Mechanical testing procedure for local building materials : rammed earth and laterite building stones

by Abhilash Holur Narayanaswamy

Doctoral thesis in Génie civil

Under the supervision of Claude-Henri Lamarque and Jean-Claude Morel.

Thesis committee President: Jean-Emmanuel Aubert.

Thesis committee members: Antonin Fabbri, Anne-Sophie Colas.

Examiners: B. V. Venkatarama Reddy, Domenico Gallipoli.


  • Abstract

    Locally available building materials are proven energy efficient and eco-friendly, making them a sustainable building material. In the last two decades, use of raw earth as building material is augmented, owing to the environmental concerns construction industry is also reconsidering the use of raw earth, researchers on the other hand are working to understand the mechanical and dynamic behaviour of earthen buildings, yet the study of mechanical parameters possess multiple challenges due to material inert properties exposing the need of new experimental approaches to extract accurate mechanical parameters. Building techniques such as adobe, compressed earth blocks, rammed earth, and laterite building stones are on a verge of reclaiming elite position in construction industry. In this study, experimental investigation on two naturally available building materials, unstabilised rammed earth (USRE) and laterite building stones (LBS) are carried out. The work focuses on the parameters that need to be considered in the experimental procedures, which influences the mechanical properties of USRE and LBS are seen. The locally available soils in the region of Rhone-alps, France and laterite building stones from Burkina Faso are used in this experimental campaign. Rammed earth walls are constructed by compacting moist soil in layers, due to manufacturing technique there is a density gradient within the layer that leads to heterogeneity. On the other hand, the manufacturing parameters of the USRE such as compaction energy and manufacturing water content have a direct influence on the dry density of the material and therefore the strength. The manufacturing parameters and specimens replicating the in-situ condition are very important to understand the behaviour of USRE wall. Hence an experimental procedure to study the unconfined compressive strength, considering the influence of manufacturing parameters and specimens replicating in-situ conditions are performed along with the cyclic loading and unloading to study the elasto-plastic property of the USRE. The test procedure is performed on two different soils that are used to build USRE structures. Along with the compressive strength of USRE, the tensile strength and flexural strength are also presented by subjecting specimens under split tensile test and four point bending test. Another important parameter is the mechanical strength properties of USRE layer interface under lateral loads. A novel experimental procedure to study the interface strength properties are discussed in this study. The experimental procedure is simple and xii compact that can be performed using a simple uniaxial press using inclined metallic wedges that allows rectangular prism to undergo bi-axial loading. With the help of inclined metallic wedges, shear stress and normal stress can be induced on the specimen interface allowing to obtain coulomb’s failure criteria and hence the strength properties of the interface. Laterite building stones (LBS) which are mainly used in tropical countries are porous in nature. The moisture retention capacity of porous building material will bring indoor comfort, but the presence of water molecules within the material and their variation to the outdoor environment is responsible for complex mechanical behaviour. Hence an experimental investigation to analyse the moisture ingress of LBS and their influence on mechanical strength is designed. The moisture ingress is studied by subjecting LBS for moisture sorption and desorption test and moisture buffering test. Then the influence of moisture ingress on mechanical strength (flexure and compression) are investigated using three point bending test and unconfined compression test with loading and unloading cycles. This experimental investigation allows studying the moisture ingress and their influence on strength along with elasto-plastic behaviour of LBS.

  • Alternative Title

    Procédure d'essai mécanique de matériaux de construction locaux : terre battue et pierres de construction en latérite


  • Abstract

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