Fly Ash Makes Better Concrete -Langley

8/12/2019 Fly Ash Makes Better Concrete -Langley

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BY

DR. WILBERT LANGLEY,

P. ENG

Ecuador , January 2012

High Volume Fly ASH Concrete - ASustainable Solution by Making

Better Concrete


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What is Fly Ash?

When pulverized coal is burned to generate

electrical power, extremely large quantities of fly

ash and bottom ash are produced. Fine grade fly

ash has acquired considerable importance in thebuilding materials sector.


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Fly Ash Characteristics

Coal is formed in the earth over periods of 300

to 400 million years. Over this period, thedifferent plant material from which coal is

formed undergoes complex transformation so

that the nature and properties of the variety ofcoals are dependent on the nature of plants in

their makeup.


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Properties of Fly Ash

Fly ash is a solid fine grained material resulting

from the combustion of pulverized coal inpower station boilers. The material is collected

in mechanical or electrostatic separators. Fly

ashes capable of reacting with Ca(OH)2 atroom temperature can act as pozzolanic

materials. This activity is attributable to the

presence of SiO2 and Al2O3 in amorphousform.


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Fly Ash Chemical Composition

Fly ashes from coal combustion contain

particularly high percentages of SiO2, Al2O3, andFe2O3, and also contain other oxides such as

CaO, MgO, TiO2, Na2O, K2O, SO3, etc. Trace

metals such as Cr, Cd, Pb, Mo, Hg, etc. mayalso be present which has recently caused some

concern and will be addressed later in this

presentation.


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Concrete Strength Development

0

510

15

20

25

30

35

4045

50

7 Days 28 Days 60 Days 90 Days

CompressiveSt

rength,

MPa

100% PC

80% PC+20% FA

70% PC+30% FA

60% PC+40% FA

W/C+F = 0.45

Air Entrained


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Durable Concrete

Low diffusion coefficient ~ 10 -13 m2/sec

Low unit water content < 150 l/m3

Low adiabatic heat


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HVFA Concrete Structural

Properties

Creep less than conventional concrete;

Fatique strength equivalent to conventionalconcrete;

Modulus of Elasticity similar to conventional

concrete; Drying shrinkage is less;

Strength gain continues over a longer period;

Adequate early stripping strength; and

Superior quality of formed surfaces.


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Typical Concrete Mixture

Proportions - Low Calcium Ash

W/C+F Mixture Proportions, kg/m3

Cement Fly Ash Sand Stone

0.35 150 190 750 1100

0.28 180 220 660 1110

0.39* 340 0 860 1020

*Denotes control mixture


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Compressive Strength Data

Laboratory Tests

W

C+F

Compressive Strength, MPa

3 D 7D 28D 91D 365D

0.35 15.5 20.5 37.5 53.0 69.0

0.28 22.4 34.2 57.1 75.2 86.0

0.39 33.2 40.4 50.7 57.3 60.6


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Large Blocks 1987


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Compressive Strength Development

of Cores (56 % fly ash)

010203040

5060708090100

1 10 100 1000 10000

Comp

ressive

Strength,

MPa

Test Age, days

Control HVFA HVFA (lean)

Up to 23 years


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Parklane Beams and Slabs


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Parklane Developments Complex

Concrete Mixture Proportions

Component Quantity

Portland Cement

Class F Fly AshFine Aggregate20 mm Coarse AggregateWaterSuperplasticizer

180 kg/m3

220 kg/m3

800 kg/m31100 kg/m3

110 l/m33.5 l/m3


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Parklane Developments Project

Field Test Results

0

20

40

60

80

7 28 120

Age in Days

Compressive

Strength,M

Pa


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Windsor Casino Project

Concrete Mixture Proportions

Type 20 Cement 130 kg/m3

Type F fly ash 130 kg/m3

40 mm aggregate 430 kg/m3

20 mm aggregate 640 kg/m3

Concrete sand 945 kg/m3

Water (including ice) 130 l/m3


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San Marga Iraivan Temple

1000 Year Design Life


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San Marga Iraivan Temple

Type 1 Cement 106 kg/m3

Class F Fly Ash 142 kg/m3

Concrete Sand 945 kg/m3

1" Stone 682 kg/m33/8 Stone 445 kg/m3

Water 95 kg/m3

Air Entraining 110 ml/m3

HRWR 3330 ml/m3

Concrete Mix Proportions Temple Dome


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Strength Testing on Site

0

5

10

15

20

25

30

3 7 28 90

Test Age, days

Compre

ssive

Strength

,MPa

Bottom

Top


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Strength and DurabilityWe as engineers seem to be obsessed with

concrete strength, and what experience hasshown us is that the concept/philosophy of

Durability through Strength is simply not valid

and attainable. There is no simple or uniquerelationship between Strength and Durability;

we should design for Durability and check to

ensure design strength is met.


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Concrete Durability Common physical tests conducted on concrete to

assess quality are conducted between cracks oron non-cracked concrete at least. Most forms of

concrete deterioration will likely occur at cracks

first. We do not adequately address this issue in

concrete assessment for durability.

High volume fly ash concrete with low unit water

content and very low heat of hydration will have

minimal cracking from either drying shrinkage or

thermal volume change.


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Sustainability StrategyIn 1992, the UN Conference on Environment

and Development (the Earth Summit) washeld, and the importance of sustainable

development to achieve a balance between

environmental conservation and economicgrowth was reconfirmed.

The concept of sustainability was developed in

1987 by the World Commission onEnvironment and Development.


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SustainabilityIn simple terms, Sustainability implies

development that meets the needs of thepresent, without compromising the ability offuture generations to meet their own needs.

