Development of Stabilised Extruded Earth Masonry Units

Student thesis: Doctoral ThesisPhD


The UK is committed to reducing the environmental impact of construction, but due to growing population there is a requirement for new domestic housing. The embodied environmental impact is going to become an increasingly significant proportion of the whole life cycle of a building. There is therefore a requirement for research into low environmental impact construction materials. There has been a resurgence of earthen construction techniques as a response to growing environmental awareness and consideration. This has led to a renewed interest in earth construction and an increased use of earth within contemporary architecture. However, there are many barriers to the mainstream adoption of traditional methods of earthen construction, and only with the widespread adoption can the benefits be fully utilised. Extruded earth bricks that are manufactured using the well established fired brick production methods, without the firing can produce consistent, high quality, low cost bricks. As the bricks are of the same dimensions as current masonry there are fewer barriers to the adoption. This form factor, crucial for contemporary construction, relies on wall thicknesses of only 100mm. It has been shown that extruded earth bricks have a suitable strength for typical domestic loading. However, there are concerns about structural use due to loss of strength under elevated moisture contents; representing the greatest barrier to adoption. Stabilisation is a method by which the soil properties can be changed to increase strength under saturated condition. This thesis aim is to develop suitable methods of stabilisation for extruded earth bricks, with a lower environmental impact than existing masonry units. The scope is limited to the extrusion process and the soil currently used for fired brick production. To this extent seven brick soils used in the manufacture of commercially fired bricks were investigated into their physiochemical properties and engineering properties with respect to the identified mineralogy. There has been limited literature focusing on extruded earth bricks which is in part due to the difficulties of specimen manufacture. Two methods of laboratory scale specimen production were investigated and compared to full scale unfired bricks. A small scale extruder was used to make one third linear scale bricks and was shown to be suitable representation for unstabilised conditions. This allowed for laboratory scale testing of extruded specimens.Three categories of chemical stabiliser were investigated including cement, lime and alkali hydroxides. Compressive strength development over 7, 14 and 28 days was determined for specimens tested in ambient conditions and following 24 hours fully submerged in water. Varying mass fractions and initial curing regimes were investigated to determine the effect on compressive strength. Only 5% lime initially cured at 60 ◦C met the required structural criteria of a ‘dry’ and ‘wet’ compressive strength of 2.9 and 1.0MPa respectively. Metakaolin was subsequently added as a secondary stabiliser to improve the strength for all the primary additives. The change in compressive strength was variable, but did enable a total of six specimens to meet the required criteria, all with 5% lime as the primary stabiliser.A cradle-to-gate LCA was undertaken for the unstabilised and stabilised extruded earth bricks. The analysis only considered embodied energy and global warming potential and compared the results to conventional masonry units. Environmental criteria were developed based on the conventional masonry unit with the minimum impact. Considering this criteria, only two mixes were able to offer an improvement of the global warming potential.The reliance on highly processed commercial metakaolin was investigated by the partial thermal treatment of the brick soil. While the investigated chemical properties of this material were comparable to the metakaolin, the particle size distribution was significantly different. This resulted in a decrease in density, and no strength development when used with 5% lime.This study has shown the potential for extruded earth masonry to be used structurally and the requirement for stabilisation. A possible stabilisation technique has been proposed which will allow for the reduction of the embodied global warming potential, whilst meeting the structural requirements.
Date of Award12 Dec 2013
Original languageEnglish
Awarding Institution
  • University of Bath
SupervisorPete Walker (Supervisor) & Andrew Heath (Supervisor)

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