Self-healing and Chloride Ingress in Cracked Cathodically Protected Concrete Exposed to Marine Environment for 33 years

Self-healing and Chloride Ingress in Cracked Cathodically Protected Concrete Exposed to

Marine Environment for 33 years

Tobias Danner, SINTEF Community, Norway Karla Hornbostel, NPRA, Norway

Mette Geiker, NTNU, Norway

The 4th International RILEM conference Microstructure Related Durability of Cementitious Composites, Den Haag, The Netherlands, 2020

Background and Motivation

Contradicting conclusions regarding long-term impact of cracks on reinforcement corrosion and only few long-term field studies

Initiation Period:

A: Faster Ingress of chlorides and CO₂

Propagation Period:

B: Faster corrosion rate C: Same corrosion rate

D: Initial faster corrosion rate, but slowing down after some time

Degradationlevel

Time

Acceptable extent of corrosion

Initiation period Uncracked concrete Cracked concrete

A

B C D

Propagation period

Danner and Geiker, NCR 58, 1/2018 Structure Cecilie

Bridge Tåsen

Tunnel Moholt

Bridge Field station

Sandnessjøen DNV Field

Station Hafrsfjord Bridge Type Beam (Box-girder)

Bridge Kulvert Slab bridge Field station Field station Beam bridge

Location Trondheim Oslo Trondheim Sandnessjøen Bergen Stavanger

Structural part Edgebeam Tunnel wall Edgebeam Beams Column Foundation

Age (years) 16 20 25 25 33 50

Exposure De-icing salt

(minor) De-icing salt

(minor) De-icing salt

(minor) Tidal seawater

(heavy) Tidal seawater

(heavy) Tidal seawater (heavy)

Climate Inland Inland Inland Marine Marine Marine

Concrete C55, SV-40 N/A C45 Varying C60 B35

Cover 55 50 50 25 50 90

Tåsentunnel DNV field station

Hafrsfjord Bridge

Sandnessjøen

Field Investigations 2016-2019

• Impact of cracks on ingress (chloride, CO₂) and reinforcement corrosion

• Impact of exposure, binder type, crack width (and orientation) on self-healing

1) 2)

3)

4)

5)

Andersen and Espelid, 1993

Pictures: Tobias Danner (2016)

DNV Field station 1983-2016, Bergen, Norway

• Marine exposure of different concretes

• Dynamically loaded

• Cathodically protected

5 m

Mean water

level 3 concentric

reinforcement nets, Loading rig

Coring and cutting in the field

Investigated column in the laboratory

• Normal density concrete (C60), used in Norwegian offshore structures

• Middle part exposed to tidal zone

• Horizontal crack (Crack width 0.15 – 0.55 mm)

cutting

Chloride profiles µ-XRF

Picture: Tobias Danner (2017)

-500 -450 -400 -350 -300 -250 -200 -150 -100 -50 0 mV

Chloride Ingress at crack in the tidal zone of DNV column

R = Reinforcement, St = Stirrup

% Cl by weightofconcrete

• Cl – concentration at reinforcement above accepted critical valuse

• No apparent influence of cracks on chloride ingress depth

• ~ equally distyributed chloride over whole width of cores

Chloride Ingress at cracks (other studies)

Danner et al., NPRA report No. 374, 2019

• Long term experiment (Sandnessjøen Field Station)

• Normal density concrete

• Exposure: 25 years marine exposure

• Horizontal cracks; Crack width 0.1 – 0.3 mm

• Short term laboratory experiment

• Crack width: 0.15 mm

• Exposure: 3% NaCl solution, 2 weeks

• Exposure from top

25 mm

AgNO₃ µ-XRF

Picture: Tobias Danner

Self-healing of the crack in the tidal zone of DNV column

• Precipitation of Mg and Ca inside the crack

• Sulfate accumulation in the crack surrounding concrete

• Sulfate precipitation at larger crack depth

• No silicium detected inside crack

 Further hydration of cement seems not to play a major role

Self-healing mechanism in marine exposure

Danner et al., Minerals, 2019, 9, 284

• Typical behavoiur in tidal zone

• Precipitation of ions from seawater in outer part of the crack

(calcite and brucite, partly intermixed)

• Dissolution and repricipation of phases from cement paste in the inner part (ettringite)

• Typical mineralogical sequence with increasing crack depth due to increasing pH of solution inside the crack

Excavation of reinforcement (DNV column)

• Despite high chloride content at reinforcement, almost no corrosion was observed.

• Minor corrosion only found at one stirrup in combination with largest carck width

 Sacrificial anodes were functioning for major part of the field exposure

 Not possible to find any link between cracks and reinforcement corrosion

Perspectives –

Potential crack repair

Initial cathodic protection to

• Limit early chloride ingress

Negative ions migrate to the concrete surface

• increase early self-healing

positive ions move towards reinforcement

vegvesen.no

"Mineral accretion" and

"electrochemical precipitation of minerals"

(Hilbertz 1981, US4440605A &

1980 US4246075A)

+

-

Hilbertz 1981

Summary

• No apparent influence of cracks on chloride ingress depth (and only minor corrosion)

• Considerable self-healing of cracks

• 33 years exposure to tidal zone in North Atlantic (Bergen, Norway) of CP protected cracked concrete column

The study suggests use of sacrificial anodes to

• limit early chloride ingress

• increase early self-healing

References for further reading

DNV

• Danner et al., Self-healing and Chloride ingress in Cracked Cathodically Protecetd Concrete Exposed to Marine Environment for 33 years exposure, NTNU report R-1-2019

• Rodum E. and Danner T., Kloridbestandighet av 1980-tallets offshorebetong – 30 års eksponering ved DNV GLs feltsstasjon i Bergen, Statens Vegvesen report series No. 504, 2019

• Øyvind Strømme, Influence of cracks and spacers on chloride penetration and reinforcement corrosion in concrete, Master thesis, NTNU, 2017

Other studies

• Danner T. and Geiker M., Relevance of crack width requirements due to durability aspects of conventional reinforcement, Presentation, E39 Seminar, Trondheim, Norway, 2018 (https://www.youtube.com/watch?v=M_- iODDx8f8&feature=youtu.be)

• Geiker et al., 25 years of field-exposure of pre-cracked concrete beams; combined impact of spacers and cracks on reinforcement corrosion, submitted to Construction and Building Materials, 2020

• Danner T. and Geiker M., Long-term influence of Concrete Surface and Crack Orientation on Self-healing and Ingress in Cracks – Field Observations, Nordic Concrete Research, No. 58, 2018

• Danner et al., Mineralogical sequence of self-healing products in cracked marine concrete, Minerals, 9, 284, 2019

Contact:

[email protected]

[email protected] [email protected]

Acknowledgements:

The first author was financed through the Norwegian Public Roads Administration (NPRA) Ferry-free coastal route E39 project.

We appreciate the funding.

DACS project (Durable Advanced Concrete Structures) is acknowledged for financial support and contributing to the discussion.

DNV GL is acknowledged for providing the concrete columns and

Norwegian Public Roads Administration (NPRA) NPRA is acknowledged for facilitating the collaboration with DNV GL and contribution to discussion as well as providing insight to further results from own studies on the field station.

Thank you for your attention