Concrete meets the definition in that it isenvironmentally friendly; it uses no hazardousmaterials; does not pollute waterways;

recycled materials can be used; and itconserves petroleum products.


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SustainabilityDevelopment at the cost of the environment, is

no longer acceptable. Economic growth mustbe achieved without the cost to futuregenerations.

Sustainability is a global issue and only byembracing sustainability at the global level canwe be sure that the environment will be

protected, the natural resources used wiselyand maintain stable economic development.


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SustainabilityPortland cement plants have made major stridesin reducing CO2 emissions. The reduction oflimestone alone produces approximately 0.7tonnes of CO2per tonne of cement; thus, this limits just howmuch further the industry can practically go in thisdirection. Blending or intergrinding othermaterials such as limestone will provide furtheremission reduction. Replacement of highpercentages of cement with supplementarycementing materials can also provide attractivealternatives.


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SustainabilityThe environmental impact of material usage

requires:- better design

- less waste

- more reclamation

- more recycling


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Sustainability LEED (leadership in energy &environmental design)

The LEED mission is to promote the design and

construction of buildings that are environmentallyresponsible, profitable, and healthy places towork.

LEED promotes green design design and

construction practices that significantly reduce oreliminate the negative impact of buildings on theenvironment and occupants in various areas as:

Sustainable site planning; safeguarding water;energy efficiency; conservation of materials; andindoor environmental quality.


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Concrete to Meet LEED Certification

There is currently a building under

construction that is to achieve LEEDcertification with a specified greater than

normal amounts of fly ash. At the same time

the specifications state that the more thannormal quantity of fly ash does not relieve the

contractor of his responsibility to meet the 28-

day strength requirement. This is not thecorrect approach to achieve sustainability.


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Durability & Sustainability High volume fly ash concrete and extended life

structures keeps material impacts on theenvironment to a minimum;

Structure durability means that the structure is

rarely out of service for maintenance and thushave minimal social disruption; and

Extended life structures are stable and durable

and thus, maintenance costs are reduced toprovide economic advantages.


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Reduction of CO2 by Concrete

Industry

Use less portland cement

Use more supplementary cementing materials Use less unit water with superplastizers

Incorporate recycled aggregates in concrete

Use stainless steel reinforcement in long life

structures

Specify later age strength Design for durability instead of strength


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High Volume Fly Ash Concrete

Benefits

Utilization of under-utilized resource; Reduction in CO2 emissions;

Reduction in concrete costs;

Elimination of thermal cracking; and

Improvement of architectural surfaces.


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TVA Kingston Ash DisasterIn December 2008, a large ash lagoon was

breached at the Kingston Tennessee PowerStation and released some 5.4 million cubic

yards of fly ash sludge over an approximately

300 acre area and into the Emory River. Theash flowed through a residential area and

demolished a dozen homes along with

contamination of acres of land.


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12 Homes were covered with fly ash

Kingston, Tennessee Ash Spill

Site Prior to the Spill Site After the Spill


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Ash Flow Through Town


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25 foot wall of ash 1-mile downstream


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Is fly ash a hazard?


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Is Fly Ash a Toxic Waste?With the breach of the lagoon in Tennessee,

pressure was put on the EPA of the US tocategorize fly ash as a hazardous waste in order

to remove responsibility for fly ash

impoundments from state control to Federalcontrol. Under Federal control, all dams and

lagoons would require rigid guidelines and

annual inspections similar to dams for watersupply.


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EPA has been a long-time supporter of the

beneficial use of fly as a construction material.This is not likely to change, however it is likely

that fly ash will be treated as a special waste

and exempt from many restrictions on wastesin landfills. It is anticipated that new guidelines

will be put in place as to how retention ponds

are constructed and the frequency ofinspection.

EPA Response to Fly Ash Spill

What Has Been the Affect of the


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What Has Been the Affect of the

Kingston Spill on the Fly Ash Industry?

The impact of the fly ash issue in Tennessee

has had a far reaching affect on fly ash andthe concrete industry in North America. If theEPA bent to the pressures of the uninformed it

would have a very negative impact on theconcrete industry. Nova Scotia fly ash cannotbe used in water containment structures byorder of NSE (following the Kingston

impoundment failure).


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Is Fly Ash a Hazardous Waste?

It has always been my contention that

regardless of the nature of fly ash with respectto undesirable elements, it would be better tied

up in concrete than placed in a landfill. Fly

ash, as well as portland cement does notcontain any elements or compounds not found

in the earth from which they originate.


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Summary of Typical Data to Date

ElementWater

Standard1-day 4-day 9-day 16-day

Antimony 6 g/L 1.3 1.2 1.4 1.8

Arsenic 10 g/L 3.5 3.7 4.6 4.4

Barium 1000 g/L 89.3 1370 1390 1450*

Boron 5000 g/L - ND ND ND

Cadmium 5 g/L ND ND ND ND

Chromium 50 g/L 4.3 13.8 10.1 87.5*

Lead 10 g/L 36.1* ND 1.16 ND

Mercury 1 g/L ND ND ND 0.03Selenium 10 g/L ND 2.0 2.4 4.3

Thallium 2 g/L ND ND ND ND

Vanadium - 60.3 17.0 20.1 25.7


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Woodrow Wilson Bridge


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Ota Ri er Bridge


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Otay River Bridge


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Four Bears Bridge, North Dakota

S S


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Sixth Street Viaduct, Wisconsin

This structure indowntown Milwaukee

is unique in that thespecificationsrequired a minimumof 46 percent recycled

material in the overallproject. The concretecontained 35 percentfly ash, the highest

percentage used todate (2002) byWisDOT.

S t i bilit


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Sustainability


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Thank You!Questions?

Fly Ash Makes Better Concrete -Langley

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