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Blended cement with reduced CO2 emission- utilizing the fly ash-limestone synergy
2011 (English)Doktorsavhandling, sammanläggning (Other academic)
Abstract [en]

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 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 Ostfold

Place, publisher, year, pages
NTNU, 2011.
Series
Doktoravhandlinger ved NTNU, ISSN 1503-8181 ; 2011:32
National Category
Construction technology
Identifiers
urn:nbn:no:ntnu:diva-12038 (URN)978-82-471-2584-7 (printed ver.) (ISBN)978-82-471-2585-4 (electronic ver.) (ISBN)oai:DiVA.org:ntnu-12038 (OAI)
Public defence
2011-02-03, 00:00
Available from2011-11-01 Created:2011-02-16 Last updated:2011-11-01Bibliographically approved
List of papers
1. Microstructure of binder from the pozzolanic reaction between lime and siliceous fly ash, andthe effect of limestone addition
Open this publication in new window or tab >>Microstructure of binder from the pozzolanic reaction between lime and siliceous fly ash, andthe effect of limestone addition
2008 (English)In: Proceedings of the First International Conference on Microstructure Related Durability of Cementitious Composites / [ed] Ed. W. Sun, K. Van Breugel, C. Miao, G. Ye and H. Chen, RILEM, 2008, 107-116Konferensbidrag (Other academic)
RILEM, 2008
Identifiers
urn:nbn:no:ntnu:diva-12028 (URN)978-2-35158-065-3 (ISBN)e- 978-2-35158-084-4 (ISBN)
Conference
RILEM PRO 61
Available from2011-02-16 Created:2011-02-16 Last updated:2011-11-01Bibliographically approved
2. Fly ash-limestone ternary cements: effect of component fineness
Open this publication in new window or tab >>Fly ash-limestone ternary cements: effect of component fineness
2011 (English)In: Advances in Cement Research, ISSN 0951-7197, Vol. 23, no 4, 203-214Artikel i tidskrift (Refereed) Published
Identifiers
urn:nbn:no:ntnu:diva-12031 (URN)10.1680/adcr.2011.23.4.203 (DOI)
Note
The final published version may be found http://www.icevirtuallibrary.com/content/serial/adcrAvailable from2011-02-16 Created:2011-02-16 Last updated:2011-11-01Bibliographically approved
3. Fly ash -limestone ternary composite cements: synergetic effect at 28 days
Open this publication in new window or tab >>Fly ash -limestone ternary composite cements: synergetic effect at 28 days
2010 (English)In: Nordic Concrete Research, ISSN 0800-6377, Vol. 42, no 2, 51-70Artikel i tidskrift (Refereed) Published
Identifiers
urn:nbn:no:ntnu:diva-12034 (URN)
Available from2011-02-16 Created:2011-02-16 Last updated:2011-11-01Bibliographically approved
4. Synergy between fly ash and limestone powder in ternary cements
Open this publication in new window or tab >>Synergy between fly ash and limestone powder in ternary cements
2011 (English)In: Cement & Concrete Composites, ISSN 0958-9465, E-ISSN 1873-393X, Vol. 33, no 1, 30-38Artikel i tidskrift (Refereed) Published
Abstract [en]

The interaction between limestone powder and fly ash in ternary composite cement is investigated. Limestone powder interacts with the AFm and AFt hydration phases, leading to the formation of carboaluminates at the expense of monosulphate and thereby stabilizing the ettringite. The effect of limestone powder on OPC may be restricted due to the limited amount of aluminate hydrates formed by the hydration of OPC. The additional aluminates brought into the system by fly ash during its pozzolanic reaction amplify the mentioned effect of limestone powder. This synergistic effect between limestone powder and fly ash in ternary cements is confirmed in this study and it translates to improved mechanical properties that persist over time. (C) 2010 Elsevier Ltd. All rights reserved.

