Papers by Keyword: Fly Ash (FA)

Abstract: The use of fly ash in cement and concrete has long been a common practice. However, in the Czech Republic, one of the largest producers of fly ash in the world, there is still a great mistrust of this material. One of the main reasons is variability properties of fly ash. But standard ČSN EN 450-2 defines the possibilities of optimizing the properties of fly ash. This paper is dedicated to optimizing the properties of fly ash, namely sorting and mixing.

Abstract: Loss of durability of concrete materials in sewage and chemical treatment facilities exposed to acidic environments is a key issue that affects the life cycle performance. Applications of organic coating such as epoxy and acrylic usually covers the concrete surface by physical addition normally failed to act as an effective coating due to debonding when the organic coating absorbs water. In this work, geopolymer was used as alternative material for concrete coating. Preparation of geopolymer involved fly ash, a materials containing high aluminosilicate and calcium mixed with various concentrations (6, 8 and 12M) of sodium hydroxide (NaOH). Subsequently, all samples were tested and analysed through compressive strength test and gel time. Geopolymers synthesised from 12M NaOH concentration exhibited high compressive strength and low gel time, hence was chosen as a coating for the concretes for the erosion evaluation. Results show that, concretes coated with geopolymers yielded low percentage of mass loss compared to the uncoated concretes. This suggest that geopolymers has high potential to be used as erosion mitigation coating to prevent the concretes from degrading due to the acidic environment.

Abstract: The current work presents the effect of alkali concentration and water content on fly ash based geopolymer material. In this paper geopolymer material was prepared where Si/Al ratio (1.85: 1) is fixed and solid to water ratio (S/W) and NaOH concentration (4M, 8M, 12M) were varied. All samples were tested to establish the roles of water and alkali on the setting time and strength. At low solid to water ratio, (S/W= 3:1), the water quantity is high and the hardening of gel phase take more time. However, as water content is reduced from S/W 3:1 to 4:1 ratio, the setting point decreased significantly and only small change in setting time is observed when S/W shifted from 4:1 to 5:1. Sample prepared with 8M of NaOH showed the highest compressive strength. In this regards, Fourier transform infrared spectroscopy (FTIR) results support this observation where broad band (asymmetric strectching band) become sharper and shift towards lower wavenumber (1082.36 cm^-1 to 985.16 cm^-1). This finding shows that, to obtain required processing time at desired mechanical strength (20-30 Mpa) for a specific application of geopolymer, the suitable amount of water must be established.

Abstract: Geopolymer is associated with the alkali activation of materials rich in Si and Al, and alkali activator such as sodium hydroxide is used for the dissolution of raw material with the addition of sodium silicate solution to increase the dissolution process. However, the trend of strength development of geopolymer using sodium hydroxide alone is not well established. This paper presents an evaluation on compressive strength of fly ash–based geopolymer by varying curing time with respect to different curing temperature using sodium hydroxide as the only activator. The samples were cured at room temperature and at an elevated temperature (60°C). Further analysis on the microstructure of geopolymer products cured at 60°C was carried out using Field Emission Scanning Microscopy (FESEM). It can be observed that the compressive strength increased as the curing time increased when cured at room temperature; whereas at elevated temperature, the strength increased up to a maximum 65.28 MPa at 14 days but gradually decreased at longer curing time. Better compressive strength can be obtained when the geopolymer was cured at an elevated temperature compared to curing at room temperature.

Abstract: Anorthite good sintering properties and strength, there promotion prospects in oil and gas fields in the ceramic proppant fracturing. In this experiment, fly ash, coal and limestone as raw materials by high-temperature reaction sintering ceramics, Explore mineral composition, the sintering temperature of the final preparation phase of the resulting composition and physical properties of the impact, better product performance obtained at 1250 °C.

