Subject matter

In the current context of climate change and the limitation of anthropogenic activities on the planet, the construction sector must meet challenges to significantly reduce its environmental impacts. Among the approaches, the use and development of new building materials is promising. By being a low-embodied energy and low-carbon building material, earth-based construction materials can significantly contribute to reducing global greenhouse gas emissions and limit the depletion of raw materials through a circular economy approach. However, the main weakness of these earthen materials is their sensitivity to liquid water. To overcome this, the materials could be reinforced thought stabilisations methods, which are divided into 1/ mechanical stabilisations that increase the density and thus the properties of earth materials; 2/ chemical stabilisations that develop secondary mineralogical phases.

The most frequently hydraulic binders (lime or cement) are used as chemical stabilisers, but they have the disadvantage to increase the carbon footprint of the earthen materials due to the emission of greenhouse gases during admixtures manufacturing and to change the soil in a permanent way, that limits drastically the its recyclability. In place of hydraulic binder’s stabilisation, alternative bio-sourced methods with low environmental impact are increasingly used. These, inspired by centuries-old practices or biomimetic, are highly variable and act differently. At present, there is no fully established classification of bio-additives and bio-stabilisation methods, but they can be grouped according to their nature or effects. In particular, a distinction can be made between bio-additives or bio-stabilisers and bio-stabilisation methods. Bio-stabilisers are additives originated from plants, animals, and minerals (e.g. oils, fats, tannins, from vegetal or fibres, bio-ashes, urine, casein, oils from animals) that promote precipitations of supplementary mineralogical phases or their transformation, improving materials properties such as strength and water resistance through enzymatic induced calcite mineral precipitation, bio-polymerisation, mineral transformation. Others bio-additives do not modify the mineralogical phases into the materials, but could improve water sensibility by occluding the external open porosity.

Bio-stabilisation technics include, for example, the addition of hemp fibres, straw fibres, or mycelium, which can strengthen the materials. All these stabilisations would be included together and in this document referred as “bio-stabilisation methods”.

This TC is focused on the definition of testing procedures for bio-stabilised earth as a construction material for buildings and structures, in the context of new construction and rehabilitation.

The SCOPE of the TC will be focused on the following areas:

1– Understand how bio-additives and bio-stabilisation methods can modify mineralogy, microstructure and textural properties of different construction earth-based materials;

2– Understand how bio-additives and bio-stabilisation methods can modify performance of different earth-based materials (focusing on physico-mechanical properties, hygro-thermal properties);

3– Understand how bio-additives and bio-stabilisation methods can improve durability performance of different earth-based materials;

4– Assessment of the contribution to climate change adaptation of new and existing earth-based buildings;

5– Suggest a definition and classification for different types of bio-additives and bio-stabilisation.

Level of investigation and limit of the scope:

Understanding and evaluating bio-additives and bio-stabilisation characteristics, availability and local/regional impact is the first step to develop solutions for climate change adaptation of new and existing earth-based buildings and structures with longer service life. The definition of a minimal number of tests – at the lab and in situ - will be done for an accurate assessment of physico-mechanical properties, hygro-thermal properties and durability of earthen materials and elements. This investigation at two different scales will have the potential to contribute to an increase of the technology readiness level of the activities. Experimental protocols and design of the nature of each test may be modified as a function of the round robin tests that will be performed. Therefore, this TC will contribute with guidelines for the development of international/European standards on earth testing procedures and on testing procedures for the use of bio-additives and bio-stabilisation methods for the construction materials sector. This highlights the relevance of this new TC, which will focus on mechanical and hygro-thermal properties for durability purpose, and then to develop simplified testing methodologies based on a performance-based approach according to the constraints imposed by the targeted application concerning these properties.

Terms of reference

As previously stated, this technical committee will focus on investigating the effects of bio-additives and bio-stabilisation methods of raw earth materials.

