Microbial biofilm communities associated with degradation of sprayed concrete in subsea tunnels
Doktorsavhandling, 2021

Deterioration of concrete leads to reduced structural strength implying high societal challenge with huge economic impact. In the Oslofjord subsea tunnel, complex microbial biofilm activity together with abiotic attack from saline groundwater are responsible for concrete matrix degradation and steel fiber corrosion. Previous research has revealed that microbial attack causes disintegration of cement paste matrix and thinning of sprayed concrete at rates varying from 0.5-10 mm/year in areas with leakages of saline groundwater. General knowledge about biodegradation of concrete infrastructures in marine environment is lacking and research in this area is therefore needed. A long-term study of biofilm microbial community composition and dynamics was performed between 2015-2020 in the Oslofjord subsea tunnel. Due to its complexity it was necessary to work multi-disciplinary, including studies of the microbial community structure by using advanced molecular techniques in combination with chemical analysis to get a comprehensive picture of the prevailing micro-environmental conditions within the biofilm. High throughput amplicon sequencing of 16S rRNA gene together with metagenomics shotgun sequencing revealed temporal dynamics in microbial community structure, and metabolic potential of biofilms in the Oslofjord tunnel. Water chemical analysis and microsensor measurements of oxygen and pH profiles within the biofilm were performed on-site to assess environmental conditions in the biofilms. Additionally, SEM microscopy together with XRD analyses were used to investigate concrete degradation beneath the biofilms over time. In parallel, a mesocosm experiment was performed over a period of 65 weeks to study the role of concrete material properties and fiber reinforcement for microbial colonization and composition. The long-term study preformed in the Oslofjord subsea tunnel revealed a complex microbial community involved in cement paste matrix degradation and steel fiber corrosion. The microbial communities at the different tunnel localities were composed of nitrogen converting bacteria, iron-oxidizing bacteria, sulfur oxidizing bacteria, heterotrophic aerobic bacteria, putative manganese-oxidizing bacteria and many microorganisms that could not be assigned to any function. Microsensor measurements showed relatively stable pH around 7-8 throughout the biofilm, whereas the dissolved oxygen profiles decreased with biofilm depth. Significant differences in community structure and richness between biofilms at the different tunnel locations were revealed with alpha and beta-diversity analysis. However, the microbial communities at the three sites shared many taxa. Pairwise comparisons suggested that deterministic factors were important for the assembly of the microbial communities of mature biofilms. Results from the mesocosms study indicate that stochastic factors were important during the initial colonization and time was the main factor which drives turnover in the biofilm communities on concrete material. Presence of steel fiber reinforcement was found to have a greater effect on the biofilm community composition than the surface roughness. The results obtained in this thesis help us to understand the complexity of microbial induced concrete deterioration and corrosion of steel fiber reinforcement observed in the subsea tunnel environments.

metagenomics.

concrete

surface structure

marine environment

steel fibers

microbially induced deterioration

amplicon sequencing

biofilm

subsea tunnels

Zoom; ACE Room SB-K373, Chalmers
Opponent: Associate Professor Torben Lund Skovhus, VIA University College, Research Centre for Built Environment, Energy, Water and Climate, Denmark.

Författare

Sabina Karacic

Chalmers, Arkitektur och samhällsbyggnadsteknik, Vatten Miljö Teknik

Microbial attack on subsea sprayed concrete

International RILEM Conference on Microorganisms-Cementitious Materials Interactions,; (2016)p. 63-75

Paper i proceeding

Subsea tunnel reinforced sprayed concrete subjected to deterioration harbours distinct microbial communities

Biofouling,; Vol. 34(2018)p. 1161-1174

Artikel i vetenskaplig tidskrift

Sabina Karačić, Carolina Suarez, Per Hagelia, Frank Persson, Oskar Modin, Britt-Marie Wilén. Using metagenomics to understand sprayed concrete biodeterioration in a subsea road tunnel.

Sabina Karačić, Oskar Modin, Per Hagelia, Frank Persson, and Britt-Marie Wilén. The role of time and surface type on the development of biofilm communities on concrete exposed to seawater (submitted)

Who is living on the concrete?

 In this thesis, it was investigated how microorganisms degrade concrete structures in marine environments, which is a large societal problem with enormous economic impact. In marine and fresh waters, microorganisms such as bacteria, algae and fungi, often grow on surfaces and form thin layers of biofilm. When microorganisms grow they form various acidic compounds. Biofilms growing on concrete can therefore deteriorate and even dissolve the cement, the binding material in the concrete. In the Oslofjord subsea tunnel, microbial activity together with abiotic attack from saline ground water are responsible for degradation of the sprayed concrete used for rock support and for corrosion of the steel fibers used to reinforce the concrete. Difficulties isolating specific microorganisms from the biofilm in order to analyse their effect on concrete biodegradation and separating various biotic and abiotic degradation processes are main reasons for the limited knowledge in this field. In this thesis, molecular methods were used to address these issues.

High throughput amplicon sequencing of 16S rRNA genes together with metagenomics shotgun sequencing revealed that microbial communities at the Oslofjord subsea tunnel concrete were composed of nitrogen converting bacteria, iron-oxidizing bacteria, sulfur oxidizing bacteria, heterotrophic aerobic bacteria, putative manganese-oxidizing bacteria and microorganisms that could not be assigned to any function. Scanning electron microscopy (SEM) together with X-ray power diffraction (XRD) analyses were used to investigate subsea tunnel concrete degradation beneath the biofilms over time. Water chemical analysis and microsensor measurements of oxygen and pH profiles within the biofilm were performed on-site to assess environmental conditions in the biofilms. In parallel, a mesocosm experiment which simulates the condition when cement is exposed to seawater, was performed over a period of 65 weeks to study the role of concrete material properties and fiber reinforcement for biofilm formation and microbial composition.

The results obtained in this thesis help us to understand the complexity of microbial induced concrete deterioration and corrosion of steel fiber reinforcement observed in the subsea tunnels.

 

 

 

 

 

 

 

 

The role of microbiol. biofilm communities for degradation of sprayed concr. in subsea tunnels

Statens vegvesen (2011 067932), 2014-10-14 -- 2018-12-31.

Ämneskategorier

Biokemi och molekylärbiologi

Ekologi

Mikrobiologi

ISBN

978-91-7905-560-8

Doktorsavhandlingar vid Chalmers tekniska högskola. Ny serie: 5027

Utgivare

Chalmers tekniska högskola

Zoom; ACE Room SB-K373, Chalmers

Online

Opponent: Associate Professor Torben Lund Skovhus, VIA University College, Research Centre for Built Environment, Energy, Water and Climate, Denmark.

Mer information

Senast uppdaterat

2021-09-28