Setting Time and Compressive Strength of Geopolymers Made of Three Indonesian Low Calcium Fly Ash with Variation of Sodium Silicate Addition (original) (raw)
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The Investigation on Setting Time and Strength of High Calcium Fly Ash Based Geopolymer
Fly ash based geopolymer normally gets the optimum strength by heat curing. This is considered as a hindrance to in-situ applications. Therefore, development of fly ash based geopolymer that suitable for ambient curing will widen the application to the concrete structure. This paper reports the results of an experimental study on setting time and development of compressive strength of class C fly ash based geopolymer paste produced in ambient curing condition. The main synthesis parameters such as water to the geopolymer solid ratio, alkali to cementitious ratio and molarity of NaOH were varied to understand their individual effect on setting time and the mechanical properties of the resulting geopolymer. The results suggested that generally the setting time increased with the NaOH molarity and the compressive strength of 59 MPa was obtained for geopolymer mixture cured at ambient temperature for 28 days with alkali to a cementitious ratio of 0.35 and 10 M NaOH. The results will be useful for developing the knowledge of the use of high calcium fly ash in producing geopolymer. This would be beneficial to the understanding the future applications of this material as new binding material.
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2011
Fly ash was used as raw material for making geopolymer. The samples were prepared by mixing fly ash and activator: sodium hydroxide (NaOH) with varying the proportion of H2O and Na2O. In addition, the possibility of using rice husk ash (RHA) as a partial replacement for fly ash raw material was studied. After mixing, the mixtures were casted in a plastic mold and left to harden for 48 hr at room temperature and 60 ๐ C and further cured for 7 days. The existing phases were investigated by using XRD. Bending strength and density of the geopolymers were also examined. Results showed that the amount of H2O and Na2O in the mixtures had an effect on the properties of geopolymer. The strength decreased with an increase in H2O mol ratio and the appropriate mol ratio of Na2O was 1.0. The addition of RHA as a silica source also had an effect on the strength of geopolymer. The strength increased with an increase in silica content. Table1. Mixture compositions of sample in 1 st series Formula M...
Applied Mechanics and Materials, 2014
Geopolymer is produced from the alkali activation of materials rich in Si and Al with addition of silicate solution in order to improve the mechanical property. Limited research has been done with the absence of silicate solution in the geopolymerization process by varying solid/liquid ratio and on how it works for that condition on mechanical and physical properties. This paper presents an investigation on the mechanical and physical properties of fly ash based geopolymer by varying solid to liquid ratio using sodium hydroxide as the only activator. In addition, the strength development also been investigated. The samples were prepared using 50mm x 50mm x 50mm mould and cured at an elevated temperature (60 o C). It can be observed that the optimum compressive strength and density were obtained at solid/ liquid ratio of 4. In addition, the compressive strength of fly ash based geopolymer for all the solid to liquid ratio increased until 14 days and started to decrease later.
Effect of Variability of Fly Ash Obtained from the Same Source on the Characteristics of Geopolymer
MATEC Web of Conferences, 2017
Geopolymer properties is notably influenced by the quality of fly ash used as the precursor material. Fly ash obtained from the same source may have varying physical and chemical characteristics. The characteristics are influenced by, among other, the method and temperature of burning, the degree of grinding and the quarry sources of the coal. In this study, high calcium fly ash from a single power plant was investigated, to analyze the effect of its variability on the characteristics of geopolymer mortar. Fly ash samples were collected at ten different sampling periods. Three mixture compositions, with different sodium silicate solution to sodium hydroxide ratios, were prepared to produce geopolymer mortars. From the results, it was found that there are broad variation of fly ash chemical properties, however only small variation on the fineness and LOI was discovered. The setting time and compressive strength of geopolymer are influenced by the fly ash particle size, pH value and chemical content. Higher level of calcium oxide content increases the compressive strength, while finer particle size could have effect on the later age increase of the compressive strength. Faster setting time is also correlated with the higher pH value of the fly ash, with the tendency of flash setting occurrence for geopolymer using fly ash of high pH level.
Effect of chemical admixtures on properties of high-calcium fly ash geopolymer
International Journal of …, 2011
Owing to the high viscosity of sodium silicate solution, fly ash geopolymer has the problems of low workability and rapid setting time. Therefore, the effect of chemical admixtures on the properties of fly ash geopolymer was studied to overcome the rapid set of the geopolymer in this paper. High-calcium fly ash and alkaline solution were used as starting materials to synthesize the geopolymer. Calcium chloride, calcium sulfate, sodium sulfate, and sucrose at dosages of 1wt% and 2wt% of fly ash were selected as admixtures based on concrete knowledge to improve the properties of the geopolymer. The setting time, compressive strength, and degree of reaction were recorded, and the microstructure was examined. The results show that calcium chloride significantly shortens both the initial and final setting times of the geopolymer paste. In addition, sucrose also delays the final setting time significantly. The degrees of reaction of fly ash in the geopolymer paste with the admixtures are all higher than those of the control paste. This contributes to the obvious increases in compressive strength.
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Chemical Industry & Chemical Engineering Quarterly, 2015
This study deals with the mechanical and microstructural characterization of geopolymers synthesized from locally available fly ash. A low calcium fly ash was activated using a sodium silicate solution. Samples were characterized by means of flexural and compressive tests, Fourier transform infrared (FTIR) spectroscopy, X-ray powder diffraction (XRD), and scanning electron microscopy (SEM). Porosity and pore size distributions were identified using mercury intrusion porosimetry and gas sorption. The compressive strength of the produced geopolymers, which is in the range of 1.6 to 53.3 N/mm 2 , is strongly related to the water content as well as SiO 2 /Na 2 O mass ratio of an alkali activator. The compressive strength significantly increased with decreases in the water content and increased silicon concentration used for the synthesis of geopolymers.
