Presentation 2

Concrete self-healing strategies
Prof. dr. ir. Nele De Belie
Magnel Laboratory for Concrete Research – Department of Structural Engineering
I. DIFFERENT STRATEGIES FOR
CONCRETE SELF-HEALING
Magnel Laboratory for Concrete Research
One of the “coolest” biomimetic applications:
self-healing concrete
Nature : not designed to withstand everything
In case of failure :
‣ Rapid & autonomous
detection
‣ ‘massive’ & efficient action
‣ “after” as strong as “before”
‣ ‘inexhaustable’
‣ cheap
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One of the “coolest” biomimetic applications:
self-healing concrete
Nature : not designed to withstand everything
In case of failure :
‣ Rapid & autonomous
detection
‣ ‘massive’ & efficient action
‣ “after” as strong as “before”
‣ ‘inexhaustable’
‣ cheap
Magnel Laboratory for Concrete Research
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Strategies for concrete self-healing
1. Autogenous healing
2. Improved autogenous healing
3. Stimulated autogenous healing
4. Autonomous healing by bacteria
5. Autonomous healing by encapsulated
polymers
Magnel Laboratory for Concrete Research
Strategies for concrete self-healing
Autogenous healing
(a) Crystallization: precipitation of CaCO3
(b) Blockage by impurities and products
(c) Further hydration & pozzolanic activity
(d) Expansion of C-S-H
Autogenous healing © N. ter Heide & precipitation of CaCO3
Magnel Laboratory for Concrete Research
Strategies for concrete self-healing
Improved autogenous healing:
fibre reinforcement to restrict crack width
ECC (Victor Li): cracks < 60 µm
Magnel Laboratory for Concrete Research
Strategies for concrete self-healing
Stimulated autogenous healing:
hydrogels
+ fibres to limit
crack width
Enhance precipitation of CaCO3
Block cracks
Stimulate further hydration
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Hydrogels or superabsorbing polymers
Hydrogel
swelling
de-swelling
 Sealing of the crack
 Binder hydration, CaCO3
precipitation and healing
500 times their own weight (50 times own volume)
Impression of swelling absorption by hydrogels (D. Snoeck, UGent)
Magnel Laboratory for Concrete Research
Hydrogels
Magnel Laboratory for Concrete Research
Strategies for concrete self-healing
Stimulated autogenous healing:
alkali activation
Stimulate further hydration & pozzolanic activity
Magnel Laboratory for Concrete Research
Hydration of cement and slag in slag-blended pastes (E.Gruyaert)
Scanning Electron microscopy (BSE)
αcementt  
initial volume of cement - anhydrous volume cement at time t 
Pores
CS(A)H (hydration products)
initial volume of cement
CH
αslagt  
initial volume of slag - anhydrous volume slag at time t 
acement
Unhydrated slag
Unhydrated cement
initial volume of slag
2 days
2 years
CP0
55%
74%
CP50
78%
94%
CP85
28%
91%
aslag
2 days
2 years
CP50
28%
72%
CP85
4%
39%
Magnel Laboratory for Concrete Research
Strategies for concrete self-healing
Autonomous healing: bacteria
Enhance precipitation of CaCO3
(Block cracks: carrier)
Magnel Laboratory for Concrete Research
Strategies for concrete self-healing
Autonomous healing: encapsulated
polymers
Seal cracks completely
(and restore mechanical properties)
Magnel Laboratory for Concrete Research
II. HYDROGEL STRATEGY
SEALING AND SUBSEQUENT
HEALING
Ongoing PhD of Didier Snoeck
Magnel Laboratory for Concrete Research
Hydrogel swelling capacity in different solutions
SAP B: a crosslinked potassium salt polyacrylate
(∅ 476.6 ± 52.9 µm)
- vacuum drying with silica gel
- add fluid and filter after one day
- determine retained water
ΔV demineralised water [g / g SAP]
283.2 (±2.4)
ΔV cement slurry [g / g SAP]
58.4 (±1.7)
Swelling time [s]
120
Difference ΔV: 1) screening effect cations; 2) complex formation Ca2+
with carboxylate groups  new cross-links
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Experiments at the Neutron Line of PSI
SNOECK D, STEUPERAERT S, VAN TITTELBOOM K, DUBRUEL P, DE BELIE N.
(2012). Visualization of water penetration in cementitious materials with
superabsorbent polymers by means of neutron radiography. Cement and Concrete
Research, 42(8):1113-21.
