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Grammatikos S.A.,Center for Innovative Construction Materials | Grammatikos S.A.,University of Bath | Zafari B.,University of Warwick | Evernden M.C.,Center for Innovative Construction Materials | And 3 more authors.
Polymer Degradation and Stability | Year: 2015

This paper studies the moisture uptake characteristics of a pultruded E-glass fibre reinforced (isophthalic polyester) polymer after long-term exposure to hot/wet conditions. Both fully exposed samples of varying aspect ratios and selectively exposed samples were immersed in distilled water at 25 °C, 40 °C, 60 °C and 80 °C for a period of 224 days. For the fully exposed condition, bulk and directional diffusion coefficient values were determined. A three-dimensional approach using Fickian theory was applied to approximate the principal direction diffusions at 60 °C by using mass changes from samples having different aspect ratios. This revealed that the diffusion coefficient in the longitudinal (pultrusion) direction to be an order of magnitude higher than in the transverse and through-thickness principal directions. Diffusion coefficients in the three principal directions have also been determined for the selectively exposed condition at 60 °C through the application of one-dimensional Fickian theory. It was found that the size and shape of the samples influences moisture uptake characteristics, and thereby the values determined for bulk and directional diffusion coefficients. Furthermore, the influence of exposure temperature on moisture uptake and mass loss with time was examined. Investigation of the water medium by means of electrical measurements suggested that decomposition of the polymeric composite initiates very early, even after the very first day of immersion. Comparison between the infrared signatures from the pultruded material and the water's residual substances revealed significant decomposition, and this behaviour is verified by Fourier Transform Infrared Spectroscopy (FTIR), Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopic (EDS) analysis as well as the recorded mass loss after 224 days of aging. © 2015 The Authors. Published by Elsevier Ltd.


Grammatikos S.A.,Center for Innovative Construction Materials | Grammatikos S.A.,University of Bath | Evernden M.,Center for Innovative Construction Materials | Evernden M.,University of Bath | And 4 more authors.
Materials and Design | Year: 2016

This paper presents the effects of hygrothermal aging on the durability of a pultruded flat sheet, immersed in distilled water at 25 °C, 40 °C, 60 °C or 80 °C for a period of 224 days. Elevated temperatures noticeably increase the moisture diffusion coefficient and moisture uptake behaviour. Measured changes in the tensile and in-plane shear mechanical properties were examined after 28, 56, 112 or 224 days. Tensile properties remained practically unaffected by aging whereas matrix dominated shear properties revealed an initial drop which was recovered to a substantial degree after further hygrothermal aging. Visco-elastic property changes due to the superimposing mechanisms of plasticization, additional cross-linking etc. were recorded. Scanning Electron Microscopy micrographs indicate that the fibre/matrix interface remained practically intact, even after the most aggressive hot/wet aging. X-ray Energy Dispersive Spectroscopy analysis showed no chemical degradation incidents on the fibre reinforcement surfaces and infrared spectroscopy revealed superficial chemical alteration in the aging matrix. Optical microscopy revealed matrix cracking in samples aged at 80 °C for 112 days. Lastly, Computed Tomography scans of un-aged material showed internal imperfections that undoubtedly enhanced moisture transport. After aging at 60 °C for 112 days, Computed Tomography detected preferentially situated water pockets. © 2016 The Authors.


Grammatikos S.A.,Chalmers University of Technology | Jones R.G.,University of Bath | Evernden M.,University of Bath | Evernden M.,Center for Innovative Construction Materials | Correia J.R.,University of Lisbon
Composite Structures | Year: 2016

This paper investigates the effects of thermal cycles on the structural integrity of a pultruded Glass Fibre Reinforced Polymer (GFRP). Through a critical review of current literature alongside a comprehensive experimental campaign, the material's response to cyclic thermal loading has been ascertained, defined by the rate of degradation of its physical, mechanical and visco-elastic properties. Matching sets of both dry and soaked samples conditioned in distilled water for 224 days. Freeze-thaw cycling of both dry and soaked samples was conducted between 20 °C and -10 °C for a total of 300 cycles. Computed Tomography scanning (CT-scan) was undertaken to assess the microstructural physical changes throughout freeze-thaw cycling. After exposure, GFRP samples exhibited a minor decrease in glass transition temperature (Tg) which indicated minor structural degradation. Dry GFRP sample's mechanical response exhibited negligible changes in both tensile and in-plane shear properties. However, as a result of the higher induced thermal stresses, soaked samples showed a significant degradation of their tensile and shear strengths. Yet, the soaked material's stiffness remained largely unaffected due to the potential reversible nature of plasticization, which acts to increase the material's molecular mobility when initially moisture-saturated, but is later recovered as the soaked samples lose moisture throughout freeze-thaw cycling. © 2016 The Authors.


Lawrence M.,Center for Innovative Construction Materials | Shea A.,University of Bath | Walker P.,University of Bath | de Wilde P.,University of Plymouth
Proceedings of Institution of Civil Engineers: Construction Materials | Year: 2013

Bio-based insulation materials have the potential to make a significant contribution to the reduction in the global warming potential of the construction industry world-wide. They contribute in two ways. First they provide the opportunity to reduce the embodied energy in the fabric of buildings. They do this because they are renewable and recyclable. Plant-based insulation materials also sequester carbon dioxide through photosynthesis, sealing up atmospheric carbon dioxide for the life-time of the building. Second they are able to reduce the in-use energy consumption of buildings in more ways than by simply reducing energy transmission. They have the ability to buffer heat and moisture, which is most evident in dynamic situations. This paper discusses the hygrothermal performance of bio-based insulation materials, examining the hygrothermal effects associated with their vapour activity. The incremental performance offered by these materials is not allowed for in building regulations, nor is it readily accounted for in many commercially available building physics models. The paper discusses the reasons for this and identifies the need for the transient performance of bio-based insulation materials to be taken into account, because this will better reflect their actual contribution to the energy performance of a building.


Lawrence M.,Center for Innovative Construction Materials | Heath A.,Center for Innovative Construction Materials | Walker P.,Center for Innovative Construction Materials
Proceedings of Institution of Civil Engineers: Construction Materials | Year: 2013

Interest in traditional unfired clay building materials, including cob, earth brick, and rammed earth, has grown in the UK in recent years. Although the use of vernacular techniques, such as cob and rammed earth, has raised the profile of earthen architecture, a wider impact on modern construction is more likely to come from modern innovations such as unfired extruded clay masonry units and premixed plasters. Traditional unfired clay walls often have basal widths of 300 mm or more, providing an inherent stability and resistance to toppling through self-weight. Masonry units extracted from UK brick production lines before the firing process are typically 100 mm wide, which requires good mortar-brick bond strength to meet structural robustness requirements in a typical 2.4 m high wall. In testing, traditional mortars based on clay, cement or lime, have not provided sufficient strength. This paper examines the bonding of unfired clay units with unconventional mortars based on novel binders. It reports on the development of a mortar which appears to be suitable for a wide range of clay types. This mortar can be readily recycled and has a carbon footprint lower than many alternative binders. Results of long-term bond strengths and the structural performance of masonry walls are given, which demonstrate the suitability of this mortar for use with unfired clay masonry units.

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