NEW GENERATION STAINLESS STEEL AS REINFORCEMENT BAR

NEW GENARATION STAINLESS STEEL REINFORCEMENT BAR FOR CONCRETE STRUCTURE

CONTENTS

Sl. No. Page No.

1 Introduction 2

2 Stainless Steel 4

3 Types of Stainless steel 5

4 Properties of Stainless steel 8

5 Life Cost Analysis of Stainless Steel 11

6 Advantages of Stainless steel 14

7 Applications of Stainless Steel 16

8 Conclusion 22

9 References 23

DEPARTMENT OF CIVIL ENGINEERING 1 M.C.E Hassan.


1. INTRODUCTION

Construction builds the basic framework and infrastructure of a country, which stimulates

further economic, commercial and industrial activities. In building construction role of

steel is same as that of bones in a living being. Reinforced concrete has been used

successfully in the construction industry since the beginning of this Century. One of the

products traditionally used to reinforce concrete is plain carbon steel. At present a large

number of reinforced commercial buildings, domestic dwellings, marine structures,

bridges, etc., are starting to show serious signs of deterioration, particularly those over 30

years of age. This deterioration is mainly caused by corrosion of the reinforcement. This

carbon steel has low strength and poor resistance to corrosion. Hence, carbon steel

corrodes fast and reduces the load bearing capacity of the structure resulting in reduced

life and collapse of the structure in extreme case. This necessitates costly and time-

consuming repairs and maintenance of the structure

1.1 What Causes Corrosion?

Chloride ion is the main culprit. Corrosion of carbon steel rebars is greatly accelerated

when chlorides are present in the concrete (along with the requisite moisture and oxygen

levels to sustain the corrosion reactions). In some parts of the world, chlorides may be

incorporated into the original mix due to their presence in the sand, aggregate or water.

Most often, chlorides penetrate through the "cover" when the external surfaces of the

concrete are exposed to seawater, marine atmospheres or de-icing salts. When steel

corrodes, it forms an oxide layer. These corrosion products-oxides-have a larger volume

than the original steel. This expansion puts pressure on the concrete cover. Since the

concrete is already set and hard, it causes cracks as it expands to accommodate the larger

volume of steel inside. This is the basic phenomenon of cracking or spalling of any

concrete structure. Hence, carbon steel corrodes fast and reduces the load bearing

capacity of the structure resulting in reduced life and collapse of the structure in extreme



case. This necessitates costly and time-consuming repairs and maintenance of the

structure

Deterioration of reinforced concrete caused by corrosion of the carbon steel reinforcing

bars (rebars) is a worldwide problem. Here are some pictures showing the deterioration of

structures due to carbon steel reinforcement

Several methods are currently employed in an attempt to reduce the corrosion of carbon

steel rebars.

Rebar coatings

Increased concrete cover;

Reduced water/cement ratios;

Corrosion inhibiting admixtures added to the concrete mix,



Cathodic protection;

Application of waterproofing membranes, penetrants and sealers on concrete

surfaces,

Electrochemical removal of chlorides.

These methods have their own advantages and limitations, but they all represent

secondary efforts to control the corrosion

However, there is increasing interest in the use of reinforcing materials that have

inherently good corrosion resistance, thus minimizing the need for maintenance and

monitoring of the structure. To address the problem at its source, we must focus attention

on the steel reinforcing bar before it becomes encased in the concrete.

In practice, stainless steel rebar has been used in many concrete structures to provide high

strength and long term resistance to the corrosive attack of chlorides from road salt and

harsh marine environments, as well as chlorides formed by concrete in which the rebar is

buried, and may be the preferred option for bridges that are inaccessible for future

maintenance (i.e. high traffic areas).

2. STAINLESS STEEL

Stainless steel is low carbon steel. Stainless is an alloy of iron with chromium content

over 10.5%. Chromium is the alloying element that imparts to stainless steel their

corrosion resistance qualities by combining with oxygen to form a thin,

invisible, chromium oxide protective film on the surface. This means improved corrosion

resistance, as can be seen in the Fig 1. (Reference 1)

In the event that the protective (passive) film is disturbed or even destroyed, in the

presence of oxygen in the environment, reform immediately and continue to give

maximum protection.

