Hygro-thermal characterization of the hemp concrete modified with the gum Arabic admixture

Abstract

This paper presents the investigation of the hygro-thermal properties of hemp concrete modified with gum Arabic (GA) admixture. The effects of modifying agents on the composite: density, total porosity, thermal conductivity, vapor permeability, sorption/desorption curves, and capillary uptake were studied. The main findings were the following. A slight tendency to increase density (i.e., from 444.2 to 450.2 kg/m3) and decrease porosity (i.e., from 79.5 to 79.0 %) with an increase in the admixture content was observed. The exception was the composite with the lowest amount of GA admixture (i.e., 1 % wt.), which had a lower density (i.e., 440.5 kg/m3) and higher porosity (i.e., 79.8 %) than the reference composite with no admixture. Thermal conductivity for dry composites rose by approximately 10 % for higher amounts of GA admixture (i.e., to 0.1179 and 0.1181 W/m/K for 3 and 5 % wt. of GA, respectively), while for lower ones (i.e., 1 % wt.), it was comparable to reference hempcrete (0.1067 W/m/K for reference vs 0.1053 W/m/K for 1 % wt. of GA). An increase in the moisture content of composites increased thermal conductivity but also reduced its variation for different GA contents. All composites had similar water vapor permeabilities on the levels of 3∙10-11 and 5∙10-11 kg/m/s/Pa for dry and wet caps, respectively, and no simple relationship was found between water vapor permeability and GA content. The addition of GA caused the shift of sorption/desorption curves in the direction of higher moisture contents, increasing amounts of absorbed water more than two times in higher relative humidities. The presence of higher amounts of GA (i.e., 3 and 5 % wt.) reduced the height of the water rise by capillaries, i.e., by 10.3 and 21.0 %, respectively, after 8 days of testing, and slowed down the progress of capillary uptake. However, the composite with 1 % wt. GA absorbed 16.7 % more water than the reference sample.