supplementary cementitious materials - wisconcrete.org · supplementary cementitious materials: why...

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Supplementary Cementitious Materials:Why do we incorporate these into concrete?

WCPA Technical WorkshopFebruary 16, 2018

Country Springs Hotel, Pewaukee

Andréa Breen, LafargeHolcim

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Learning Objectives

• Discuss available cementitious materials, origins and performance characteristics

• Become more familiar with terminology• Gain useful references to ASTM and ACI • Relate materials to improve concrete

project success

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ASTM C150Standard Specification for

Portland Cements

ACI Chapter 225Guide to the Selection and Use of

Hydraulic Cements

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Ball Mill -Grinds clinker into Portland cement powder

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A thin section of clinker

sliced through the

crystals

(900X)

8020

6040

4060

2080

6040 8020CaO Al O2 3

SiO2

Class F Fly Ash

Class C Fly Ash

High Alumina CementsPortland Cements

GGBFS or Slag Cement

Silica Fume

Cementitious Chemistries

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C3S Tricalcium Silicate “The glue” main contributor to strength rapid hydration high initial strength, good final strength

C2S Dicalcium Silicate “More glue” low early strength but good final strength.

The Calcium Silicates:

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C3A Tricalcium Aluminate “Heat” rapid hydration (heat) workability/plasticity some early strength higher levels decrease sulfate resistance

C4AF Tetracalcium Alumino Ferrite “Color” slow hydration determines the color of cement.

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Ground Granulated Blast Furnace Slag for Use in Concrete and Mortars

ACI Chapter 233-98 GGBFS as a Cementitious Constituent in

Concrete

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Slag Cement Terminology

• Blast Furnace: A furnace used to reduce iron ore.

• Blast-Furnace Slag: The non-metallicproduct, consisting essentially of silicates and aluminosilicates of calcium.

• Granulated Blast-Furnace Slag: The glassy, granular material formed when molten blast-furnace slag is rapidly chilled by immersion in water.

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What is Slag?(Ground Granulated Blast Furnace Slag)

• When Portland cement is made, limestone is powdered and melted (sintered). Trace minerals of iron, aluminum, magnesium and silica are added. These chemically react to form cement clinker.

• When steel is made, powdered limestone is added to molten iron to draw out impurities. These impurities just so happen to be aluminum, magnesium and silica. Therefore…

If cooled properly and ground, slag is a cement!

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The Blast Furnace

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Slag Processing

AIR COOLED SLAG PELLETIZED/EXPANDED SLAG GRANULATED SLAG

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Slag Granulator

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Slag Granulator

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Slag Grinding Ball Mill

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Comparison of Typical Chemistries

Compoundor element

PortlandCement

Granulated blast-furnace slag

CaOSiO2A12O3Fe2O3MgOSO3S totalAlkalisMnO

60 – 6717 – 253 – 83 – 8

0.1 – 4.01 – 3

-0.2 – 1.3

-

32 – 4532 – 427 –16

0.1 – 1.55 – 15

-0.7 – 2.2

-0.2 – 1.0

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Classifying GGBFS

In accordance with ASTM C 989, slag is classified by performance in the slag activity test in three grades:

Slag Activity Index, % = (SP/P) x 100

SP = Average compressive strength of slag-reference cement mortar cubes, psiP = Average compressive strength of reference cement mortar cubes, psi

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Comparing compressive strengths of3 grades of slag cement

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Performance of Slag Cement

The performance of slag as a mineral admixture in mortar or concrete depends on several factors. The following are most important:

• Chemical Composition: The more basic (non-acidic) materials are expected to be more cementitious.

• Glass Content: High glass content is desirable, but is determined by the slag’s thermal history.

• Fineness of grind: This determines the rate of reaction. A single factor like surface area can be misleading due to differences in grain size.