The protective film is stable and protective in normal atmosphere or mild aqueous

environments, but can be improved by higher chromium and by molybdenum, nickel and

other alloying elements. Nickel is added to enhance corrosion resistance and also to



improve engineering properties (cold and hot working, bending, welding etc.). Addition

to molybdenum enhances resistance to pitting.

This film protective layer is Uniform, Stable, Tenacious, Continuous, Self-repairing and

Transparent

Effect Of Chromium

3. TYPES OF STAINLESS STEEL

Austenitic

Ferritic

Austenitic-Ferritic (Duplex)

Martensitic

Some of the commonly used grades of stainless steel for rebar applications are type

304,316(austenitic) and 2205(duplex). The alloy is selected based on mechanical

properties and the expected exposure or corrosivity of the service environment, i.e. the

level of corrosion resistance required.


Fig 1.Corrosion Resistance of Stainless steel


3.1 Austenitic

Austenitic is the most widely used type of stainless steel. It is made by adding nickel

(from 8 to 25 percent) and increasing the chromium level (from 17 to 25 percent).

Molybdenum can also be added (up to 7 percent) to increase the corrosion resistance.

These stainless steels are not magnetic. They can be easily welded. Austenitic have

exceptional resistance to high and low temperatures. The most common example is Type

304 (S30400)-the most widely used stainless steel in the world. The lower carbon

version, Type 304L (S30403) is always preferred in more corrosive environments where

welding is involved. Molybdenum (Mo) is added to some stainless steels to increase their

corrosion resistance, particularly in marine and acidic environments. It increases an

alloy's pitting and crevice corrosion resistance. These corrosion forms are caused by the

common and highly aggressive chloride ion (Cl¯), which is present in salts, such as sea

salt and table salt. When 2-3% molybdenum is added to Type 304 or 304L, we create

Type 316 (S31600) or 316L (S31603) stainless steel. They are sometimes referred to as

the marine grades of stainless steel.

Basic properties:

Excellent corrosion resistance in organic acid, industrial and marine

environments.

Excellent weldability (all processes)

Excellent formability, fabricability and ductility

Excellent cleanability, and hygiene characteristics

Good high and excellent low temperature properties (high toughness at all

temperatures)

Non magnetic (if annealed)

Hardenable by cold work only (These alloys are not hardenable by heat treatment



3.2 Ferritic

Ferritic stainless steel has properties similar to mild steel but with the better corrosion

resistance. These alloys are somewhat less ductile than the austenitic types. These are

plain chromium stainless steels with varying chromium content between 12 and 18%, but

with low carbon content. A commonly used grade is Type 430 (S43000)

Basic properties:

Moderate to good corrosion resistance increasing with chromium content

Not hardenable by heat treatment and always used in the annealed condition

magnetic

Weldability is poor

Formability not as good as the austenitic

3.3 Austenitic-Ferritic (Duplex)

Austenitic-Ferritic (Duplex) Duplex stainless steels have a metallurgical structure that is

a combination of both ferritic and austenitic. They have a high chromium content (from

18 to 26 percent) and a low nickel content (from 4 to 7 percent). Most grades also contain

some molybdenum (from 2 to 3 percent). A common grade is 2205. Nitrogen (N) is

added to some stainless steels, but is very important in duplex grades. It has several

beneficial effects. Like nickel, nitrogen promotes austenite (especially important for

welding) and, like molybdenum, it improves resistance to pitting and crevice corrosion. It

also increases strength. Duplex stainless steels are inherently stronger, but a grade such as

2205, which contains about 0.15% nitrogen, has over twice the yield strength of Type

316L.

Basic properties:

High resistance to stress corrosion cracking

Increased resistance to chloride ion attack



Higher tensile and yield strength than austenitic or ferritic steels

Good weldability and formability

3.4 Martensitic

Martensitic stainless steel contains mostly 11 to 13% chromium and is both strong and

hard with moderate corrosion resistance. Martensitic stainless steels were the first

stainless steels commercially developed (as cutlery) and have relatively high carbon

content (0.1 - 1.2%) compared to other stainless steels. Type 420 (S42000) is a typical

example

Basic properties

Moderate corrosion resistance

Can be hardened by heat treatment and therefore high strength and hardness levels

can be achieved

Poor weldability

Magnetic

GradeUNS No.