NEUTRA beam line at the Paul Scherrer Institute
Magnel Laboratory for Concrete Research
Self-sealing properties of SAP
Self sealing of a cracked specimen
SAP block the crack
Possible to measure absorption of large SAP
Swelling SAP
Magnel Laboratory for Concrete Research
Self-healing: Mortar sample composition
polycarboxylate superplast
PVA fibres (volume fraction Vf)
SAP (1-2 m-% of cement)
OPC: 571 kg/m³
FA: 685 kg/m³
Silica sand 0/2: 456 kg/m³
Water: 332 kg/m³
Stored at 20°C and 90% RH for 28 d
Crack formation
F/2
F/2
u
F/2
F/2
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Overview of variable combinations
Specimen
prism
cylinder
Code
REF
P90
P60
B1
B90
B60
B2
REF
B1
B2
Vf
2
2
2
2
2
2
2
1
1
1
m% SAP
0
0
0
1
1
1
2
0
1
2
Cracking
4 point bending
4 point bending
4 point bending
4 point bending
4 point bending
4 point bending
4 point bending
Splitting
Splitting
Splitting
Prisms: 160.40.15 mm³
Cylinders: ∅ 78 mm, height 20 mm
Curing
Wet/dry cycles
RH > 90%
RH = 60%
Wet/dry cycles
RH > 90%
RH = 60%
Wet/dry cycles
Permeability
Permeability
Permeability
Number
3
3
3
3
3
3
3
5
3
4
Curing for 28 d
Repeat four-point
bending test
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Typical stress/strain curve
Multiple cracking + strain hardening
Preloading
Bending stress [MPa]
[2]
Reloading
6
[3]
[1]
[8]
[7]
[9]
4
[4]
[6]
2
[5]
0
0
Regain in stiffness =
1
2
Strain [%]
3
4
[5  6]  [ 4  5]
[0  1]  [4  5]
Regain in peak load =
Regain first-cracking strength =
[8 ]  [ 4 ]
[2]  [ 4]
Regain in multiple crack formation =
[7  9 ]
[1  3]
Regain strength =
[6]
[1]
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[7 ]  [ 4 ]
[1]  [ 4]
Bending ductility
Multiple cracking enhanced by SAP
Large ductility 7.5 mm thickness
9 mm vertical displacement
Crack widths: 5-150 µm
Bending ductility, 9 mm vertical displacement
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Regain of mechanical properties
Wet/dry cycles: m% SAP ↑
→
σfc ↓
healing ↑
Magnel Laboratory for Concrete Research
Regain of mechanical properties
Only with SAP: Healing at RH>90% and RH=60% !
Magnel Laboratory for Concrete Research
Microscopic observations
0 µm < total closure < 30 µm < partial < 150 µm < no closure
Wet/dry cycle without SAP
100
RH>90% with SAP
RH=60% with SAP
60-90% RH without SAP
Percentage closure [%]
80
60
40
20
0
0
50
100
150
Initial residual crackwidth [µm]
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200
Self-healing of crack with SAP
Before
After
Composition of white crystals?
→ ThermoGravimetric Analysis
Self-healing of a 138 µm crack
Hydration products
Precipitation of CaCO3
Magnel Laboratory for Concrete Research
Water permeability of healed samples
decreases a lot by SAP addition
m% SAP B ↑
coarsening of the matrix
SNOECK, D., VAN TITTELBOOM, K., STEUPERAERT, S., DUBRUEL, P., DE BELIE, N.
(2012) Self-healing cementitious materials by the combination of microfibres and
superabsorbent polymers. Journal of Intelligent Material Systems and Structures, online.
Magnel Laboratory for Concrete Research
Water uptake in specimens
Water uptake ↓ with SAP
18
REF - CRA
Total water uptake [l/m²]
16
14
1B - CRA
12
1C - CRA
10
8
2C - CRA
6
REF - UNC
4
2
1C - UNC
0
0
0,5
1
1,5
2
Root of time [√(h)]
Total water uptake after 4 hours and uptake in time
Magnel Laboratory for Concrete Research
III. MICROBIAL STRATEGY
BIODEPOSITION OF CALCIUM
CARBONATE
Magnel Laboratory for Concrete Research
Biotechnology in conservation
Calcite Bioconcept
Microbial deposition of a protective CaCO3 layer
Magnel Laboratory for Concrete Research
Mechanism of microbiologically induced
carbonate precipitation
Microbiology
Precipitation parameters
Metabolism
[dissolved inorganic carbon]
pH
[Ca 2+ ]
Cell wall
nucleation site
If [Ca 2+ ]*[CO32-] > Ks : precipitation occurs
Magnel Laboratory for Concrete Research
UGent research on concrete: Mechanism
Example of a nitrogen conversion process:
Hydrolysis of urea
CO(NH2)2
+
H2O

Cell wall:
Precipitation parameters
CO32+
2NH4+
[dissolved inorganic carbon]
pH
nucleation site
Negatively charged
De Muynck, W., Belie, N. & Verstraete, W. (2010). Microbial carbonate precipitation in
construction materials: a review. Ecological Engineering, 36 (2), 118-136.
De Muynck, W., Cox, K., Belie, N. & Verstraete, W. (2008). Bacterial carbonate
precipitation as an alternative surface treatment for concrete. Construction and Building
Materials, 22, 875-885.
