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Husbyggnadsbetong med höga halter av tillsatsmaterial - En studie av hur stora mängder av kalcinerad lera, flygaska och mald granulerad masugnsslagg förändrar betongens hållfasthetsutveckling, uttorkning, böjstyvhet, böjdraghållfasthet och krympning

Ali, Abdel LU and Lundberg, Joacim LU (2015) In TVBM VBM820 20151
Division of Building Materials
Abstract (Swedish)
Problemställning: Cementproduktionen står idag för ca 5% av världens koldioxidutsläpp, vilket har stor negativ påverkan på klimatet. För att minska utsläppen behöver cementanvändningen reduceras genom t.ex. ersätta cement med andra material, såsom flygaska, mald granulerad masugnsslagg och kalcinerad lera.

Syfte: Syftet är att undersöka den maximala vol.% cement som kan ersättas med flygaska, slagg och kalcinerad lera för husbyggnadsbetong och vidare undersöka hur betongens egenskaper som hållfasthetutveckling, uttorkning, böjstyvhet, böjdraghållfasthet och krympning förändras utan att dessa egenskaper minskas för mycket.

Metod: Studien inleddes med en litteraturstudie för att få mer kunskap om ämnet. Sedan genomfördes flera... (More)
Problemställning: Cementproduktionen står idag för ca 5% av världens koldioxidutsläpp, vilket har stor negativ påverkan på klimatet. För att minska utsläppen behöver cementanvändningen reduceras genom t.ex. ersätta cement med andra material, såsom flygaska, mald granulerad masugnsslagg och kalcinerad lera.

Syfte: Syftet är att undersöka den maximala vol.% cement som kan ersättas med flygaska, slagg och kalcinerad lera för husbyggnadsbetong och vidare undersöka hur betongens egenskaper som hållfasthetutveckling, uttorkning, böjstyvhet, böjdraghållfasthet och krympning förändras utan att dessa egenskaper minskas för mycket.

Metod: Studien inleddes med en litteraturstudie för att få mer kunskap om ämnet. Sedan genomfördes flera experimentella studier för att undersöka olika egenskaper för att svara på frågeställningarna. För att försöka få representativa prover för husbyggnadsbetong försöktes vct hållas till 0,6. Genom kalorimetrimätningar avgjordes vilken maximal ersättningsgrad som kunde användas för de slutgiltiga provkropparna. Proverna testades regelbundet efter produktion. För speciellt hållfasthettesterna provades kubhållfastheten efter 3-, 7- respektive 28-dygn. Av de olika betongsorterna utfördes en sulfatoptimering av den kalcinerade leran för att få en uppfattning om en sådan kunde medföra en högre ersättningsgrad. Sulfatoptimering gjordes endast för den kalcinerade leran då tanken uppstod efter att övriga recept redan var gjutna.

Slutsatser:
Flygaska: I denna studie ersattes 55 resp. 75 vol.% cement med flygaska och visar att vid ökande mängd flygaska försämras samtliga undersökta egenskaper. Vid mer än 55 vol.% sker det ingen uttorkning, vilket innebär att det inte är lämpligt att använda så höga ersättningsmängder i husbyggnadsbetong där snabb uttorkning krävs, t.ex. vid mattläggning.
Jämfört med referensbetongen ökar krympningen, dock är denna krympning marginellt större än referensbetongen. Det är svårt att bedöma risken för krympsprickor men troligtvis är risken större för betong med hög vol.% flygaska då denna betong har sämre elasticitetsmodul än referensbetongen (betong utan ersättning av cement).
Både böjdraghållfastheten samt böjstyvheten minskar med ökande mängd flygaska. Det är dock oklart huruvida betongsorterna är användbara i produktion ur böjstyvhetssynpunkt.
Studien visar också att det inte är lämpligt att gjuta betong med 75 vol.% flygaska eller mer då betongen är för svag och benägen att spricka samt kraterbildning om den utsätts för slag eller borrning.