Family Crc Nic Moc Nc C(max)

Yield strength MPa (min)b

Tensile strength MPa (min)b

Elong % (min)b

430 S43000 Ferritic 17 0.12 205 450 22

420 S42000 Martensitic 130.15

min1480c 1720 8c

304 S30400 Austenitic 18 9 0.08 205 515 40

304L S30403 Austenitic 18 9 0.03 170 485 40

316 S31600 Austenitic 17 11 2.1 0.08 205 515 40

316L S31603 Austenitic 17 11 2.1 0.03 170 485 40

2205S31803

S32205Duplex 22 5 3

0.1

50.03 450 620 25



b Annealed condition except for grades 420c Typical values

4 PROPERTIES OF STAINLESS STEEL

Physical and Chemical Properties of stainless steel are Presented in the Table 1

(Reference 2)

4.1 Mechanical Properties of Stainless Steel

In terms of mechanical properties, stainless steels can be roughly divided into four groups

with similar properties within each group: martensitic and ferritic-martensitic, ferritic,

ferritic-austenitic, austenitic. The difference in the mechanical properties of different

stainless steels is seen more clearly in the stress-strain curve below Fig 2 (Reference 3d)

From the graph we can say that,

For austenitic grade as ultimate strength increases ductility also increases hence energy

absorbing capacity also increases.

But in case of martensitic as the ultimate strength increases ductility decreases at a very

gradual rate and hence the percentage elongation also decreases


Table 1.Physical and Chemical Properties Of stainless Steel

Fig 2 Stress-Strain Curve


IS STAINLESS STEEL COSTLY?

It is a commonly held perception that stainless steel is "costly". There is only a grain of

truth in this perception because the initial cost of stainless steel products will definitely be

higher. However to work out the cost of ownership and usage over the design life of the

structure, say 50 or 80 years, one has to include the initial cost and add the cost of

maintenance, repair, replacement, downtime and other factors. This method called as the

life cycle costing (LCC) analysis, will show how much the choice of different materials is

actually going to affect the cost of ownership and use of the structure. Viewed in this

manner stainless steel always proves itself to be the most cost-effective choice over the

design life of the structure or the product. The application could be a kitchen utensil, a

railway coach, a handrail or an RCC structure. The end result is always the same stainless

steel is cost-effective to the user.

5. LIFE COST ANALYSIS OF STAINLESS STEEL


UNEXPECTED COSTADDITIONAL OPERATING COSTREPLACEMENT COSTLOST PRODUCTION COSTMAINTANANCE COSTINSTALATION COSYMATERIAL COST

INSTALATION COSY MATERIAL COST


STAINLESS STEEL CARBON STEEL

In developed countries, bridges, which were built about 50 years ago, are crumbling.

Expensive repairs, which cost much more than the original cost of the project itself, are

imposed on hapless governments, which have no other choice. Repairs also lead to large-

scale disruption of traffic, the economy and the lives of the commuting public. Because

of these reasons, they are now specifying stainless steel reinforcement bars for concrete

for such mega projects. (Reference 3b)

Take for instance the repair cost of Old Thane Creek Bridge. A-5 year life extension after

just 10 years of service cost eight times the original cost (800% increase) Partial repair to

Janak Sethu built in 1981 in Delhi cost Rs 32 crore in 1999, whereas the initial cost of the

bridge was only Rs. 9 crore (250% increase).

All of us witness the amount of distress in concrete in infrastructural projects in India.

And at a time when infrastructure is being expanded in our country, introduction of

stainless steel reinforcement bars for concrete may prove to be an ideal solution. We can

also avoid the mistakes committed by the developed countries.

The increase in overall cost of the project by the introduction of stainless steel

reinforcement bars can vary from 0.5% to 15% depending on the design. But given the

huge amount of savings in repair and maintenance, we feel that this increase is nominal

and justified.

