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Samband mellan isbildning och längdändring i betong med olika bindemedel

Karlsson, Timmie LU (2017) VBM820 20171
Division of Building Materials
Abstract (Swedish)
Betong har under lång tid varit ett av de vanligaste byggnadsmaterialen och används idag i stor utsträckning till framförallt bärande konstruktioner. En bärande konstruktion utsätts för olika typer av påfrestningar och en av de mer problematiska för betong är frostangrepp. Problematiken beror på betongens begränsade draghållfasthet och att vid låga temperaturer fryser vattnet i betongen till is. Expansionen när vattnet övergår till is skapar dragspänningar i betongen som då kan medföra skador.

Dagens samhälle strävar efter att bli mer och mer miljövänligt och innebär utmaningar för betongindustrin. Vid cementtillverkning släpps stora mängder koldioxid ut och den stora utmaningen för betongindustrin är att minska de utsläppen. Ett av... (More)
Betong har under lång tid varit ett av de vanligaste byggnadsmaterialen och används idag i stor utsträckning till framförallt bärande konstruktioner. En bärande konstruktion utsätts för olika typer av påfrestningar och en av de mer problematiska för betong är frostangrepp. Problematiken beror på betongens begränsade draghållfasthet och att vid låga temperaturer fryser vattnet i betongen till is. Expansionen när vattnet övergår till is skapar dragspänningar i betongen som då kan medföra skador.

Dagens samhälle strävar efter att bli mer och mer miljövänligt och innebär utmaningar för betongindustrin. Vid cementtillverkning släpps stora mängder koldioxid ut och den stora utmaningen för betongindustrin är att minska de utsläppen. Ett av sätten att minska utsläppsproblemet är att byta ut en del av cementet i betong mot tillsatsmaterial med mindre miljöpåverkan (Lothenbach et al. , 2011). I den här rapporten behandlas två av de vanligaste tillsatsmaterialen, slagg och flygaska.

Studien omfattar två olika typer av försök där båda utfördes i en unik utrustning som samtidigt kan mäta isbildning och längdändring. I det första försöket fick provkroppen frysa och tina en gång samtidigt som provet var fuktisolerat. Det här försöket omfattar tre olika material med två olika lufthalter. Materialen är betong med CEM I, betong där 35% av cementet är utbytt mot slagg och betong där 35% av cementet är utbytt mot flygaska. Varje material är testat med lufthalter på omkring 2% och 5%. I det andra försöket fick provkroppen frysa och tina flera gånger samtidigt som provet hade tillgång till natriumkloridlösning. Under det andra försöket studerades bara betong med 35% flygaska och 5,7% luft. Målet med det första försöket var att studera eventuella skillnader i hur betong med olika bindemedel bildar is samt hur isbildningen påverkar dilatationen i de olika materialen. Målsättningen för det andra försöket var att ta reda på om det var möjligt att kontinuerligt studera islinsbildning genom längdändringsmätningar när provet har tillgång till vätska.

Resultatet i studien visade att betong med CEM I har en relativt linjär isbildning medan isbildningen i betong med slagg och flygaska till stor del sker vid temperaturer omkring -40 °C. Dilatationen följer den termiska rörelsen med små bidrag från isbildningen. Anledningen till att dilatationen i studien inte blir större beror troligtvis på att isen får plats i befintliga porer. Studien visar också att det är möjligt studera islinsbildning genom längdändringsmätningar i betong när provet har fri tillgång till vätska. Dilatationen på grund av islinsbildningen liknar resultatet från ett experiment av Powers & Helmuth (1953) där de visade att längdutvidgningen ökar trots att temperaturen var konstant. (Less)
Abstract
Concrete has been one of the most common construction material for a long time and today it is used to a large extent in load-bearing structures. Load-bearing structures are exposed to different types of stresses and one of the most severe is frost damage. The problem with frost damage is due to the low tensile strength of concrete. When the water in concrete freezes at low temperatures the water expands and create tensile stresses that might damage the concrete.

Today’s society is striving to be more and more environmentally friendly and it creates challenges for the concrete industry. The manufacturing of cement cause a large amount of carbon dioxide emissions and the biggest challenge for the concrete industry is to reduce these... (More)
Concrete has been one of the most common construction material for a long time and today it is used to a large extent in load-bearing structures. Load-bearing structures are exposed to different types of stresses and one of the most severe is frost damage. The problem with frost damage is due to the low tensile strength of concrete. When the water in concrete freezes at low temperatures the water expands and create tensile stresses that might damage the concrete.