Sötvattengranulerad masugnsslagg
I denna studie har cementersättning av 70 resp. 90 vol.% slagg undersökts. Hållfasthetsutvecklingen försämras (31 MPa respektive 15,5 MPa vid 28 dygn i jämförelse med referensbetongens 41 MPa) men båda betongsorterna verkar lovande för användning inom husbyggnation i t.ex. platta på mark där dagens tryckhållfasthet är mycket överdimensionerande.
Efter ungefär två veckor har betongen med 70 vol.% slagg torkat mer än referensbetongen, medan betongen med 90 vol.% slagg torkar långsammare än referensbetongen. Däremot kommer troligtvis betongen med 90 vol.% slagg någon gång i framtiden ha torkat mer än referensbetongen, vilket beror på att slaggreaktionen sker senare och är dessutom mycket långsammare än cementreaktionen.
Både böjdraghållfastheten och böjstyvheten minskas med ökande andel slagg. Det är dock oklart om dessa betongsorter är användbara ur dessa avseenden.
Till skillnad från 75 vol.% flygaska har 90 vol.% slagg ingen benägenhet att spricka vid slag eller borrning.

Kalcinerad lera
I denna studie har cementersättning av 30 resp. 55 vol.% sulfatoptimerad kalcinerad lera undersökts. Dessa betongsorter har ungefär samma egenskaper som referensbetongen förutom när det gäller uttorkningen. 30 vol.% lera torkar snabbare än referensbetongen samtidigt som 50 vol.% knappt uppvisar uttorkning. (Less)
Abstract
Problem: The production of cement stands today for approximately 5% of the world total emission of carbon dioxide, which has negative impact on the environment. In order to reduce the emission, the use of cement has to be reduced by e.g. replacing some of the cement with other materials.

Purpose: The purpose is to find the maximum amount of fly ash, slag and calcined clay that can be used in concrete and study how this may change the properties of the concrete without achieving a too large reduction of these properties.

Method: This study was initiated by doing a literature study to get more knowledge about the subject. Later on several experimental studies was performed to study different properties to answer the questions. By... (More)
Problem: The production of cement stands today for approximately 5% of the world total emission of carbon dioxide, which has negative impact on the environment. In order to reduce the emission, the use of cement has to be reduced by e.g. replacing some of the cement with other materials.

Purpose: The purpose is to find the maximum amount of fly ash, slag and calcined clay that can be used in concrete and study how this may change the properties of the concrete without achieving a too large reduction of these properties.

Method: This study was initiated by doing a literature study to get more knowledge about the subject. Later on several experimental studies was performed to study different properties to answer the questions. By trying to achieve representative samples of a house building concrete, a water-cement ratio of 0,6 was used. By calorimeter measurements the maximum replacement rates usable for the final samples was conducted. The samples were tested regularly after production. Especially for the compressive strength measurements the samples was tested at 3, 7 and 28 days. A sulphate optimization was performed for the recipes with calcined clay to achieve an indication if an optimization might allow a greater cement replacement. This optimization was only done for the calcined clay since the idea came after the other recipes already were produced.

Conclusions:
Fly ash
In this study 55% respectively 75% of cement volume was replaced with fly ash. The study shows that increase of fly ash has a negative effect on all the studied properties. If more than 55 vol.% is used, then there will be no dehydration. This means that concrete with this high amount of fly ash is not suited for concrete that is going to be used in projects were fast dehydration is desired.
The early shrinkage of both concrete types is almost the same as the reference concrete, but even so it’s still hard to evaluate the risk of cracks cause by shrinkage. The risk of cracks is probably higher for these fly ash concretes due to that the concrete with high amount of fly ash has much lower elastic modulus (Young’s modulus) than the reference concrete (concrete without cement replacement).
Both the flexural strength and the bending stiffness decrease with increased replacement rate of fly ash. It is unclear however if these concrete types are still useable in production from a bending stiffness point of view.
The study also shows that concrete with more than 75 vol.% fly ash has a high risk of cracking when drilling or dropping something heavy. This means that it’s not suitable to build with concrete that has this high amount of fly ash.