Selective substitution: Maximum durability is obtained with total substitution of

stainless steel rebar in the structure. However, recognition of the benefits of using

stainless steel rebar has greatly increased interest in its application and stimulated

research and development activity leading to selective substitution being considered as a

means of achieving enhanced durability at minimum increase in initial cost. For example,



enhanced durability can be achieved by substituting stainless steel for carbon steel rebar

in the parts of the bridge considered to be at high risk to corrosion while the remainder of

the reinforcement will be normal carbon steel. (Schaffhausen Bridge - Only half percent

increase in initial project cost).

The situation with the bridges in Sweden is given in the Fig 4. On an average, most

bridges need a repair between 18-22 years, at an average cost of the original cost of the

bridge itself. If selective use of stainless steel rebar were to be made in the initial stages,

there would have been tremendous savings for the government concerned, and the bridge

would easily last over a hundred years -- trouble free. In the above example, the initial

capital cost increase amounts to 4% for Type 304 and 8% for Type 316

To illustrate the point further, the costs associated with the UK Midlands Link

Viaduct are given:


Actual life costing Example-Oland Bridge, Sweden.

Fig 4


Built in 1972 at a cost of £28 million, evidence of corrosion became apparent

after two years of operation.

By 1989, £45 million had been spent on repair.

By 2010 it is estimated that a further £120 million will be spent on repair.

Estimated first cost of installing stainless steel reinforcement in critical locations

-- £3.4 million (i.e. a 12% increase in the initial cost of the via duct).

The total cost of repair of the carbon steel reinforcement till the year 2010 would

be £45 plus a further £120 million = £165 million or nearly six times the original

cost of building the viaduct. For a 40-year service life of the viaduct, the price to

be paid for not using stainless steel rebar is indeed exorbitant.

Although the initial cost of stainless steel rebar is higher than carbon steel the use of

stainless steel reinforcement in the viaduct would have been an extremely cost effective

solution and an ensured trouble free life for over a century

Marine pier in Progresso, Mexico

The marine pier in Progresso, Yucatan (Mexico), was built in 1937-1941A detailed

account of the history and remarkable performance of this pier has been provided by

Torben Skovsgaard (ARMINOX) and Asger Knudsen (RAMBØLL) in the

August/September 1999 issue of Concrete Engineering International. According to this

publication, the 2.1 km long pier was constructed by a Danish contractor. Stainless

reinforcement (Type 304) was incorporated in view of the severely corrosive exposure

conditions and the relatively high porosity of the concrete.

According to the Progresso Port Authority, no major repairs or significant maintenance

activities have taken place over the lifetime of this structure. In contrast, severe

degradation has occurred on an adjacent pier built much later, in the 1960's, with carbon



steel reinforcement. The photograph shows the destruction of the conventional structure

in the foreground, with the stainless steel reinforced pier in the background.

An excellent comprehensive report on the history, inspection and condition of the

Progresso pier has also recently been published by ARMINOX. This report documents

inspection work performed in December 1998 by RAMBØLL Consulting Engineers and

Planners on the initiative by ARMINOX.

6. ADVANTAGES

The following benefits of stainless rebar inherently good corrosion resistance

Corrosion resistance: Stainless steel's ability to resist corrosion has been well

established in hundreds of applications in numerous industries. When embedded in

concrete, rebar made of S31600, for example, shows superior (five to ten times better)

resistance than that of carbon steel. Stainless steel rebar has been used in several

highway overpasses and parapets in the U.K., Michigan, Oregon, New Jersey, and

Ontario; in concrete structures constructed in aggressive marine environments; and in

the repair and renovation of historic buildings.

Ease of handling and shipping: Unlike coated rebar, stainless steel is much easier

to work with during shipment and while on site. Its inherent protective oxide layer is

resistant to damage; it cannot chip, crack or fail. Stainless steel is also easily welded

and can be bent into desired shapes.

Lighter structure (greater strength): When bridge-builders make use of either

duplex stainless steel rebar or austenitic stainless steel that has been cold-worked,

several design changes are possible. For instance, a thinner concrete cover could

potentially be used on the deck of a bridge (reduced to, say, 50 millimeters), and

because its mechanical properties (specifically, yield and tensile strengths) are

superior to those of carbon steel, smaller-diameter stainless rebar can be employed.



Also, if carbon steel rebar is replaced with stainless steel of a similar size, the space

between the rebar latticework can be widened. Stainless is being considered in many

expansion joint designs as well.