Abstract: The objective of the present study is to ascertain the effect of fly ash (FA) on the lifecycle CO₂ assessment of reinforced concrete structures. The reliable lifecycle CO₂ assessment approach of concrete structures were established and then specified using the developed CO₂ a performance evaluation table. The system boundary studied was from cradle to recycling of concrete, which includes material system, concrete production, transportation, construction, use and recycling activity phases. The assumed time and regional boundaries for concrete mixes were 2012 and Seoul, South Korea, respectively. The carbonation depth of concrete and CO₂ uptake during use of structure and recycling phases were calculated based on the Yang et al.’s model. Using the performance evaluation table, the effect of FA on the lifecycle CO₂ assessment of concrete columns and beams in an office building was examined under the different concrete strengths. The parametric study clearly showed that high-strength concrete is favorable to the reduction of lifecycle CO₂ amount of concrete columns, whereas the reduction is not expected for concrete beams. The lifecycle CO₂ amount of concrete structures decreases with the increase in the substitution level of FA up to 20%, beyond which the decreasing rate is insignificant.

Abstract: In the present paper the durability of fly ash geopolymer mortars compared to that of cement mortars is investigated. Geopolymers can improve the ecological image of building materials, especially when their production is based on industrial by-products such as fly ash. Three series of fly ash based geopolymer mortars were prepared using calcareous sand to fly ash ratio (S/FA) varying from 0.5 to 2. In addition, cement mortar specimens were prepared using cement CEM I 42.5 N and CEM II 32.5 N. Durability of geopolymer and cement mortars was evaluated by means of compressive strength development, acid resistance, chloride diffusion and sulfate resistance. It was found that fly ash can be effectively used to produce geopolymer mortars with calcareous sand. Geopolymers exhibit competitive compressive strength compared to that of cement mortars. Geopolymer mortars develop their maximum compressive strength a few days after their casting. Geopolymer and cement mortars exhibit satisfactory resistance to sulphate attack. Cement mortars, generally, show better behaviour (compared to geopolymers) in chloride diffusion. Finally, geopolymers indicate improved performance against acid attack, compared to that of cement mortars.

Abstract: Inorganic foams offer several unique properties such as low thermal conductivity, fire resistance, or UV stability. Inorganic foam specimens were synthesized from fly ash and aluminium powder through an alkali-activation process. Depending on mix proportions, bulk densities ranged between 400 and 800 kg/m³. Thermal treatment at 80°C for 12 hours accelerated curing process. Compressive strength was found in the range 4.5-9.0 MPa, flexural strength 0.6-1.7 MPa, Young's modulus 0.6-1.1 GPa, thermal conductivity 0.14-0.16 W/m/K and thermal capacity around 1100 J/kg/K. Exposing the foams to temperature 800°C led to a small decrease of compressive strength while exposure to 1100°C sintered the foam to higher strength of 13 MPa. Volumetric shrinkage 20% occurred at 1100°C without further disintegration. Residual compressive strength was determined after exposure to NaCl, HCl, Na₂SO₄, MgSO₄, H₂SO₄. The highest reduction to 20% occured in both acids with pH=2 after one year of exposition. Digitized microstructures entered finite element analysis to validate a stress-strain diagram.

Abstract: In this research, the fly ash (F/A) discharged from a thermal power plant was recycled to manufacture geopolymer containing granules instead of sand. Several types of granules using fly ash were assessed. The properties of the geopolymer/granule composites were analyzed as a function of the crystalline phase and size of the granules, as well as the molding pressure. The compressive strength and density of the geopolymer composites containing the hydrated granules fabricated by hand-tapping were 5.7 MPa and 1.47 g/cm³, respectively, while composites created by pressure molding were 15.6 MPa and 1.73 g/cm³. These results are comparative or superior to those of commercial cement bricks (8 MPa according to KS F 4004). Therefore, the geopolymer/granule composites fabricated in this study can be applied to cement bricks and can be a base for the enhancement of the recycling rate of fly ash.

Abstract: This paper presents the workability properties of Self-Compacting Concrete (SCC) containing a ternary mix binder using Ordinary Portland Cement and agro-industrial wastes i.e; palm oil fuel ash (POFA) and low calcium based fly ash (FA). The mixtures were prepared with 0 to 40% cement replacement using agro-industrial wastes at 10% intervals. Water to binder ratio and cement content is kept constant at 0.38 and 540 kg/m³ respectively. Self-compact-ability parameters investigated were Slump flow, J-Ring, V-Funnel, Sieve Stability and Visual Stability Index Tests. It is found that agro-industrial wastes provide a positive effect on the workability properties of self-compacting concrete.