Stainless Steel Reinforcement is the best in class solution for
building sustainable concrete constructions in an almost endless range of
applications. deliver, durable, corrosion and maintenance free stainless
steel concrete reinforcement solutions.
EN 10088-1:2005 Stainless Steels:
List of Stainless Steels
•
Stainless Steels are defined as…
• “as steels with at least 10.5 % of chromium and maximum 1.2 % of
carbon”
Corrosion of Concrete Reinforcement
Carbon steel reinforcement in concrete will not normally corrode due to the
formation of a protective oxide film (passive layer) on the steel surface.
This passive layer is as a result of the strong alkaline conditions found within
concrete (typically pH13-14).
However, loss of passivation can occur as a
result of:
• Carbonation of the concrete
• High level of chlorides in the concrete at
the rebar surface
•
Key properties of Stainless rebar; The chromium oxide formed after the
pickling of the stainless rebar is passive and will not corrode in concrete
regardless of alkalinity given no other corrosive conditions.
The high alkalinity of concrete offers carbon steel
protection through a passive film
•
The passive oxide layer breaks
down because of two
mechanisms
•
Carbonation of concrete
•
•
•
The ingress of carbon dioxide
from the atmosphere
Causes the lowering of the
alkalinity of the concrete to the
point where the oxide layer is no
longer passive
Chloride attack
•
Ingress of chlorides from
•
Chlorides build up to a
concentration at the surface of
the film that breaks it down
This is known as the Critical
Chloride Threshold Level (CCTL)
•
• sea water or
• De-icing salts on the roads
Chloride Transport Processes in
a Marine Environment
• Diffusion
As a result of a concentration gradient
• Permeation
Occurs when there is a pressure difference
or hydraulic gradient
• Capillary Absorption
Capillary absorption occurs where liquids
are sucked into empty pores at the contact
surface
• Wick Action
A form of capillary absorption. Occurs
where the lower part of an element is in
contact with water and the upper part of
the same structure is exposed to a strong
drying environment. This is of particular
concern in predominantly hot, dry areas
such as the Middle East.
About SSR
• SSR’s passive layer remains
passive regardless of the alkalinity
of the concrete
• SSR is therefore resistant to
carbonation
• SSR can tolerate chloride levels 10
times higher than carbon steel
• These levels can rarely be reached
• SSR is used selectively where the
chlorides can reach the carbon
steel but won’t affect the stainless
steel
In-solution CCTL
• Experiments in synthetic pore solutions with
incremental chlorides (room temp., +200mVSCE)
12,00
10,00
CCTL / wt%
8,00
6,00
4,00
2,00
0,00
4311
4436
LDX 2101®
2304
2205
Carbon Steel
In-solution CCTL with a 90% probability
In-concrete CCTL
•
One step further to the real environment… in
cement with fixed chloride level (4weight% by
mass of cement, room temp., +200mVSCE)
4311
4432
LDX 2101®
2304
CS
Number of tests
10
12
13
12
3
Number of tests approved
10
9
11
11
0
Number of tests failing
0
1
1
0
3
Stainless steel designation
Bi Metallic Corrosion (Galvanic Coupling)
When both are embedded in concrete, the use of stainless steel lapped with carbon
steel rebar does not lead to an increase in the corrosion rate of the carbon steel
compared with carbon steel used alone.
Why?
If the carbon steel rebar is outside of the corrosion zone, it is passive.
If designed correctly, the stainless steel rebar is passive wherever it is.
Passive + Passive means no current and no corrosion!
Active (corroding) carbon steel coupled with stainless steel rebar produces less
coupling than active carbon steel with passive carbon steel because stainless steel is
a poor cathode in concrete when compared with carbon steel rebar.
Reference Documents and Reports
•
•
•
•
The Concrete Society Technical Report TR51: Guidance on the use of stainless steel reinforcement
Nordic Innovation Centre: Guide for the use of stainless steel reinforcement in concrete structures
British Stainless Steel Association: Stainless Steel Reinforcement for Concrete
Effects of Galvanic Coupling between Carbon Steel and Stainless Steel Reinforcement in Concrete:
Bertolini, Gastaldi, Pedeferri and Pedeferri
Plus many others!