Effect of Particle Size on Physical and Mechanical Properties of Fly Ash Based Geopolymers
Transactions of the Indian Institute of Metals, 2019
The particle size of fly ash has influenced the physical and mechanical properties of geopolymers. Fly ash completely was ground to different pre-decided sizes, sieve sizes 180 lm, 90 lm and 45 lm (80 mesh, 170 mesh, 325 mesh) for formulation of geopolymer paste, and two activators were used: 8(M) NaOH and 1:1 mixture of NaOH and Na 2 SiO 3. The heat evolution increased with increasing fineness of fly ash. The increase in ambient temperature enhanced the extent of geopolymerization. The maximum heat flow was obtained with the finest fly ash particle of size 45-lm (325 mesh). The microstructures of the various geopolymers revealed the compactness of the structure which had the finest 45-lm (325 mesh) particle size and silicate-activated geopolymers. Apparent porosity was found to decrease with increasing fineness and addition of sodium silicate. Mercury intrusion porosimetry (MIP) revealed the total porosity; median pore size and average pore diameter were found to decrease with increasing fineness. However, mesopores were seen to be more in 45-lm (325 mesh) fly ash geopolymers compared to 180-lm (80 mesh) fly ash geopolymers. Compressive strengths of geopolymer formed by 45-lm (325 mesh) particle size had greater compressive strength in comparison with the coarser one. Inclusion of sodium silicate in the activator solution was helped in enhancing the compressive strength.
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This paper is focused on the utilization of deposited fly ash as a main component of geopolymer. After determination of particle size distribution, moisture content, real and bulk density and specific surface area of the raw fly ash, mechanical activation was performed by laboratory scale ball mill. This step is introduced for improving the reactivity of raw material. Then test specimens were produced by geopoliomerisation using a caustic spent liquor (NaOH). Compressive strength was determined on cilindrical specimens. Finally, samples of the ground fly ash based geopolymer specimens were analyzed by X-ray diffraction, optical and scanning electron microscopy. Results prove that geopolymer production with proper strength from the investigated F-type deposited fly ash is possible. The uniaxial compressive strength of obtained composites strongly depends on the fineness of the ground fly ash. XRD results show that comparing the crystalline components for different geopolymer samples,...
Chemical Reactions in the Geopolymerisation Process Using Fly Ash-Based Geopolymer: A Review
The development of our world, demanding the power supply which is produced by combustion of coal. Unfortunately, the million of tons of fly ash and related-products have been generated. To overcome these problems, fly ash was used in term of geopolymer to produce precast structure, non structural elements, concrete pavements, concrete products and immobilization of toxic waste that are resistant to toxic waste that are resistant to heat and aggressive environment Geopolymer is a material produced by inorganic poly-condensation, i.e., by so-called "geopolymerization." The process comprises dissolution of aluminosilicate followed by condensation of free silicate and aluminate species to form a three-dimensional structure of silico-aluminate structures. This process involving alumino-silicate materials is a complex process that has yet to be described fully. Several studies focused the dissolution reaction of fly ash, rate of reaction, thermodynamic properties of the reaction and mechanism of hardening process involved in geopolymerisation.The raw materials of geopolymer, such as kaolinitic clays, metakaolin, fly ashes, blast furnace slag, mixtures of fly ashes and slag, mixtures of fly ashes and metakaolin, mixtures of slag and metakaolin, mixtures of slag and red mud, and mixtures of fly ashes and non-calcined materials like kaolin and stilbite have significant effects on the properties of the resulting geopolymer. Recent studies have been conducted to determine the effect of SiO 2 /Al 2 O 3 ratios on the properties of the geopolymer, such as compressive strength, setting time, strength development, composition of the gel phase, and the microstructure of the alkaliactivated material. It is evident that several factors related to the chemistry of the raw materials and the production of the geopolymer affect the performance of the final geopolymer products.
Comparison of Using NaOH and KOH Activated Fly Ash-Based Geopolymer on the Mechanical Properties
Materials Science Forum, 2014
Geopolymer synthesis has two main requirements to fulfil which are the source material that is rich in Silicon (Si) and Aluminum (Al) and alkali activator such as sodium/potassium hydroxide. Sodium hydroxide (NaOH) is widely used for the synthesis of geopolymer compared to potassium hydroxide (KOH) with addition of silicate solution for the purpose of increasing dissolution process. However, the comparison of using different activator in the absence of silicate solution for geopolymer synthesis is not well established. This paper presents an evaluation on compressive strength of fly ash-based geopolymer by using different activator (KOH and NaOH) with respect to different curing conditions (time and temperature) in the absence of sodium silicate. The samples were mixed using mortar mixer and prepared in 50mm x 50mm x 50mm mould for determination of compressive strength. It can be observed that the highest compressive strength up 65.28 MPa was obtained using NaOH. Meanwhile, synthesis using KOH only recorded 28.73 MPa. The compressive strength was better when cured at elevated temperature (60 o C) than room temperature (25 o C). Further analysis on the microstructure of the highest compressive strength geopolymer samples for both activators was carried out using Field Emission Scanning Microscopy (FESEM) and Raman spectroscopy.