  In this work, the effects of Si/Al ratio and moisture content on thermal
transport in sustainable geopolymers has been comprehensively investigated by
using the molecular dynamics simulation. The thermal conductivity of geopolymer
systems increases with the increase of Si/Al ratio, and the phonon vibration
frequency region which plays a major role in the main increase of its thermal
conductivity is 8-25 THz, while the rest of the frequency interval contribute
less. With the increase of moisture content, the thermal conductivity of
geopolymer systems decreases at first, then increases and finally tends to be
stable, which is contrary to the changing trend of porosity of the system. This
is mainly because the existence of pores will lead to phonon scattering during
thermal transport, which in turn affects the thermal conductivity of the
system. When the moisture content is 5%, the thermal conductivity reaches a
minimum value of about 1.103 W/(mK), which is 40.2% lower than the thermal
conductivity of the system without water molecule. This work will help to
enhance the physical level understanding of the relationship between the
geopolymer structures and thermal transport properties.
