Optimization of minor-LiCl-modified gypsum as an effective indoor moisture buffering material for sensitive and long-term humidity control

Abstract

Porous gypsum materials buffer indoor humidity autonomously by adsorbing/desorbing moisture but are limited by poor adsorption capacity. Adding hydrophilic salt, such as lithium chloride (LiCl), is known to improve the capacity; however, the hydrophilic salt may block moisture desorption when overused, which is detrimental to moisture buffering and materials durability, particularly on humid days. This paper investigates the effects of minor LiCl addition on the fundamental (thermal conductivity, etc.), hygroscopic (adsorption/desorption), and moisture buffering performance of gypsum in daily and weekly humidity fluctuations. Results showed that minor addition of LiCl (1%–8%) substantially improves the gypsum board's fundamental properties and hygroscopic performance but avoids significant microstructure alteration. The improvement is reinforced with increasing LiCl ratio but then leveled off. The minor-LiCl-modified composites absorbed and desorbed moisture repeatedly without hysteresis for daily and weekly humidity fluctuations. The composite's moisture buffering effects on indoor air and the resulting energy-saving potentials were then modeled with study cases set in Shanghai and Paris; the composites effectively controlled indoor humidity, yielding a good energy-saving on dehumidification. Based on the results, a LiCl-mixing-ratio of ∼4% was proposed to serve as the optimum, under which the composited gypsum presented a remarkable capacity of 0.16 kg/kg and marked energy-saving by lowering indoor latent load from 7.8 W/m2 to 3.4 W/m2 and compensating for the investment increase in 1–2 years. These findings emphasize that implementing minor LiCl to porous gypsum materials enables distinct moisture buffering ability for sensitive and long-term humidity control on indoor air.