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Superabsorbent polymer (SAP) for
self-healing concrete
JEONG Yeonung, Ph.D.
Research Fellow
National University of Singapore
Content
1. Background
2. Concept of self-healing concrete
3. Introduction to SAP
4. Absorption kinetics of SAP
5. Experimental results
6. Summary
BackgroundH2O
Cl-
SO32-
=> serious durability problems
+
+
Time
Concept of self-healing concrete
Self-healing concrete is a concrete which heals itself when it comes
in contact with air, water, or specific agents.
Example of self-healing concrete
using an expansive agent and
an active geo-material
T.-H. Ahn and T. Kishi, (2010)
J. Adv. Conc. Tech. 8(2), 171-186
Crack healing by formation
of C-A-S-H gel
Concept of self-healing concrete
► Various approaches of self-healing concrete
Approach Strategy
Autogenous healing - Hydration of unhydrated cement particles
- Dissolution and carbonation of calcium
hydroxide
- SCMs and expansive agents
Vascular healing - Vascular approach
Shape memory
materials
- Shape memory alloy (SMA)
- Shape memory polymer (SMP)
Capsule-based system - Encapsulation of chemicals
- Encapsulation of bacteria
Concept of self-healing concrete
► Autogenous healing concept
V. Li and E. Herbert, (2012)
J. Adv. Conc. Tech. 10, 207-218
▪ Good compatibility with cement
matrix
▪ High amount of cementing
components and water supplies
are required
▪ Healing performance highly
depends on age of concrete
Concept of self-healing concrete
► Vascular healing concept
K. V. Tittelboom and N. D. Belie, (2013)
Materials 6, 2182-2217
▪ Large amount of healing agent
can be supplied
▪ Difficult to cast network of tubes
on large scale
▪ Introduction of supply tubes
may weaken the concrete
structures
Concept of self-healing concrete
► Shape memory materials
G. Song et al., (2006) Eng. Struct. 28(9), 1266-1274
▪ Effectiveness under multiple damage events
▪ Significantly cost intensive
▪ Heating and shrinkage can lead to uncertainties
Concept of self-healing concrete
► Capsule-based system
K. V. Tittelboom and N. D. Belie, (2013)
Materials 6, 2182-2217
▪ Healing agents release on
necessity
▪ Difficulty in casting
▪ Negative effect on the
mechanical properties of the
cement matrix
Introduction to SAP
Structure of sodium polyacrylate after absorption [by BASF]
Superabsorbent polymer (SAP) is a hydrogel having the ability to absorb water up
to 1000 times of its own weight.
Most (>95%) of SAP is used for disposable diapers.
Global demand (in 2016): 2.4 million tonnes.
Price (in 2014): $2.9-3.1/kg (in the US), €2.07-2.22/kg (in Germany) and ¥15.5-16.7 (in
China).
SAP used for diaper
×200 times
Absorption kinetics of SAP
Osmotic
pressureLoss of
internal RH
(a) (b) (c)
First minutes Until initial setting After few days
“Absorption” “Desorption”
A new method to determine absorbency of SAP in cementitious materials
Tea-bag
test
Conventional method (Schröfl et. al., CCR,
2012)New method (Kang et. al., CCR, 2017)
External
solutionFiltrated cement slurry (w/c=4.3)
Artificial pore solution
(which reflects cement pore solutions)
Revomal of
excessive
solution
Gently wiping with a towel Centrifugation with 1000 rpm
Absorbency = (Wswollen SAP - Wdry SAP) / Wdry SAP
Absorption kinetics of SAP
0
5
10
15
20
25
0 10 20 30 40 50 60 70 80 90 100110120130140150160170180
Ab
so
rben
cy [
g/g
]
Absorption time [min]
y = 0.25x - 0.28R² = 0.96
0
10
20
30
40
50
60
70
80
90
0 50 100 150 200 250 300
Excess s
olu
tio
n r
ati
o [
g/g
]
Absorbency by conventional method [g/g]
0
5
10
15
20
25
30
35
0
50
100
150
200
250
0 10 20 30 40 50 60
Ab
so
rben
cy (
in s
olu
tio
n)
[g/g
]
Ab
so
rben
cy (
in D
I w
ate
r) [
g/g
]
Absorption time [min]
Modified tea-bag test
Excess solution ratio in the conventional method Reproducibility of the new method
SAP in filtrated
cement slurry
(w/c=4)
SAP in
artificial pore
solution
Different sorption kinetics of SAP depending on external solution (by new method)
Experimental results
• UHPC structures can be used for 100-200 years.
• Therefore, it has to be maintained for a long period. Durability
• UHPC structure is very thin and slender.
• Thus, micro-cracks can affect the structure’s performance.Strength
• About half of cement does not hydrate, but merely acts as an expensive filler.
• This is due to the lacks of available space and water for hydration.Mix proportion
Necessity of self-healing in UHPC
Self-healing can be achieved by water released from SAP, consuming unhydrated
cement particles and filling micro-cracks with newly formed products.
The self-healing can contribute to a more sustainable use of UHPC.
Sample OPCSilica
fume
Silica
flour
Fine
aggregateW/C
SPPL
(PCE)SAP/C
Steel fiber
[Vol.%]
Slump flow
[mm]
UHPC
1 0.25 0.35 1.1
0.215
0.04
0
2
750
UHPC_SAP1 0.255 0.4% (AA) 800
UHPC_SAP2 0.275 0.3% (AM) 700
Mix proportion of UHPC with or without SAP
Experimental results
w/o SAP
Promotion of hydration
w SAP
Initial
setting
0
0.01
0.02
0.03
0.04
0.05
0.06
0.07
0.08
1 100 10000 1000000
Log
diffe
ren
tia
l in
tru
sio
n [m
L/g
]Pore size diameter [nm]
Pore refinement
w SAP
w/o
SAP
Application of SAP promotes hydration of cement, reducing UHPC
porosity.
Kang et.al., under review in CCR Kang et.al., under review in CBM
Experimental results
Effect of SAP on compressive strength and durability
0
20
40
60
80
100
120
140
160
180
0 7 14 21 28
Co
mp
ressiv
e s
tren
gth
[M
Pa]
Time [d]
Ref_0.215 [D]
AA_0.255 [D]
AM_0.275 [D]
w/o
SAPw SAP
UHPC
(98 columbs)
UHPC_SAP1
(351 columbs)
UHPC_SAP2
(122 columbs)
Charge passed
(Coulombs)
Chloridepermeability
Typical of concrete
>4,000 HighHigh W/C (>0.60) conventional PC
Concrete
2,000∼4,000
Moderate
Moderate W/C (0.40–0.50)
conventional PC Concrete
1,000∼2,000
LowLow W/C (<0.40) conventional PC
Concrete
100∼1,000
Very Low
Latex-modified concrete or
internally-sealed concrete
<100 Negligible
Polymer-impregnated
concrete, Polymer concrete
Kang et.al., under review in CCR
Summary
Concepts of various self-healing approaches are introduced.
For several years, our group has studied on the application of SAP in
UHPC, especially for its mix design, internal curing and self-healing
capacity.
Self-healing is a potential way to make UHPC more sustainable.
SAP can be a promising and practical material when considering its
absorption capacity, productivity and reasonable price.
The use of SAP in UHPC has no negative effects on strength and
durability, while it improves the microstructure of UHPC.
Thank you