Subject matter

Earth is one of humankind’s oldest building materials, and it is still present across the world. Currently, the interest in earth-based building materials is revived by their low environmental impact and the need for answering global warming issues. Indeed, the building sector contributes by a significant share to the entropic carbon emissions. In this context, earth appears as a promising solution for low carbon emission, recycling, and reuse in the construction field.

However, earth-based materials face many challenges to be considered as a relevant modern building material. The variability of the resources should be integrated with the formulation strategy. At the hardened state, water sensitivity should be better assessed. At fresh state, vernacular technique and new processes need a scientific review in order to obtain better control of material density and prediction of the hardened properties. This Technical Committee will focus on fresh state and early age issues.

This TC scope will include new techniques under development, such as extrusion-based 3D printing and poured earth. The technical novelty applied to earth-based materials generates complex inter-disciplinary problems; moreover, processing requirements usually play a key role in the mix design.

Robotics and Information Technologies allow revisiting most building processes. For the last decade, new construction processes have been developed with digital tools. These innovations were also related to a better formulation control of cement-based materials. Similar contributions are now focusing on earth-based materials.

New techniques and formulations are real opportunities for earth: as vernacular technique is not well standardized; they could be directly included in the general effort on earth material characterization and discussions on standards. Indeed the evolution should be in line with the broader goal to maintain the environmental benefit of earth materials.

In recent years, various rheometric and characterisation tests have been developed for earth-based building materials. However, some large scope aspects are often lacking and should be discussed in this TC. Indeed the underlying behavior is postulated but rarely fully assessed. For instance, materials are often considered purely plastic. However, they may also exhibit frictional and viscous behavior as in 3D printing. These contributions should be taken into account in the description of processing routes. Moreover, depending on the mineralogical nature of fine particles, particle size distribution and water content, earth can show a large range of behavior from very fluid to granular like. The boundary between these different types of behavior should be linked to the material microstructure and shared rheological tools should be adopted for each earth consistency.

Although mix design main consequences are on rheology, its influence on drying and mechanical build-up is detrimental. It is necessary to avoid cracks, limit shrinkage and obtain homogenous materials. Indeed, new formulations with additives offer ways to reduce the water content and suppress cracks while improving mechanical behavior. There is a need to understand the underlying physics behind the additives effect in order to have mix-design strategies not only based on trials and errors or empirical methods.

Terms of reference

This TC will deal with the behavior of earth-based material in its fresh state and during hardening.

This TC is intended to take five years.

This TC is expected to gather around 25 RILEM members from academia and private sectors. Based on members of TC 274-TCE, potential members are located in Europe, North America and Asia. Efforts will be conducted to include African members and the industry. PhD students and young researchers (under 35) will be involved thanks to specific programs.

The main work will be a bibliographic review on the developments made since the 2000s on fresh state and early age for earth-based materials. The work may include round-robin tests in a second phase or a following TC.

Indeed, mix-design strategies are complex and the relevant parameters are not clearly identified. At this stage, it seems appropriate to federate a growing community, harmonize test methods and define terminology.

The main topics of this TC are:

1) to describe the rheological behavior of earth materials.

2) to define the rheometric characterization tools suitable for earth materials

3) to describe the curing and early-age behavior.

4) to describe new processing methods

Detailed working programme

Work packages are as follows:

0) 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 Resilience and durability of bio-stabilised earth-based construction materials: testing methods based on performances approach - chaired by Ana A. Bras and C. Perlot-Bascoules” and “TC on processing of earth-based materials – chaired by 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.

1) Rheology of earth-based system

Objectives:

A basic plastic behavior with yield stress may not represent well enough shear and compression of every type of multi-phase material.  The microstructure and interactions at stake, the role of clay will be studied and the effect of admixtures will be considered, in particular biosourced ones.

Expected results:

• Definition of earth-based material behaviors and categories of classification based on the composition (clay content, particle size distribution, volume fraction…)
• Suitability of resources and appropriate techniques
• Working mechanisms of admixtures
• Bibliographic review

2) Rheological characterization of earth materials

Objectives:

Rheometry tools and methodologies are developed in many laboratories to deal with fluid to stiff pastes or even granular-like materials. There is a need to evaluate these existing methods, provide the physical basis and harmonize practices.

Expected Results:

• Review of existing methods
• Round robin tests to assess relevance of methods and define common practices

3) Curing and early-age behavior

Objectives:

Drying is a main stage of earth-based material processing that often dictates the rhythm of the construction process. Indeed, the microstructure consolidation and the mechanical properties build-up while drying. Moreover, shrinkage, cracks and heterogeneity could be detrimental to the final structure. The role of fibers will also be investigated.

Expected Results:

• Review on drying phenomena
• Development of tests to evaluate both drying and mechanical build-up kinetics

4) New processing methods

Objectives:

Digital fabrication is a new technique for building materials combining trends of robotics with sustainability. Moreover, the implementation of self-compacting earth is also an attractive prospect as earth would be cast with existing concrete processes. These new processing routes are now focusing attention and are expected to become the future of earth construction.

Results:

• Review of ongoing research
• Define common outlooks