Determination of potential reactivity of MSWI fly ashes in cementitious materials Thibault LENORMAND1, Aurore DE BOOM2, Marc DEGREZ2, Christian PIERRE3, Stéphanie STAQUET1

1: Université Libre de Bruxelles, BATir 2: Université Libre de Bruxelles, CREA-SURF 3: CRIC-OCCN Conference WASCON 2012, 31-05-2012 Gothenburg, Sweden

Contents

• Introduction

• Materials and methods

• Results

• Conclusion

2

• What to do with a solid containing….?

Introduction

3

CaO SiO2

Al2O3 Fe2O3

It looks cement,

doesn’t it?

• but also…

Introduction

4

CaO SiO2

Al2O3 Fe2O3

NaCl KCl

ZnO PbO

…

A salty cement…

• “Just” remove chlorides and heavy metals!

Introduction

5

CaO SiO2

Al2O3 Fe2O3

NaCl KCl

ZnO PbO

…

• How?

Introduction

6

CaO SiO2

Al2O3 Fe2O3

NaCl KCl

ZnO PbO

…

Introduction

• Municipal Solid Waste Incinerator (MSWI) fly ashes – Hazardous materials

• Currently landfilled

• Different problems

– Environmental problems

– Shortage of place

– Lack of natural materials

• Goal of this research – Use MSWI fly ashes in cementitious materials as mineral addition

• In partial replacement of cement

7

Introduction

• Treatment methodology

8

Treatment

Incorporation in

cementitious

materials

Modifications to

apply to the

treatment

Validation of

treatment

modifications

Treatment validation

Bibliographic

study

Materials and methods

• Replacement of a part of cement CEM I 52.5N by MSWI fly ashes

• Ratio Water/Binder = 0.5 – Binder : cement + MSWI fly ashes

9

Cement

MSWI fly ashes

Cement

Materials and methods

• Characterisation methods

Compressive strength

Calorimetric analyses

Setting time

Gravimetric measurements

10

Materials and methods

• Compressive strength

– According to EN 196-1 standard

– Carried out on mortars prims 4*4*16 cm3

• Calorimetric analyses

– Isothermal measurement at 20°C

– Carried out on cement paste samples

11

Methods - Compressive strength - Heat flow - Setting time - Volume

Materials and methods

• Setting time measurement

– Determined by ultrasounds velocity

measurement

• With FreshCon device

– Carried out on mortar or cement paste

12

0

500

1000

1500

2000

2500

3000

0 5 10 15 20

Ult

raso

un

ds

velo

city

(m

/s)

Time (hour)

Initial setting

Final setting

Step 1 : Fresh mortar or cement

paste

Step 2 : Hardening of material,

acceleration of ultrasounds

Step 3 : Hardened material

Methods - Compressive strength - Heat flow - Setting time - Volume

Materials and methods

• Gravimetric measurement – Determination of volumetric variations of a cement paste sample

according to Archimedes' principle

– Cement paste was put in an elastic waterproof membrane

13

Thermo-

statically

controlled

water bath

Scale

Data-gathering

system

Cement paste

sample

water

membrane

MV

Methods - Compressive strength - Heat flow - Setting time - Volume

• MSWI fly ashes ONLY from the electrostatic precipitator

Materials and methods

14

CaO SiO2

Al2O3 Fe2O3

NaCl KCl

ZnO PbO

…

Results

• Water treatment to reduce chloride quantity – Washing with distilled water

• Ratio Liquid/Solid = 5

• 1 hour

• Use of water treated MSWI fly ashes (notation WT) – As replacement of cement

• 12.5%

• 25%

• 37.5%

– Reference :

• Without cement substitution

15

Effects on - Compressive strength - Heat flow - Setting time - Volume

Results

• Compressive strength

16

0

10

20

30

40

50

60

70

80

0 20 40 60 80 100Co

mp

ress

ive

str

en

gth

(M

Pa)

Time (day)

Reference WT 12.5

WT 25 WT 37.5

Important decrease of compressive strength with the increase of WT MSWI fly ashes

Different explanations → Diminution of cement quantity → Anhydrite Ettringite → Oxidation of metallic aluminium

→ Emission of hydrogen → Creation of bubbles and crackings

222 32222 HAlOOHOHAl

Mortar prism WT 37.5

Water treatment effects on - Compressive strength - Heat flow - Setting time - Volume

0

0.5

1

1.5

2

2.5

3

3.5

0 1 2 3 4 5 6 7

No

rmal

ize

d h

eat

flo

w

(mW

/g)

Time (day)

Reference

WT 12.5

WT 25

WT 37.5

Results

• Hydration – Heat flow

• Setting time

17

3.1 4.512.4 16.2

38.944.5

85.792.7

0

20

40

60

80

100

Initial setting Final setting

Tim

e (

ho

ur)

Reference WT 12.5 WT 25 WT 37.5

Important delay in hydration and setting time → Impact of heavy metals (Pb, Zn), known as setting retarders

Water treatment effects on - Compressive strength - Heat flow - Setting time - Volume

Results

• Volume

18

Treatment with water → Swelling of cement paste membrane → Not efficient to oxidize metallic aluminium

90%

100%

110%

120%

130%

140%

150%

0 20 40 60 80 100

Vo

lum

e (

%)

t (h)

ReferenceWater treatment

142%

97.3%

Water treatment effects on - Compressive strength - Heat flow - Setting time - Volume

Results

• Water treatment

19

Decrease in compressive strength → Oxidation of metallic aluminium → Emission of hydrogen in cementitious materials

Important delay in hydration → Heavy metal concentration (Pb, Zn)

→ Oxidize metallic aluminium during the treatment step

→ Heavy metal concentration to be decreased

Results

• Decrease in heavy metal concentration

20

Separation of MSWI fly ashes in 3 fractions :

• < 38 µm • 38 – 90 µm • > 90 µm

→ Increase in heavy metals concentration with the decrease in fraction size → Setting times were measured for each fraction

• Incorporation rate of 25%

3.1 4.5

44.9 50.2

41.847.9

15.0 17.8

0

10

20

30

40

50

60

Initial setting Final setting

Tim

e (

ho

ur)

Reference WT F90 25

Results

• Oxidation of metallic aluminium

21

Treatment with sodium hydroxide → Shrinkage of cement paste membrane

→ Efficient to oxidize metallic aluminium

97.0%

97.5%

98.0%

98.5%

99.0%

99.5%

100.0%

0 5 10 15 20 25 30

Vo

lum

e (

%)

t (h)

ReferenceBasic treatment

99.3%

97.3%

→ Treatment with sodium hydroxide selected

Results

• New treatment

22

3.1 4.57.3 9.8

38.944.5

15.0 17.8

0

10

20

30

40

50

60

Initial setting Final setting

Tim

e (

ho

ur)

Reference BT 25 WT 25 WT F>90 25

Combining size-based separation and basic treatment → Water washing to remove chlorides → Selection of the less contaminated fraction → Oxidation of metallic aluminium during treatment step

BT: Basic treatment combining water WT: Water treatment WT F>90: Water treatment and selection of the fraction upper 90 µm

Basic treatment • Setting times were the less delayed • Delays were reduced compared

with WT 25

No damage was observed because of hydrogen emission

Conclusion

• Raw MSWI fly ashes have to be treated before their incorporation in cementitious materials – Water washing to remove chloride

– Size-based separation to decrease heavy metals concentration

– Basic treatment to oxidize metallic aluminium

• After this treatment – Use of treated MSWI fly ashes in cementitious materials without

damage

– Further study of the reactivity of treated MSWI fly ashes in cementitious materials

• Carried out currently

23

Thank you for your attention