Elsevier, 2011
Keyword
Cement, Fly ash, Limestone, AFm, Ternary, Calcium carboaluminate hydrates
Identifiers
urn:nbn:no:ntnu:diva-12032 (URN)10.1016/j.cemconcomp.2010.09.006 (DOI)000285228100004 (ISI)
Note
The article is reprinted with kind permission from Elsevier, sciencedirect.comAvailable from2011-02-16 Created:2011-02-16 Last updated:2011-11-01Bibliographically approved
5. Quantification of the degree of reaction of fly ash
Open this publication in new window or tab >>Quantification of the degree of reaction of fly ash
2010 (English)In: Cement and Concrete Research, ISSN 0008-8846, E-ISSN 1873-3948, Vol. 40, no 11, 1620-1629Artikel i tidskrift (Refereed) Published
Abstract [en]

The quantification of the fly ash (FA) in FA blended cements is an important parameter to understand the effect of the fly ash on the hydration of OPC and on the microstructural development. The FA reaction in two different blended OPC-FA systems was studied using a selective dissolution technique based on EDTA/NaOH, diluted NaOH solution, the portlandite content and by backscattered electron image analysis. The amount of FA determined by selective dissolution using EDTA/NaOH is found to be associated with a significant possible error as different assumptions lead to large differences in the estimate of FA reacted. In addition, at longer hydration times, the reaction of the FA is underestimated by this method due to the presence of non-dissolved hydrates and MgO rich particles. The dissolution of FA in diluted NaOH solution agreed during the first days well with the dissolution as observed by image analysis. At 28 days and longer, the formation of hydrates in the diluted solutions leads to an underestimation. Image analysis appears to give consistent results and to be most reliable technique studied. (c) 2010 Elsevier Ltd. All rights reserved.

Elsevier, 2010
Keyword
Blended cements, Chemical dissolution, Scanning electron microscopy (SEM), Image analysis (IA), Degree of reaction
Identifiers
urn:nbn:no:ntnu:diva-12033 (URN)10.1016/j.cemconres.2010.07.004 (DOI)000283964800006 (ISI)
Note
The article is reprinted with kind permission from Elsevier, sciencedirect.comAvailable from2011-02-16 Created:2011-02-16 Last updated:2011-11-01Bibliographically approved
6. Hydration mechanisms of ternary Portland cements containing limestone powder and fly ash
Open this publication in new window or tab >>Hydration mechanisms of ternary Portland cements containing limestone powder and fly ash
Show others...
2011 (English)In: Cement and Concrete Research, ISSN 0008-8846, E-ISSN 1873-3948, Vol. 41, no 11, 1620-1629Artikel i tidskrift (Refereed) Published
Elsevier, 2011
Identifiers
urn:nbn:no:ntnu:diva-12035 (URN)10.1016/j.cemconres.2010.11.014 (DOI)
Note
The article is reprinted with kind permission from Elsevier, sciencedirect.comAvailable from2011-02-16 Created:2011-02-16 Last updated:2011-11-01Bibliographically approved
7. The effect of limestone powder additions on strength and microstructure of fly ash blended cements
Open this publication in new window or tab >>The effect of limestone powder additions on strength and microstructure of fly ash blended cements
2011 (English)In: Proceedings of 13th International Congress on the Chemistry of Cement, 2011Konferensbidrag (Other academic)
Identifiers
urn:nbn:no:ntnu:diva-12036 (URN)
Conference
13th International Congress on the Chemistry of Cement
Available from2011-02-16 Created:2011-02-16 Last updated:2011-11-01Bibliographically approved
8. The effect of temperature on the hydration of Portland composite cements containing limestone powder and fly ash
Open this publication in new window or tab >>The effect of temperature on the hydration of Portland composite cements containing limestone powder and fly ash
Show others...
(English)Manuskript (preprint) (Other academic)
Identifiers
urn:nbn:no:ntnu:diva-12037 (URN)
Note
The article is under consideration for publication in Materials and Structures Available from2011-02-16 Created:2011-02-16 Last updated:2011-11-01Bibliographically approved

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