Mechanical properties of cob-earth composites: Variability and focus on the different calculation methods of Young's modulus

Mechanical property data for earthen materials are currently lacking. Usually, only average values are available. This study investigates the mechanical properties (tensile and compressive strength, Young's modulus) of cob. The results obtained for different cob mixes with and without fibres are analysed. Four different moduli - Ecycle, Etan, Emono and Edyn - are examined. Probability density functions, mean, standard deviation and percentiles are determined for each mechanical property. Value dispersion for all the properties studied is large and the difference between mean value and 5th percentile is 82%, 81% and 77% for tensile strength, compressive strength and Young's modulus, respectively.Modulus values are highly dependent on the calculation method used. Ecycle obtained during the unloading phase of the cyclic compression test is more relevant than Etan and Emono because only elastic deformations occur. The modulus increases with applied stress (from 120 to 327 MPa for specimens without fibres and from 70 to 232 MPa for specimens with fibres) highlighting the evolution of material microstructure during loading. Edyn is higher than Ecycle: the average dy-namic Young's modulus is 6917 MPa without fibres and 2088 MPa with fibres.