Performance of Protective Coatings on Small Bridges Subject to Bushfires. William McLean, Peter Golding, Ann Sheehan,

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1 Performance of Protective Coatings on Small Bridges Subject to Bushfires William McLean, Peter Golding, Ann Sheehan,

2 Galvanizers Association of Australia Established in 1963, the GAA represents the hot dip galvanizing industry throughout Australia We conduct research and compile case studies in various areas dealing with corrosion protection and hot dip galvanizing We provide technical and design advice on hot dip galvanizing and corrosion protection to industry We offer free CPD presentations in offices throughout Australia

3 Outline Increasing number of enquiries asking about condition of protective coatings after building fires and bushfires Common coating options for small bridges Durability to corrosion Performance in bushfires Properties of bushfires and the effect they have on steel Recommended Inspection Repair Options Examples

4 Protective Coatings

5 Batch hot dip galvanizing to AS/NZS 4680

6 Metallurgical bond, Batch HDG Hardness

7 Corrosivity in Australia described in AS 4312 Category Generic examples Specific examples CX Shore-line severe surf Surf beach shoreline regions with very high salt deposition Some Newcastle beaches C5 Sea-shore surf Within 200 m of rough seas & surf beaches. May be extended inland by prevailing winds & local conditions More than 500 m from the coast in some areas of Newcastle C4 Sea-shore calm From 200 m to 1 km inland in areas with rough seas & surf. May be extended inland by prevailing winds & local conditions From the shoreline to 50 m inland around sheltered bays In the immediate vicinity of calm salt water such as harbour foreshores All coasts C3 Coastal From 1 km to 10 km inland along ocean front areas with breaking surf & significant salt spray May be extended inland to 50 km by prevailing winds & local conditions From 100 m to 3 6 km inland for a less sheltered bay or gulf Metropolitan areas of Perth, Wollongong, Sydney, Brisbane, Newcastle, & the Gold Coast Adelaide & environs From 50 m to 1 km inland around sheltered bays Port Philip Bay & in urban & industrial areas with low pollution levels C2 Arid Urban Inland Most areas of Australia at least 50 kilometres from the coast Inland 3 6 km for a less sheltered bay or gulf Can extend to within 1 km from quiet, sheltered seas Canberra, Ballarat, Toowoomba and Alice Springs Adelaide & environs Suburbs of Brisbane, Melbourne, Hobart C1 Dry indoors Inside heated or air conditioned buildings with clean atmospheres Commercial buildings

8 AS/NZS Table 6.2: Life to first maintenance (part) System Reference Standard Minimum thickness Selected corrosivity category & Calculated life (minimum-maximum, years) Batch HDG HDG sheet AS/NZS 4680 AS 1397 g/m 2 µm C2 C3 C4 C5 CX HDG > HDG >100 HDG > Z > Z > HDG tube ZB140/ > AS/NZS 4792 HDG > AS 4750 ZE

9 AS/NZS Table 6.3: Life to first maintenance (part) SYSTEM DETAILS Estimated Life to First Maintenance System Des. ACC5 Surface Prep. Sa 2½ 1 st Coat 2 nd Coat 3 rd Coat 75 µm zinc rich primer 125 µm high build epoxy 50 µm acrylic 2-pack Total DFT C2 C3 C4 C5-M T 250 µm IZS1 Sa 2½ 75 µm inorganic zinc silicate µm PUR4 Sa 2½ 75 µm zinc rich primer 125 µm high build epoxy 50 µm polyurethane gloss 250 µm

10 Bushfires

11 Bushfires Quite different temperature profile to building fires Typically an intense heat that moves through quickly Assumed flame temperature of 1090K (820ºC) by AS 3959 Temperature curves in AS/NZS for large flame testing Intensity varies based on Fuel Vegetation management Weather conditions Slope of ground 11

12 Steel in Bushfires

13 Surface Temperature of Steel Steel surface unlikely to reach same temperature as the flame Heat from fire can be reflected, conducted or radiated, thus temperature lags behind fire temperature Behaviour of steel has been tested extensively for building fires and ISO834 fire curve Graph shows 100mm diameter, 200mm long steel rod in a furnace

14 Steel Thickness Galvanized steel tested to building fire curve, similar behaviour to bare steel 10, 20 and 30mm plates Thicker plates can absorb more heat Zinc metallurgically bonded to steel and acts as single part, heat can be conducted Paint coatings may limit this or have different expansion rates to steel on heating

15 Steel Strength Graph based on Eurocode 3 for building fires Yield strength and Young s Modulus greatly reduced at raised temperatures Can cause small bridge to deform in fire (example of thin steel later) Burning material can keep steel at higher temperature for longer (e.g. timber slats) Oftentimes structural integrity of small bridges maintained during and after a fire

16 Protective Coatings in Bushfires

17 Galvanized Coatings in Bushfires Solid state reaction occurs for some coatings, converting pure zinc to alloy layers If this doesn t occur, pure zinc will melt and can drip off Pure zinc vaporises at 907 C, unlikely to occur during fire Testing performed on utility poles in past Melting Temperature 420 C 650 C 1,500 C

18 Bushfire Testing of Galvanizing Tested in 2006 by BlueScope in conjunction with Bushfire CRC Grid of liquid propane burners Simulates from radiant heat through to flame immersion High heat flux achieved during testing A maximum air temperature of 675 C was recorded and the maximum surface temperature measured was 520 C. The galvanized coating remained intact even at the highest temperatures

19 Appearance After Testing Surface staining on poles after flame immersion Could be soot from liquid propane burners More likely burning of protective sleeves on poles to protect from aggressive soils

20 Paint Coatings in Bushfires Paint manufacturers usually list upper temperature limit on their technical data sheets (TDS) This is for corrosion protection to continue, aesthetics not needed to be maintained Rarely list performance in flame exposures, dry heat only Failure modes include peeling or crazing of the paint, ignition and burning, or melting. Particular care if paints are combustible, can keep steel at higher temperatures for longer Paint Type Zinc rich Inorganic Zinc Epoxy Acrylic Polyurethane epoxy Silicate Temperature 120 C Up to 400 C 120 C 120 C 120 C

21 Appearance After Bushfire Testing of Powder Coating

22 Recommended Inspection of Small Bridges After Bushfire

23 1. Verify Structural Integrity a) Engineer should perform this b) Temperature steel reached is important (condition of coating can give hints) c) Typically highly annealed steel in Australia, verify no phase changes d) Check if distortion occurred when steel had lower yield strength

24 2. Clean Steel and Visually Inspect a) Remove any soot or burnt products b) Look for bare areas where steel is exposed c) Check for blistering, peeling, crazing or delamination

25 3. Measure Thickness of Remaining Coating a) Devices such as Elcometer 456 and Positector 6000 use a magnetic method to determine distance from probe tip to steel b) For zinc coatings remaining durability can be calculated based on AS/NZS corrosion rates c) For paint coatings thickness typically doesn t change over time, if original specification is known damage can be identified

26 Repair of Protective Coatings After Bushfires

27 Localised Repair (Small Areas) Taking steel off site unlikely to be economical Paint repair most frequently used, with paint selected: Having similar durability to remaining undamaged coating Suitable for surface preparation possible (e.g. epoxy mastics are usually more surface tolerant and power tool cleaning without blasting may be adequate) If remaining coating is galvanized with high estimated durability, thermal zinc spray could be considered

28 Full Repair (Large Areas) If steel can be taken off site it can be galvanized if the design is suitable Blasting and painting is the most common repair option when steel isn t removed from site Paint systems from previous table usually suitable Achieving required cleanliness over large areas difficult with power tool cleaning Thermal zinc spraying another possible repair option

29 Examples

30 Images Images from the Western Australian Department of Parks and Recreation (DPaW) Had a lot of infrastructure including small bridges affected by bushfires Elcometer 456 used to measure coating thicknesses Original coating system used can be difficult to determine after a fire, making keeping accurate records of specifications important Comments made based on images (often remote areas), not by physical inspection on site

31 Continuously Galvanized Sections with Paint Repair

32 Coating Measurements After Fire

33 Cold Formed Sections

34 Continuously Galvanized Section

35 Hot Dip Galvanized Sections

36 Thank You More information: w: t: e: e: