Design of hemp aggregate concretes for rehabilitation and retrofit works of vernacular architecture. Valorisation of hemp waste

Abstract

The present investigation is carried out as part of the rehabilitative action needed by the architectural heritage of a social nucleus, inhabited in the main by Senhaja Srair Berbers (Central Rif, Morocco) focussing on a positive impact on the environment, improved habitability and cultural valorisation of the same. Mortars and concretes found in several locations of this vernacular architecture (walls, coatings, floor and roof slabs) require attention due to their poor state of maintenance. According to this challenge, it is proposed a design of plant aggregate concretes for the needed interventions, that envision the incorporation of natural binders existing in the region and aggregates from local hemp, giving way to green concretes which include a light weight and insulation value by recycling of material, actually considered agricultural waste. Through the characteristics of the local hemp straw and the regions meteorology this study focuses on the use of chopped, whole stem materials and highlights the advantages of a wet preservation process of the same. Formulations with hemp aggregates and sieved soil are tested in their performances with sodium water glass as additive compared to lime, found in previous formulations. Samples were characterized compositionally, chemically (DRX, FRX, SEM) and physically tested and evaluated in their compressive and flexural strength, thermal conductivity, specific heat, open porosity and water vapor permeability. The proposed hemp concretes perform between insulation and construction materials and confirm their aptitude in retrofit interventions being their mechanical strength in the range of wall, slab and plaster applications and their thermal properties suitable for inside and outside coatings in Mediterranean climate conditions. Positive results are more evident in formulations with siliceous additive, whose properties overcome mortars with lime addition especially in their mechanical performance and resistance to water absorption without suffering undesired disabilities in their water vapor permeability. The proposed solutions minimize the use of commercial binders with negative environmental impact or incompatible properties for restoration works of natural structures, manage the use of local resources of rural surroundings with difficult access, allow better comfort conditions and promote integral socioeconomic rural development. © 2020, University of Cantabria - Building Technology R&D Group. All rights reserved.