Blended cement with reduced CO2 emission- utilizing the fly ash-limestone synergy

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Doctoral theses at NTNU, '%&&/32

Klaartje De Weerdt

Blended Cement with Reduced CO ² Emission - Utilizing the Fly Ash-Limestone Synergy

ISBN 978-82-471-2584-7 (printed ver.) ISBN 978-82-471-2585-4 (electronic ver.) ISSN 1503-8181

NTNU Norwegian University of Science and Technology Thesis for the degree of doctor philosophiae Faculty of Engineering Science and Technology Department of Structural Engineering

D o ct o ra l t h e se s a t N T N U , 2011:3 2 Klaartje De W eer dt

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Klaartje De Weerdt

Blended Cement with Reduced CO ² Emission - Utilizing the Fly Ash-Limestone Synergy

Thesis for the degree of doctor philosophiae Trondheim, February 2011

Norwegian University of Science and Technology

Faculty of Engineering Science and Technology Department of Structural Engineering

Klaartje De Weerdt

Blended Cement with Reduced CO ² Emission - Utilizing the Fly Ash-Limestone Synergy

Thesis for the degree of doctor philosophiae Trondheim, February 2011

Norwegian University of Science and Technology

Faculty of Engineering Science and Technology Department of Structural Engineering

Klaartje De Weerdt

Blended Cement with Reduced CO ² Emission - Utilizing the Fly Ash-Limestone Synergy

Thesis for the degree of doctor philosophiae Trondheim, February 2011

Norwegian University of Science and Technology

Faculty of Engineering Science and Technology Department of Structural Engineering

Klaartje De Weerdt

Blended Cement with Reduced CO ² Emission - Utilizing the Fly Ash-Limestone Synergy

Thesis for the degree of doctor philosophiae Trondheim, February 2011

Norwegian University of Science and Technology

Faculty of Engineering Science and Technology

Department of Structural Engineering

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NTNU

Norwegian University of Science and Technology Thesis for the degree of doctor philosophiae

Faculty of Engineering Science and Technology Department of Structural Engineering

©Klaartje De Weerdt

Doctoral Theses at NTNU, 2011:32 Printed by Tapir Uttrykk

NTNU

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I

Acknowledgements

The research project presented in this thesis was carried out at SINTEF Building and Infrastructure in cooperation with the Department of Structural Engineering at the Norwegian University of Technology (NTNU) in Trondheim.

This project is part of the Concrete Innovation Centre (COIN), a centre for research based innovation, funded by the Norwegian Research Council and industrial partners (www.coinweb.no). I acknowledge COIN for the financial support, and for facilitating the interaction between experts, students and industry.

It would not have been possible to complete this thesis without the help and support of many.

First and foremost, I would like to express my gratitude to my co-supervisor Professor Harald Justnes for giving me the opportunity to come to Norway, for coming up with the fascinating idea which lead to this thesis, and for watching over me during four years while travelling the world. I would like to thank my supervisor Professor Knut O. Kjellsen for his enthusiasm and solid support, and Professor Erik J.

Sellevold, for spending many hours of his spare time correcting my drafts, encouraging me and always being ready for a good discussion.

Special thanks go to Dr. Barbara Lothenbach for inviting me to EMPA, Dübendorf in Switzerland, giving me the opportunity to work in their excellent laboratories during 6 months, and for introducing me into the world of GEMS as well as charming Switzerland. I would like to thank Dr. Mohsen Ben Haha and Dr.

Gwenn Lesaout for their assistance with respectively scanning electron microscopy techniques and XRD- Rietveld analysis. The discussions with Florian Deshner, Dr. Frank Winnefeld and Dr. Josef Kaufmann were inspiring, and their help with the experiments was much appreciated. I should not forget the invaluable support in the laboratory from Angela Steffen, Luigi Brunetti, Boris Ingold and Walter Trindler. Further, I want to thank the whole crew for making my stay at EMPA unforgettable.

I want to thank Dr. Maciej Zajac from the Heidelberg Technology Centre for his interest in the project, his advice, and the invitation to the research centre in Leimen.