Lean Duplex LDX2101® (1.4162 EN or S32101 UNS)
•
LDX 2101® is Outokumpu’s new low
nickel proprietary duplex designation
•
21% Chrome means excellent
corrosion resistance
•
Max. 1.7% Nickel means LOW and
STABLE price
•
Included in BS6744 2009 amendment
as 1.4162
•
Reported by potentiostatic methods to
have corrosion resistance higher than
1.4301(304) stainless steel
Steel
Number
Common
Name
Cr
1.4311
1.4436
1.4462
1.4162
1.4362
304 LN
316
2205
LDX2101
2304
Price
Ratio
Typical analysis
Ni
N
18.3 8.3 0.07
17.3 11.2 0.03
21.3 4.6 0.15
21.5 1.5 0.22
22.7 4.7 0.15
Mo
0.0
2.6
3.1
0.3
0.3
133%
175%
175%
100%
112%
Difference between carbon steel and
SSR
Microstructure LDX 2101® versus 1.4301
Duplex
=
high strength
Austenitic
=
high ductility
Mechanical and Corrosion Properties
Rp0.2 [MPa]
750
[%]
LDX 2101
C
N
Cr
Ni
Mo Mn
0.03
0.22
21.5
1.5
0.3
5.0
Duplex
SAF2507
650
LDX 2101
500
2304
2205
Austenitic
254SMO
C Staal
304
316
904L
Corrosion resistance 
Life Cycle Costs
Fib Bulletin 49 Corrosion Protection of Reinforced Steels
Cost analysis given of a highway bridge in Schaffhausen, Switzerland
Stainless steel rebar was used selectively in
• Bridge deck longitudinal beams – subjected to splashing by de-icing salts.
• Bottom 7.6m of the bridge pylon – subject to sulphates from the salt water.
Conclusions of the life cycle cost analysis
• The selective use of stainless steel reinforcement led to a 0.5% increase in the total
bridge cost.
However …
• Total life cycle costs over the full design life time period resulted in a 13% cost reduction.
“Although the initial cost of stainless steel is much higher than that of carbon steel. Its
use can be justified on the basis that the increase in total project cost is small and is
easily overtaken by the benefits of lower maintenance and repair costs, particularly
where disruption times and cost of such work are taken into consideration”
Straight Lenghts & Cut & Bend Facilities
1.4162
LDX 2101®
1.4311
Low Magnetic
1.4362
Duplex
According to BS6744: 2001+A2
Range Nominal size, mm straight lenghts
Grade 500: Length 6 and 12 mtrs. Ø 6, 7, 8, 10, 12, 14, 16, 20, 25, 32, 40 mm
Grade 650: Length 6 and 12 mtrs. Ø 6, 7, 8, 10, 12, 14, 16, 20, 25, 32, 40 mm
What about ….
Epoxy Coated Reinforcement: High risk of damage during transport,
handling, construction, cut & bend. Not used in Europe, banned in the
UK, starting to get banned in the USA due to high level of corrosion
problems & repair costs involved. Low Chloride resistance. No advantage
over carbon steels but almost twice the price !
Galvanized Steel Reinforcement: damage of the zinc surface during
cut & bend, transport, construction and welding. Still low chloride
resistance. Banned in cut and bend shapes in German Standards. Hardly
any advantage over carbon steels with a 50/60% higher price level.
GRP Glass fiber Reinforced Plastic: No cut & bend or only against
reduced strength by prefab forming before cooling down, limited
fire resistance, total different design required, no compressive
strength, easy to damage, risk for alkali silica reactions, overall
limited use, price comparable with stainless steel.
Resume
Chloride induced corrosion of rebar is the main reason why concrete structures fail
in the world today !
Traditional durability measures in structural codes of practice have been
found to be inadequate in high chloride environments:
The selective use of stainless steel reinforcement can prevent corrosion occurring!
• Will not corrode in carbonated concrete
• Has a chloride threshold level at least 10 times than of carbon steel in concrete
• Predictive modelling is used now as a tool for assessing the levels of
chloride at depth and with time, within the concrete
• The introduction of lean duplex steel designations will make stainless rebar an
even more cost effective solution to durability