Manuscript title: Optimal mix study of sustainable lightweight composite bricks incorporating clay, wool and cork materials using circular economy approaches

Sustainable insulation is an integral part of energy efficient building design. Buildings have a significant carbon and energy footprint and using sustainable material is key to their decarbonization especially in cladding. In additional traditional cladding materials are not environmentally friendly. In developing countries with constrained construction budgets, limited resources and existing energy poverty using local resources is important to sustainable development, reducing building energy demand and supporting the local circular economy. Hence the aim of this research is to assess the thermal insulation and mechanical properties to identify an optimal mix of clay, cork, and sheep wool in composite bricks to improve energy efficiency in buildings. The novelty is that wool was introduced into the composite via an innovative method in the form of yarn network layers. The obtained results revealed that the thermomechanically optimal composite, which is clay specimen incorporating 12 % of the cork mass percentage with 2 % of wool in one layer (ClW2Co12) provides a gain of 64 % in thermal conductivity, 49 % in thermal effusivity, and 50 % in thermal diffusivity. Furthermore, the specimen ClW2Co12 is 14 % higher in flexural and 24 % lower in compressive strength compared to the reference material (clay alone) at the 30-day setting period. This innovative method ameliorates the lightness of the elaborated ClW2Co12 brick by about 52 %. These findings indicate that the developed composite made with locally available and economically local sustainable materials can be well used as thermal insulator in buildings using a circular economy approach.