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