275-HDB : Hygrothermal behaviour and Durability of Bio-aggregate based building materials
Technical Committee 275-HDB
Deputy Chair: Florence COLLET
In less than 10 years, the construction of houses in the world using plant based materials has exited the field of a limited use by a few environmentalists and emerged as a valuable concept for healthy, ecological and comfortable habitat (moisture management, thermics and acoustics). The introduction of a high concentration of bio-aggregate-building material in the construction design is the fundamental principle of this concept. The use of crushed hemp (shiv), flax and other plants associated to mineral binder represents the most popular solution adopted in the beginning of this revolution in building materials.
Global warming, energy savings, and life cycle analysis issues are factors that have contributed to the rapid expansion of plant-based materials for buildings, which can be qualified as environmental-friendly and efficient multifunctional materials.
Concerning energy savings, COP 21 requires that from 2020 on, all new buildings meet the positive energy criteria in many countries. This improvement of energy performance of buildings induces modifications in the distribution of environmental impacts, and places the manufacture of the building materials as the most important phase when the energy consumption decreases from 200 to 15 kWh/m²/yr. So, to reduce these impacts, it makes sense to go on moving towards plant-based materials, whose impacts are very limited, and can even be positive on the environment.
The work of the Technical Committee (TC) will be to study hygrothermal behaviour and durability of building materials made from plant particles. The main issue is to meet the expectations of building materials with low environmental impact. The TC will focus on bio-composites made from particles or fibres issued from hemp and flax for which the industry is structured. These particles and fibres are used as aggregates or admixtures in combination with one binder or more. All binders that are compatible for use with plant material can be considered in the TC’s work: mineral binders which have been developed for use with bio-aggregate or organic binder which have been less investigated.
The first objective is to characterize the hygrothermal behaviour of bio-aggregate based building materials. Actually, such materials show a particular hygrothermal behaviour due to their particular porosity. They are highly hygroscopic and show a high moisture buffering capacity. Their hygric behaviour widely affect the heat balance as it impacts the thermal conductivity and it induces internal source (or well) of heat and/or another flow of heat (by convection notably). The usual thermal conductivity value is thus not sufficient to characterise the thermal performance of such material. The aim of this TC is to define a parameter which allows highlighting the hygrothermal performance of bio-aggregate based building materials and how to measure it.
The second objective relates to the durability of bio-aggregate based composite materials. Actually, such materials may show a decay when exposed to several ambient conditions. This may affect their physical properties (density, porosity, mechanical properties, hygrothermal….) and induce mould growth. However, durability test are aggressive. In reality, several factors act at the same time. This study should simulate the conditions and then compare several materials.
In summary, the working group will provide a comprehensive view and a critical review of:
- Characterization of the hygrothermal behaviour of bio-aggregate based building materials
- Investigation of durability of bio-aggregate based building materials
Links between these two objectives are really narrow and it is difficult to split this TC in two different parts as moisture is one of the main factor both for hygrothermal behaviour and for durability. Analysis must be driven in a TC teaming up physicians, mechanical scientists and bio-chemists skills. Subgroups could be eventually constituted around more specific topics.
Terms of reference
The expected work duration is 5 years.
During the first year, a first meeting will be organized to identify precisely the different composite materials typology.
This will enable to make up on works concerning the different kind of materials. A summary will be given as state of the art.
This initial assessment will then permit to focus the work on group\'s specific goals.
The first objective relates to hygrothermal behaviour of bio-aggregate based building materials. A review of various methods will be done and then crossover studies will be conducted between the different teams. First direction will be to identify investigated hygric and thermal properties and to compare the performances of the test method. Then, a new parameter should be define to assess the hygrothermal performance of bio-aggregate based building materials and the experimental method, associated with this parameter, should be developed. This method will then be tested under round robin test.
Regarding the durability, bio-aggregate based building materials being organic, they may be subject to the decay and may show evolution of their physical properties. A review of existing studies on bio-based materials will be performed. Then experimental studies will be performed within round robin tests.
