ALTERNATIVE WAYS TO THE MARKET

FOR MOIST FLY ASH

Michael McCarthy

Concrete Technology Unit

School of Science and Engineering,

University of Dundee,

SCOTLAND, UK

TOPICS COVERED

• Background

• Effect of Moisture on Fly Ash

• Using Wet-Stored Fly Ash in Concrete

• Processing / Beneficiation

• Concluding Remarks

WET-STORED FLY ASH

Stockpile

Lagoon

Lagoon (Pond) : Fly ash slurried with

water (water to fly ash ratios 10:1 to

3.5:1)* where it is allowed to settle

Stockpile : water added to fly ash at

low levels (moistened 10 to 25%)

and kept in a storage area

* Sear (2001)

MOISTURE LIMITS

1.5

3.0

1.01.5

3.0

1.0

3.0

0.5

3.0

0

2

4

6

8

10

LIM

IT O

N F

A M

OIS

TU

RE

, %

Lower end of moisture range

for moistened FA (10-20%)

COUNTRY

No

lim

it

1995 : Stored and transported

to the purchaser in a dry

condition.

2005 : Reference made to

processing (including drying).

Fly ash should be stored and

delivered in a dry condition.

2012 : Reference made to

processing (including drying).

Data from 1990s* BS EN 450 / BS EN 450-1

* Based on Alonso and Wesche (1991)

VARIABLES EXAMINED

Dry FA Characteristics

Fineness

Fine

Medium

Coarse

Lime content

Low

High

Moistening / Storage Variables

Moisture level

1, 10, 20 and 40% by mass

Conditioning water properties

pH 6, 7 and 8

Seawater

Storage regime

Laboratory (20 and 5°C)

Site stockpile

Periodically wetted

Lagoon

MOISTURE EFFECTS ON FINENESS

0

10

20

30

40

50

dry 0 m 1 m 3 m 6 m 12 m 18 m

FIN

EN

ES

S, %

ret

45μ

m

STORAGE TIME (10% moisture)

60

FA P1

FA D2

FA P2

FA P3

FA D4

FA D8

FA D6

0

10

20

30

40

50

60

dry 1% 10% 20% 40%

MOISTURE CONTENT (6 months)

FA P1

FA D2

FA D4

FA D6 FA P2

FA P3FA D8

Wet-stored

Fly Ash

Dry Fly Ash Wet-stored

Fly Ash

SEM IMAGES

(a) General view of dry PFA (2,000 x)

(b) General view of conditioned PFA after

18 months storage (2,000 x)

(c) Early stages of inter-particle bonding in

conditioned PFA after 18 months storage

(18,000 x)

10% moisture, 18 months storage

10 µm 10 µm1 µm

LOSS-ON-IGNITION

0

1

2

3

4

5

6

7

8

9

10

LO

I, %

FA P1

FA P2FA P3

FA D2

FA D4FA D6

FA D8

dry 0m 1m 3m 6m 12m 18m

STORAGE TIME (10% moisture)

