Fly Ash Alternatives For Texas

Fly Ash Alternatives for TexasMaria JuengerSaif Al-Shmaisani, Dr. Ryan Kalina, Jae Kyeong Jang, Dr. SaamiyaSeraj, Rachel Cano, Dr. Raissa Ferron and Michael RungSponsored by the Texas DOT under projects: 0-6717, 5-6717, and 0-6966

Fly ash in Texas Fly ash is important to TxDOT forconcrete for the following reasons(Andy Naranjo):- Control of expansion due toalkali-silica reaction (ASR)Wikipedia- Reduction of permeability/protection against corrosion- To produce high performance concrete- To reduce risk of thermal cracking in mass concrete(i.e. temperature control)

Fly ash supply is threatened Coal-fired power plants are:- Closing Gibbons Creek, Monticello, Big Brown, Sandow - Producing Class C fly ash- Producing off-spec fly ashearthjustice.org

Solutions to fly ash supply problem1. Better storage and logistics- Store fly ash during timesof low demand- Transport fly ash sman.com

Solutions to fly ash supply problem2. Beneficiate off-spec fly ashes

Solutions to fly ash supply problem3. Harvest ponded orlandfilled fly ash

Solutions to fly ash supply problem4. Use alternative SCMs-Raw natural pozzolansCalcined claysLimestone-SCM blendsGround glass

Case Studies for Texas1. Beneficiated fly ashes-Harvested from landfill, dried, and ground/classifiedOff-spec fly ash blended with natural pozzolansChemically treated fly ashClass C/Class F blended fly ash2. Natural pozzolans

Harvested, Beneficiated, and Off-SpecFly Ashes Reclaimed from landfills and ponds, dried and groundor classified. Chemically or thermally treated to reduce LOI and/orabsorption of air-entraining admixtures. Blended with other fly ashes or natural pozzolans to:- Reduce SO3 content- Reduce CaO content Bottom ash Economizer ash Trona-impacted ashhttp://charah.com

Harvested Fly Ash Landfilled fly ash is an untapped resource Low calcium, siliceous ashes can be unreacted and needminimal processingKaladharan et al.

Example 1:Harvested (Reclaimed) and Beneficiated Fly Ash Tested several fly ashes:- Non-compliant, blended or treated ashes- Reclaimed from landfills and treated by grinding anddrying Some important observationsTypeDesignationMaterial Classification/PropertiesRM-CRM-LRemediated (RM) Fly AshNon-compliant Fly Ash; Blended or TreatedRM-MRM-SRC-GReclaimed (RC) Fly AshClass F Fly Ash; Ground and tions/5-6717-01-1.pdf

They all (mostly) pass ASTM C618 Class FDesignationSiO2 (%)Al2O3 (%)Fe2O3 (%)CaO (%)MgO (%)SO3 (%)Na2O (%)K2O .20.8R-M47.019.98.414.13.40.90.81.0DesignationSiO2 Al2O Fe2O3(%)SO3(%)MoistureContent(%)Loss 15.9YESR-G77.82.723.90.9NOR-M75.20.860.90.7YES

ESEM Images – Beneficiated Fly AshesB-SB-Ld50 9.8 µmd50 9.5 µmB-Cd50 6.3 µm

ESEM Images – Reclaimed Fly AshesR-GR-Md50 22.2 µmd50 12.8 µm

Paste Rheology120Average Shear Stress, τ (Pa)100OPCFA80B-C60B-LB-S40R-GR-M20001020Shear Rate3040(s-1)Angular particles of beneficiated fly ashes interlockand impede flow of paste. Round particles ofreclaimed fly ashes have “ball-bearing” effect50

Concrete Compressive Strength8000Compressive Strength (psi)700060005000R² 0.875440003000Concrete compressivestrengths strongly correlatedwith median particle size ofreclaimed and remediated flyashes200010007 Day00510d50 (µm)152025

Concerns about ASR1. For reclaimed materials that are ground orclassified, if the ash is coarse (i.e. less reactive) willit still control ASR expansion?2. For materials beneficiated though blending withnatural pozzolans, does ASR performance meetexpectations?3. What is the role of alkalis in fly ash on ASR?

Fly Ashes Beneficiated by BlendingTypeBeneficiated (B) Fly AshControlMaterial DescriptionCoal Combustion Residual;Blended to meet ASTM C618 Class FProduction Class F Fly AshDesignationCaO 10.82B-V16.98FA10.6All of these materials pass ASTM C618 sum of oxides for Class F

1. Role of Fly Ash FinenessExpansion LimitDiagram from J. Ideker Mortar mixtures with 20% replacement of cement with fly ash OPC control expansion 0.36%

2. Impact of BlendingExpansion Limit Mortar mixtures with 25%replacement of cement with fly ash OPC control expansion 0.36%

3. Role of AlkalisExpansion After 2 Years (%)0.20Na2Oe 4.0%0.180.160.140.120.10C1293 0.04%Expansion Threshold0.080.060.040.020.005101520CaO (%)Fly ashes at 25% replacement amount (Shehata and Thomas 2000)2530

Expansion After 2 Years (%)0.20High alkali fly ash, still passing (Replacement/Age in Months/Na2Oe)0.18High alkali fly ash, failed (Replacement/Age in Months/Na2Oe)Na2Oe 0.040.020.00C1293 0.04%Expansion Threshold(20/18/4.4)510152025CaO (%) High-alkali fly ashes follow trend for low-CaO content High-alkali fly ashes deviate from trend at CaO contents greater than 10%30

Summary: Fly Ashes1. You can beneficiate fly ash to meet ASTM C 618Class F.- The fly ash performance is dependent on particle sizeand shape, which can be controlled by thebeneficiation process.2. Beneficiated fly ashes can control ASR expansion.- Be careful of high CaO contents and high alkalicontents.

