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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 SiO 2 -Al 2 O 3 -rich minerals and Portland cement (PC) powder. The finely pulverized mineral powder with the particle size distribution (PSD) of 0.4-40 µm was mixed with the vehicle solvent containing some agents, cement powder with PSD of 2-100 µm, 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 SiO 2 -Al 2 O 3 promoted by the alkali product Ca(OH) 2 were proposed as the main mechanism of ceramic formation.

The effect of moisture and porosity on thermal conductivity of tobermorite 14 Å as the major component of cement paste is studied by using molecular dynamics simulation with ClayFF potential. The calculated results show that the thermal conductivity increases monotonically as the moisture content by mass within the interior pores increases and the slope of the linear fitting function decreases as the porosity increases. Meanwhile, the normalized thermal conductivity is found to increase exponentially as increasing the moisture content by volume. Phonon density of states of porous and moist tobermorite 14 Å is used to explain the contribution of individual atoms and molecules to the thermal properties. The results can be potentially used to design higher thermal insulating materials with cement and concrete for energy saving buildings.