In the last decades, bio-based building materials have regained interest in a global warming acceleration context. Hemp concretes, composed of hemp aggregates and binders (mostly lime or cement), are nowadays regularly investigated. Their good hygrothermal properties and the use of fast-growing bio-based resources that can store carbon in the building stock during its lifetime are their major features. However, the use of hydraulic binders in their composition presents some drawbacks with their embedded carbon footprint, thus the partial or full replacement of these binders with unfired clayey materials can be relevant. In this study, the use of different clayey quarry co-products, washing sludge, in replacement of traditionally used hydraulic lime is investigated. In laboratory, the studied materials are processed at a same rheological state that is equivalent to the on-field consistency of a conventional sprayed lime-hemp concrete. The hemp/binder ratio is remaining constant as far as possible. Two main issues are targeted in this work. Firstly, with a given clayey material one first aim is to highlight the effect of the reduction of lime content (from 20% to 2% in mass of the clayey binder) on dry mechanical properties (density, compressive strength) and thermal conductivity of these hemp concretes. Then at a given clay/lime ratio (lime addition of 10% in mass of the clayey binder) three other clayey materials are studied to highlight the effect of their variability (clay activity, particle size distribution, mineralogy) on the same properties. The first obtained results display the fact that the lime content reduction for a given clayey binder seems to lead to higher thermal conductivity, higher dry densities, and higher dry compressive strengths. For this given material the thermal conductivities (measured at 10 °C at dry state) are ranging from 0.06 to 0.072 W.m^-1.K^-1,(better than the conventional performances of lime hemp concretes) while their dry densities are ranging from 250 to 350 kg/m³. The second study highlights the fact that the mechanical and thermal properties of hemp concrete are much more impacted by the variability of clayey part of the binder. For all of the studied materials the thermal conductivities (measured at 10 °C at dry state) are ranging from 0.06 to 0.11 W.m^-1.K^-1, while their dry densities are ranging from 250 to 600 kg/m³. For some clayey materials that displayed low clay activity the hemp/binder ratio was modified in order to obtain a suitable consistency to be processed. Finally, the use of clayey quarry co-products in replacement of hydraulic lime in the binding phase of hemp concretes seems to be easily achievable, leading to robust thermal and mechanical behavior if the clayey materials is carefully chosen. It also seems possible to adapt the mix compositions to the variability of clayey materials with weaker thermal performances.

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