Effective adhesive systems and optimal bonding parameters for hybrid CLT Blake Larkin Oregon State University Materials Science and Wood Science & Engineering Co-authors: Lech Muszynski, Arijit Sinha, Andre Barbosa, Rakesh Gupta, and Vahid Mahdavifar
Presentation Overview Brief intro to cross laminated timber (CLT) Hypothesis Approach Screening study goals Preliminary results Further Research
Cross Laminated Timber (CLT) What is CLT? Layers: Typically 3, 5, or 7 Area: Up to ~ 10 X 60 ft 2 http://www.prosalesmagazine.com/products/lumber/x-marks-the-opportunity_o http://www.internationaltradenews.com/klh_massivholz_gmbh/portrait/ http://www.structurearchives.org/article.aspx?articleid=1474 "KLH: Sustainability." KLH UK. Web. 30 Oct. 2014. <http://www.klhuk.com/sustainability.aspx>.
Our Hypothesis is that CLT panels with hybrid layups (layers arranged from high- and low-grade lamellas or composed of mixed species) can meet the critical performance parameters specified in the ANSI PRG 320 2012 and that adhesive systems alternative to polyurethane (PUR) can be successfully utilized in hybrid CLT products.
Approach Screen for species/grade/adhesive combinations that pass bond integrity criteria (varying pressing parameters) Test viable combinations for: engineering performance criteria connector performance
Goal of Screening Study 1. Check the compatibility between standard sampling scheme and the inherent variability of the bond integrity characteristics in the product 2. Adjust the standard sampling scheme (if needed) 3. Screen the combinations using the adequate sampling scheme
Screening Study Testing 2 x 2 foot panels with 3 layers Qualification Standard: ANSI/APA PRG 320-2012 Bond line shear Delamination
Screening Study Test Variables Face Layers Douglas-fir (High) Lodgepole Pine (High) Pressure (MPa) [psi] 0.69 [100] 0.40 [58.0] 0.10 [14.5] Core Layer Lodgepole Pine (Low) Douglas-fir (Low) Hemlock (Low) Lodgepole Pine (High) Adhesive Types PRF PUR 4 panels per combination
Bond Line Shear Test Modified ASTM 1037 Modified for 90 o grain orientation between layers 2x1.5 inch bond area 1 inch thick layers Focus: Shear strength Percent wood failure
Percent Wood Failure Goal: Automatic optical assessment of the % WF 1) Initial Image 2) Red Spectrum 3) Thresholding
Shear Test Results: assessing variability A7 B7 C7 A6 B6 C6 A5 B5 C5 A4 B4 C4 A3 B3 C3 A2 B2 C2 A1 B1 C1
3 sample Average Shear Test Results: assessing variability Strength (psi) Strength (MPa) Wood Failure 553 ±179 3.81 ±1.24 70 ±13.3% Variance 32% 32% 19% Panel Average 518 ±140 3.57 ±0.97 66 ±15% Variance 27% 27% 23% A7 B7 C7 A6 B6 C6 A5 B5 C5 A4 B4 C4 A3 B3 C3 A2 B2 C2 A1 B1 C1 Average variance in Industry Panel Stress Wood Failure 30% 14%
Delamination Test AITC Test T110-2007: Cyclic Delamination Test 1) Vacuum Soak 2) Pressure Soak h 3 3 30 minutes @ 25±5 mm Hg 2 hours @ 75±5 psi [0.517±0.0344 MPa] 5) Repeat steps 1-4 with failed specimens 4) Measure Delamination 3) Oven Dry to original weight ± 15% If delamination <10%, Pass If <5%, Pass If >5%, step 5 Within 10-15 hrs @ 160±5 o F [71±2.7 o C]
Common Modes of Sample Delamination Mixture of Delamination and Wood Failure Delamination only in early wood.
Delamination Test Results: assessing variability A B C 7 7.95% 0.00% 4.14% 6 0.00% 2.15% 2.65% A7 B7 C7 A6 B6 C6 A5 B5 C5 A4 B4 C4 A3 B3 C3 A2 B2 C2 A1 B1 C1 5 2.15% 2.73% 0.00% 4 0.41% 0.00% 0.00% 3 0.00% 0.00% 3.16% 2 0.00% 0.00% 3.97% Key Pass after 2 cycles Failed to dry within tolerance 1 0.00% 0.00% 3.33%
Preliminary Conclusions Large variation in shear of shear block strength and wood failure within a single panel Optical measurements offer semi-automatic method to measure WF% while reducing user input, but shallow wood failure is hard to categorize.
Future Work Investigate variation between billets produced within the same test variables Determine reference rolling shear values for all species involved in the study Develop and Test PUR optical WF% assessment Develop automated optical method for assessment of delamination
Acknowledgments USDA NIFA Forest Products Research Grant Program (proj. ref. #2013-05978) Swanson group and Interfor for lumber Momentive and Henkel for adhesives OSU Lab manager: Milo Clauson Oregon State University faculty and graduate students http://www.henkel.com/contactus?pageid=184414 http://www.momentive.com/caree rs/ http://www.interfor.com/careers http://www.ute1stop.org/home/ut e/smartlist_127 http://commons.wikimedia.org/wik i/file:usda_nifa_twitter_logo.jpg
Preliminary Shear Test Results A7 B7 C7 A6 B6 C6 A5 B5 C5 A4 B4 C4 A3 B3 C3 A2 B2 C2 A1 B1 C1
ASTM D905: Precision and Bias Precision has two components: repeatability at a given test site and reproducibility between test sites. The precision of this test method is affected by many factors including, but not limited to: 1. the wood species, 2. the boards selected, 3. grain direction, 4. growth ring orientation, 5. the quality of the bonded joint, 6. the condition of the shear tool, 7. the precision on the testing machine, 8. the operator. When the specimen fails primarily in the wood, the normal variability of the wood strength affects the precision. The coefficient of variation of shear strength parallel to the grain is 14 % for a given species of wood.
ASTM D905: Precision and Bias Precision has two components: repeatability at a given test site and reproducibility between test sites. 13.1.2 Repeatability at a Given Site: In a study in which all the above factors were closely controlled and the specimens were bonded with PRF adhesive, the COVs ranged from: 2.4 up to 13.0 %, with most values in the range of 3 to 6%. 13.1.3 Reproducibility from site to site: In a study in which all the above factors, except board & growth ring orientation, were controlled, the COVs ranged from: 8 to 11 % for casein bonded specimens, 4 to 12 % for two polyvinyl acetates, 22 to 27 % for an elastomer-based, and 14 to 21 % for PRF adhesive bonded specimens. The reproducibility of this test method has not been established.