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Investigation of the frost resistance in bacteria treated self-healing concrete

Persson, Karin LU (2016) VBM820 20161
Division of Building Materials
Abstract (Swedish)
Vattenkraften står för hälften av vårt elbehov i Sverige idag. Merparten av vattenkraftverken är gjutna i betong och som många andra betongkonstruktioner så drabbas betongen av sprickbildning av olika orsaker. För vattenkraften är genomgående sprickor ett problem då dessa skapar läckage.

För att förhindra dessa sprickor har en ny metod börjat undersökas där bakterier som kan avsätta kalciumkarbonat blandas in i betongen i sporform. När sedan en spricka uppstår aktiveras sporerna av vatten och syre och avsätter kalciumkarbonat som fyller igen sprickorna. Metoden anses miljövänlig och kalciumkarbonat är samma material som cementet har sitt ursprung från och man får samma elasticitetsmodul och värmeutvidgningskoefficient på... (More)
Vattenkraften står för hälften av vårt elbehov i Sverige idag. Merparten av vattenkraftverken är gjutna i betong och som många andra betongkonstruktioner så drabbas betongen av sprickbildning av olika orsaker. För vattenkraften är genomgående sprickor ett problem då dessa skapar läckage.

För att förhindra dessa sprickor har en ny metod börjat undersökas där bakterier som kan avsätta kalciumkarbonat blandas in i betongen i sporform. När sedan en spricka uppstår aktiveras sporerna av vatten och syre och avsätter kalciumkarbonat som fyller igen sprickorna. Metoden anses miljövänlig och kalciumkarbonat är samma material som cementet har sitt ursprung från och man får samma elasticitetsmodul och värmeutvidgningskoefficient på lagningsmaterialet. Metoden anses också kostnadseffektiv eftersom bakterieblandningen är relativt billig och framför allt för att kostnader för inspektion och lagning kan hållas till ett minimum, då bakterierna spontant lagar sprickorna utan mänsklig inblandning.

I laborativ miljö har sprickor med sprickvidder uppemot 0,5 mm lyckats lagas helt, detta att jämföra med maximalt godkända sprickvidder på grund av last som ligger i spannet 0,2-0,4 mm. Metoden att gjuta in bakterierna i betong har dock aldrig testats i ett fullskaligt projekt, i alla fall inte vad som framgår av publiserade artiklar. För att metoden ska kunna testas måste dock några parametrar fungera lika bra för självläkande bakterie-betong som för vanlig betong, bland annat hydratationsförlopp, hållfasthet och frostbeständighet, vilket studeras i denna studie.

Tre olika betongrecept användes i denna studie, alla baserade på Anläggningscement. Ett innehöll bakterier, kalciumlaktat och luftporstillsats och ett recept hade luftportillsats. Det sista receptet hade ingen luftporstillsats vilket då skapar en dålig betong frostmässigt.
För att testa hydratationsförlopp och hållfasthet genomfördes två test med isoterm kalorimeteri, ett tryckhållfasthetstest och ett draghållfasthetstest. Det första kalorimetertestet visade tendenser på skillnader i hydratationsförlopp mellan bakteriebetongen och de två övriga med cirka en timmes retardation för huvudreaktionen och en liten förhöjning av effekten. Ett nytt test där bakteriebetongen delades upp i tre olika grupper (en med laktat, en med bakterier och en med bakterier och laktat) visade att bakterierna troligtvis var ansvariga för retardationen och laktatet för den förhöjda effekten. Skillnaderna är dock små och den ackumulerade värmeutvecklingen var inom den normala spridningen för Anläggningscement.

I draghållfasthet och tryckhållfasthet kunde inga skillnader upptäckas.

För god frostbeständighet krävs tomma luftporer. För att se så att bakterierna inte hade skapat utfällningar i luftporerna gjordes en SEM-analys. Den visade inget som ansågs påverka frostbeständigheten. I ett frystest med sötvatten påvisades även att skillnaderna mellan betong med både tillsatta luftporer och bakterier och betong med enbart tillsatta luftporer är små. Detta tyder också på att luftporerna är intakta och tomma, precis som SEM-analysen visade. I saltvatten är skillnaderna lite större.

