Utilization of tree-bark in cement pastes

The climate change and the mineral resources reserves reduction highlight the necessity to find alternative ecological materials concerning the construction, energy and transport sector, among others. The development of bio-based thermal insulation products using agricultural and forest biomass has come recently to the forefront. The bark of the trees is a readily available, biological raw material of unique properties that outperforms as a bio-insulating material, alone or introduced in different polymeric matrices. In this study, bark powder of two pine species (scots pine and black pine) is chemically characterized and incorporated at 30% and 50% b.v. (of solids content) in cement matrix, aiming at the production of innovative insulation composites. The cement-bark composites were characterized, in terms of their resistance to compression, modulus of elasticity, thermal conductivity, thermal resistance and hygroscopic properties (swelling and absorption rate). The presence of bark in the cement matrix, concerning both bark species, decreased the compression strength of the composites, though a higher post-fracture resistance was observed. The bark share of 50% revealed lower strength compared to the share of 30%, as well as lower weight and density. The mild hydrothermal treatment was proved beneficial in the case of black pine bark specimens (30% share), which marked the highest compression strength after control specimens. The composites elasticity was increased by the bark introduction, especially of the hydrothermally treated bark. Additionally, the bark introduction improved the composites thermal resistance, with the bark share of 50% (especially the black pine one) to provide the highest thermal resistance. The hydrothermal treatment did not enhance further the composites thermal properties, but revealed a positive effect on their hygroscopic properties, namely lower water absorption and swelling values (especially the 30% bark content). The results demonstrated a high potential for the proposed cement-bark composites to be utilized in insulation, as well as several non-load bearing building applications. •Cement-bark composites present lower weight, density and compression strength.•Bark in composites entails increased thermal resistance, elasticity and ductility.•Bark mild hydrothermal treatment favors elasticity, strength, dimensional stability.•30% bark content more beneficial to strength, elasticity, hydrophobicity than 50%.•Cement-bark comp