The “concrete”-colleagues at “grønn bygget” have contributed immensely to my personal and professional time in Trondheim. The colleagues have been a source of optimism, passion for research, warmth and joy; thanks Hedda, Marit, Bjørn Erik, Hans, Randi, Gudrun, Erik T., Helge, Per Arne, Lars, Harald, Anja, Ola, Tone, Mari, Tore, Sindre, Jan, Gunrid, Kristin, Knut, Stig, Chris, Roger, Eirik and Tor Arne. I want to express my gratitude to Knut Lervik, Stig Roar Rudolfsen, Øystein Mortensvik and Ove Loraas for their assistance with the mortar tests, and Tone Østnor and Kristin Mjøen for helping me with the analyses in the chemistry lab. Special thanks go to Hedda Vikan and Tone Østnor for being so supportive and inspiring, and for the laughter and good times we shared.

I am very grateful to my family and friends for supporting me and reminding me that the world does not only turn around concrete or cement.

My final thanks go to Robert for his love, support and patience.

Klaartje, February 2011

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Acknowledgements

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Abstract

During cement production large amounts of CO2 are emitted, about 1 tonne CO2 per tonne clinker, if no measures are taken. About 40% originates from fuel combustion, grinding and other operations, and 60% from the de-carbonation of limestone to form the clinker phases. One way to reduce these emissions on the short term is by replacing part of the clinker with other materials such as slag, limestone powder, fly ash, silica fume and natural pozzolans. The type of replacement materials used depends on their availability (e.g. amount available, price and transportation) and is therefore dependent on the geographical location of the cement plant. The aim of this study is to contribute to the development of a novel all-round Portland composite cement for the Norwegian market. When this study was started, the cements produced at the Norwegian cement plants were: CEM I Portland cements containing up to 5% limestone powder and CEM II/A-V Portland fly ash cements containing up to 18% fly ash but no limestone powder. In this study, the effect of increasing the replacement levels of the ordinary Portland cement (OPC) (up to 35% replacement), and combining siliceous fly ash (FA) and limestone powder (L) to replace OPC are investigated.

Using a combination of fly ash and limestone to replace OPC seems to be better than using only one of them. Limestone powder accelerates the early hydration more than fly ash, but fly ash contributes to strength development at later ages due to its pozzolanic reaction. Additionally a chemical interaction between fly ash and limestone has been observed, first in simplified cementitious system and later also in Portland composite cement. Limestone powder interacts with the AFm and AFt phases formed during the hydration of OPC. At first, ettringite forms during the hydration of OPC. When all gypsum is consumed, ettringite will react with the remaining aluminates and form monosulphate. In the presence of limestone, hemi- and monocarboaluminate are formed instead of monosulphate. The ettringite does, therefore, not decompose. This leads to higher volume of the hydrates, which on its turn might reduce the porosity and enhance the compressive strength. The effect of limestone powder on OPC is limited due to its low aluminate content. However, when part of the OPC is replaced by fly ash, the fly ash will introduce additional aluminates to the system as it reacts. This will lower the SO3/Al2O3 and increase the AFm/AFt ratio and thereby amplify the impact of limestone powder. These changes in the AFm and AFt phases have been experimentally observed by TGA, XRD and EDX, and predicted using thermodynamic modelling.

Only a few percent of limestone powder are required to prevent ettringite from decomposing to monosulphate. The changes in hydration products resulting from these small limestone powder contents coincides with an increase in compressive strength. Replacement of 5% fly ash with 5%

limestone powder in a 65%OPC+35%FA cement resulted in a compressive strength increase ranging between 8 and 13% after 28 days of curing. At higher limestone contents the compressive strength decreases again as the additional limestone mainly serves as an inert filler. Replacing 5% of OPC with limestone powder resulted, on the other hand, in a strength reduction or a slight increase up to 4% after 28 days of curing. The beneficial effect of limestone is maximal at 28 days, and reduces slightly upon further curing. It is furthermore valid at 5, 20 and 40°C. However, at 40°C the fly ash reaction is accelerated and over time the fly ash content is more important than the synergetic effect.

The observed increase in compressive strength has to be partly due to the chemical interaction described above as an inert filler (crystalline quartz) with a similar psd does not have the same beneficial impact on strength as limestone. Additionally, the presence of limestone powder does not seem to affect the reactivity of OPC and fly ash significantly.

