The Effect of Different Modifying Methods on Physical, Mechanical and Thermal Performance of Cellular Geopolymers as Thermal Insulation Materials for Building Structures

Abstract

Geopolymers represent a new class of inorganic materials that have great potential for practical application due to the properties of used raw materials, as well as the peculiarities of the cementitious matrix structure formed during the geopolymerization process. Cellular geopolymer specimens were produced in this study using class F fly ash product, which is characterized by low reactivity during geopolymerization. Several standard methods, as well as microstructural studies were applied to evaluate the effect of the following factors on the physical-mechanical and thermophysical characteristics of cellular geopolymers: the use of various mineral modifying components for synthesis of geopolymer systems; high-temperature treatment; the introduction method of alkaline activator. It was observed that “ageing” an aqueous alkali solution for 24 h before mixing with fly ash and foam agent was able to provide a boost of compressive strength of cellular geopolymer specimens up to about 2.5 times, while decreasing the average density by about 28% for all experimental mixes, except for PC-modified mixes. Additionally, high-temperature treatment at 600 °C enables an enhanced strengthening effect of pore structure in cellular geopolymer matrix up to 1.5 times. This phenomenon is especially pronounced for the mixes with 24 h “aged” alkaline solution with exception for PC-modified mixes; for those, high-temperature treatment at 600 °C leads to strength decrease up to 40%. The introduction method of alkaline activator and high-temperature treatment showed a controversial effect on thermal conductivity coefficient depending on the mineral modifying component used for the synthesis of cellular geopolymers. The proposed method for calculation of total porosity of cellular structure of geopolymers as a polycomponent material demonstrated a high degree of correlation with the R2 value of at least 0.96 between the average density and the calculated total porosity. However, a low degree of correlation with R2 not exceeding 0.29 was observed for the measured nanoporosity, regardless of the introduction method of alkaline activator and high-temperature treatment.

Biosafety binder based on gypsum-bearing waste

“…The binder obtained by sintering citrogypsum is a white powder with a specific surface area (SSA) of the order of 350-400 m 2 /kg [4].…”

“…1). At present time, the technology has been developed for processing this waste into a binder by sintering it in drum dryers [4].…”

Physical, Mechanical and Microstructural Characteristics of Perlite-Based Geopolymers Modified with Mineral Additives

“…In the reference [30], the authors investigated the modification of metakaolin-based geopolymer with silicon phosphate to provide waterproof characteristics. Reference [31] is devoted to the combination of fly ash and various mineral additives (Portland cement, metakaolin, kaolin, citrogypsum) and the study of their effect on mechanical, thermal and physical characteristics of geopolymer cement. The literature review showed that scientific research focused on the study of geopolymers based on natural aluminosilicates is widespread.…”

Scientometric Analysis of Global Research on the Utilization of Geopolymer Composites in Construction Applications

“…Accordingly, geopolymer mortars produced with low CaO binders have higher fire resistance characteristics compared to their cementitious or high CaO counterparts. In addition, the compressive strength of a cellular geopolymer produced with class F fly ash and a foam agent used as a thermal insulation material was increased up to 250% after a thermal exposure of 600 • C [62]. In another study on the microstructure change of fly ash-based geopolymer material under high temperatures, it was noted that the alkaline-activated matrix became denser and the strength increased owing to the high solubility of aluminosilicate components that result in the synthesizing of vitreous phases and the formation of new nanosized crystals [63].…”