Abstract
Production parameters affect hydration/carbonation and density of hemp concrete which consequently determine the strength and the hygric and thermal properties of the concrete. This chapter investigates the effect of production parameters including curing conditions (65% vs. >95% RH), time of demoulding and specimen geometry (cylinder vs. cube) on the concrete’s strength which relates to density and therefore to thermal and hygric properties. It studies hydration in the concrete’s microstructure and measures the compressive strength development at intervals between 1 day and 1 month. Moulding time and curing conditions influence drying and therefore may impact binder hydration and consequently strength evolution. Specimen geometry may affect drying and can also determine how strain builds up in the concrete and thus when failure occurs. The chapter concludes that curing hemp-lime concrete with hydraulic content (50%CL90:50%CEMII) at high RH (>95%) lowers compressive strength (65.4% drop at 10 weeks). It is unclear why this happens, as the presence of water vapour during curing at high RH should enhance hydration and consequently increase strength. It was also found that delaying specimen demoulding increases compressive strength of the CL90:CEMII concrete (22.9% increase at 10 weeks), probably due to the presence of moisture for longer enhancing hydration. The specimen geometry does not significantly impact the ultimate compressive strength of hemp-lime concrete however, it affects behaviour in compression. Initially, cylinders and cubes deform on load application up to a similar yield point. However, following this yield point, the cylinders fracture showing a more brittle behaviour while the cubes keep crushing to finally experience an additional stiffness produced by mechanical bridges being formed between opposing cell walls.
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Notes
- 1.
EN 459-2:2010 Building lime. Test methods.
- 2.
EN 196-1-2005 Methods of testing cement. Determination of strength.
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Acknowledgements
All testing was carried out in the Department of Civil Engineering, Trinity College Dublin. The authors thank Dr. Kevin Ryan and Michael Grimes for their assistance with testing. The authors also wish to thank the Traditional Lime Company and Clogrennane Lime for the provision of materials. The authors thank Dr. Heath Bagshaw (Centre for Microscopy and Analysis) for his assistance with the SEM. This research follows up from a former research project funded by the Environmental Protection Agency and it is largely based upon experimental work published in: ‘Effect of testing variables on the hydration and compressive strength of lime hemp concrete’ S. Pavía, R. Walker, J. McGinn. First Int. Conf. on Bio-based Building Materials June 22nd–24th 2015 Clermont-Ferrand, France.
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Pavía, S. (2017). Effect of Testing Variables (Method of Production). In: Amziane, S., Collet, F. (eds) Bio-aggregates Based Building Materials . RILEM State-of-the-Art Reports, vol 23. Springer, Dordrecht. https://doi.org/10.1007/978-94-024-1031-0_9
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