WATER REQUIREMENT / STRENGTH FACTOR

Dry 0 1 3 6 12 1890

95

100

105

WA

TE

R R

EQ

UIR

EM

EN

T %

FA P1

FA P3

FA P2

10% moisture

STORAGE TIME, months

Dry 0 1 3 6 12 180.5

0.6

0.7

0.8

0.9

1

ST

RE

NG

TH

FA

CT

OR

FA P3

FA P1

FA P2

10% moisture

STORAGE TIME, months

INITIAL CONCRETE TESTS

350 kg/m³ cement content, 30% Fly Ash by mass

0 10 20 30 40

IN ITIAL DRY STATE

25

30

35

40

45

CU

BE

ST

RE

NG

TH

(2

8 d

ay

), N

/mm

²

0 10 20 30 40 50 60 70

AFTER CONDITIONING

25

30

35

40

45Dry

0 months

1 month

6 months

18 mths

DRY &

0 MONTHS

6 MONTHS

10% mois ture

FINENESS, % ret 45 µm

Increasing

storage

1 MONTH

FINENESS, % ret 45µm

10% moisture

0 10 20 30 40

IN ITIAL DRY STATE

0

20

40

60

80

100

SL

UM

P, m

m

0 10 20 30 40 50 60 70

AFTER CONDITIONING

0

20

40

60

80

100

Dry

0 months

1 month

6 months

18 months

Dry

Conditioned

PC and dry PFA

75 mm nominal for

10% mois ture

FINENESS, % ret 45 µm

Increasing

storage

FINENESS, % ret 45μm

10% moisture

25

35

50

CONCRETE MIXES

NATURAL AGGREGATE

20 mm

810

810

810

265

330

445

PC

185

230

310

80

100

135

FREE

WATER,

l/m³

165

165

165

10 mm

410

410

410

Sand

705

645

555

DRY

FATOTAL

CEMENTSTRENGTH,

N/mm²W/C

0.62

0.50

0.37

Fine FA

Superplasticized concretes

Workability 75 mm slump

DRY FLY ASH MIX PROPORTIONS, kg/m3

CONCRETE MIXES

0.3 0.4 0.5 0.6 0.7

W/C RATIO

10

20

30

40

50

60

70

28 D

AY

CU

BE

STR

EN

GTH

, N

/mm

² Dry

1 month

6 months

Fine PFA

Dry

6 m

onth

s

35 N/mm²

concrete

(10% moisture)Fine FA (10% moisture)

INITIAL SURFACE ABSORPTION

0 10 20 30 400

20

40

60

ISA

-10

, ml/m

² x

10

-2

Dry PFA

1 month

6 months

Increasing

storage

Grade 35 N/mm²

10% PFA moisture

0 10 20 30 400

2

4

6

8

INT

RIN

SIC

AIR

PE

RM

EA

BIL

ITY

, m² x

10

-17

FINENESS OF DRY PFA,

% ret. 45 µm

FINENESS OF DRY FA,

% RET. 45µm

Strength: 35 N/mm²

10% FA moisture

Strength : 35 N/mm2

10% moisture

Dry

6 months

CARBONATION RESISTANCE

Test exposure: 4.0% CO2, 20°C, 55% RH

0 10 20 30 40

FIN EN ESS OF D R Y PFA ,

% ret. 45 µm

0

10

20

30

40

Increasing

storage

1 2 3 4 5 6

EXPOSU R E PER IOD , (weeks) 0.5

0

10

20

30

40

CA

RB

ON

AT

ION

DE

PT

H, m

m

D ry

1 month

6 months

R = + 0.96

Grade 35 N /mm²

Fine PFA

(10% moisture)

Strength :

35 N/mm2

Fine FA

CHLORIDE DIFFUSION

10% moisture

0 10 20 30 40

FINE NE S S OF DRY P FA,

% r et. 45 µm

0

2

4

6

8

10

CO

EFFIC

IEN

T O

F C

HLO

RID

E D

IFFU

SIO

N,

m²/s x

10

-3

Dry P FA

1 month

6 months

Incr easing

stor age

Gr ade 35 N/m m ²

10% P FA m oistur e

Strength: 35 N/mm2

Dry

FINENESS OF DRY FA

-9c

Main objective to examine moistened FA handling

characteristics and concrete performance

Concrete element: mesh reinforced foundation

Concrete produced at ready mix plant

Visual observations made of production process.

Tests made for concrete workability and cube strength

FULL-SCALE TRIAL – READY MIX

Dry FA batched from powder silo. Moistened FA

batched following fine aggregate procedures

To minimise compaction, moistened FA moved from

stockpile just before batching

Material discharged to hopper slowly

Concrete produced in 6.0 m3 transit mixer

No problems encountered in concrete production

CONCRETE PRODUCTION

FULL-SCALE TRIAL

WET FA STOCKPILE FA DISCHARGED TO HOPPER FA CONVEYED TO TRUCK

FA CONCRETE MIXED FOUNDATION ELEMENTS

Property Fine Coarse

FA

Fineness, % ret 45 5.7 35.5

LOI, % 5.9 9.4

Moisture, % 0.2 13.7

CONCRETE

Slump, mm 70 50

Plastic density, kg/m3 2340 2350

Cube strength, 7d, N/mm2 23.0 17.0

Cube strength, 28d, N/mm2 36.5 29.0

Cement content 355 kg/m3, 30 % Fly Ash, w/c ratio 0.48,

nominal slump 50 mm, strength (cube) 25 N/mm2

FLY ASH/CONCRETE PROPERTIES

• Feasibility for moistened / stockpiled fly ash

use in concrete

• Some practical challenges associated with

handling

• Alternative routes for using stockpile fly ash

may be considered

• Processing / Beneficiation?