Economical cost (life cycle cost analysis): Bridges constructed of stainless steel

rebar can be expected to last more than 100 years. So when the total cost of repairing

and maintaining carbon steel rebar in a concrete structure over this length of time is

taken into account, the higher up-front cost of stainless is justified. Stainless rebar is

so durable that new high-strength concrete mixes (containing, for example, bentonite,

plasticisers, superplasticisers or polypropylene) would likely be used in conjunction

with the stainless rebar to utilize its long-life potential. Also, to reduce costs, stainless

steel may be used only in those areas of a structure where carbon steel is judged to be

at high risk of corroding.

Fire and heat resistance: Special high chromium and nickel-alloyed grades resist

scaling and retain strength at high temperatures.

Impact resistance: The austenitic microstructure of the 300 series provides high

toughness, from elevated temperatures to far below freezing, making these steels

particularly suited to cryogenic applications

Environmentally friendly: Once their service is complete, they should be 100%

Recyclable, thereby completing the life cycle to be used once again. Stainless Steel is

such a material. The longevity of stainless is the result of the alloying composition

and, therefore, it has a natural corrosion resistance. Nothing is applied to the surface

that could add additional material to the environment. It does not need additional

systems to protect the base metal; the metal itself will last. Stainless steel products

complete their service life. There is less concern about disposal since this material is

100% recyclable. In fact, over 50% of new stainless steel comes from old remelted

stainless steel scrap, thereby completing the full life cycle.

Durability: In composite structures like RCC bridges, 125 years of trouble-free

service life can be guaranteed if stainless steel rebar is used



Available in many different product forms - plates, sheets, strips, bars, rods, wires,

wire products, tubes, angles, sections, fasteners, castings, extrusions etc.

Good strength

Good weldability for common rebar grades

Good ductility for common rebar grades (capable of 3D 180E bends)

No coatings to chip, crack, deteriorate

No coatings to damage and repair

Good mechanical properties for common rebar grades at high and low temperatures

7. APPLICATIONS

Possible applications for corrosion resistant stainless rebar could include

A host of marine structures such as bridge decks, sidewalks, ramps, parapets, pilings,

barriers, retaining walls, anchoring systems, parking garages, sea walls, columns,

piers, jetties and moorings

Supports for reinforced concrete (i.e., bridge decks)

Balconies and frames for front-elevation units

Anchorages and any kind of joints

Offshore platforms

Framers and anchorages for damp environments, tunnels, Underpasses and subways

Bridges, viaducts, overpasses

Cement frameworks with magnetic characteristics

Frameworks which are prone to breaking up due to frost or because of low

temperatures

Concrete slabs for drainage in environments with corrosive agents

Supports/restoration for statues, monuments, cement, stone and marble works



Stainless steel rebar applications in various countries is listed below

1) The marine pier in Progresso, Yucatan (Mexico), was built in 1937-1941.

2) A coastal replacement bridge under construction at North Bend, Oregon has used

2205 stainless steel rebar instead of carbon steel rebar for critical structural elements

in a harsh marine environment. Oregon Department of Transportation (ODOT),

which has chosen to use 2205 duplex stainless, expects the new bridge to provide

maintenance-free service for an amazing 120 years. That is 2.5 times the service life

of the bridge it is replacing!

3) New Haynes Inlet Slough Bridge

Completed state of the New Haynes Inlet Slough Bridge from north bank of the inlet,

with retired timber trestle bridge at right and contractor's partially dismantled work

bridge in left background.



4) More than 75 tons of Type 316LN stainless rebar was used for the Brush Creek

highway bridge in Oregon (1998).

5) 165 tons of 2205 (duplex) stainless rebar were supplied for the new ramp of the

Garden State Parkway in New Jersey (1998).

