Painting of Bridges

7/23/2019 Painting of Bridges

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Painting of Bridges

G.Radhakrishnan, SE/Bridges/MDU

STEEL GIRDERS

Maintenance painting scheme is as per IRBM-1998 common to all Zones& Diagram No.53 for respective Zone and new girder painting is as per IRS-B1specifications. With all that our painting scheme is mainly based on coastal &non-coastal areas.

Corrosion map was published in India during the year 1968 and inSouthern Railway, the coastal areas were identified & circulated vide HQLetter No.W.310/5 dt.27.08.86.

Present scenario

While high corrosion is normally expected in coastal areas, the firstphase of the nation-wide survey done during 2005 by NCCI & CECRI has shownthat Mettupalayam, a town in interior Tamil Nadu state, is one of the fiveplaces in the country where corrosion is "extremely severe."

In the case of Mettupalayam, though it is considerably inland, it wasfound that a combination of rainfall, relative humidity and industrial pollutionhad been its bane,

It contains a warning for other industrialised zones too

The four other towns in this "extremely severe" category areSriharikota, Chennai, Marmugoa and Port Blair - all in the coastal region.

Mumbai, Mangalore, Kochi and Tuticorin are places where corrosion is"severe" but not "extreme" while Kanyakumari is among the towns wherecorrosion is the least.

We are revising the painting scheme but not the corrosion prone areas.From the above example, it is essential to revise the corrosion prone areasduly considering not only coastal but also industrial pollution. In addition, topsurfaces of bottom flanges of welded girders due to warping, outer flanges ofshallow type girders, cross girders & bottom lateral bracings of through type

girders due to drop out from carriages and other areas affected to beconsidered for periodical patch painting. Hence it is essential to revise thescheme of painting and also its periodicity.

Diagram No.53 (issued on 17.05.1985) requires amplification due to

ban on Paint red lead to IS-102

Withdrawal of Paint red oxide to IS-123

adopting metalizing at site

application of epoxy based paints

The Bridge Manual, which was published in the year 1998, contains

elaborate procedure to be followed for the painting scheme includingmetalizing & epoxy based painting for bridge girders only. But, Bridge manualalone cannot be referred for the Painting of steel girders because no


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mention about the periodicity of painting for which Diagram-53 is required.Scheme for painting of concrete bridges is not finding place in the manual.

At this juncture, one circular is needed for reference duly amalgamatingthe scheme to be followed with periodicity for both steel & concrete girderbridges. To bridge the above gap, the following points may be considered.

Painting scheme to be followed for girder bridges can be divided in tofour categories.

1. Coastal area2. Non-Coastal area where corrosion is severe3. Noncoastal area where corrosion is not severe4. Area requires periodical patch painting

Coastal area:

The circular indicating the coastal area may be extended further forhighly polluted area mainly due to industrial growth and floor system ofthrough type, semi-through type & shallow type girders.

Painting scheme:

I. Epoxy based paints.

a) Surface preparation by sand blastingb) Painting:

(i) Primer coat:Apply by brush / airless spray two coats of epoxy zinc phosphate

primer to RDSO specification No. M & C /PCN-102/2009 givingsufficient time gap between two coats to enable first coat ofprimer to hard dry.

(ii) Intermediate coat:Apply by brush/airless spray-one coat of epoxy micaceous ironoxide to RDSO specification No. M & C /PCN-103/2011 allow it tohard dry.

iii) Finishing coat:Apply by brush/airless spray two coats of polyurethanealuminium finishing to RDSO Specification No. M & C /PCN-110/2006 giving sufficient time gap between two coats to enable

the first coat to hard dry.

II. MetallisingMetallising by spraying with aluminium painting with one coat of ETCHprimer to IS.5666 or wash primer to SSPCPT -3537, followed by one coatof Zinc chromate primer to IS.104 and two coats of paint Aluminium toIS.2339

Non-Coastal area where corrosion is severe

i) Priming Coat:One coat of ready mixed paint zinc chromate priming to IS: 104

followed by one coat of zinc chrome - red oxide priming to IS:2074


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ii) Finishing coat:Two coats of aluminium paint to IS: 2339.