Slag
In this study 70% respectively 90% of cement volume was replaced with slag. Higher amount of slag results in lower compressive strength (31 MPa and 15,5 MPa respectively at 28 days compared to the reference concretes 41 MPa), but the compressive strength is still promising to be high enough to be used in buildings, for example an slab on the ground where the compressive strength today is oversized.
After approximately two weeks the relative humidity, RH, in the concrete with 70 vol.% slag was lower than the reference concrete while the concrete with 90 vol.% slag had a higher RH. However, since the slag reaction starts later than the cement reaction, there is a possibility that sometime the RH will be lower in the concrete with 90 vol.% slag.
Both the flexural strength and the bending stiffness decrease with increased replacement rate of fly ash. It is unclear however if these concrete types are still useable in production from a bending stiffness point of view.
Unlike the concrete with 75 vol.% fly ash, the concrete with 90 vol.% slag doesn’t crack when drilling.

Calcined clay
In this study 30% respectively 50% of the cement volume was replaced with calcined clay. The study shows that both these concrete types have almost the same properties as the reference concrete except when it comes to dehydration.
The concrete with 30 vol.% clay dehydrates earlier and faster than the reference concrete while the concrete with 50 vol.% clay only shows small signs of dehydration. (Less)
Popular Abstract
Background:
The production of cement stands today for approximately 5% of the world’s CO2-emission. Most of
the emissions are coming from the process when CO2 leaves the raw material during heating, also
known as calcination. The production of cement is today very efficient and the only way to reduce
CO2 is by replacing some of the cement with other materials like fly ash, slag and calcined clay.
Both fly ash and slag are rest products from coal- and steel industry that was earlier considered to be
waste, but have lately been useful in concrete structures. This is in a climate perspective very positive
since both waste deposit and use of cement is reduced. Despite these positive points there must be
some consideration regarding if... (More)
Background:
The production of cement stands today for approximately 5% of the world’s CO2-emission. Most of
the emissions are coming from the process when CO2 leaves the raw material during heating, also
known as calcination. The production of cement is today very efficient and the only way to reduce
CO2 is by replacing some of the cement with other materials like fly ash, slag and calcined clay.
Both fly ash and slag are rest products from coal- and steel industry that was earlier considered to be
waste, but have lately been useful in concrete structures. This is in a climate perspective very positive
since both waste deposit and use of cement is reduced. Despite these positive points there must be
some consideration regarding if the concrete still is useful after replacing large amounts of the cement,
since it most probably will lead to a change of the properties, e.g. lowered strength (compressive,
flexural). Another interesting question to be made is if today’s empirical relations between different
properties (e.g. compressive strength and flexural strength) are still valid and useable for concrete with
large replacement of cement.
In this study different volumes of cement have been replaced with fly ash (55% and 75%), slag (70%
and 90%) and calcined clay (30% and 50%). Concrete properties like compressive strength,
dehydration, flexural strength, bending stiffness and shrinkage. All these different concrete recipes
were compared to a reference concrete which had no fly ash, slag or calcined clay. Unlike the
reference concrete, concrete with fly ash and slag, the concrete with calcined clay was optimised by
adding 1% CaSO4. (Less)
Please use this url to cite or link to this publication:
author
Ali, Abdel LU and Lundberg, Joacim LU
supervisor
organization
alternative title
Concrete for buildings with high levels of supplementary cementitious materials
course
VBM820 20151
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
shrinkage., flexural strength, compressive strength, bending stiffness, dehydration, carbon dioxide, calcined clay, ground granulated blast furnace slag, krympning. Fly ash, böjdraghållfasthet, tryckhållfasthet, böjstyvhet, uttorkning, koldioxidutsläpp, cement, kalcinerad lera, mald granulerad masugnsslagg, Flygaska
publication/series
TVBM
report number
5103
other publication id
ISRN LUTVDG/TVBM-15/5103-SE (1-160)
language
Swedish
id
8230941
date added to LUP
2017-01-16 10:57:09
date last changed
2017-01-16 10:57:09
@misc{8230941,
  abstract     = {Problem: The production of cement stands today for approximately 5% of the world total emission of carbon dioxide, which has negative impact on the environment. In order to reduce the emission, the use of cement has to be reduced by e.g. replacing some of the cement with other materials.

