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Ahmad Z.,University Technology of MARA | Ansell M.P.,University of Bath | Smedley D.,Rotafix Northern Ltd
Journal of Engineering Materials and Technology, Transactions of the ASME | Year: 2011

Adhesives used for bonded-in steel or composite pultruded rods and plate to make connections in timber structures are commonly room temperature cure adhesives. The room temperature cure, applied without pressure, thixotropic, and shear thinning characteristics of the adhesives, is for ease of application when repairs and reinforcement are being made in situ in the field. The room temperature cure adhesive may not fully cross-link and this may cause brittleness. Therefore to improve the toughness properties of such adhesives, nanoparticles can be added. This paper reports the experimental investigation carried out on the fracture toughness of three thixotropic and room temperature cured epoxy-based adhesives formulated specifically for in situ timber bonding, namely, CB10TSS (standard adhesive), Albipox is CB10TSS with the addition of nanodispersed carboxyl-terminated butadiene acrylonitrile (CTBN), and Timberset is an adhesive formulation containing ceramic microparticles. The fracture toughness behavior of the adhesives was investigated using the Charpy impact test on unnotched and notched specimens conditioned at 20 C / 65 % RH to evaluate notch sensitivity, and a single-edge notched beam (SENB) test was performed to evaluate the stress intensity factor K IC. The fracture surfaces were investigated using scanning electron microscopy. Under high impact rate, toughness was in the order of CB10TSS, Albipox, and Timberset. CB10TSS and Albipox were found to be ductile in the unnotched state and brittle when notched. Timberset was brittle in both unnotched and notched states. Under low strain rate (SENB) conditions the addition of CTBN significantly improved the fracture toughness of Albipox compared with CB10TSS and Timberset. Examination of the topography of the fractured surface revealed marked changes in crack propagation due to the addition of nano- or microfillers accounting for the variation in toughness properties. © 2011 American Society of Mechanical Engineers. Source


Ahmad Z.,University Technology of MARA | Ansell M.P.,University of Bath | Smedley D.,Rotafix Northern Ltd
Journal of Engineering Materials and Technology, Transactions of the ASME | Year: 2010

The environmental stability of three room temperature cure epoxy adhesives was evaluated following exposure to temperatures of 20°C, 30°C, and 50°C at 95%RH, to 50°C in air and soaked in water for up to 90 days. The adhesives contained nano- and microparticles and were especially formulated for bonded-in timber connections, and the properties of bulk adhesives and adhesively bonded block shear specimens were evaluated. After 90 days of aging the results demonstrate critical temperature effects controlled by the glass transition temperature. The apparent free volume for all the adhesives remains constant as moisture is absorbed but plasticization takes place at high temperature and relative humidity, evidenced by the increased elongation and yield observed by strain values and scanning electron microscope. Exposure at 50°C in air causes the adhesives to postcure enhancing strength but high humidity causes degradation. Nanofiller additions enhance environmental stability but the addition of microparticles provides better moisture resistance. Copyright © 2010 by ASME. Source


Ahmad Z.,University Technology of MARA | Ansell M.P.,University of Bath | Smedley D.,Rotafix Northern Ltd
IOP Conference Series: Materials Science and Engineering | Year: 2011

For in-situ bonding of pultruded rod into timber structural members, such as in the construction of bonded-in timber connection, strengthening and repair of timber structures, the adhesive used must be thixotropic, room temperature cure, environmentally stable and friendly and applied at without pressure. This study investigates the moisture absorption characteristics of three adhesives specially formulated for bonded-in timber connections where the adhesives are reinforced with nano- and micro-particles denoted as CB10TSS (standard adhesive), Albipox (CB10TSS/CTBN) and Timberset (ceramics filled adhesive) with the aim to improve mechanical properties and raise glass transition temperature. The effect of high temperatures and high humidity on the properties of adhesives were determined following conditioning at different temperatures (20°C, 30°C and 50°C) and relative humidities (65%, 75% and 95%) and soaking in water at 20°C In all cases the properties of Albipox were least affected by environment but Timberset exhibited the lowest moisture uptake. Exposure to humid environments at temperatures 20°C and 30°C for CB10TSS and Albipox and 50°C for Timberset resulted in water uptake characterized as Fickian which had only a modest effect on properties. However, exposure to humid environments at temperature (50°C) which is higher than Tg resulted in non-Fickian uptake of water for CB10TSS and Albipox and a more adverse effect on properties. Source


