Assessment of the hygrothermal, microstructural and chemical evolution of a hemp-based cementitious mortar under ETICS total weathering aging protocol

Abstract

Biobased composites are widely used for building insulation because of their hygrothermal performance, and their economic and environmental benefits. Among the different types of organic fibers for these materials, hemp shives are interesting because of their high availability in France and their low price. Nevertheless, the wide application of the hemp-based insulation mortars is hampered by the lack of data on its durability and behavior over the long term. The objective of this study, in a first part, consists in providing an original accelerated aging protocol inspired by the standardized one used for External Thermal Insulation Composite Systems (ETICS). In a second part, the selected aging weathering cycles were applied to investigate the hygrothermal stresses on the morphology, chemical composition and properties of hemp mortar samples. Experimentally, microstructural characteristics (as total porosity, SEM observation) and hygrothermal properties (as thermal conductivity, Moisture Buffer Value (MBV) and water vapor permeability) were measured and evaluated for both the reference state (after 28 days of conditioning) and after aging (after 28 days of conditioning and the aging cycles).Furthermore, X-ray diffraction and PH analysis were performed to investigate the chemical composition, especially the effect of carbonation. The obtained results reveal the presence of two processes in the aged hemp mortars: the carbonatation of the mineral matrix and the cracking of the interface between the hemp shives and the cement matrix. This later was quantified too. Despite the microstructural degradation, small deteriorations were recognized concerning the hygrothermal properties and behavior of hemp mortar, that is essential for an insulation material. These results provide data for better forecast on the degradation of the hemp mortars.