In-depth Analysis of Lime-Hemp Concrete and Water Vapor Interactions: Effect of water default and prediction of the sorption behavior

Abstract

Lime-hemp concrete (LHC) emerges as a sustainable building material due to its low embodied energy, carbon storage capabilities, and interesting properties for both winter and summer comfort. However, a comprehensive understanding of its moisture behavior is pivotal for its development and application in construction. This study investigates the moisture sorption behavior and isotherm characteristics of LHC across four formulations varying in density (321–478 kg/m³) and binder/particle weight ratios (BP = 1 and 2). Using a strict equilibrium criterion, over 3000 hours of Dynamic Vapor Sorption (DVS), experiments revealed some formulations failed to reach equilibrium during adsorption at RH levels above 60%, indicating irreversible processes characterized by offsets in equilibrium moisture content (EMC) at 0% RH after a complete cycle. These phenomena were attributed to insufficient water availability during mixing and/or excessive compaction. Formulations with a higher weight ratio (B/P=2) and significant compaction, such as BP2_420, exhibited the highest desorption offset (7.5% EMC), while those with a lower B/P weight ratio (B/P=1), such as BP1_379, showed reduced offsets below 2%, due to better water distribution. The study also showed that reversible sorption behavior, corrected for offsets, could be accurately described using the Guggenheim-Anderson-de Boer (GAB) model. Finally, the rule of mixtures reliably predicted sorption isotherms by combining the GAB parameters of hemp shive particles and binders, with deviations limited to a maximum error of 2.3%.