  Enhancement of thermal performance of concrete wall is nowadays of great
importance in reducing the operational energy demand of buildings. We developed
a new kind of inorganic coating material based on \ce{SiO2}-\ce{Al2O3}-rich
minerals and Portland cement (PC) powder. The finely pulverized mineral powder
with the particle size distribution (PSD) of 0.4-40 $\mu$m was mixed with the
vehicle solvent containing some agents, cement powder with PSD of 2-100 $\mu$m,
and water in the certain weight ratio, producing the colloid solution. After
application within 2 hours to the plaster layer of concrete wall and sufficient
long hardening period of over three months, the coating layer of 0.6-1.0 mm
thickness was observed to become a densified ceramic. Powder X-ray diffraction
(XRD) experiments were performed to identify the crystalline components of
minerals, cement and ceramic coating powders. Three- and two-dimensional
surface morphologies and chemical compositions of coating material were
obtained with the optical interferometer and scanning electron microscope (SEM)
equipped with an energy dispersive X-ray analyzer (EDX). These XRD and SEM/EDX
analyses demonstrated obviously that the coating layer is mainly composed of
the calcium-silicate-hydrate (C-S-H) and the calcium-aluminate-hydrate (C-A-H)
ceramics with the relatively small number of closed pores (10\% porosity)
compared with the cement mortar and concrete layers. Two-step hydrations of
cement and subsequently \ce{SiO2}-\ce{Al2O3} promoted by the alkali product
\ce{Ca(OH)2} were proposed as the main mechanism of ceramic formation.

Materials Science