor to develop the mixture to meet requirements• w/cm (within limits)• SCM dose (within limits)• Aggregate gradation• Iowa’s QM-C and C-SUD mix specs

are informed by these principles

29 Payne

PresenterPresentation NotesAnd are changing for the better

Measuring what we need

• ASR• Follow AASHTO R80 / ASTM C1778

• Oxychloride• LTDSC• Expansion at 40°F

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Measuring what we need

• Permeability / Transport• Resistivity

• Strength

• Heat• Calorimetry

• Air void system• SAM

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Measuring what we need

• Workability• VKelly• Box

Measure the response to vibration

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• Likely to continue seeing reduced fly ash production

• Events in 2020 causing a short-term supply crunch:• Mild winter • COVID-19

• Other issues• Consistency• Substitutes are not immediately available

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Fly Ash in Iowa

• What can we do right now with our Iowa mixes to maximize durability?

• Save the fly ash for where you need it• The C-SUD mix specification can be used regardless of fly

ash content• Follow good principles (control the paste):

• Lower total cementitious content via optimized gradation• Appropriate w/cm• Good air void system

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Iowa Specifications

The Future

• Blended ashes• “Good enough for engineering purposes”• Coming soon to Iowa?

• Reclaimed ash• Quality control• Transportation

35 Sutter 2020

• Reclaimed ash• CP Tech Center September 2020 Tech Brief:• Fly ash harvesting is being done in PA, SC,

and WI, and should continue to expand

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The Future

The Future

• Local powders• Limited availability• Testing can be onerous

(ASTM C 1709)• But all help is good help• Economics may be helping

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Philosophical Ramblings

• What about those old pavements?• Cements have changed• Placement methods have changed• Curing!!!!!

• Traffic has changed• Salting has changed

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Philosophical Ramblings

• Life is changing – we have to adapt• There are solutions• We have to think• Quality matters

• Call us if you need help

Dan King515-963-0606dking@concretestate.org

Jerod Gross515-669-7644jgross@snyder-associates.com

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mailto:dking@concretestate.orgmailto:jgross@snyder-associates.com

Durable Concrete in a �Low-Ash WorldWhat’s Coming Up…Special Thank youOverviewIntroductionCementitious MaterialsFly Ash ProductionFly Ash ContaminantsHow SCMs WorkCalcium HydroxideHow SCMs WorkIntroductionIntroductionWorkabilityDurabilityOxychlorideReviewControlled mixturesControlled mixturesTrue or False?Controlled mixturesHow do we proportion to achieve design goals?Controlled mixturesOther ProductsButButAASHTO PP84AASHTO PP84AASHTO PP84Measuring what we needMeasuring what we needMeasuring what we needFly Ash in IowaIowa SpecificationsThe FutureThe FutureThe FuturePhilosophical RamblingsPhilosophical RamblingsSlide Number 40