Nowadays geopolymer is promising and relevant material that can be effectively used in wide range of application areas. It is possible because of there are a lot of potential sources of raw materials for geopolymer synthesis. Raw components are the one of the key parameters that effect on geopolymer performance. On the other hands, the technological stages of geopolymer synthesis is no less important factor. The purpose of this study was to determine effect of technological parameters of geopolymer synthesis such as component composition of solid state phase, alkaline activator preparation and its introduction onto geopolymer paste as well as curing temperature on performance characteristics of geopolymer. Fly-ash based geopolymer samples were prepared with adding of different mineral components: Portland cement (PC), kaolin, metakaolin; different curing temperature conditions: ambient temperature and temperature treatment at 70 °C in oven during 24 hours; different methods of preparation and application of alkaline activator: using of fresh alkaline solution and using alkaline solution after 24 hours of cooling. The results show that efficiency of curing temperature conditions strongly depend on component composition of geopolymer paste. Samples, containing PC and metakaolin demonstrate better characteristics after curing under ambient temperature. Samples, containing kaolin and reference composition (fly ash only) the temperature treatment in oven is the best curing method (increasing in compressive strength up to 13 times). Using alkaline solution of NaOH after 24 hours of cooling gives a good effect on geopolymerization process and provides increasing in compressive strength value from 13 to 84 % for all experimental geopolymer pastes. However, average density for all compositions is varied slightly.
Production of high-performance construction materials, meeting the requirements of construction process when development of up-to-date buildings and structures is very relevant and requires the usage of effective polycomponent binding systems, including geopolymers This work studied mechanical performance, as well as strength, water absorption and water resistance of portland cement – Class F fly ash – NaOH hybrid geopolymer binding system. The bench scale testing was conducted on different mixes, including regular portland cement-based and Class F fly ash-NaOH geopolymer binders used as reference compositions. The developed hybrid binders demonstrated, that incorporation of portland cement up to 40% as a modifying agent, reduces the formation of water soluble mineral phases such as sodium carbonates and hydroxycarbonates in low reactive class F fly ash geopolymer binders. It was found, that the presence of portland cement in the system positively affects strength development and noticeably reduces water absorption and improves water resistance of the developed binders, which is related to formation of water resistant and stable calcium hydrosilicate phases (C-S-H)
Fly ash based hybrid geopolymers (HGP) containing different type of mineral admixtures such as portland cement (PC), kaolin and metakaolin (MK) were developed in this study. The improved values of compressive strength, water absorption and water resistance for PC-modified hybrid geopolymers versus MK-modified HGP and reference mix was observed. High-temperature treatment (600 °C) enables to boost compressive strength by 177 % and 55 % as well as water resistance by 34 % and 40 % for MK-modified and kaolin modified HGP, respectively. At the same time, the PC-modified HGP demonstrated a very low thermal resistance, which was confirmed by a rapid drop of compressive strength and distracted structure of the specimen subjected to high temperature.
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.
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