Subject matter

Definition of the TC subject and of the studied material

The goal of this TC is to define dedicated testing procedures for stabilized and unstabilized earth as a building construction material (crude earth). This construction material is currently increasing in interest for quite evident ecological reasons since the use of local earth as a building material can divide the embodied energy of a house by 2 and the transportation energy by 4.5 (cf. Morel et al., 2001), without increasing the energy consumption during service life of the building. Interest is also increasing because of the large number of earth-based buildings constructed before 1948: a good understanding of the behaviour of crude earth is crucial to develop proper methodologies for the rehabilitation and maintenance of these buildings.

The relevance of building with earth in the 21^st century has already been shown in showcase examples built in Switzerland (by Martin Rauch), France (by Nicolas Meunier) and China (by Lu Wenyu and Wang Shu - 2012 Pritzker Prize). However, the prospects of earthen and bio-based materials of entering mainstream construction, and a fortiori as the main structural materials, are limited notably due to the lack of knowledge on the assessment of their performance and durability.

The first task of the previous round of this TC was to realize the “state of the art” report that presents a critical analysis of existing testing protocols for earthen materials and construction. This activity led to the publication of two papers in the Journal “RILEM Technical Letters” (Fabbri et al., 2018, 2021) and the aforementioned STAR book (Fabbri et al., 2022). On the basis of the results of this bibliographic work, a second stage of this TC comprised “round robin” testing whose aim was to determine and propose robust and reliable measurement protocols to estimate the performance of earthen materials. This second stage lead to recommendations concerning water vapour measurements and 3-point bending tests on compressed earth bricks (publications under finalisation).

The proposed technical committee would be a direct continuation of the previous committee on earthen construction, namely the TC-274-TCE (06/2016-06/2022). The primary goal will be to build upon the good work initiated on the study of mechanical behaviour and durability in order to publish RILEM recommendation papers and to inform global standardisation practices.

Level of investigation

Two scales of tests will be investigated: lab tests and on-site tests. A critical objective, for both scales, will be to define the type and minimal number of tests required in order to provide an accurate assessment of mechanical performance and durability of earthen materials and elements. We will start by using existing testing protocols, developed for similar materials, as these are familiar to researchers and practitioners. However, due to the particularities of the material, development of new experimental protocols and/or the adaptation of existing ones may be necessary. These tests procedures and the way to analyse their results will be defined in the view of recent theoretical developments published in literature and/or developed elsewhere by the members of the TC.

Importance will be given to the repeatability and the robustness of the tests. For laboratory tests, round robin campaigns will be performed, and, in function of the obtained results, the experimental protocols and even the nature of the test may be modified. For on-site tests, we will use instrumented earthen houses which are already studied by members of this TC. In particular, for that task, the TC will benefit from the results obtained within the framework of the French National Project on earthen construction.

Limit of the scope

This TC will be mainly focused on unstabilized earth. Time permitting, some exploration of methods to define properties of cement and/or lime stabilized earths may be included but no work will be done on new stabilization procedures (bio-polymers, enzymes…). Along the same line, this TC will only focus on traditional constructions techniques (i.e. Rammed Earth, Cob, Adobe, plasters, Compressed Earth Bricks). Newer construction techniques like printed earth and poured earth will be assessed in the two others technical committees which are submitted alongside this proposal.

No standardisation activity, in its strict sense, will be made during the lifetime of this TC. However, all the experimental developments should be able to serve as a basis for the development of international/European standards on earth testing procedures. This TC will focus on mechanical behaviour and durability, which means that thermal and hydrothermal behaviours will not be studied. Indeed, in our view, a first consensus had been reached during the TC-274 TCE among the community of researchers on earthen construction. At that stage, we think that hydrothermal behaviour of earthen materials should rather be treated alongside TCs on bio-based materials. Finally, only experimental studies will be performed within the framework of this TC; no numerical studies (e.g. finite element analyses) will be undertaken, except to provide support for publication if appropriate. All the theoretical developments underpinning the testing procedures examined under the proposed TC will extracted from a bibliographic survey and/or realized elsewhere.

Terms of reference

This TC is mainly based on experimental research and round-robin testing, which is quite time consuming. Thus, an estimation of 5 years should be quite realistic.