Magnel Laboratory for Concrete Research
NH4+
CO32-
UREA
Magnel Laboratory for Concrete Research
Precipitation of carbonate crystals
Thin sections, SEM pictures of A) reference; biodeposition with B) CaCl2 and C) with Ca acetate
Magnel Laboratory for Concrete Research
Precipitation of carbonate crystals
Microbial mediation of precipitation
Magnel Laboratory for Concrete Research
Bacteria for self-healing
Carrier
• porosity
• pore size distribution
• strength
• compatibility
Concrete
activity
survival (spores)
workability
strength
PhD / postdoc of Jianyun Wang
permeability
Magnel Laboratory for Concrete Research
Self-healing systems based on
different carriers used
+
Wang, J.Y., Van Tittelboom, K., De Belie, N.,
Verstraete, W. (2012). Use of silica gel or
polyurethane immobilized bacteria for self-healing
concrete. Construction and building materials, 26,
532–540.
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Porous carrier: Bacteria immobilized
on diatomaceous earth (DE)
Particle size:
4μm to 15μm
Wang, J.Y., De Belie, N., Verstraete, W. (2012). Diatomaceous earth as a protective vehicle
for bacteria applied for self-healing concrete. Journal of Industrial Microbiology and
Biotechnology, 39, 567–577.
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Specimens with DE immobilized bacteria and
nutrients
Influence on 28d strength
80
2
Tensile strength(N/mm)
2
Compressive strength(N/mm)
8
6
4
2
0
60
40
20
0
reference
DE 5
DE 5N
DE 5BN
reference
DE 5
DE 5N
DE 5BN
DE slightly increases the strength
DE with bacteria and nutrients will not decrease the strength
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Crack making
(0.15mm~0.17mm)
Immersion
(40 days)
H2O
urea + Ca2+
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In water
Partly filled
crack
In deposition
medium
Completely
filled crack
R
DE5
DE5N
DE5BN
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•Water penetration resistance
increased due to the precipitation
specimen
Aluminum
foil
water
•Water absorption of the specimens
with DE immobilized bacteria
decreased 50% ~ 70%.
1
2
Water absorped (g/cm )
DE,W
DE,M
0.8
DEBS,W
DEBS,M
0.6
0.4
0.2
0
0
50
100
150
200
250
300
350
Time (h)
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400
42
SEM
SEM images of the precipitation
in cracks of DE+BS
Based on EDS, the
precipitation was CaCO3
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IV = II + III
Self-healing by bacteria
encapsulated in hydrogels
Hydrogel
Distinct properties:
1) High water absorption and retention capacity;
2) Moisture uptake from the air;
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Encapsulation process
Bacteria
Polymer
solution
wet-dry
cycles 28d
Test procedure
2% of cement (w/w)
wet-dry
cycles 28d
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Bacterial spores keep viable after
immobilization
25
Urea decomposed (g/L)
After UV
After UV+FG+VD
After UV+FG
After UV+FD+VD
20
urea decomposed after
48h by free spores
urea decomposed
after 48h
15
urea decomposed after
24h by free spores
10
urea decomposed
after 24h
5
0
S
H
HY
HU
HYU
HS
HYS
Magnel Laboratory for Concrete Research
HUS
HYUS
46
Healing with biohydrogel after 0, 7, 14 days
Maximum crack width healed…
With hydrogel only: 184μm
With biohydrogel: 507μm
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Crack healing ratio: (Wi-Wf)/Wi
100
90
Healing ratio (%)
80
70
R
60
N
H
50
HYU
40
HYUC
30
HSYU
20
HSYUC
10
0
0-50
50-100
100-150
150-200
200-250
250-300
Initial crack width ranges (μm)
300-350
350-400
400-700
Crack healing ratio in the
bacterial series was much
higher compared with R series:
(50% ~ 100%) / (1% ~ 7%)
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SEM
Hydrogel remains
CaCO3 precipitation
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X-ray Tomography (3D)
Before
After
All
Precipitation
precipitation
inside
R
Volume ratio:
0.5%
R+
bio-hydrogel
Volume ratio:
2.2%
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V. CONCLUSIONS
- hydrogels stimulate autogenous healing in fibre
reinforced concrete; cracks of around 150 µm can
be sealed immediately and then healed
- with hydrogels, healing can be obtained without
liquid water
- CaCO3 precipitation by immobilized bacteria can
provide autonomous crack healing, but bacteria
need water to become active
- hydrogels can be used to protect the bacteria and
provide humidity; cracks of 500 µm can be healed
in 14 days time
Magnel Laboratory for Concrete Research
SECEMIN
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FP7 Marie Curie Action:
Training network for self-healing
materials: from concept to
market
FP7 NMP:
Self-healing concrete to create durable
and sustainable concrete structures
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With special thanks to: PhD students and postdocs; technical staff;
FWO, IWT, SIM-Flanders, BOF, EC for financial support
Magnel Laboratory for Concrete Research