8020

6040

4060

2080

6040 8020CaO Al O2 3

SiO2

Class F Fly Ash

Class C Fly Ash



Silica Fume


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Benefits of Slag Cement

• Works like a cement and a pozzolan

• Improves mid to late strength

• Improves workability, pumpability

• Increases density; decreases permeability

• Increases sulfate resistance

• Can decrease water demand

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Review

• Performance of slag as a mineral admixture depends on 3 main characteristics

• Chemistry, Glass Content Fineness of Grind• It hydrates like Portland cement, so it is considered• Hydraulic• and in a secondary reaction, also consumes • CaOH2 (free lime)

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Coal Fly Ash and Raw or Calcined Natural Pozzolan for

Use as a Mineral Admixture in Concrete

ACI Chapter 232.2R-96Use of Fly Ash in Concrete

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Fly Ash is…

• a co-product of coal-fired electric generating power plants

• a co-product of pulverized coal which is ignited in a burning chamber, in which the remaining solids are fly ash and bottom ash.

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Coal Fly Ash

• Fly ash is a product of the combustion of pulverized coal in thermal power plants

• Removed by dust collection systems as a fine powder from the combustion gas stream

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Schematic Diagram for a Typical PC Combustion System

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Fly Ash

• Comprised of glassy spherical particles

• The spheres range in diameter from 1 to 100 microns

• Average size is approximately 7 microns.

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Classifications of Coal Fly Ash and Natural Pozzolans

Class Source

N Raw or calcined natural pozzolan; opalinecherts/shales, volcanic ash, pumicite,clays/shales that are calcined.

F Fly ash produced by burning antracite orbituminous coal; pozzolanic properties

C Fly ash produced by burning sub-bituminouscoal; pozzolanic and cementitious properties

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ASTM C 618 Classification

• Based on elemental chemical composition • Chemical composition is controlled by the minerals in

the coal• Inorganic matter (primarily clays and limestone) that

were present in coal seams before combustion• Constitutes between 8 and 14 percent of the coal by

weight• Consists of primarily the elements silicon, aluminum,

iron, calcium and magnesium

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Mineral Inclusions in Coal

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Class C Fly Ash

• Sub-bituminous coal• Pozzolanic and self-cementing• Sum of SiO2 + Al2O3 + FeO3, min % = 50.0• Characterized by low LOI• Suitable for concrete, aggregate and soil applications• Higher calcium oxide content, lower silicate content• Light grayish buff to buff in color• Higher specific gravities (2.5 – 2.8)

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Class F Fly Ash

• Bituminous coal• Pozzolanic• Sum of SiO2 + Al2O3 + FeO3 min % = 70.0• Typically has a higher LOI than class C fly ash• Lower calcium oxide content, higher silicate content• Suitable for concrete• Light gray to dark gray• Lower specific gravities (2.2 – 2.5)

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ASTM C618, Table 1: Chemical Requirements

Class: N F C Ty IIcmt

Ty Vcmt

SiO2 plusFe2O3, min %

70.0 70.0 50.0 20.0,6.0

SO3,max %

4.0 5.0 5.0 3.0 2.3

Moisture content,max %

3.0 3.0 3.0 LOI,3.0

LOI,3.0

Loss on Ignition,max %

10.0 6.0, up to12.0 w/history

6.0

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Cement hydration produces four parts CSH (the glue) and one part CaOH2(free lime)

“Glue”

“Free Lime”

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Fly Ash +

Free Lime

= CSH!!!(more glue)

8020

6040

4060

2080

6040 8020CaO Al O2 3

SiO2

Class F Fly Ash

Class C Fly Ash



Silica Fume


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Fly Ash“ball bearings”

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In RM concrete:• Improves strength, workability • Increases density• Decreases permeability• Increases sulfate resistance• Can decrease water demand

Other Applications:• Fly ash stabilized soils,

drying agent• Flowable fill/CLSM• RCC• Recycled asphalt

pavements• Stabilized aggregate

bases

Benefits of Fly Ash

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Quality Assurance Processes

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Blended Hydraulic Cements

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Types of Blended Cements

• Blends with Portland cement and...• …slag are IS(xx)• …fly ash or silica fume are IP(XX)• …limestone are IL(xx)”in an intimate and uniform blend”

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The Water-Cement Ratio LawDuff Abrams

All other things being equal:

The strength of concrete is inversely proportional to the ratio of water to cement

The higher the w/c, the lower the strength!!!