OUTCOMES OF RESEARCH

• Investigate what can be achieved with

wet-stored fly ash by laboratory processing

• Stockpile at a 1500 MW power station,

operational since mid 1960s

• Several million tonnes of fly ash stored there

• Sampling carried out at several locations

INITIAL PROCESSING TESTS ON FLY ASH

• Material was oven dried in the laboratory

• Passed through 600 µm sieve

• 63 µm sieve

• Air classifier (target BS EN 450-1

Category S fineness)

• Grinding (laboratory ball mill, 20 minutes)

INITIAL PROCESSING TESTS ON FLY ASH

EFFECTS ON FINENESS AND LOI

Sample / Process

Characterisation of the Sample

Fineness, 45µm

sieve ret., %LOI, %

Original properties 33.8 15.1

Passing 63 µm sieve 10.2 10.7

Air classification 12.9 13.1

Grinding in ball mill 0.6 14.1

PARTICLE SIZE DISTRIBUTION

CU

MU

LA

TIV

E V

OL

UM

E,

%

0

20

40

60

80

100

0.1 1 10 100 1000

PARTICLE DIAMETER, µm

Original

63 µm sieved

Air-classified

Ground

0

10

20

30

40

50

0 20 40 60 80 100

AGE, days

Original

63 µm sieved

Air-classified

GroundCO

MP

RE

SS

IVE

ST

RE

NG

TH

, N

/mm

2

COMPRESSIVE STRENGTH DEVELOPMENT

w/c ratio 0.53, fly ash level 30%

INITIAL SURFACE ABSORPTION

POND 1 POND 2 STOCKPILE0

10

20

30

40

50

60

70

80

90

Original

63 µm sieved

Air-classified

Ground

ISA

T-1

0,

ml/

m2×

10 -

2

w/c ratio 0.53, fly ash level 30%

• Literature Review

• Survey of Stockpile Material Characteristics

• Laboratory Processing Tests

• Reactivity / Concrete Tests

• Pilot / Full-scale Trials

RESEARCH PROJECT : PROCESSING OF

STOCKPILE FLY ASH (UKQAA / EPSRC)

Fly ash tends to coarsen / agglomerate when wet-

stored in a stockpile. The effects tend to be greatest

around 10% moisture addition and increase with time

Water requirement and reactivity of fly ash were

correspondingly affected with wet storage

By minor adjustment to the concrete mix via w/c

ratio, equivalent hardened concrete properties to

dry fly ash could be achieved

Trials have been carried out which indicate that

concrete can be produced with the material at

full-scale. There may be issues with handling

CONCLUDING REMARKS

CONCLUDING REMARKS

Details of initial tests to consider processing of

stockpile fly ash are described

By sieving, air classifying and grinding

enhancements in strength and other properties

were achieved

A new project is extending this work, with a view

to enabling processed stockpile material use in

concrete

SOURCES FOR FURTHER INFORMATION

McCarthy, M.J., Jones, M.R., Zheng, L., Robl, T.L. and Groppo, J.G. Characterizing long-term

wet-stored fly ash following carbon and particle size separation. Fuel Journal, Vol 111, pp 430 -

441, 2013.

McCarthy, M.J., Dhir, R.K., Halliday, J.E and Wibowo A. Role of PFA quality and conditioning in

minimising damaging ASR in concrete. Magazine of Concrete Research. Vol 58, No 1, pp 49 -

61, 2006.

McCarthy, M.J., Tittle, P.A.J., Dhir, R.K. and Kii, K.H. Mix proportioning and engineering

properties of conditioned PFA concrete. Cement and Concrete Research, Vol 31, pp 321 - 326,

2001.

McCarthy, M.J., Tittle, P.A.J and Dhir, R.K. Influences of conditioned PFA as a cement

component in concrete. Magazine of Concrete Research, Vol 52, No 5, pp 329 - 343, 2000.

Dhir, R.K., McCarthy, M.J. and Tittle, P.A.J. Use of conditioned PFA as a fine aggregate

component in concrete. Materials and Structures, Vol 33, No 1, pp 38 - 42, 2000.

McCarthy, M.J., Tittle, P.A.J. and Dhir, R.K. Characterisation of conditioned PFA for use as a

cement component in concrete. Magazine of Concrete Research, Vol. 51, No 3,

pp 191 - 206, 1999.

ACKNOWLEDGMENTS

The UKQAA and its members, Aggregate Industries

UK Ltd, BAA plc, Castle Cement, DETR, EPSRC, John

Doyle Ltd, QPA, RMC Environment Fund and WS

Atkins Ltd are thanked for supporting the work

described / now in progress.

Thanks are also given to colleagues at the University

of Dundee, Professor R K Dhir and Drs P A J Tittle,

K H Kii, L Zheng, J E Halliday and G Tella for their

contributions to the research described.