Non - Coastal area where corrosion is not severe

i) Primer coat:One coat of ready mixed paint zinc chromate priming to IS : 104,followed by one coat of ready mixed paint red oxide zinc chromepriming paint to IS : 2074.

ORTwo coats of zinc chromate red oxide primer to IRS - P 31

ii) Finishing coat:Two cover coats of red oxide paint to IS: 13607 (Revised code for

IS 123)

CONCRETE GIRDERS

No any instructions available to carryout the painting of concrete bridges. Thefollowing aspects may be considered in this regard.

In Aggressive environment (Severe, Very severe and extreme environment):

Sub-structures of bridges - Coal tar epoxy (In affected parts only)

Super structures of bridges - Epoxy-Phenolic IPN coating or CECRIIntegrated four coat system

In non-aggressive environment (Mild and Moderate environment):

No coating is necessary.

Good dense cover-concrete with good cement content with low water

cement ratio and extra depth of cover is enough, Usage of blended cement to make the concrete impermeable

Using clean reinforcing bars.

CBRI/Roorkee & CECRI/Karaikudi have developed the painting scheme forconcrete bridges and any one method can be adopted for our requirement.

I. Specification of coating material specified in technical literature oncorrosion/carbonisation protection in concrete structures by RDSO (BS-88) for IPN coating.

S.No. Description Primer coat Middle coat Top coat

1. BaseInterpenetratingPolymer (Epoxyphenolic)

InterpenetratingPolymer (Epoxyphenolic)

InterpenetratingPolymer(AliphaticPolyurethane)

2. Pot life 1 Hour for 2 lt.mix1 Hour for 2lt.mix

1 Hour for 2 lt.mix

3. Curing Air curing Air curing Air curing4. Colour Clear Yellow/Grey Yellow/Grey

5. Shelf LifeOne year in tightlysealed container

One

One year intightly sealed

container

One year in tightly

sealed container6. Dry film 55-65 per coat 90-100 per coat 40-50 per coat


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thickness(Microns)

7. Coverage 5-6 sq.mt/lt. 4-5 sq.mt/lt 6-7 sq.mt/lt

8.RecommendedNo. of coats

One One One

II. Epoxy Painting System by CECRI System:

Central Electro-chemical Research Institute at Karaikudi has developed acoating system for controlling corrosion. This system is applied on theconcrete surface and helps in controlling carbonation and weathering effects.

Primer: Zinc Ethyl Silicate Primer. (Two Pack Inorganic Zinc Coating-Ethylsilicate Binder Pack 1 & Zinc dust powder Pack 2) 65 70 microns percoat.

Middle coat: Two Pack epoxy MIO undercoat. This is a high build

intermediate coat paint based on epoxy polyamide system formulated withleafy MIO pigments to permit application at DFTs higher than 100 microns.

Top coat: This is a two pack polyurethane system consisting of a polyacrylatepolyol with appropriate pigments extenders etc. and an aliphaticpolyisocyanate ambient curing agent (50 microns per coat).

Before application, the substrata is thoroughly cleaned to remove the dust,hardened cement slurry, oily residues etc., by scrubbing with coarse wirebrushes, grinding or sweep blasting methods depending on site requirements.Residual amounts of de-moulding agents, curing agents should be completelyremoved. Any cracks, crevices or surface blemishes should be treated withsealant prior to primer application. The subsequent coats shall be applied bybrush or spray with an interval of 24 hours between the two coats.

The paint application should aim to achieve minimum dry film thickness asspecified by CECRI.

The DFT (Dry film thickness) shall be measured on 100x100mm steel plateattached with epoxy on the concrete surface at the rate one per 10m2.

COMPOSITE GIRDERS

As per extant instructions, the steel portion of composite girders has tobe metalised and specified painting scheme after metalising to be followed

Patch painting:

With closer interval, the affected portions mainly in steel girders may bepainted with local scrapping & painting. This is done departmentally. But, thestaff strength of bridge wing has drastically come down and no any in put hasbeen done. So, patch painting, hereafter, can be done thro agency only forwhich suitable guidelines/clear instructions are required so as to carryout thesame with agency

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Painting of Bridges