In terms of organisation, we have assigned a work package to each of the identified objectives (see description above). The TC will be divided into 5 main working groups (WG). These groups may be divided in a second stage into sub-working groups if necessary.

The main topics of this TC are organised into work packages:

WP1 – Literature review - Investigation of current efficiency and evaluation of bio-additives and bio-stabilisation methods for earth stabilisation in new construction and existing buildings.

WP2 – Effects of bio-additives and bio-stabilisation on earth based materials properties - microstructure and mineralogical characterisation.

WP3 – Impact of bio-additives and bio-stabilisation methods on short and long-term performances related to hygro-thermal and mechanical behaviours.

WP4 – Durability characterisation and performance-based assessment of bio-stabilised earth-based materials.

WP5 – Bio-additives and bio-stabilisation methods contribution to climate change adaptation of new and existing earth-based construction.

WP0 –Common dissemination & communication activities between the 3 TCs to increase impact of activities developed at RILEM.

This TC proposal for 5 years was designed together and in parallel with the following proposals: “TC on Characterisation of the mechanical performance and durability of earthen materials and structures - A. Fabbri & Ch. Beckett” and “TC Processing of earth-based materials – E. Keita & A. Perrot”. The objective is to ensure that the community stays together with a common focus on earth-based materials characterisation at different domains for new construction and building rehabilitation.

Therefore, we propose a transversal WP (WP0) to ensure throughout the duration of the 3 TCs the dissemination of scientific results (writing of articles and recommendations), scientific animation (doctoral school, participation in conferences, organisation of a conference), but also for transfer of knowledge to industrialists (writing of a practical guide, technical days).

The content of the WPs is detailed below. Each WP is led by a person with recognised expertise in the field. The leader of WP0 would be a person that participates in the 3 different TCs related to earth-based materials mentioned above and submitted together with this proposal.             

The group will consist of academic members (researchers) and engineers from private sectors working for several years on these subjects. We already expect to gather around 25 RILEM members. The environmental context and the new incentive policies regarding the environmental impact of construction in several countries are pushing construction companies and manufacturers to take an interest in this material. However, the lack of linkage between scientific knowledge and construction practices hinders the dissemination of these methods. This TC proposes to devote a large part of the work on improving this knowledge transfer to the whole chain of construction actors, giving a very applicative dimension to this work.

Detailed working programme

Work packages details

WP1 – Literature review (M1-M12)

Lead: Snezana Vucetic (Novi Sad University, Serbia)

To specify the framework of this work, as much from the point of view of the existing stabilisers, of their effects, but also of the test methods with a performance-based approach, a meticulous review of the literature must be performed.

Initially, it will be conducted a survey to TCs members for the selection of bio-additives and bio-stabilisation methods to focus on this TC.

A review of various methods will be done and then crossover studies will be conducted between the different thematic. Investigation of current efficiency and evaluation methods of earth stabilisation with bio-stabilisers in new construction and existing buildings in the following strands:

Challenges and advantages on the impact of bio- stabilisation methods on: earthen materials microstructure, mineralogy and texture; earthen materials hygro-thermal; mechanical performances and durability (stabilised due to water/ion intrusion and damage leading to service life decrease)- current efficiency and evaluation methods; effects of different environmental solicitations on stabilised and unstabilised earthen materials; local resources impact related to climate change adaptation. Collection of data being used for Life Cycle Assessment (LCA).

This literature review and proposed biostabilisers classification will lead to the creation of a book proposal.

Milestone 1: Proposal for classification of bio-stabilisation methods (month 6).

Milestone 2: Complete the review on current status (month 12).

Deliverable of WP1: Review report and state of the art paper in a Springer journal special issue.

WP2 – Effects of bio-stabilisation methods on earth-based materials properties - microstructure and mineralogical characterisation (M6-M24)

Lead: Céline Perlot (Université de Pau et des Pays de l’Adour, France)

The durability and physical behaviour of materials are strongly linked to their composition and microstructure. Consequently, modifying the microstructure of raw earth materials is a key issue to improve their resistance to contact with liquid water. This WP will be focused on a classification of bio-stabilisers/soil in function of the effects (e.g. formation of new mineralogical phases and porosity modifications.

Milestone 2: Complete report on the WP2 (month 24)

Deliverables of WP2: Classification of bio-stabilisers/soil in function of the effects  - Journal article or technical letter. Doctoral course/webinar (e.g. during RILEM week).

WP3 - Impact of bio-stabilisation methods on short and long-term performances related to hygro-thermal and physico- mechanical behaviours (M6-M48)

Lead: Agostino Walter Bruno (Università degli studi di Genova, Italy)

After defining the micro-scale effects, the changes in macro-properties in the hardened state are studied focusing on hygrothermal behaviour and mechanical properties. Three different environments are considered in this TC: wet, dry and cycles of moisture (tidal/splash).

The environmental conditions in which these materials are used determine their properties. These in situ aspects are rarely studied, although crucial.  This WP will be developed following the selection of 2 tests for performance-based approach (in agreement with the other two TCs running at the same time on earth-based materials).

A link will be established between the effects at the macroscopic scale and those at the microscopic scale studied in WP2. A link will be done with WP4 to enable the implementation of performance-based approach.

Milestone 3: Complete report on the WP3 (month 48)

Deliverable of WP3: Recommendations paper from the RILEM TC or papers submitted for publication. Doctoral course/webinar.

WP4 - Performance-based assessment of bio-stabilised earth-based materials (M6-M54)

Lead: Ana Bras (Liverpool John Moores University, United Kingdom)

The approach that this committee proposes is to understand the major effects of these bio-stabilisation methods on the performance of earth-based materials exposed to wet, dry and cycles of moisture and then to develop simplified testing methodologies based on a performance-based approach according to the constraints imposed by the targeted application. This WP will be developed following the selection of 2 tests for performance-based approach (in agreement with the other two TCs running at the same time on earth-based materials). The durability is here defined as the ability to maintain the required performances during building service life. A review of existing studies will be done through bibliographical research, which will help to define the needs for development of new methodology and equipments. We will use the testing methods recommended in agreement with the TC on durability from Fabbri and Beckett. The results obtained with the design mix will be used as input parameters for service life models. The WP outcome might require the development of new equipments for durability assessment of earth-based materials aligned with performance-based design approaches.

Milestone 4: Complete report on the WP4 (month 54)

Deliverable of WP4: Recommendations paper from the RILEM TC. Doctoral course/webinar. Papers submitted for publication. 

WP5 – Bio-stabilisation methods contribution to climate change adaptation of new and existing earth-based construction (M12-M60)

Lead: Guillaume Habert & Magda Posani (ETH-Zurich, Switzerland)

In order to support the development of bio-stabilised earth construction but also to encourage the prescription among the whole chain of actors, factual data on the contribution to the reduction of environmental impacts must be provided. How the earth-based constructions will respond to projected climate impacts will be addressed in the WP5. Understand maturity and gestation of bio-stabilisers locally available is the focus on this WP. The socio-economic aspect can also be addressed to justify methods according to users' expectations. From understanding of bio-stabilisation methods used locally in different regions/countries, evaluation of regional impacts and current operational and maintenance targets aligned with results obtained in WP3 and WP4 is proposed.

Milestone 5: Complete report on the WP5 (month 60)

Deliverable of WP5: Guidelines to promote bio-stabilised earth construction. Technical conferences, Industry event.

WP0 – Common dissemination & communication activities between the 3 TCs to increase impact of activities (M1-M60):

The transversal WP0 (WP0) will ensure throughout the duration of the TC the dissemination of scientific results (writing of articles and recommendations), scientific animation (doctoral schools, participation in conferences, organization of a conference), but also for transfer of knowledge to industrialists (writing of a practical guide, technical days).