<figure><img src="image_1.png" /></figure>

HAL
open science

# Visco-elasto-plastic behavior of unstabilized rammed earth wallet

Taini Chitimbo, Feras Abdulsamad, Noémie Prime, Olivier Plé

► To cite this version:

Taini Chitimbo, Feras Abdulsamad, Noémie Prime, Olivier Plé. Visco-elasto-plastic behavior of unstabilized rammed earth wallet. First International RILEM Conference on Earthen Construction, Mar 2022, Marne La Vallee, France. hal-05007839

HAL Id: hal-05007839

https://hal.science/hal-05007839v1

Submitted on 27 Mar 2025

HAL is a multi-disciplinary open access
archive for the deposit and dissemination of sci-
entific research documents, whether they are pub-
lished or not. The documents may come from
teaching and research institutions in France or
abroad, or from public or private research centers.

L'archive ouverte pluridisciplinaire HAL, est
destinée au dépôt et à la diffusion de documents
scientifiques de niveau recherche, publiés ou non,
émanant des établissements d'enseignement et de
recherche français ou étrangers, des laboratoires
publics ou privés.

Public Domain
Visco-elasto-plastic behavior of unstabilized rammed earth wallet

Taini Chitimbo*, Feras Abdul Samad, Noémie Prime, Olivier Plé

Université Savoie Mont Blanc, CNRS, LOCIE, 60 rue du lac Léman, 73000 Chambéry, France.

*taini.chitimbo@univ-smb.fr; noemie.prime@univ-smb.fr

**Extended Abstract**

Currently, the buildings exploitation and construction are responsible for over one-third of global final energy consumption and nearly 40% of total direct and indirect CO2 emissions [1]. Concerning the manufacture of the material a large part of this energy demand is used cement/lime production and to transport building materials.

Develop alternative construction materials to minimize the energy consumption in building construction sector is a must. One of these alternatives is the use of rammed earth because of its low embodied energy and reduction of carbon footprint. However, rammed earth structures are very sensitive to hydric conditions (more generally weather conditions such as rainfall, freeze-thaw, capillarity, etc.).

Studies on apparent mechanical behavior (stiffness, compression and shear strength) of rammed earth at different hydric state i.e. water content have been done. However, there are few effective stress approaches as well as large-scale studies involving mechanical behavior over time. Moreover, there are no studies on the behavior of these materials with both fluid and elastic properties at the same time.

This paper presents experimental results of determining dynamic viscosity and stiffness on unstabilized rammed earth wallet. The aim is to evaluate the link between the apparent mechanical performance and the varying hydric state inside the drying wallet after manufacture.

In this study, rammed earth wallet of 1.5m x 0.75m x 0.2m were manufactured with initial water content equal to 10%. The wallet was then left to dry for 8 weeks. While drying, the wallet was periodically mechanically tested at each week. Compression test followed by apparent stress relaxation test were performed for 8 weeks. Alongside, the hydric state inside the wallet was monitored by humidity sensors.

The compression test was done with loading-unloading cycle. The cycles were done at 0.1MPa to avoid damage on the wallet and in order to be representative of a classical vertical apparent stress for a one-story building. The strain was calculated using fields displacement coming from Digital Image Correlation technique in the central part of the wallet in order to avoid border effects. The total strain calculated varied from 0.18 to 0.1%. The apparent rigidity of a wallet was determined from the
unloading path. Results show that the apparent stiffness of the wallet increased from 100 MPa to 1500 MPa. These results are very comparable to those obtained at structural scale [2].

The dynamic viscosity was calculated from stress relaxation test. Figure 1 shows the dependency of stress with time, during stress relaxation of a wallet, while displacement is fixed. It was observed that, the stress reduces exponentially until it reaches an asymptotic value. This behavior was modeled using the combination of Maxwell and Kelvin Voight viscoelastic model; the combination is known as Three-Element model [3]. Figure 1 is showing the experimental curves with their respective model curves. Figure 2 shows the model adapted. Using this model, the coefficient of viscosity increased from $10^{10}$ to $10^{12}$ Pa.s during 8 weeks of drying. The apparent relaxation modulus of rammed earth structure increases as the sample dries. This means, the viscous behavior of rammed earth is highly dependent on the hydric state. That means creep effect can be considered in the same time that the hydro-mechanical coupling behavior. It is a significant factor to consider when constructing rammed earth wall.

<figure><img src="image_2.png" /><figcaption>Fig 1: Stress relaxation test results showing experimental and modelled curve at each week on a drying wallet</figcaption></figure>
<figure><img src="image_3.png" /><figcaption>Fig 2: Three element model for viscoelastic material</figcaption></figure>

**Reference:**

1. Levermore, Geoff J. "A review of the IPCC assessment report four, part 1: the IPCC process and greenhouse gas emission trends from buildings worldwide." *Building Services Engineering Research and Technology* 29.4 (2008): 349-361.

2. Chitimbo T, et al. "Hydro-Mechanics Coupling on Rammed Earth Material: Drying Experiment at Structural Scale" *Construction Technologies and Architecture* (2021): pp 698-706.

3. Kelly, P. Solid mechanics part I: An introduction to solid mechanics. *Solid mechanics lecture notes, University of Auckland* (2013): Pp. 298