The Role of Material Structure in Compacted Earthen Building Materials: Implications for Design and Construction

Rammed earth is an earthen construction material and an ancient construction technique. It is formed by compacting layers of moist sandy loam subsoil into formwork which is then removed, exposing the material and creating a freestanding, monolithic structure. In this thesis, the behaviour of rammed earth is investigated in terms of unsaturated soil mechanics of compacted earthen materials. Basic unsaturated soil mechanics theory is discussed and a method for linking the behaviour and material structure of an unsaturated soil is presented through the development of a model for predicting a soil's water retention curve using the soil pore size distribution and capillary and adsorption phenomena. A series of experiments is then performed in order to explain the behaviour of rammed earth in tension and compression under varying conditions in terms of the material micro-- and macrostructures. An analysis of the sample manufacturing process is presented in order to understand formation of rammed earth's structure in both natural and laboratory-prepared materials. The effects of temperature and humidity, related to a number of sites around the world, on the compressive strength and of changing water content and clay flocculation on the tensile strength of rammed earth are then investigated and combined in order to determine the sources of strength in rammed earth. The pore networks of several rammed earth samples under compression and those of rammed earth samples comprising multiple compacted layers are then investigated using X-Ray computed tomography in order to determine the effects of loading and layering on the material macrostructure and to support results presented in previous chapters. In the final chapter, implications for the design, construction and conservation of rammed earth structures are discussed based on the findings of investigations presented in the preceding chapters