Sammanfattningsvis, med den använda koncentrationen av bakterier kunde ingen negativ påverkan påvisas. Förslagsvis bör dock fler och då högre koncentrationer testas samt bakteriernas spricklagande förmåga. Dessutom är denna studie mycket begränsad i tid och eventuella långtidseffekter av bakterietillsatsen fortfarande okända. (Less)
Abstract
Half of the electricity needed in Sweden today is produced by hydro power. Most structure parts in hydro power stations are made of concrete and as many of other concrete structures they contain cracks. Cracking through dams are a big problem for hydro power since they create leakage.

To prevent cracking a new method is under investigation. It consists of incorporating calcium carbonate precipitating bacterial spores in the cement matrix. Upon cracking the spores get activated by water and oxygen and precipitate calcium carbonate that will fill the cracks. The method is considered to be environmental friendly and the precipitation is the same material that the cement has its origin from. The filling then obtains the same modulus of... (More)
Half of the electricity needed in Sweden today is produced by hydro power. Most structure parts in hydro power stations are made of concrete and as many of other concrete structures they contain cracks. Cracking through dams are a big problem for hydro power since they create leakage.

To prevent cracking a new method is under investigation. It consists of incorporating calcium carbonate precipitating bacterial spores in the cement matrix. Upon cracking the spores get activated by water and oxygen and precipitate calcium carbonate that will fill the cracks. The method is considered to be environmental friendly and the precipitation is the same material that the cement has its origin from. The filling then obtains the same modulus of elasticity and coefficient of thermal expansion as concrete. The method is also considered to be cost efficient since the bacterial mix is relatively inexpensive, but most of all the costs for inspection and repairs can be held to a minimum, since the bacteria repair the cracks spontaneously without human intervention.

In a laboratory environment crack widths up to 0.5 mm has been totally repaired by this method. This value can be compared with the maximum allowed crack widths from different loading cases that are between 0.2-0.4 mm. The method to incorporate bacteria in the cement matrix has never been tested in a full scale project, not that has been verified in articles at least. To be able to test the method in full scale there has to be a certainty that some parameters work as well in bacteria-treated concrete as it does in the normal concrete, e.g. hydration, strength development and frost resistance.

Three different concrete recipes has been used in this study, all based on CEM I cement. One recipe had bacteria, lactate and air entrainment agent (AEA), one recipe had only AEA and the last one did not have any AEA which created a concrete that is not frost resistant.

To test hydration and strength development two isothermal calorimetry tests, one compressive strength test and one tensile strength test was preformed. The first calorimetry test showed small differences in hydration between the bacteria treated concrete and other two with about one hour delay of the start of the main reaction and a small increase in the thermal power. The second test where the bacteria treated concrete was divided in three groups (one with lactate, one with bacteria and one with both bacteria and lactate) showed that the bacteria probably was responsible for the delay in main reaction and that the lactate for the increase in thermal power. The differences were small though and the accumulated heat was in the normal range for the CEM I cement.

The tensile and compressive strength were not effected by the addition of bacteria.

To receive a good frost resistance the added air voids need to be empty. To see whether the bacteria had created precipitations in the air voids pictures were taken with a scanning electron microscope (SEM). They showed nothing that would effect the frost resistance. A freeze-thaw test was also performed, both with fresh water and salt water. The test with fresh water showed only small differences in scaling between the concrete with both bacteria and added air voids and the concrete with only added air voids. This indicates that the air voids are unaffected by the added bacteria, as the SEM-analysis also showed. In salt water the differences in scaling are larger.

To sum it up, with the concentration of bacteria solution used no negative effects was seen in this study. However, higher concentrations should be tested and also the crack healing efficiency. This study was also limited in time and the long term effects are still unknown. (Less)
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author
Persson, Karin LU
supervisor
organization
course
VBM820 20161
year
type
H3 - Professional qualifications (4 Years - )
subject
keywords
Concrete, Hydraulic Structures, Hydro Power, Frost Resistance, Self- healing, Bacteria, Precipitation, Calcium Carbonate Betong, Vattenbyggnader, Vattenkraft, Frostbeständighet, Självläkn- ing, Bakterier, Utfällning, Kalciumkarbonat
report number
TVBM 5107
ISSN
0348-7911
language
English
id
8892820
date added to LUP
2016-10-10 08:30:03
date last changed
2016-10-10 08:30:03
@misc{8892820,
  abstract     = {Half of the electricity needed in Sweden today is produced by hydro power. Most structure parts in hydro power stations are made of concrete and as many of other concrete structures they contain cracks. Cracking through dams are a big problem for hydro power since they create leakage.

To prevent cracking a new method is under investigation. It consists of incorporating calcium carbonate precipitating bacterial spores in the cement matrix. Upon cracking the spores get activated by water and oxygen and precipitate calcium carbonate that will fill the cracks. The method is considered to be environmental friendly and the precipitation is the same material that the cement has its origin from. The filling then obtains the same modulus of elasticity and coefficient of thermal expansion as concrete. The method is also considered to be cost efficient since the bacterial mix is relatively inexpensive, but most of all the costs for inspection and repairs can be held to a minimum, since the bacteria repair the cracks spontaneously without human intervention.

In a laboratory environment crack widths up to 0.5 mm has been totally repaired by this method. This value can be compared with the maximum allowed crack widths from different loading cases that are between 0.2-0.4 mm. The method to incorporate bacteria in the cement matrix has never been tested in a full scale project, not that has been verified in articles at least. To be able to test the method in full scale there has to be a certainty that some parameters work as well in bacteria-treated concrete as it does in the normal concrete, e.g. hydration, strength development and frost resistance.

Three different concrete recipes has been used in this study, all based on CEM I cement. One recipe had bacteria, lactate and air entrainment agent (AEA), one recipe had only AEA and the last one did not have any AEA which created a concrete that is not frost resistant.

To test hydration and strength development two isothermal calorimetry tests, one compressive strength test and one tensile strength test was preformed. The first calorimetry test showed small differences in hydration between the bacteria treated concrete and other two with about one hour delay of the start of the main reaction and a small increase in the thermal power. The second test where the bacteria treated concrete was divided in three groups (one with lactate, one with bacteria and one with both bacteria and lactate) showed that the bacteria probably was responsible for the delay in main reaction and that the lactate for the increase in thermal power. The differences were small though and the accumulated heat was in the normal range for the CEM I cement.

The tensile and compressive strength were not effected by the addition of bacteria.

To receive a good frost resistance the added air voids need to be empty. To see whether the bacteria had created precipitations in the air voids pictures were taken with a scanning electron microscope (SEM). They showed nothing that would effect the frost resistance. A freeze-thaw test was also performed, both with fresh water and salt water. The test with fresh water showed only small differences in scaling between the concrete with both bacteria and added air voids and the concrete with only added air voids. This indicates that the air voids are unaffected by the added bacteria, as the SEM-analysis also showed. In salt water the differences in scaling are larger.

To sum it up, with the concentration of bacteria solution used no negative effects was seen in this study. However, higher concentrations should be tested and also the crack healing efficiency. This study was also limited in time and the long term effects are still unknown.},
  author       = {Persson, Karin},
  issn         = {0348-7911},
  keyword      = {Concrete,Hydraulic Structures,Hydro Power,Frost Resistance,Self- healing,Bacteria,Precipitation,Calcium Carbonate Betong,Vattenbyggnader,Vattenkraft,Frostbeständighet,Självläkn- ing,Bakterier,Utfällning,Kalciumkarbonat},
  language     = {eng},
  note         = {Student Paper},
  title        = {Investigation of the frost resistance in bacteria treated self-healing concrete},
  year         = {2016},
}