The group will consist of academic members working for several years on these subjects. Following academic institutions have been identified to contribute to the TC. These institutions are not only specialized in civil engineering and construction but also in bio-chemistry and biophysics of plant material.
The group will also be open to participation for both institutional representatives of each field (linen, hemp sector...) but also to the industrials of these fields (manufacturers of binder, prefabricated blocks ...).
Detailed working programme
The main goals are the following ones.
After the first meeting, the project of the TC will be based on the following actions:
A0 – Investigated bio-aggregate based materials:
- Identification of the bio-aggregate based materials to be investigated
- Choice of bio-aggregate
- Choice of binders (mineral and/or organic binder)
A1 – Hygrothermal behaviour of bio-aggregate based building materials:
- Identification and characterisation of hygric and thermal parameters
- Existing method for highlighting the wide effect of hygric behaviour (sorption/desorption, heat balance, associated heat flow…)
- Definition of a new hygrothermal parameter to qualify hygrothermal behaviour of bio-aggregate based building materials (such as “global” or “apparent” thermal conductivity)
A2 – BioDurability of bio-aggregate based building materials:
The main objective of A3 part of the TC is to build bridges between the functional (mechanical, acoustical, thermal and hygrothermal), bio-physico-chemical and microstructural properties during natural and accelerated (environmental and microbiological) ageing of bio-aggregate based building materials. To carry out this part five points are defined:
- Design and work out the hygrothermal and biological ageing protocols the initial characterisation of raw materials (bulk shiv and binder), the choice of the formulation and the fabrication of bio-aggregate based building materials according to professional rules.
- Survey about the different forms of ageing (natural, environmental and microbiological).
- Survey of the methods characterising the functional, bio-physico-chemical and microstructural properties before, during and after ageing.
- Study on how to correlate the various properties, link them to the ageing of hempcrete, and to derive usage-driven recommendations on formulations.
This TC will be performed in the continuity of the TC 236 BBM (Bio-aggregate based Building Materials) where Round Robin Test on bio-aggregate characterization and mechanical properties of hemp concrete measurement were performed. The hygric behaviour of bio-aggregate based material widely impact the global energy balance of building, while this aspect is not taken into account in rules. It is necessary to highlight the contribution of hygric behaviour in the global heat balance of a wall to assess the hygrothermal behaviour of bio-aggregate based building material. This TC should thus be in the same cluster as the TC 236 BBM.
This TC will lead to several documents:
- State of the art on hygrothermal behaviour characterisation of bio-aggregate based building materials,
- State of the art on durability characterisation of bio-aggregate based building materials,
- Definition and development of testing method of a global parameter all, to qualify hygrothermal behaviour of bio-aggregate,
- Testing method for durability characterisation.
This TC will also organise the second ICBBM, in the continuity of the first ICBBM which took place in Clermont Ferrand in June 2015.
Group of users
Many persons involved in construction field may be concerned by these works outcomes. First, state of the art will help to better target research programs to carry out in order to remove vegetable based materials development bolts. Researchers will then find a way to better coordinate their actions in progress and future.
Moreover, testing and characterization procedures establishment will allow a wide and secure diffusion of these materials on the market. Finally, information diffusion actions will contribute to the networks development among professionals as architects, craftsmen, owners, contractors…
Specific use of the results
The results from this TC will be useful on several points of view.
The hygrothermal characterisation will allow highlighting the high performance of bio-aggregate based building materials which is better than the one reached from the calculation taking into account the thermal conductivity only.
This will contribute to the development of bio-aggregate based building material, and thus allow development of specific production and processing channels for these materials, including:
- a non-food recovery of agricultural products,
- allowing short cycle distribution of building materials since these raw materials are available quite everywhere,
- with low environmental impact (natural materials, storing CO2, easily renewable, reusable, ...).