Purpose: The purpose is to find the maximum amount of fly ash, slag and calcined clay that can be used in concrete and study how this may change the properties of the concrete without achieving a too large reduction of these properties.

Method: This study was initiated by doing a literature study to get more knowledge about the subject. Later on several experimental studies was performed to study different properties to answer the questions. By trying to achieve representative samples of a house building concrete, a water-cement ratio of 0,6 was used. By calorimeter measurements the maximum replacement rates usable for the final samples was conducted. The samples were tested regularly after production. Especially for the compressive strength measurements the samples was tested at 3, 7 and 28 days. A sulphate optimization was performed for the recipes with calcined clay to achieve an indication if an optimization might allow a greater cement replacement. This optimization was only done for the calcined clay since the idea came after the other recipes already were produced.

Conclusions: 
Fly ash
In this study 55% respectively 75% of cement volume was replaced with fly ash. The study shows that increase of fly ash has a negative effect on all the studied properties. If more than 55 vol.% is used, then there will be no dehydration. This means that concrete with this high amount of fly ash is not suited for concrete that is going to be used in projects were fast dehydration is desired.
The early shrinkage of both concrete types is almost the same as the reference concrete, but even so it’s still hard to evaluate the risk of cracks cause by shrinkage. The risk of cracks is probably higher for these fly ash concretes due to that the concrete with high amount of fly ash has much lower elastic modulus (Young’s modulus) than the reference concrete (concrete without cement replacement).
Both the flexural strength and the bending stiffness decrease with increased replacement rate of fly ash. It is unclear however if these concrete types are still useable in production from a bending stiffness point of view.
The study also shows that concrete with more than 75 vol.% fly ash has a high risk of cracking when drilling or dropping something heavy. This means that it’s not suitable to build with concrete that has this high amount of fly ash.

Slag
In this study 70% respectively 90% of cement volume was replaced with slag. Higher amount of slag results in lower compressive strength (31 MPa and 15,5 MPa respectively at 28 days compared to the reference concretes 41 MPa), but the compressive strength is still promising to be high enough to be used in buildings, for example an slab on the ground where the compressive strength today is oversized.
After approximately two weeks the relative humidity, RH, in the concrete with 70 vol.% slag was lower than the reference concrete while the concrete with 90 vol.% slag had a higher RH. However, since the slag reaction starts later than the cement reaction, there is a possibility that sometime the RH will be lower in the concrete with 90 vol.% slag.
Both the flexural strength and the bending stiffness decrease with increased replacement rate of fly ash. It is unclear however if these concrete types are still useable in production from a bending stiffness point of view.
Unlike the concrete with 75 vol.% fly ash, the concrete with 90 vol.% slag doesn’t crack when drilling.

Calcined clay
In this study 30% respectively 50% of the cement volume was replaced with calcined clay. The study shows that both these concrete types have almost the same properties as the reference concrete except when it comes to dehydration.
The concrete with 30 vol.% clay dehydrates earlier and faster than the reference concrete while the concrete with 50 vol.% clay only shows small signs of dehydration.},
  author       = {Ali, Abdel and Lundberg, Joacim},
  keyword      = {shrinkage.,flexural strength,compressive strength,bending stiffness,dehydration,carbon dioxide,calcined clay,ground granulated blast furnace slag,krympning. Fly ash,böjdraghållfasthet,tryckhållfasthet,böjstyvhet,uttorkning,koldioxidutsläpp,cement,kalcinerad lera,mald granulerad masugnsslagg,Flygaska},
  language     = {swe},
  note         = {Student Paper},
  series       = {TVBM},
  title        = {Husbyggnadsbetong med höga halter av tillsatsmaterial - En studie av hur stora mängder av kalcinerad lera, flygaska och mald granulerad masugnsslagg förändrar betongens hållfasthetsutveckling, uttorkning, böjstyvhet, böjdraghållfasthet och krympning},
  year         = {2015},
}