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w/c ratios by weight

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Cement grains

Water

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As the cement grains chemically react with water...

…fuzzy, “finger-like” crystals reach out to each other

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These fingers start to lock together...

…and grab onto sand and gravel particles as well

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Eventually, these crystals get so intertwined that the concrete stiffens...

…this is what we call “setting.”

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As the water and cement are used up, the crystals form a hard, dense structure

…water that isn’t used in the chemical reaction evaporates, leaving spaces and channels in the concrete

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How can three components be better than two?• There are practical limits and

potential side effects from individual SCMs

• Ternary blends allow the designer to best optimize mix properties for the project – for design and construction:

• Strength, permeability, durability, heat of hydration, plastic properties (finishing, pumping, segregation & bleeding)

• May result in higher total cement replacement / lower cement factor

o Improved mix economicso Sustainability implications

“SCM’s”

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US HW 287 – Lamar, CO• Owner: Colorado Department of Transportation• Contractor and Concrete: Castle Rock Construction Company• 6.5 Miles PCCP. Phase 1 completed in 2008. • CDOT Class P mix design with class F fly ash• GU (Type IL) cement

QC Testing: JA Casare/CTS

QA Testing: CRCC

Avg w/c = 0.34

28 Day Flex = 695

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104th South, Salt Lake City, Utah• Pooled Fund Ternary

Study (2009)• University of Utah*

(Tikalsky)• 10% Limestone Cement• 25% Class F Fly ash

• Single days production• Control Section

Strength*• Compressive 4454 psi• 28Day

• Actual Test Section Strength*

• Compressive 5396 psi• 28Day

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SR 201, Salt Lake City, Utahn Eastbound lanes paved August

2009 with ASTM C150 Type II/Vn Westbound lanes paved

October 2009 with ASTM C1157 10% portland-limestone cement

o Both mixes contained 25% Class F fly ash

n Eastbound Strengtho Compressive ~5000 psio Average Concrete Temp ~70 F

n Westbound Strengtho Compressive ~4500 psio Average Concrete Temp ~50 F

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US HW I-25 Near Castle Rock, CO

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US HW I-25 Near Castle Rock, CO• 5 Miles PCCP (2008)• Major Interstate

Highway• 20% Class F fly ash• 720 psi average 28-day

flexural strength• Contractor received

quality incentive per CDOT specifications

• Used in concrete paving on a regular basis in Colorado

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Other Sources of Information• ACI International - www.aci-int.org• PCA, Portland Cement Association

www.cement.org• SCA, Slag Cement Association

www.slagcement.org• ACAA, American Coal Ash Association -

www.acaa-usa.org• SFA, Silica Fume Association -

www.silicafume.org• Lafarge North America –• www.lafargenorthamerica.com

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Other Sources of Information• American Institute of Architects- www.aia.org• Am. Society of Civil Engineers www.asce.org• Am. Society for Testing & Materials

www.astm.org• Construction Specifications Institute -

www.csinet.org• Ready Mixed Concrete - www.nrmca.org• Masonry: www.ncma.org• Pavement: www.acpa.org

http://www.nrmca.org/

http://www.ncma.org/

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Wisconsin Sources of Information

• Ready Mix: www.WRMCA.com• Pavements: www.wisconcrete.org• Precast: www.pci-iw.org• Masonry: www.concretemasonry.org• UWM Center for By-Products Utilization:

www4.uwm.edu/cbu

http://www.wrmca.com/

http://www.wisconcrete.org/

http://www.pci-iw.org/

http://www.concretemasonry.org/

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