On the contribution of virgin cork treatment in improvement of lightweight concrete performances

The use of cork aggregates in development of biobased concretes constitutes a promising solution. However, because of their chemical composition and surface characteristics, enhancing their compatibility with cement remains challenging. This study investigates, for the first time, the contribution of virgin cork treatment in improvement of lightweight concrete performances. The experimental work was carried out on cork concretes incorporating, in volume of aggregates, 50% of cork aggregates. Before incorporation, cork aggregates were treated using one of five treatments: NaOH, Ca(OH)2, hot water, ethanol and hornification. These treatments were selected based on previous studies where they proved effective in improving the surface of vegetal aggregates and in removing soluble compounds that may hinder cement hydration, thereby enhancing the interfacial bonding between cork and cementitious matrix. Concretes with treated cork aggregates were compared with a reference mix in terms of workability, physical, mechanical and thermal properties. Results showed that cork treatment decreased aggregates density and remarkably changed their microstructure, increasing hence both porosity (by 6.3-62%) and water absorption of cork concrete. Compared to the reference mix, treated-cork concretes unveiled significant improvement of both thermal and mechanical performance. The enhanced thermal behavior mainly results from the increased porosity, which promotes insulation through the creation of air voids, whereas the improvement in compressive strength, especially for hot-water and ethanol treatments, stems from the removal of inhibitory compounds and better interfacial bonding observed through SEM analysis. With compressive strength varying between 1.9 and 3.1 MPa and thermal conductivity of 0.33–0.66 W/(m.K), the studied cork concretes presented encouraging performances suitable for several building applications including thermal insulation elements, auto-bearing walls and lightweight screeds.