John Ruddick Alkaline Copper Treated Wood for Residential Use. Preservative mobility in decking. Approach. Shell treated wood.

Transcription

1 Preservative mobility in decking Alkaline Copper Treated Wood for Residential Use University of British Columbia Professor John Ruddick Objectives Investigate: How shell treatments work in treated wood exposed above ground; The factors influencing the migration of copper in amine copper wood preservative treated decking Monitor depletion during natural weathering Shell treated wood Approach 2-4 mm Typical lumber yard production Isolate fungi from exposed CCA treated decking after 1, 15 and 2 years Identify fungi Recover samples for chemical analysis Confirm the difference between spore and mycelial tolerance Possible explanations for good performance of CCA shell treated wood used above ground Check main avenue for fungi to access treated wood used above ground Limited moisture content High proportion of heartwood The role of minor amount of mobile CCA preservative 1

2 Spore germination in above ground wood Migration of chemical onto check surface Unfixed chemical Checks Treated surface Spore germination in above ground wood Decay of treated decking associated with checks Spore Fruiting body on decking Externally Sound Minimum Inhibitory Copper Concentration (on agar media) Approach Cu concentration (mm) Oligoporus placentus Gloeophyllum sepiarium Mycelia 1 Basidiospores 2 Install pressure treated boards Section to provide samples for chemical analysis and field exposure Sections for field exposure are approximately 3 mm long Support two 2 x 6 samples or three 2 x 4 samples over basins and collect run off 2

3 Chemical analysis Chemical analysis Treated surface of reference section removed using a computerised routing system Analysed by x-ray spectroscopy to provide reference retention Penetration of the copper determined for each surface, including end penetration Factors being examined Preservative mobility in decking Wood species Preservative retention Preservative penetration 2 x 4 vs 2 x 6 Treated vs untreated ends Water repellants Pressure wash Redistribution into checks Monthly amount (%) of copper leached - ACQ Influence of the environmental conditions in the field leaching Amount of copper (CuO) leached per Month (%).9 16 CuO leached (%) Leachate (ml) Aug- Sep- Oct- Nov- Dec- Jan- Feb- Mar- Apr- May- Jun- Aug- Sep- Oct- Nov- Dec- Jan- Feb- Mar- Apr- May- Jun- Jul- Aug Jul Leachate(ml) Amount Cu Leached = f (time of exposure, volume of leachate, sun hours, temperature) Cu leached(mg)= t+.3v+.55s-.923temp. Where: T: time of exposure in months V: volume of leachate (ml) S: sun hours Temp: Temperature Coefficient of determination: R²=.74 At retention of 5.21 kg/m 3 Month 3

4 Cumulative amount (mg/m 2 ) of copper leached after 4 years exposure - ACQ Final vs Initial losses after 2 years exposure Cumulative amount of copper (as CuO) leached (mg/m²) 6 35 Cumulative amount of Cu Precipitation (mm) Aug-2 Sep-2 Oct-2 Nov-2 Dec-2 Jan-3 Feb-3 Mar-3 Apr-3 May-3 Jun-Jul Aug-3 Sep-3 Oct-3 Nov-3 Dec-3 Jan-4 Feb-4 Mar-4 Apr-4 May-4 Jun-4 Jul-4 Aug-4 Sep-4 Oct-4 Nov-4 Dec-4 Jan-5 Feb-5 Mar-5 Apr-5 May-5 Jun-5 Jul-5 Aug- Oct-5 Nov-5 Dec-5 Jan-6 Feb-6 Mar/Apr May-6 Jun-6 Jul-6 6-Aug 6-Sep 3 Sep 5-6 Months Precipitation (mm) Final (mg/m²) y = x R 2 = Initial (mg/m²) Final vs Initial losses after 4 years exposure Cumulative amount (mg/m 2 ) of copper leached CA-B Final (mg/m 2 ) y = 53.21x R 2 = Initial (mg/m 2 ) Cumulative amount of copper (mg/m²) Jack pine Hem fir Lodgepole pine Jun-Jul-3 Aug-3 Sep-3 Oct-3 Nov-3 Dec-3 Jan-4 Feb-4 Mar-4 Apr-4 May-4 Cumulative amount (mg/m 2 ) of copper leached after 3 years CA-B Leaching of copper 6 35 Cumulative amount of copper leached (mg/m²) Jun-Jul-3 Aug-3 Jack pine Lodgepole pine Sep-3 Oct-3 Nov-3 Dec-3 Jan-4 Feb-4 Hem fir Rain Mar-4 Apr-4 May-4 Jun-4 Jul-4 Aug-4 Sep-4 Oct-4 Nov-4 Dec-4 Jan-5 Feb-5 Mar-5 Apr-5 May-5 Jun-5 Jul-5 Aug-Sep-5 Oct-5 Nov-5 Dec-5 Jan-6 Feb-6 Mar/Apr-6 May-6 Jun-6 Jul-6 Aug-6 Sep Rainfall (mm) Cu Unfixed copper leached from the surface Cu Surface content is depleted during initial rain events 4

5 Leaching of copper Migration of copper into checks During drying mobile copper moves to the surface Cu During further rain events mobile copper at the surface is moves into checks or is leached CA-B hem-fir Avge..43 mg Cu/g wood ( mg Cu/g wood ) ACQ hem-fir Avge..49 mg Cu/g of wood ( mg Cu/g wood CCA hem-fir Avge..29 mg Cu/g wood Corrosion of fasteners and connectors in contact with treated wood Corrosion of fasteners and connectors used in contact with alkaline copper treated wood the real world Objectives Investigate the performance of commercial fasteners and connectors in contact with alkaline copper treated wood Evaluate field performance of fasteners and connectors What is corrosion? What is corrosion? Metals react with oxygen in the presence of water to form oxides. The problem with iron (and many metals) is that the oxide formed does not attach well to the metal surface. It flakes off easily causing pitting which weakens the fastener. The amount of water complexed with the iron controls the colour of rust. It may be black to yellow to orange brown (red). 5

6 Wood is corrosive to metals Treated wood Factors affecting iron reactions are Tannin content ph Moisture Content Oxygen Temperature Factors affecting corrosion in treated wood Same as untreated plus- Corrosion inhibitors (Cr, As etc.) Residual solvent (ammonia, amine, acids, etc) Mobile noble metal e.g. copper How do we control corrosion? How do we test fasteners? Organic and Inorganic coatings Metallic coatings Combination coatings Materials Fasteners before exposure ACQ treated wood purchased from local Home Depot stores CX and ACQ supplied from commercial treatment CCA wood samples purchased from Home Hardware, Vancouver Nails selected for the corrosion research based on suppliers recommendation as suitable for alkaline copper treated wood 6

7 Fastener preparation Effects of mechanical action Nails hammered into wood and removed by carefully splitting wood Nails weighed before placing in the sandwiched samples Fasteners placed in wood sandwich Climate conditions Harshaw Environmental chamber.7 x.76 x 1 m Water temperature 32 C Water mist pressure 1 Pa No direct spraying of fastener heads Continuous misting except during evaluation Evaluation Protocol Treated wood Evaluation of Corrosion Level Visual Observation (ASTM D61-1 based on white rust and red rust formation. 1% red rust = 1 %) Weight Loss Diameter Loss (Steel Core Cross-Section Reduction) Pit depth Bending Yield Strength Testing ACQ treated spruce CCA treated hem-fir ACQ treated lodgepole pine CX treated hem-fir Western red cedar 7

8 Visual Results Bright 83 hrs Visual Results - hot dipped Zn 83 hrs CCA CCA ACQ ACQ Weight loss Weight loss CCA vs ACQ 3 Weight Loss. Ultrasonic Bath used to clean the corrosion Products. Less accurate than diameter measurement due to difficulty of removing corrosion products. Weight loss % Magni #599 Weight loss - ACQ Weight loss in CCA" HG + Ph Stainless steel PT 2 Weather Beater Alumoweld HG Bright nail Diameter loss (%) Diameter loss (%) Diameter loss (Steel Core Cross-Section Reduction) Measured with Caliper to.25 mm Can also be used to calculate cross sectional area loss Fails to assess pitting corrosion pit depth Diameter loss (%) ACQ CCA 2 Magni #599 HG + Ph Stainless steel PT 2 Weather Beater Alumnoweld Hot dipped Bright 8

9 Influence of water repellants on ACQ spruce weight loss Visual corrosion rate ACQ+WR 12 1 % weight loss in ACQ + WR % weight loss ACQ 1 8 % weight loss Red rust grade (%) 6 4 Bright PG Deck screw Hot dipped Magni Stainless 2 2 Hot dipped Hot dipped +phosphate Bright 188hrs 387hrs 575hrs 811hrs 1hrs 1188hrs Incorrect fasteners and connectors Common nails Electroplated galvanized nails Aluminum connectors Inadequate barrier coatings Incorrect fasteners Incorrect connectors Red rust on common iron fasteners Electroplated zinc coated 9

10 Incorrect fasteners and connectors Incompletely fixed copper in alkaline copper treated wood Copper deposits on wood surface, but no watermarking, suggesting reaction with unfixed copper in wet wood copper deposits Red rust Red rust on G185 connector from ACQ treated wood Copper plated onto fasteners Red rust White rust Incorrect fasteners and connectors Incompletely fixed copper in alkaline copper treated wood Red rust formed on unprotected edges of G185 connectors Will this red rust lead to accelerated corrosion of galvanized face? 1

11 Red rust White rust over surface and on fasteners Moisture on wood Damage to heads and shank during nailing? Incorrect fasteners and connectors Incompletely fixed copper in alkaline copper treated wood Red rust formed on unprotected edges of G185 connectors Surface loading of copper due to perceived end use or incising Copper deposits and white rust Incised lumber Not all fasteners or connectors corrode Good performance 11

12 Real world Good performance Alkaline copper treated wood is more corrosive than CCA treated wood Some connectors with G185 galvanizing showed red rust in less than 2 years Red rust was found on some galvanized connectors, even though no signs of wetting, suggesting mobile chemical in wet wood when delivered was causing corrosion Incised lumber appeared more corrosive than unincised lumber Real world But will they give 2 years? Fastener heads appeared susceptible to damage of the galvanizing during hammering resulting in corrosion Aluminum connectors, brackets, and flashing should not be used in contact with alkaline copper treated wood Lack of fixation of alkaline copper treated wood prior to use, will increase corrosion Acknowledgements Newsha Ashari Baekyong Choi Sungmee Choi Pablo Chung Sofya Soldkin Tree Island Industries Homeowners Protection Office of BC Arch Viance (CSI) Dr. Wolman GmbH Hot dipped galvanised nails after 2 years in CCA decking 12