Protection from corrosion

PROTECTION FROM
CORROSION
TESSIN PAUL
S2 M.TECH
SECM
S.J.C.E.T
KOTTAYAMADVANCED CONCRETE TECHNOLOGY1

CONTENTS
INTRODUCTION
METHODS OF CONTROL
ADVANCED CONCRETE TECHNOLOGY
2

INTRODUCTION
CORROSION-destruction or deterioration
– materials in environments to which they
are exposed
40% -failure of structures is due to
corrosion of embedded steel in concrete
Therefore, corrosion control- important
3

GENERAL CONTROL
 First –good quality of concrete through good
construction practices should be produced.
 It begins at the stage of choosing constituent
material and includes good rules to be followed
during various stages of production of concrete.
 Proper mix design, use of right quality and
quantity of cement for different exposure
conditions is to be adopted.
4

 Lower w/c ratio and lower permeability is not enough to
make impermeable concrete with high durability.
 Therefore, supplementary cementitious materials
such as fly ash, ground granulated blast furnace
slag(ggbs),silica fume, etc. are used as admixtures/ in
the form of blended cement along with lowest possible
w/c ratio to make concrete dense.
 These improve properties of concrete which will
eventually reduce corrosion of reinforcement.
 GGBS- reduces water permeability by a factor upto
100, -reduces diffusion of chloride ions
 Silica fume- contributes to all round improvements in
quality of concrete- esp. improvement in microstructure
of hydrated cement paste-protects from corrosion
5

OTHER METHODS OF
CONTROL
 If we make good concrete with low permeability and improved micro-
structure, it will be durable by itself and reinforcement is protected to
a great extent.
 But such ideal concrete production is not possible always.
Further, the inherent long term drying shrinkage and micro-cracks in
concrete, the problems become more serious.
 So, different methods of control are adopted.
]They are:
1. METALLURGICAL METHODS
2. CORROSION INHIBITORS
3. COATINGS TO REINFORCEMENT
4. CATHODIC PROTECTION
5. COATINGS TO CONCRETE
6. DESIGN AND DETAILING
6

1.METALLURGICAL METHODS
 Steel can be made corrosion resistant- by
altering it’s structure through metallurgical
processes.
 Different methods:
 Rapid quenching of hot bars by series of water
jets
 Or by keeping the hot steel bars for a short
time in a water bath
 Or by using stainless steel reinforcements
7

2.CORROSION INHIBITORS
Corrosion can be prevented or delayed by chemical method by using
certain corrosion inhibiting chemicals like the following:
 Nitrites and nitrates- efficient inhibitors of corrosion in autoclaved
products
 Sodium nitrate : 2-3% by weight of cement
 Calcium nitrite: most widely used, 10-30 litres per m3 of concrete
and on addition of calcium nitrite increases the corrosion threshold-
i.e, if 20 litres/m3 is added, corrosion will not begin until over 7.7
kg/m3 of chloride is present in the concrete at rebar
 Benzoates: either2 %sodium benzoate(also an accelerator of
compressive strength) is used in the mixing water or a 10%
benzoate cement slurry is used to paint the reinforcement or both
 Phosphates
8

2.CORROSION INHIBITORS(contd.)
 In the high pH of concrete, steel is protected by a
passivating layer of ferric oxide on the surface of
steel.
 It also contain some ferrous oxide which can
initiate corrosion when the chloride ions reach the
steel.
 The nitrite ions present in the admixture will oxidise
the ferrous oxide to ferric oxide, thus stabilising the
passivating layer even in the presence of chlorides.
9

3.COATINGS TO
REINFORCEMENT
 Coatings provide a durable barrier to aggressive
materials such as chlorides
 They should be robust to withstand fabrication of
reinforcement cage and pouring of concrete, and
compaction by vibrating needle
Methods:
i.Simple cement slurry coating is used for
temporary protection against rusting of reinforcement in
storage.
10

3.COATINGS TO REINFORCEMENT(contd.)
ii. Central Electro Chemical Research Institute(CECRI)-
patented a method and it involves the following steps:
 Derusting- Reinforcements are cleaned with a derusting
solution and then by wet waste cloth and cleaning
powder. Then rinsed in running water and air dried.
 Phosphating- Phosphate jelly is applied to bars with fine
brush-left for 45-60 minutes and then removed by wet
cloth. Then an inhibitor solution is brushed over the
surface.
11

3.COATINGS TO
REINFORCEMENT(contd.)
ii.CECRI Method(contd.)
 Cement coating- A slurry is made by mixing the
inhibitor solution with Portland cement and applied on
the bar. a sealing solution is brushed after the rods are
air cured. The second coat of slurry is then applied and
the bars are air dried.
 Sealing- two coats of sealing solution are applied to
the bars to seal the micro-pores of cement coat and to
make it impermeable to corrosive salts.
Limits: Doubts the efficacy of the method
12

iii. Fusion bonded epoxy coating:-effective method of
coating rebars-used for structures like flyovers
 Plants are specially designed to coat straight bars in a
continuous process.
 Initially- bar is shot blasted to remove all mill scale and to
give the required surface finishing and ensures adequate
bond between epoxy and steel.
 Then bar is heated carefully to a controlled temperature,
before passing through a spray booth.
 Now, electrostatically charged epoxy powder particles are
deposited evenly on the bar surface- gives a greenish
colour
 Coating thickness: 130-300 microns
13

Limits Of Fusion Bonded Epoxy Coating:
 Cutting and bending may injure steel which needs site treatment
 Any defects in treated body can induce severe localised
corrosion
 Bars cant be welded
 Not resistant to UV rays of sun and shouldn’t be exposed to sun
before use
 Coating gets damaged during vibration of concrete
 Very costly
iv. Galvanised reinforcement- consists of :
 Dipping steel bars in molten zinc
 Coating will be bonded to the surface of steel
 Zinc surface reacts with calcium hydroxide in concrete to form a
passive layer and prevents corrosion
14

4.CATHODIC PROTECTION
 Its one of the effective – extensively used
method- in advanced countries
i.Cathodic protection:
-it is the application of impressed current to an
electrode laid on concrete above steel
reinforcement
-electrode acts as anode(it undergoes
corrosion) and steel acts as cathode
-here, -ve cholride ions responsible for damage
of passivating film are driven away from steel to
anode
15

ii.Realkalisation process-
 makes concrete alkaline again and passivate
the reinforcement steel by electro chemical
method
 Brings back the lost alkalinity-maintains the
passive layer
Iii.Desalination process-
 Chloride ions are removed from concrete
-esp. from steel by electrical method-to re-
establish the passive layer
16

5.COATINGS TO
CONCRETE
 In addition to coating steel- concrete is also coated- for
protection and decoration
 For bridges, flyovers, chimneys, etc.
 They are coated with epoxy or like materials–allowing
concrete to “breathe”to seal off and prevent
internal moisture from going out w.r.t atm.conditions
and preventing water to enter it
 Acrylics-based coatings are also given
Limits:
 Epoxy –not resistant to UV while acrylics –resistant
 Acrylics- provides decoration alsoADVANCED CONCRETE TECHNOLOGY
17

6. DESIGN AND DETAILING
 Nominal cover to rft. :
 Cover not less than 40 mm or less than the
dia. Of bar
 For columns- min. 200 mm or under: bars
less than 12 mm- 25 mm cover is used
 Footings- min. over 50 mm
18

6.DESIGN AND DETAILING(CONT.)
 Cover region concrete – likely to have wall
effect- so colloidal agents or anti-washout
agents or anti bleeding admixtures are used
to eliminate phase separation problems
 Adopt permeable formwork technique-
covercrete-like vaccum dewatering technique
19

REFERENCE
 Concrete technology/M.S. Shetty
20

THANK YOU
21

Protection from corrosion

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Viewers also liked

Viewers also liked (9)

Similar to Protection from corrosion

Similar to Protection from corrosion (20)

Recently uploaded

Recently uploaded (20)

Protection from corrosion