The observed effect between fly ash and limestone enables higher replacement levels than when only one of them is used. The applicability of the study is demonstrated by the fact that cement with the

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III optimal composition found in this study (65%OPC+30%FA+5%L) has recently been used in the construction of the Meteorological Centre in Oslo and the Science Centre in the county of Østfold.

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IV

List of papers

This thesis includes the following papers:

I. Microstructure of binder from the pozzolanic reaction between lime and siliceous fly ash, and the effect of limestone addition.

De Weerdt K. & Justnes H.

Proceedings of the First International Conference on Microstructure Related Durability of Cementitious Composites, Ed. W. Sun, K. Van Breugel, C. Miao, G. Ye and H. Chen, 2008, Nanjing, RILEM PRO 61, Vol. 1 pp.107-116 (ISBN 978-2-35158-065-3, e-ISBN 978-2-35158-084-4).

II. Fly ash-limestone ternary cements: effect of component fineness.

De Weerdt K., Sellevold E.J., Kjellsen K.O. & Justnes H.

Advances in Cement Research. Accepted.

III. Fly ash -limestone ternary composite cements: synergetic effect at 28 days.

De Weerdt K., Justnes H., Kjellsen K.O. & Sellevold E.J.

Nordic Concrete Research, 2010, Vol.42 (2) pp. 51-70

IV. Synergy between fly ash and limestone powder in ternary cements De Weerdt K., Kjellsen K.O., Sellevold E.J. & Justnes H.

Cement and Concrete Composites,2011, Vol. 33 (1) pp.30-38, doi:10.1016/j.cemconcomp.2010.09.006

V. Quantification of the degree of reaction of fly ash Ben Haha M., De Weerdt K. & Lothenbach B.

Cement and Concrete Research, 2010, Vol. 40 (11) pp.1620-9, doi:10.1016/j.cemconres.2010.07.004

VI. Hydration mechanisms of ternary Portland cements containing limestone powder and fly ash De Weerdt K., Ben Haha M., Le Saout G., Kjellsen K.O., Justnes H. & Lothenbach B.

Cement and Concrete Research, 2010, in press, doi:10.1016/j.cemconres.2010.11.014

VII. The effect of limestone powder additions on strength and microstructure of fly ash blended cements

De Weerdt K., Justnes H., Ben Haha M. & Lothenbach B.

13^th International Congress on the Chemistry of Cement, 2011, Madrid, in review.

VIII. The effect of temperature on the hydration of Portland composite cements containing limestone powder and fly ash

De Weerdt K., Ben Haha M., Le Saout G., Kjellsen K.O., Justnes H. & Lothenbach B.

Materials and Structures, 2010, in review.

Klaartje De Weerdt’s contribution to the publications:

Paper I-IV and paper VI-VIII Major part of writing.

Paper V Major part of writing except writing concerning image analysis

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List of papers

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Content

Acknowledgements ... I Abstract ... II List of papers ... IV Content ... V Glossary of notations and terms ... VI

Chapter 1 – Introduction ... 1

Chapter 2 – Objective and limitations ... 3

Chapter 3 – Summary of used methods ... 4

Chapter 4 – Background ... 6

Chapter 5 – Main findings ... 9

Chapter 6 – Concluding remarks ... 14

Chapter 7 – Future research ... 16

References ... 18

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Content

Acknowledgements ... I Abstract ... II List of papers ... IV Content ... V Glossary of notations and terms ... VI Chapter 1 – Introduction ... 1

References ... 18

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References ... 18

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Content

References ... 18

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VI

Glossary of notations and terms

The cement chemist’s short hand:

C = CaO S = SiO2 A = Al2O3 F = Fe2O3

H = H2O S = SO3 C = CO2

The notation of the anhydrous phases and hydrates are subsequently:

