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Material Properties and Full-Scale Rain Exposure of Lime-Hemp Concrete Walls : Measurements and Simulations

de Bruijn, Paulien LU (2012)
Abstract
Lime-hemp concrete (LHC) is a building material consisting of a lime-based binder combined with hemp shiv that is suitable for various building applications. This thesis aimed to elucidate the possibilities for using LHC for exterior walls in a cold, wet climate through investigating mechanical, thermal and moisture-related properties of the material.
The mechanical properties of LHC containing both shiv and fibres of the hemp stalk in combination with different binders were tested in order to find a mixture with increased mechanical strength so that a supporting timber load-bearing structure could be omitted. A larger amount of cement in the binder mix improved compressive... (More)
Lime-hemp concrete (LHC) is a building material consisting of a lime-based binder combined with hemp shiv that is suitable for various building applications. This thesis aimed to elucidate the possibilities for using LHC for exterior walls in a cold, wet climate through investigating mechanical, thermal and moisture-related properties of the material.
The mechanical properties of LHC containing both shiv and fibres of the hemp stalk in combination with different binders were tested in order to find a mixture with increased mechanical strength so that a supporting timber load-bearing structure could be omitted. A larger amount of cement in the binder mix improved compressive strength. However, even when using unseparated hemp (both shiv and fibres) in combination with a high-cement binder, mechanical strength was not sufficient for the
material to be load-bearing without additional support.
The moisture properties of LHC were studied in order to determine its robustness and durability in cold, wet conditions. Sorption isotherms and moisture diffusivity were determined over the complete moisture
range for two LHC mixes with different lime:hemp ratios. Compared with other building materials (e.g. timber, cellular concrete and lime-based render), LHC showed a high moisture diffusion coefficient in
the 35-95% relative humidity (RH) range. The sorption isotherm of LHC appeared quite planar up to 95% RH, but steep between 95 and 100% RH.
The thermal properties of specimens with different relative humidities were found to be influenced by RH. At higher RH values thermal conductivity was higher, whereas differences in thermal diffusivity and specific heat capacity as a consequence of differences in RH were less apparent.
Four full-scale wall sections combining different renders and LHC mixes were exposed to a rain scenario in order to fully understand the hygric performance. Moisture properties were used in computer simulations of these full-scale wall sections and the simulation results compared with measured data. It was found that even after prolonged rain exposure, some wall sections had low moisture levels inside the wall. A lime-cement render allowed rain to penetrate the wall more easily than a cement render and also dried more slowly after exposure to rain. LHC with a larger proportion of
hemp absorbed moisture more slowly and dried more quickly after construction than a mix with a larger proportion of lime. This indicates that LHC with more hemp in the mix in combination with a cement render would be more suitable for use in a cold, wet climate. (Less)
Please use this url to cite or link to this publication:
author
supervisor
organization
publishing date
type
Thesis
publication status
published
subject
keywords
hemp , lime, building materials, MOISTURE
publisher
Sveriges Lantbruksuniversitet
language
English
LU publication?
no
id
2fa1978d-bdeb-40f7-b4a7-d512e8490522
alternative location
http://pub.epsilon.slu.se/9007/1/debruijn_p_120829.pdf
date added to LUP
2016-10-20 11:00:49
date last changed
2017-08-07 12:47:13
@phdthesis{2fa1978d-bdeb-40f7-b4a7-d512e8490522,
  abstract     = {Lime-hemp  concrete  (LHC)  is  a  building  material  consisting  of  a  lime-based  binder  combined with hemp shiv that is suitable for various building applications. This thesis aimed  to  elucidate  the  possibilities  for  using  LHC  for  exterior  walls  in  a  cold,  wet  climate  through  investigating  mechanical,  thermal  and  moisture-related  properties  of  the material. <br/>The mechanical properties of LHC containing both shiv and fibres of the hemp stalk in  combination  with  different  binders  were  tested  in  order  to  find  a  mixture  with  increased mechanical strength so that a supporting timber load-bearing structure could be  omitted.  A  larger  amount  of  cement  in  the  binder  mix  improved  compressive  strength.  However,  even  when  using  unseparated  hemp  (both  shiv  and  fibres)  in  combination with a high-cement binder, mechanical strength was not sufficient for the <br/>material to be load-bearing without additional support.<br/>The  moisture  properties  of  LHC  were  studied  in  order  to  determine  its  robustness  and durability in cold, wet conditions. Sorption isotherms and moisture diffusivity were determined  over  the  complete  moisture  <br/>range  for  two  LHC  mixes  with  different  lime:hemp   ratios.   Compared   with   other   building   materials   (e.g.   timber,   cellular   concrete and lime-based render), LHC showed a high moisture diffusion coefficient in <br/>the  35-95%  relative  humidity  (RH)  range.  The  sorption  isotherm  of  LHC  appeared  quite planar up to 95% RH, but steep between 95 and 100% RH.  <br/>The thermal properties of specimens with different relative humidities were found to be  influenced  by  RH.  At  higher  RH  values  thermal  conductivity  was  higher,  whereas  differences  in  thermal  diffusivity  and  specific  heat  capacity  as  a  consequence  of  differences in RH were less apparent. <br/>Four  full-scale  wall  sections  combining  different  renders  and  LHC  mixes  were  exposed  to  a  rain  scenario  in  order  to  fully  understand  the  hygric  performance.  Moisture properties were used in computer simulations of these full-scale wall sections and  the  simulation  results  compared  with  measured  data.  It  was  found  that  even  after  prolonged rain exposure, some wall sections had low moisture levels inside the wall. A lime-cement render allowed rain to penetrate the wall more easily than a cement render and  also  dried  more  slowly  after  exposure  to  rain.  LHC  with  a  larger  proportion  of  <br/>hemp absorbed moisture more slowly and dried more quickly after construction than a mix  with  a  larger  proportion  of  lime.  This  indicates  that  LHC  with  more  hemp  in  the  mix in combination with a cement render would be more suitable for use in a cold, wet climate.  },
  author       = {de Bruijn, Paulien},
  keyword      = {hemp ,lime,building materials,MOISTURE},
  language     = {eng},
  month        = {09},
  publisher    = {Sveriges Lantbruksuniversitet},
  title        = {Material Properties and Full-Scale Rain Exposure of Lime-Hemp Concrete Walls : Measurements and Simulations},
  year         = {2012},
}