Natural Pozzolans Volcanic pozzolans Pumice, Perlite, Volcanic Ashes, Zeolites Sedimentary pozzolans Calcined clays & shales (metakaolin, impure, mixed) Availability of many of these is low and regional, butincreasing Of particular interest are overburden materials (e.g.impure pumice and clays) for reduced cost Some concerns: workability, frauds, and performanceoptimization

Natural Pozzolans – ASTM C618A variety of natural pozzolans from different sources can meet the Class N criteriain ASTM C618 and not cause high water demands.

Heat of HydrationAll reduce heat of hydration from cement, so can be used in thermal control plans.

Compressive StrengthCompressive Strength, MPa6050Control20% Perlite-I20% Metakaolin-D20% Fly Ash20% Pumice-D20% Vitric Ash-S20% Shale-T4030201001 day3 day7 day28 day90 day 365 dayAll increase long-term compressive strength, some better than fly ash.

Alkali-Silica Reaction – ASTM C15670.50Control15% Perlite-I15% Metakaolin-D0.45Expansion (%)0.4015% Pumice-D25% Vitric Ash-S25% Shale-T0.350.300.250.200.1514-day expansion limit0.100.050.000510Number of Days in NaOH solutionAll can control expansion due to ASR in mortar.15

ASR in Concrete – ASTM C1293All can control expansion due to ASR in concrete.

Sulfate Resistance - ASTM C1012Some cancontrol damagedue to sulfateattack.Pass Class 3: Pumice-D Perlite-IPass Class 2: Metakaolin-D213

Caution: ZeolitesZeolite pastesCement andcalcinedzeolite pastesZeolites, as well as metakaolin, can cause increases in viscosity. These can bereduced by treatments, like calcination, but at a cost to reactivity.

0.30No Caution Needed: Alkalis & ASRExpansion After 2 Years (%)(20/18/9.7)Inert quartz, still passing (20% Replacement/18 Months/0.04% Na2Oe)0.25Inert natural minerals, failed (Replacement/Age in Months/Na2Oe)Natural pozzolans, passing (15 and 25% Replacement/18 and 24 Months/6.5-7.8% Na2Oe)Na2Oe 4.0%0.200.15(20/18/6.4)(20/18/5.8)0.10C1293 0.04%Expansion Threshold0.050.0005101520CaO (%) High-alkali inert minerals deviate from trend High-alkali natural pozzolans and inert quartz follow trend2530

Caution: Beware of Imposters ASTM C618 doesnot assesspozzolanicity Quartz qualifies asa Class N naturalpozzolanKalina et al. ACI Materials Journal, V. 116, No. 1, January 2019.

What tests could we use? Can test pozzolanic reaction- Chapelle test- Frattini test- Calcium hydroxide consumption (using TGA) Can test reactivity- Lime reactivity test- R3 test(None of these is standardized by ASTM yet, but R3 is close)

A Single Test is not Definitive ASTM C618 screens for pozzolans using sum of oxides andSAI- Quartz passes R3 tests reactivity using heat or bound water- Quartz “fails”- OPC “passes”A blend of about 40% OPC 60% quartz with sum ofoxides 70% could “pass”both ASTM C618 and R3

We know that pozzolans control ASR Why not use ASTM C1567 to test for pozzolanicreactivity? Results in 2 weeks TxDOT is doing thisThomas “Optimizing the Use of Fly Ash in Concrete,” PCA

Cannot use ASR alone For non-pozzolanic materials, ASR expansiondecreases due to dilution Strength also decreases due to dilution Need to test both strength and ASR to evaluatereactivity of materials

Idea: Test both ASR & “SAI” Step 1: Determine the amount of SCM needed topass ASTM C1567 for a highly reactive aggregate Step 2: Determine if this amount passes a modifiedSAI.- Modifications to SAI: SCM percentage can be greater than 20% Fixed w/cm of 0.485 Trying out 2 in. x 4 in. cylinders instead of cubes(greater precision)

Example: Quartz While 30% quartz is projected to be sufficient to passASR, 30% quartz does not pass “SAI”

Example: Fly Ash Approximately 15% of this fly ash should control ASRexpansion A mixture with 15% fly ash should pass “SAI”

Example: Pumice Approximately 15% of this pumice should controlASR expansion A mixture with 15% pumice will pass “SAI”

Example: Inert mineral Approximately 40% of this mineral is projected to besufficient to pass ASR, but 40% mineral won’t reliablypass “SAI” given the error inherent in the test method( 10% of the measured strength value)

Combined data In order to be classified as reactive, a material mustbe able to reliable fall into the “good zone”(accounting for measurement error)

Summary: Natural Pozzolans Natural pozzolans are excellent substitutes for ClassF fly ash- Performance is generally excellent- May not be cost-competitive in some markets- Some pozzolans (e.g. zeolites and some metakaolins)increase water demand- In spite of high alkali contents, natural pozzolanscontrol ASR well- We need better, more conclusive tests to screen outunreactive materials

Emerging Materials: Limestone CalcinedClay Cement (LC3) LC3 holds promise as a combinedcement-SCM material- High availability- Good CO2 reductions- Good performance

Natural Pozzolans – ASTM C618 A variety of natural pozzolans from different sources can meet the Class N criteria in