C3S 3CaOͼSiO2 tricalcium silicate

C2S 2CaOͼSiO2 dicalcium silicate

C3A 3CaOͼAl2O3 tricalcium aluminate

C4AF 4CaOͼAl2O3ͼFe2O3 Ferrite or brownmillerite

CSH2 CaSO4 gypsum

CC CaCO3 calcium carbonate

CH Ca(OH)2 calcium hydroxide or Portlandite

C6AS3H32 3CaOͼAl2O3ͼ3CaSO4ͼ32H2O ettringite

C4ASH12 3CaOͼAl2O3ͼCaSO4ͼ12H2O calcium monosulphoaluminate hydrate C4ACH11 3CaOͼAl2O3ͼCaCO3ͼ11H2O calcium monocarboaluminate hydrate C₄AC_0.5H_11.5 3CaOͼAl2O₃ͼ0.5Ca(OH)2ͼ0.5CaCO3ͼ11.5H2O calcium hemicarboaluminate hydrate

Terms:

C-S-H: Amorphous calcium silicate hydrate with a varying composition is able to take up A, S, Na⁺, K⁺ etc.

It is the main hydration product of ordinary Portland cement and can also be formed by the reaction of pozzolans with CH.

C-A-S-H: C-S-H with a relatively high aluminate content.

C-A-H: calcium aluminate hydrates e.g. C2AH8, C3AH6 etc.

Alite: Impure C3S as found in Portland cement containing other oxides in solid-state substitution Belite: Impure C2S as found in Portland cement containing other oxides in solid-state substitution.

AFt-phases: The phase formed in the hydration of Portland cement which is derived from pure ettringite with partial substitution of A by F, and SO4

2- by other ions.

AFm-phases: The phase formed in the hydration of Portland cement which is derived from the pure mono-sulphoaluminate with the partial substitution of A by F, and SO4

2- by other ions.

Additional abbreviations:

OPC ordinary Portland cement FA fly ash

L limestone powder Q quartz

PSD particle size distribution SEM scanning electron microscopy

BSE backscattered electron IA image analysis

EDX or EDS energy dispersive X-ray spectroscopy TGA thermogravimetric analysis DTA differential thermal analysis XRD X-ray diffraction

XRF X-ray fluorescence IC ion chromatography

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Glossary of notations and terms

H = H2O S = SO3 C = CO2

CSH2 CaSO4 gypsum

C4ASH12 3CaOͼAl2O3ͼCaSO4ͼ12H2O calcium monosulphoaluminate hydrate C4ACH11 3CaOͼAl2O3ͼCaCO3ͼ11H2O calcium monocarboaluminate hydrate C₄AC_0.5H_11.5 3CaOͼAl2O₃ͼ0.5Ca(OH)2ͼ0.5CaCO3ͼ11.5H2O calcium hemicarboaluminate hydrate

Terms:

AFt-phases: The phase formed in the hydration of Portland cement which is derived from pure ettringite with partial substitution of A by F, and SO4

2- by other ions.

VI

Glossary of notations and terms

H = H2O S = SO3 C = CO2

CSH2 CaSO4 gypsum

C4ASH12 3CaOͼAl2O3ͼCaSO4ͼ12H2O calcium monosulphoaluminate hydrate C4ACH11 3CaOͼAl2O3ͼCaCO3ͼ11H2O calcium monocarboaluminate hydrate C4AC0.5H11.5 3CaOͼAl2O3ͼ0.5Ca(OH)2ͼ0.5CaCO3ͼ11.5H2O calcium hemicarboaluminate hydrate

Terms:

AFt-phases: The phase formed in the hydration of Portland cement which is derived from pure ettringite with partial substitution of A by F, and SO₄^2- by other ions.

2- by other ions.

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Glossary of notations and terms

H = H2O S = SO3 C = CO2

CSH2 CaSO4 gypsum

C4ASH12 3CaOͼAl2O3ͼCaSO4ͼ12H2O calcium monosulphoaluminate hydrate C4ACH11 3CaOͼAl2O3ͼCaCO3ͼ11H2O calcium monocarboaluminate hydrate C4AC0.5H11.5 3CaOͼAl2O3ͼ0.5Ca(OH)2ͼ0.5CaCO3ͼ11.5H2O calcium hemicarboaluminate hydrate

Terms:

AFt-phases: The phase formed in the hydration of Portland cement which is derived from pure ettringite with partial substitution of A by F, and SO₄^2- by other ions.

2- by other ions.

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Blended cement with reduced CO2 emission- utilizing the fly ash-limestone synergy

Doctoral theses at NTNU, '%&&/32

Klaartje De Weerdt