Today’s society is striving to be more and more environmentally friendly and it creates challenges for the concrete industry. The manufacturing of cement cause a large amount of carbon dioxide emissions and the biggest challenge for the concrete industry is to reduce these emissions. One way of reducing the emissions is to replace some of the cement with supplementary cementitious materials (SCM) which have a smaller impact to the environment (Lothenbach et al. , 2011). Two of the most common SCMs, slag and fly ash, will be discussed in this report.

Two different experiments has been carried out in this study. Both experiments used a unique device that simultaneously measures ice formation and length change. The specimens in the first experiment were moisture insulated and were only allowed to freeze and thaw once. During the first experiment, three different materials were used with two levels of air entrainment. Concrete with CEM I, concrete with 35% of the cement replaced by slag and concrete with 35% of the cement replaced by fly ash was used in the study. The air entrainment levels were about 2% and 5%. In the second experiment the specimen was allowed to freeze and thaw several times and also had access to a sodium chloride solution during the cycles. During the second experiment only the concrete with 35% fly ash and an air entrainment of 5,7% was used. The aim with the first experiment was to study if the formation of ice differs between concretes with different binders and also how the ice formation affect the dilation of the different materials. The second experiment was carried out to see if it was possible to continuous study the formation of microscopic ice bodies by length change when the specimen had access to a solution.

The results from the study show that CEM I concrete form ice linearly while a major part of the ice formation in concrete with slag and fly ash occurs at about -40 °C. The dilation follows the thermal movement with small contributions from the ice formation. The reason for the small dilation is probably that the formed ice can fit into the existing pores. This study also showed that it is possible to study the formation of microscopic ice bodies by length change when the specimen had access to a solution. The dilation from the formation of the microscopic ice bodies resembles the result from the experiment carried out by Powers & Helmuth (1953) where they showed that the longitudinal extension continues even if the temperature is held constant. (Less)
Please use this url to cite or link to this publication:
author
Karlsson, Timmie LU
supervisor
organization
course
VBM820 20171
year
type
H3 - Professional qualifications (4 Years - )
subject
report number
5111
ISSN
0348-7911
language
Swedish
id
8915860
date added to LUP
2017-06-15 12:38:08
date last changed
2017-06-15 12:38:08
@misc{8915860,
  abstract     = {Concrete has been one of the most common construction material for a long time and today it is used to a large extent in load-bearing structures. Load-bearing structures are exposed to different types of stresses and one of the most severe is frost damage. The problem with frost damage is due to the low tensile strength of concrete. When the water in concrete freezes at low temperatures the water expands and create tensile stresses that might damage the concrete.

Today’s society is striving to be more and more environmentally friendly and it creates challenges for the concrete industry. The manufacturing of cement cause a large amount of carbon dioxide emissions and the biggest challenge for the concrete industry is to reduce these emissions. One way of reducing the emissions is to replace some of the cement with supplementary cementitious materials (SCM) which have a smaller impact to the environment (Lothenbach et al. , 2011). Two of the most common SCMs, slag and fly ash, will be discussed in this report.

Two different experiments has been carried out in this study. Both experiments used a unique device that simultaneously measures ice formation and length change. The specimens in the first experiment were moisture insulated and were only allowed to freeze and thaw once. During the first experiment, three different materials were used with two levels of air entrainment. Concrete with CEM I, concrete with 35% of the cement replaced by slag and concrete with 35% of the cement replaced by fly ash was used in the study. The air entrainment levels were about 2% and 5%. In the second experiment the specimen was allowed to freeze and thaw several times and also had access to a sodium chloride solution during the cycles. During the second experiment only the concrete with 35% fly ash and an air entrainment of 5,7% was used. The aim with the first experiment was to study if the formation of ice differs between concretes with different binders and also how the ice formation affect the dilation of the different materials. The second experiment was carried out to see if it was possible to continuous study the formation of microscopic ice bodies by length change when the specimen had access to a solution.

The results from the study show that CEM I concrete form ice linearly while a major part of the ice formation in concrete with slag and fly ash occurs at about -40 °C. The dilation follows the thermal movement with small contributions from the ice formation. The reason for the small dilation is probably that the formed ice can fit into the existing pores. This study also showed that it is possible to study the formation of microscopic ice bodies by length change when the specimen had access to a solution. The dilation from the formation of the microscopic ice bodies resembles the result from the experiment carried out by Powers & Helmuth (1953) where they showed that the longitudinal extension continues even if the temperature is held constant.},
  author       = {Karlsson, Timmie},
  issn         = {0348-7911},
  language     = {swe},
  note         = {Student Paper},
  title        = {Samband mellan isbildning och längdändring i betong med olika bindemedel},
  year         = {2017},
}