Formation and characterization of ceramic coating from alumino silicate mineral powders in the matrix of cement composite on the concrete wall

TL;DR

This study develops a ceramic coating from alumino silicate mineral powders mixed with cement to enhance concrete wall thermal performance, demonstrating densified ceramic formation with low porosity after curing.

Contribution

It introduces a novel inorganic ceramic coating from mineral powders and cement, with detailed analysis of its composition and formation mechanism.

Findings

Coating becomes a densified ceramic with 10% porosity after curing.

XRD and SEM analyses confirm the ceramic mainly consists of C-S-H and C-A-H phases.

The coating significantly improves thermal insulation properties.

Abstract

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.