6) Nuclear Plant in France: Stainless steel has been used to build ferroconcrete drums

for disposal of radioactive nuclear wastes. In this application, for safety reasons, is

mandatory the use stainless steel in order to avoid cracks in the concrete (caused by

reinforcing bars corrosion) and subsequent waste leaking

7) Stainless steel reinforcement has been used in order to minimize future maintenance

work of the buildings. The Guildhall Yard East project in London, England (1996),

one of the most famous historic buildings in the center of the City of London utilized



over 140 tons of Type 304 rebar. Although the new structures will not be exposed to de-

icing salts or a marine environment, the design engineers were looking for a very long

design life, in keeping with the famous historic buildings on the site

8) 240 tons of Type 316 stainless steel rebar used in the road slab of an underpass at

Cradlewell, UK (1995).

9) 46 tons of austenitic stainless rebar were used in a new laboratory building of the

National Physical Laboratory in Teddington, United Kingdom. The austenitic grade

reportedly used was 316S33 ribbed bar, in accordance with BS 6744. Sizes ranged from 8

to 40 mm diameter, with a dominant size range of 10 to 12 mm diameter.



Stainless steel is also used in restoration works

10) Colosseo, Roma - Italy

The work involved the partial restoration of the arena floor. The foundations in roman

concrete were reinforced by stainless steel ribbed bars type AISI 304L in diameters 6, 8,

10, and 14 mm. The Archeological Superintendence of Rome supervised the works.

11) Rocco Church, Dolo, Venezia - Italy

The work of restoration was realized employing stainless steel as the wall tie for the

supporting structure.

12) San Benedetto Po bridge, Mantova - Road 43, Romana, Anas Milano Italy

Maintenance work in the foundation decks and piers of the reinforced concrete bridge.

The Stainless steel reinforcing was joined with existing mild steel reinforcing.



13) Glandstone Bridge, Queenslans, Australia

The Gladstone Bridge was built in 1960 and showed corrosion of the reinforcing mild steel

on the deck. The maintenance works have seen the use of 12 mm diameter stainless steel

ribbed bars type 316L joined with the original carbon steel

14) Stainless steel rebars were used in a Sea-front building restoration in Scarborough,

UK (early 1980's). They were selected for stabilization of the sea wall, in-situ concrete

on the promenade, and pre-cast units around the main entrance. Type 316 stainless steel



rebar was utilized immediately adjacent to the sea, while Type 304 stainless reinforcing

was applied further inshore. Conventional rebar was used well back from the sea front.

8. CONCLUSIONS

The primary intention of this paper is to create awareness on the substantial advantage

one can get by using stainless steel as reinforcement in concrete structures.

The following are the conclusions drawn from the study,

Despite the initial cost, there is considerable potential in savings of life cycle cost,

especially infrastructures, which are exposed to corrosive environment.

Best suited material at all temperatures. Also stainless steel are suited for

cryogenic applications.

Available in different grades and hence significant savings can be done.

Also the material is available in different forms, which is more advantageous.

Material is new generation and environmental friendly hence can be very rightly

utilized as a new generation material for all applications.



9. REFERENCES

1. K Mani and P Srinivasan-“Service life of RC structures in Corrosive Environment: A comparison of carbon steel And Stainless steel Bars”- Indian Concrete Journal, Volume 75,1-12,2001.

2. Y Sakumoto, T Nakazato and A Matsuzaki- “Properties of Stainless Steel For Building Structures”- ASCE Journal Of Structural Engineering, Volume 122,1-6,199

3. Web Site References:

a. Use of Stainless Steel Reinforcement Bars for Concrete Structures-By Dr. N.C Mathur (President), Ramesh R Gopal (General Manager), Nickel Development Institute & Secretary Indian Stainless Steel Development Association, 55-A, Uday Park (ff) Khel Gaon Marg, New Delhi - 49(Published in New Building Materials & Construction World - September 2000)



b. www.ISSDA.com-Stainless Steel Assures Durability And Enhances Aesthetics Of Structures-By Ramesh R Gopal, Secretary, ISSDA and General Manager of NiDi.

c. www.SSINA.com- Stainless Steel Bridge-New Bridge Uses Stainless Steel Rebar To Last 120 Years, CNC West Feature Article, August • September 2002 • Vol. XX No. 6 • An Arnold Publication

d. www.Outokumpu.com

e. www.sustainable-development.gov.uk

f.www.Key-to-Steel.com


http://www.sustainable-development.gov.uk/

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NEW GENERATION STAINLESS STEEL AS REINFORCEMENT BAR