OPTIMISING MOISTURE TRANSPORT IN BIO-BASED, EARTH AND NATURAL HYDRAULIC LIME MORTARS USING HYGROTHERMAL AND CHEMICAL CHARACTERISTICS

Abstract

The utilisation of bio-based materials as a construction material presents diverse and under researched challenges that can reduce carbon emissions and improve the hygrothermal performance of buildings. Within the United Kingdom (UK), the residential construction typology of housing is vast. Just within pre-1919 dwellings, energy costs are over 70% higher by comparison to the post-1990 equivalents. This thesis intends to provide tools to effectively optimise bio-based composites for hygrothermal conditions improvement in housing and whilst the composite has been optimised for UK conditions, the impacts of this thesis is versatile and can be applied across the world for example with other construction typologies, building materials and use. This research work can provide relevant information on tailoring bio-based materials whenever indoor hygrothermal conditions are crucial for energy efficiency and comfort of building users, either in the UK, Europe or across the world. Within the scope of this work, this thesis will aim to optimise the transport of water through bio-based earth mortar composites to be used in residential properties for relative humidity moisture management. Initially, the hygrothermal performance of 11 different bio-based and recycled raw materials was analysed (four different types of (Sheep and recycled) Wool insulation, Hemp, Wood Wool Board (WWB), Saw Mill Residue (SMR), Wood Fibre (WF), Straw, Insulated Cork Board (ICB) and Polyethylene terephthalate (PET). with particular focus on Moisture Buffering Value (MBV). The best 6 performing materials were retested and analysed. It was found that the differences in MBV were negligible and this value alone was not enough to be able to ascertained which material should be selected. A new methodology of understanding the shape of the adsorption and desorption curves and then grouping this would give a better assessment of the material performance. Earth-lime mortar panels were created using locally sourced material from Liverpool (NW England) and the previous bio-based fibres. Performance analysis of the bio-based composites was done at steady and transient states for hygrothermal optimisation of the panels. Prismatic, 0.1m2 x 0.1m2 squares and disc shaped samples were cast and samples were exposed to cyclical step changes in relative humidity at 75% for 8 hours and 53% for 16 hours at 23oC, in order to mimic a UK household occupancy. Results demonstrate that an optimised mix improved thermal properties if Saw Mill Residue (SMR) is added. Further to this, traditional, thermal method of analysis (using Thermogravimetry Analysis (TGA), Differential Thermogravimetry (DTG) and Differential Scanning Calorimetry (DSC)) has been for heritage and forensic investigation of the constituent elements of the material rather than a comparison with regards to their hygrothermal performance. The best performing bio-based composite was Mix 1 SMR with an MBV of 1.26 (g/(m2 %RH)) and Water Vapour Permeability (WVP) of 2.5 (x10-11) (kg.m-1.s-1.Pa-1). Latent heat generated in the bio-based composites was explored and analysed to consider the effects within a dynamic hygrothermal environment. Heat energy is released due to the change in state of water molecule from liquid to vapour (and vice versa) due to the latent heat of vapourisation and condensation. The latent heat of both raw bio-based fibres and when combined into an earth mortar matrix was identified, analysed and is consistently demonstrated even after 21 cycles of 24 hours. After these cycles, the mix design with Wool 2 produced the greatest sustained quantity of heat generated with samples temperature increase of 1.59oC during adsorption and 0.97 oC during desorption phase. The movement of water molecules in and out of samples was researched on a physicochemical basis and organic chemistry analytical techniques were utilised to gain a better understanding of the function and important on the hydroxyl group for hygrothermal performance. Utilising analytical chemistry and thermal methods of analysis for samples conditioned at different RH, can give a greater understanding of a building materials hygrothermal properties.