Most building materials are porous

Most building materials are porous media.

As a critical environmental factor, the influence of relative
humidity on VOCs diffusion is still not well understood.

In this study, VOC transport and sorption in
a porous medium in the building materials (calcium silicate) were measured under three levels of
relative humidity (25%, 50% and 80%) by using a dynamic dual chamber method.

Tests were conducted
for water-soluble compound (formaldehyde) and non-soluble compound (toluene).

In addition, the
transport of acetaldehyde, hexanal, benzaldehyde, butanol and decane through the calcium silicate were
also tested at 50%RH to study the relationship between the effective diffusion coefficient (De), partition
coefficient (Kma) and the VOCs’ physical properties (molecular weight, vapor pressure and Henry’s law
constant).

Experimental results showed that: relative humidity in the 80%RH led to a higher partition
coefficient for formaldehyde compared to 50%RH.


however, between 25% and 50%RH, there was no
significant difference in partition coefficient.

Partition coefficient of toluene decreased with the increase
of humidity due to competition of water molecules for pore surface area and the non-solubility nature of
toluene.

Relative humidity had no significant influence on the effective diffusion coefficient on both
formaldehyde and toluene for the range of moisture conditions tested.

The solubility of VOCs was found
to correlate with the partition coefficient of VOCs.

The partition coefficient of VOCs was not simply
inversely proportional to the vapor pressure of the compound, but also increased with the increase of
Henry’s law constant.