Determination of specific heat capacity of bio-fibre earth mortars stabilised at different relative humidities using Differential Scanning Calorimetry

Understanding the relationship that earth-based mortars have with both water and temperature is imperative to optimise moisture buffering properties. Specific Heat Capacity (C-p) is a key factor to understand the benefits in terms of thermal mass and latent heat. This paper presents the results of bio-based earth mortars (with fibres consisting of two varieties of sheep wool: Wool 1 (W1), Wool 2(W2) and Saw Mill Residue (SMR)) stabilised at 53% and 75% Relative Humidity (RH). Differential Scanning Calorimetry (DSC) according to ISO 11357-4 was used to calculate C-p of the aforementioned mortars. The temperature range of this experiment was that of 0-50 degrees C with a particular focus on values at 20 degrees C as this best represented a suitable indoor temperature. From these experiments, the results demonstrate that when stabilised at different RH, the difference in C-p was bio-fibre dependant and had a range between 0.71- 1.01 kJ/kg.K at 53% RH and 0.85-1.14 kJ/kg.K at 75% RH. These differences could potentially be attributed to the materials ability to readily accept water molecules. This emphasised that incorporating bio-fibres to a plain mixture (PL) can increase the C-p by up to 60%; significantly improving the thermal inertia of the building material. By reducing this temperature differential, it will reduce the heating requirements of a building which as consequential carbon reduction and thermal comfort benefits. Overall, SMR has the largest C-p for 75% at 20 degrees C was 1.141 kJ/kg.K, therefore specifically, this fibre would be the most effective to implement within a building. It also demonstrates the differences of the samples adsorption and absorption of water in differing hygrothermal environments.

Automated summary

This study focuses on the specific heat capacity of bio-based earth mortars at different relative humidities, finding that the fiber content can affect the thermal performance of the mortars. Experimental results indicate that the specific heat capacity of mortars with sheep wool and saw mill residue varies significantly at different relative humidities.