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: [email protected]
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:
