Abstract
Ambient temperature cure adhesives are commonly used for the repair and reinforcement of timber in buildings and may also be used where bonded-in steel or composite pultruded rods and plates are employed to make connections in timber structures. The thixotropic behaviour of such adhesives is an essential factor when overhead repairs or reinforcements are being made in the field. Shear thinning characteristics are an important feature of such adhesives but glass transition temperatures (Tg) tend to be low and generally not much greater than room temperature. This paper addresses the issue of why connections bonded-in with thixotropic epoxy adhesives do not fail under constant creep loads in the field despite temperatures exceeding the material's Tg. A series of creep tests have been performed on adhesive samples under constant creep load in a dynamic mechanical thermal analyser (DMTA) whereby the temperature is increased in steps up to 80°C. The adhesive behaves as an elastic solid below Tg, as a viscoelastic solid just above Tg and as a low modulus, partially cross-linked, rubbery polymer at higher temperatures. Creep resistance is therefore a function of the cross-linked molecular structure of these adhesives. The assumption that the adhesives will creep uncontrollably above Tg is unfounded. The results of testing a miniature wood/adhesive/wood sandwich in shear in the DMTA are also reported, confirming the rubbery behaviour of the adhesive above Tg.
Original language | English |
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Title of host publication | 11th World Conference on Timber Engineering 2010, WCTE 2010 |
Publisher | Engineered Wood Products Association |
Pages | 2900-2906 |
Number of pages | 7 |
Volume | 4 |
Publication status | Published - 2010 |
Event | World Conference on Timber Engineering 2010 - Riva del Garda, Italy Duration: 20 Jun 2010 → 24 Jun 2010 |
Conference
Conference | World Conference on Timber Engineering 2010 |
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Country/Territory | Italy |
City | Riva del Garda |
Period | 20/06/10 → 24/06/10 |