The TC will mainly comprise academics (researchers, research engineers) and engineers. The ideal number of members should be around 20 academics and engineers from 10 different laboratories spread throughout Europe/the UK.

Strong interactions with architects and masons will be fostered by holding dedicated workshops. This will disseminate the TC’s work to industrial bodies.

Detailed working programme

The TC will be divided into 3 main working groups (WG). These groups may be divided in a second stage into sub-working groups.

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 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.

WG 1/ Laboratory tests to assess the mechanical performances

This WG will aim to finalise the work that was started during the TC-274 TCE. In particular, it was not possible to provide clear recommendation for the mechanical testing of earth-based material, except for the 3-point bending test. For CEB and rammed earth, testing protocols have been identified but round robin tests still need to be performed to order to reach a definitive result. Under this context, the main objective of this WG will be to:

• Finalise the work (and write RILEM recommendation) on earth masonry elements
• Provide some data on scale effect for rammed earth and cob and provide some guidelines to realise lab and on-site tests
• Determine bond strength factors for reinforcement in earth, to be compatible with existing Eurocode approaches

For that purpose, the following milestones/deliverables have been identified (where T0+x refers to the start time plus x months):

• 1 Identification of the laboratories involved in the RRT for masonry elements (T0+3)
• 2 Identification of the test procedures to analyse de scale effect on RE and Cob and of the laboratories involved in the RRT (T0+24)
• 3 Definition of a methodology to allow a compatibility between Eurocode approach and design of earthen constructions (T0+48)
• 4 Bibliographic report on bond strength factors for reinforcement in earth (T0+54)
• 1 Finalisation of the RRT for masonry and publication of the results (scientific paper or recommendation paper in function of the obtained results) (T0+18)
• 2 Finalisation of the RRT for scale effect and publication of the results (T0+48)
• 3 Publication of a methodology, compatible with Eurocode approaches, to consider bond strength factors for reinforcement in earth (T0+60)

WG 2/ Laboratory tests to assess durability

Durability issues were identified during the TC-247 TCE but the round robin testing was limited to the abrasion test. It follows that within the framework of this new TC we propose to:

• Realise the experimental campaigns on water durability and erosion test and freezing-thawing behaviour in order to produce guidelines or recommendations.
• Propose guidelines and indirect testing procedures to estimate fire/temperature (F-T) resistance of earthen materials.

For that purpose, the following milestones/deliverables have been identified:

• 1: Identification of the test procedures to analyse (1) abrasion, (2) erosion (3) resistance to water up-take and (4) F-T resistance and of the laboratories involved that would be involved in the several RRTs (T0+18)
• 1 : Finalisation of the RRTs on abrasion, erosion, resistance to water uptake and F-T resistance and publication of the results (T0+48)
• 2: Publication of the guidelines for fire resistance (T0+60).

WG 3/ On-site testing

Earth is a complex material whose implementation requires skills not always known and/or mastered by masons, and which does not have normative dimensioning methods or ‘rules of thumb’ describing the conditions and processes of implementation of the works. The challenge of this WG will be to contribute to filling this gap by developing methods to monitor the quality of the raw earth elements of a structure during their implementation, following rehabilitation operations or whilst in service. To do so this WG will be divided in the following two sub—groups:

• Quality control of new elements
• On-site diagnostic methods

Let us note that the requirement of an increasing number of complex characterization tests is not appropriate for economic, ecological and practical reasons. Therefore, a strong stake of this WG will be to propose simple methods (that can be indirect) that can evaluate or control the quality of the implementation and/or the state of damage of earthen walls.

For that purpose, the following milestones/deliverables have been identified:

• 1: Bibliographic study on diagnostic on-site measurements technics that may be used for earthen construction (T0+24)
• 2: Identification of construction sites and/or demonstrator that can be used by TC members to tests these technics (T0+30)
• 1: Summary of the results obtained by the several labs on the on-site testing campaigns through a common publication in M&S (T0+60)
• 2: On the basis of the results obtained on WP1, WP2 and on M3.1, identification of simple tests that can be realised to perform on-site quality control of new earthen elements (T0+60)

A summary of the TC progress over the 5 years is presented in the GANTT chart below: