Rice-Husk-Ash-Based Geopolymer Coating: Fire-Retardant, Optimize Composition, Microstructural, Thermal and Element Characteristics Analysis

Abstract

Geopolymer using aluminosilicate sources, such as fly ash, metakaolin and blast furnace slag, possessed excellent fire-retardant properties. However, research on the fire-retardant properties and thermal properties of geopolymer coating using rice husk ash (RHA) is rather limited. Additionally, the approach adopted in past studies on geopolymer coating was the less efficient one-factor-at-a-time (OFAT). A better approach is to employ statistical analysis and a regression coefficient model (mathematical model) in understanding the optimum value and significant effect of factors on fire-retardant and thermal properties of the geopolymer coating. This study aims to elucidate the significance of rice husk ash/activated alkaline solution (RHA/AA) ratio and NaOH concentration on the fire-retardant and thermal properties of RHA-based geopolymer coating, determine the optimum composition and examine the microstructure and element characteristics of the RHA-based geopolymer coating. The factors chosen for this study were the RHA/AA ratio and the NaOH concentration. Rice husk was burnt at a temperature of approximately 600 °C for 24 h to produce RHA. The response surface methodology (RSM) was used to design the experiments and conduct the analyses. Fire-retardant tests and thermal and element characteristics analysis (TGA, XRD, DSC and CTE) were conducted. The microstructure of the geopolymer samples was investigated by using a scanning electron microscope (SEM). The results showed that the RHA/AA ratio had the strongest effect on the temperature at equilibrium (TAE) and time taken to reach 300 °C (TT300). For the optimization process using RSM, the optimum value for TAE and TT300 could be attained when the RHA/AA ratio and NaOH concentration were 0.30 and 6 M, respectively. SEM micrographs of good fire-resistance properties showed a glassy appearance, and the surface coating changed into a dense geopolymer gel covered with thin needles when fired. It showed high insulating capacity and low thermal expansion; it had minimal mismatch with the substrate, and the coating had no evidence of crack formation and had a low dehydration rate. Using RHA as an aluminosilicate source has proven to be a promising alternative. Using it as coating materials can potentially improve fire safety in the construction of residential and commercial buildings.

Effect of Different Pre-Treatment on the Microstructure and Intumescent Properties of Rice Husk Ash-Based Geopolymer Hybrid Coating

“…In addition, RHA-based geopolymers have a high potential to be resistant to thermal exposure [ 28 ], and this has led to the improved thermal stability and fire retardancy of the coating [ 4 ]. Geopolymers possess high thermal stability and fire resistance properties and would be an ideal alternative to conventional intumescent paint due to their unique properties.…”

Geopolymers—Design, Preparation, and Applications

“…The same authors, trying to gain more information on the fire-retardant properties of these geopolymers by using thermal and spectroscopic techniques, highlighted their glassy appearance, and how the surface coating changed into a dense geopolymer gel covered with thin needles when fired. The absence of crack formation and a low dehydration rate allowed them to conclude that using RHA in geopolymer formulation can potentially improve fire safety in the construction of residential and commercial buildings [ 6 ]. Although the insulation materials possess high fire-retardant characteristics, their mechanical properties are relatively poor, thus the effect of different material behavior, namely brittle and ductile, on the compressive strength properties, and the optimum material formulation that can satisfy both compressive strength and fire-retardant properties, were also studied by these authors.…”