Wood fibres as additives in mortars: a sustainable reinforcement

Abstract

In mortars, the use of fibres has been diachronically a commonly used technique. In Ancient Greece, wood and straw fibres were particularly used to increase volume stability in clay and lime mortars. Overtime, with the evolution of technology, natural fibres were replaced by modern materials like polypropylene, steel, glass and carbon fibres. Recently, the climate change and the strong demand for independence from non-renewable mineral resources have urged the search for alternative ways to utilize bio-materials to produce innovative, high value-added products. The wood waste material, coming from loggings or trunks mechanical processing, constitutes valuable bio-degradable, non-toxic material of low environmental impact that could be utilized as reinforcements to produce advanced wood polymer composites. In the current study, fibres of two widely available wood species (black pine and beech) have been used (1-2 cm length). The fibres were added in lime-based and cement-based mortars in proportion 1.5% v/v of the mortar. Physical, thermal and mechanical properties were tested at the age of 28 and 90 days, while at fresh state, workability of the mixtures was recorded. It was found that in traditional systems, the formulations with black pine required higher amount of water for the same workability probably due to the higher hygroscopicity of the fibres. This was not the case in cement-based systems. Small reduction of the mechanical properties was recorded, as well as an increase of the water capillary absorption of the bio-fibres reinforced samples. Thermal conductivity was improved probably due to the porosity increase. In all cases, the shape of the samples was retained even after fracture and crack formation. Between the two wood species used, the black pine gave more beneficiary results. In general, wood-fibres revealed a high potential to upgrade the lime- and cement-based mortars performance and be further promoted in the construction sector.