Ahmad Z.,University Technology of MARA | Ansell M.,University of Bath | Smedley D.,Rotafix Northern Ltd
International Journal of Adhesion and Adhesives | Year: 2010

An experimental investigation has been carried out on the fracture toughness of three thixotropic and room temperature cured epoxy-based adhesives formulated specifically for in situ timber bonding namely CB10TSS (standard adhesive), Albipox is a modification of CB10TSS with the addition of nano-dispersed carboxyl-terminated butadiene acrylonitrile (CTBN) and Timberset is a commercially used adhesive formulation containing quartz, mica and bentonite and cured with an aliphatic diamine (TMD). The fracture toughness behaviour of the adhesives was investigated using the Charpy impact test on unnotched specimens conditioned at 20 °C/65%RH and 30 °C/95%RH to observe the effect of temperature and moisture. The Charpy impact tests were also performed on notched specimens to evaluate notch sensitivity, and a single-edge notched beam (SENB) test was performed to evaluate the stress intensity factor, KIC. The fracture surfaces were investigated using scanning electron microscopy (SEM) and atomic force microscopy (AFM). Under high impact rate at 20 °C/65%RH, toughness was in the order of CB10TSS, Albino and Timber set. CB10TSS and Albino were found to be ductile in the unmatched state and brittle when notched. After exposure to 30 °C/95%RH, Albino was tougher than CB10TSS due to an increase in ductility, which allowed the rubber particles to cogitate. Timber set was brittle in both unmatched and notched states. Under low strain rate (SENB) conditions the addition of CTBN significantly improved the fracture toughness of Albino compared with CB10TSS and Timber set. Examination of the topography of the fractured surface revealed marked changes in crack propagation due to the addition of nana- or micro-fillers accounting for the variation in toughness properties. The toughness of thixotropic adhesives, specified for bonding in connections in timber structures, could therefore be enhanced by the inclusion in the epoxy matrix of phase separated liquid rubber. © 2010 Elsevier Ltd. Source


Ahmad Z.,University Technology of MARA | Ansell M.P.,University of Bath | Smedley D.,Rotafix Northern Ltd
International Journal of Adhesion and Adhesives | Year: 2010

The in-situ bonding of pultruded fibre-reinforced plastic rods into timber structural members is a commonly used technique for making timber-to-timber connections and for the strengthening and repair of timber structures. Ideally, the adhesive should be thixotropic, shear thinning, room temperature cure, environmentally stable, solvent-free and applied without pressure. This study investigates the moisture absorption characteristics of three adhesives, specially formulated for bonded-in timber connections, where two of the adhesives are modified with nano- or micro-particles. The three adhesives are denoted as CB10TSS (standard adhesive), Albipox (standard adhesive with CTBN rubber additions) and Timberset (standard adhesive filled with ceramic particles). The aim of the additions is to improve the environmental stability of the standard adhesive as well as enhancing mechanical properties and raising the glass transition temperature. The effect of high temperatures and high humidity on the properties of the three adhesives was determined following conditioning at different combinations of temperature and relative humidity (20, 30 and 50 °C/95% RH) and soaking in water at 20 °C. In all cases the moisture uptake for the rubber-modified adhesive was less than for the standard adhesive, but the ceramic particle-filled adhesive exhibited the lowest moisture uptake overall. Exposure to humid environments at temperatures lower than Tg resulted in water uptake characterized as Fickian, which had only a modest effect on properties. However, exposure to humid environments at temperatures higher than Tg resulted in non-Fickian uptake of water and significant changes to the diffusion and permeability coefficients. © 2010 Published Elsevier Ltd. All rights reserved. Source

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