Investigation of Cob construction: Review of mix designs, structural characteristics, and hygrothermal behaviour

• Published in: Journal of Building Engineering 2024-06, Vol.87, p.108959, Article 108959
• Main Authors: Haddad, Kamal, Lannon, Simon, Latif, Eshrar
• Format: Article
• Language: English
• Subjects: Cob; Earthen construction; Hygrothermal testing; Mixing ratio; Structural testing
• ISSN: 2352-7102; 2352-7102
• DOI: 10.1016/j.jobe.2024.108959

Earthen construction systems have potential hygrothermal, and environmental benefits over conventional building materials such as concrete. However, such systems are not yet fully optimised to be part of an energy-efficient building. To further optimise the material, this review explores peer-reviewed research articles that relate to distinct constituents used in cob mixes and the different testing methods used to assess the produced specimen's hygrothermal and structural performance. For data collection, a systematic keyword search was carried out on ScienceDirect, Scopus and Google Scholar search engines, and relevant books were also consulted. The filtering of journal articles was based on studying the abstracts followed by analysing their content within the scope of the review. The results show that the soil's constituents and the added fibre ratios critically affect the percentages of clay and water added to the mixture. Fibres' impact on the mix was experimentally assessed by multiple researchers using distinct types of plant aggregates. The percentage of fibre addition ranged between 0.9% and 3% for structural specimens and reached 25% for non-structural specimens with optimised insulation properties. The investigation of cob's structural performance highlights that the compressive strength of cob has ranged between 0.1 MPa and 2.02 MPa, in contrast, the tensile strengths were between 0.01 MPa and 0.75 MPa. The shear strength was found to range between 0.37 MPa and 0.63 MPa. Furthermore, the hygrothermal exploration of cob demonstrated that the thermal conductivity was ranging between 0.12 W/m.K and 1.06 W/m.K. The review has also reviled that the moisture buffering value (MBV) of different mixtures ranged between 1.06 g m−2 %RH−1 and 1.74 g m−2 %RH−1. The review finds that there is no consensus and robust collated data available about the ratios of the mixes concerning the hygrothermal and structural performance of the specimens. This paper collected the tests results from the literature and highlights the missing results that needs to be considered in further research work. •The average cob mixture consists of 72% subsoil, 26% water content, and 2% added fibres.•The lengths of the fibres have ranged between 20 mm and 300 mm when used with cob.•Casted cob mixtures achieved 3.18 MPa compressive strength, whereas 3D printed ones peaked at 0.89 MPa.•Thermal conductivity varied between 0.12 W/m.K for mixtures that contained hemp shive and 1.06 W/m.K fo