Development of a method to relate the moisture content of arnbuilding material to its water activity

摘要

Subjective indicators of building dampness consistently have been linked to health,rnbut they are, at best, semi-quantitative,rnand objective and quantitative assessments ofrndampness are also needed to study dampness-relatedrnhealth effects. Investigators canrnreadily and non-destructivelyrnmeasure the “moisture content” (MC) of building materialsrnwith hand-heldrnmoisture meters. However, MC does not indicate the amount ofrnthe water in a material that is available to microorganisms for growth, that is, thern“water activity” (A_w). Unfortunately, A_w has not been readily measurable in the fieldrnand is not relatable to MC unless previously determined experimentally, because forrnthe same moisture meter reading, A_w can differ across materials as well as during moisturernadsorption vs desorption. To determine the A_ws that correspond to MC levels,rnstable air relative humidities were generated in a glove box above saturated, aqueousrnsalt solutions, and the A_w of gypsum board and the relative humidity of the chamberrnair were tracked until they reached equilibrium. Strong correlations were observedrnbetween meter readings and gravimetrically determined MC (r=.91-1.00),rnamongrnreadings with three moisture meters (r=.87-.rn98), and between meter readings and gypsumrnboard A_w (r=.77-.rn99).