In droplets of polar solvents In layered double hydroxides (LDH)

In silica nanospheres Or as such

Development and study of

self-healing coatings for reinforced concrete

Hilke Verbruggen1, Gavin Hill², Hubert Rahier², Herman Terryn1, Iris De Graeve1

1 Research Group of Electrochemical and Surface Engineering (SURF),

² Research Group of Physical Chemistry and Polymer Science (FYSC),

Vrije Universiteit Brussel (VUB), Pleinlaan 2, B-1050 Brussels, Belgium

E-mail: hilke.verbruggen@vub.ac.be

INTRODUCTION & OBJECTIVES Development and testing of a SH coating for application on

1

2

the exterior surface of reinforced concrete

containing encapsulated materials for filling or

healing surface coating, and that would be suitable

for use under different environmental

conditions, for example underwater.

the steel rebars inside the concrete 2 1

CAUSES OF CORROSION IN REINFORCED CONCRETE

In an ideal situation concrete has a pH of 12-13. In such an alkaline

environment steel is passivated. However the passive layer can break down as

a consequence of:

chloride ingress

pitting corrosion

carbonation (causing a drop in pH)

uniform corrosion

INHIBITOR EVALUATION BY LINEAR SWEEP VOLTAMMETRY

The two “critical” situations in which the inhibitor should act are

simulated by two different electrolyte solutions:

A concrete pore solution of pH 13

with 2 wt% NaCl (CPS 1_2)

A concrete pore solution of pH 9 without NaCl (CPS 2_0)

simulating pitting corrosion

simulating uniform corrosion

BTA (1H-benzotriazole)

DT (2,5-dimercapto-1,3,4-thiadiazole)

MBT (2-mercaptobenzothiazole)

NaMoO4

Ce(NO3)3

BTA (1H- benzotriazole)

DT (2,5-dimercapto-1,3,4-thiadiazole)

MBT (2-mercaptobenzothiazole)

NaMoO4

Ce(NO3)3

OCP= -0,343 vs -0,373 V

OCP= -0,391 vs -0,490 V

INHIBITOR INCORPORATION BY ENCAPSULATION

+: droplets will break for sure - : might dissolve part of the coating

+: controlled release - : compatibility problem with coating

+: controlled release - : compatibility problem with coating

+: no need for (complicated) encapsulation procedure - : spontaneous leakage, possible reaction with the coating

A shift to a more positive breakdown potential and a more noble OCP

Pourbaix diagram http://chemwiki.ucdavis.edu

100 nm

Scans taken from +-10 mV to -+ 1,6 V vs OCP, with a step of 1 mV and a scan rate of 2 mV/s

CAPSULES FOR COATING REPAIR FOR CONCRETE SURFACES

Encapsulation science is well established.

Need: Capsules which will meet VOC safety standards.

Problem: PU capsules require Aryl Halide Solvents

HO OH

OH

+

N=C=O

O=C=N

MEKPrepolymer

65 °C

Prepolymer + Solvent (Cyclohexanone or Chlorobenzene)

Encapsulation

2) Prepolymer + Solvent + Core

3) Comonomer or chain extender

1) Aqueous stabilizer/surfactant solution

For encapsulation of isophorone diisocyanate (IPDI) foaming agents,

switching to styrene/divinylbenzene or chloromethyl

styrene/divinylbenzene and carrying out a post-curing radical

polymerization which removes solvent and re-inforces capsules

Capsules contain > 80 wt% IPDI (DSC)

Shelf-life > 6 months

High yields at labscale ~ 80 g per batch

Refinement of particle size needed.

BIODEGRADABLE/BIOCOMPATIBLE CAPSULES FOR NATURAL PROTECTION

Synthesis of biodegradable prepolymers based on polylactic acid (PLA),

polyglycolic acid (PGA) and polycarpolactone (PCL) systems.

Scratch coating Agent Plugs Scratch

T=days T=Weeks

Decomposition of

Shell attracts

bacterial growth

Avoid Aryl Halides!

1,00E-11

1,00E-10

1,00E-09

1,00E-08

1,00E-07

1,00E-06

1,00E-05

1,00E-04

-2,2 -1,2 -0,2 0,8

Log

curr

en

t d

en

sity

(A

/mm

²)

E (V vs Ag/AgCl)

CPS1_2 with

10-4 M NaMoO4

Reference CPS1_2

(without inhibitor)

A shift to lower current densities, and a more noble OCP

1,00E-12

1,00E-10

1,00E-08

1,00E-06

1,00E-04

-2 -1,5 -1 -0,5 0 0,5 1 1,5

Log

curr

en

t d

en

sity

(A

/mm

²)

E (V vs Ag/AgCl)

Reference CPS1_2

(without inhibitor)

CPS1_2 with

10-4 M NaMoO4

to protect the steel against corrosion by

incorporating eco-friendly corrosion inhibitors, and

to heal local coating damages and regain the barrier

properties by incorporating healing/plugging agents

Department of Physical Chemistry and Polymer Science

2- Step Protection: