Thermal performance exploration of 3D printed cob

Abstract

This paper investigates the thermal properties of 3D printed Cob, a monolithic earth construction technique based on robotically extruded subsoil and locally available organic fibres. The relevance of 3D printed earthen construction materials and the transition from vernacular construction towards a digitally-enabled process are critically discussed. The use of robotic manufacturing is outlined and the methodology to produce the necessary samples for thermal measurement is detailed. The results of the 3D printed samples are compared with traditionally-constructed Cob material of the same dimensions. The assessment has revealed strong potential for 3D printed cob as compared to its manually constructed counterparts in terms of thermal conductivity. Moreover, the testing process has helped in identifying several challenges in the 3D printing process of cob and the assessment of its thermal properties, which will ultimately bring the work closer to full-scale applications.

Hygrothermal Properties of Raw Earth Materials: A Literature Review

“…El Fgaier et al [32] work on three extruded raw earth bricks, produced by brickworks in France and composed by fine aggregates: they measure homogeneous λ-values around 0.9 W m −1− K −1 . Gomaa et al [41] present an interesting work on 3d-printed cob elements with 2% straw and cohesive soil, realized as solid elements, with two cavities and with one single straw-filled cavity: these specimens are tested in a heat flow meter and conductivities ranging from 0.32 W m −1− K −1 to 0.48 W m −1− K −1 are found, corresponding to dry densities from 1283.7 kg m −3 to 1780.3 kg m −3 . In the same work the authors report some materials developed inside the CobBauge Project 2018, where some English and French cohesive soils, suitable for cob constructions, have been mixed with hemp shiv, chopped reed and straw, with increasing proportions of 0%, 2%, 4% and 8% of the dry weight of soil.…”

Environmental assessment of large-scale 3D printing in construction: A comparative study between cob and concrete

“…1, there are differences in volume between the 3D printed versions and the conventional method. The reason for this is that the 3D printed walls are combined with inner gaps in their design by default, which is a beneficial characteristic of the 3D printing technology that enables a reduction in the amount of construction material needed and an increase in the thermal performance of the walls (Veliz Reyes et al, 2018;Gomaa et al, 2019…”

“…Two comprehensive studies on 3DP cob have recommended a new cob mix that has reduced viscosity. Based on a number of 3D printing tests, the water content in the 3DP cob mixture was increased to 23-25%, while the amount of straw was fixed at 2% (Gomaa et al, 2019) (Table 2). (Le et al, 2012;Agustí-juan et al, 2017;Nerella et al, 2016;Anell 2015).…”

“…In recent years, researchers have started to explore 3D printing of earthbased materials, such as cob, as an eco-friendly substitute to 3D printed concrete (Perrot et al 2018). It is claimed that 3D printing of earth materials can leverage the environmental potential of 3D printing techniques by reducing waste and the transportation and carbon footprint of the construction process (Gomaa et al, 2019;Veliz Reyes et al, 2018).…”

3D printing system for earth-based construction: Case study of cob

“…These criteria suggest that a 3D printing system of cob warrants further investigation as a potential pathway toward more sustainable 3DP practices, with a lesser environmental impact when compared to concrete 3D printing (Alhumayani et al 2020). Recent evidence supports this observation; an early study conducted on small material samples (Gomaa et al 2019) provides evidence that 3D printed cob elements have competitive thermal performance standards when compared to other materials such as concrete, brickwork, and conventional cob construction. A substantial share of recent research on 3DP for construction addresses 3D printing of cement and mortar-like materials.…”