Effect of SiO2 and Al2O3 on the setting and hardening …
This study investigates the effect of silica and alumina contents on setting, phase development, and physical properties of high calcium fly ash …
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Comparative mechanical and microstructural properties of high calcium
Fly ash is categorised into Class F and Class C as accordance to ASTM C618-19 based on the calcium oxide (CaO) content. Class F fly ash has CaO content lower than 18% while the Class C fly ash has CaO content greater than 18.0%. Most studies focused on using the blend of Class F fly ash and blast furnace slag [[6], [7], [8], [9]].
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Properties of high-calcium fly ash-based geopolymer concretes …
Geopolymer properties were improved by using high-siliceous materials. In this study, the Afşin-Elbistan fly ash (FA), which is high in calcium content (≈43%) and which does …
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Calcium wastes as an additive for a low calcium fly ash …
The minimum combined content of SiO 2, Al 2 O 3, and Fe 2 O 3 of 50% was detected for the Class C fly ash, with a high calcium content of 31.0 wt%. The median particle size (D50) of the Class C ...
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Effect of silica fume on compressive strength of ultra-high …
But for mixes with 10% CAC content, a high SF dosage (>10%) negatively influenced the compressive strength. ... The specific surface areas of the low-calcium fly ash, silica fume, and CAC used were 1.12, 19.02 and 1.60 m 2 /g, respectively, and their average particle sizes were 102.53, 15.48 and 13.85 μm, respectively.
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Mineralogy and Chemical Composition of High-Calcium Fly …
To understand the formation mechanism of high-calcium fly ashes, the mineralogical, physical, and chemical properties of several high calcium fly ashes and their different density fractions (<1.0, 1.0−2.5, 2.5−2.89, and >2.89 g/cm3) from a coal-fired power plant were characterized by X-ray diffractometry (XRD), field scanning electron microscopy equipped with energy dispersive …
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Durability of ternary blends containing high calcium fly ash and …
High calcium fly ash (HCFA) is less effective in comparison to low calcium fly ash in controlling sulphate attack in concrete [1], [2], [3], [4].In fact, high calcium fly ash has shown adverse effect under sulphate exposure [3].High calcium and high aluminasilicate glass contents of ASTM Class C fly ash are generally referred to as the dominant factors causing adverse …
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Mechanical and microstructural properties of high …
The Silica-alumina ratio of the developed geopolymer paste ranges from 2.75-3.0 with a ratio of 2.87 appeared to be the best in this work. Alumina emanates from the source materials of fly ash, while silica evolves from fly ash and anhydrous …
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Influence of Silica Fume on High-Calcium Fly Ash
Influence of silica fume content on temperature increase of fly ash-silica fume paste (designations according to Table 4). Figures - available via license: Creative Commons Attribution 4.0 ...
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Influences of Silica Fume on Compressive Strength and Chemical
Although elevated temperature curing can increase the compressive strength of alkali-activated mortar, its field applications are still limited. In this study, alkali-activated mortars were prepared using high calcium fly ash (FA) as a precursor. Small amounts of silica fume were used to partially replace high calcium fly ash at 3–9% by weight to increase the strength of …
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Properties of low-calcium fly ash based geopolymer concrete
The results showed the presence of low calcium, high silica and alumina content in fly ash whereas high calcium content was observed in OPC. Fig. 1 shows the XRD analysis of fly ash and OPC particles used in the present study. For fly ash; quartz, mullite, and albite, whereas for OPC; hatrurite, alite, calcium silicate, and quartz were ...
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Performance of high volume fly ash concrete incorporating …
This is due to the addition of hydrated lime providing more portlandite than the required amount to react with amorphous silica presented in fly ash and nano silica. Thus, the highly active nano silica tends to react with the high calcium hydroxide content and form more C-S …
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Influence of Silica Fume on High-Calcium Fly Ash Expansion
The purpose of this work was to study the possibility of neutralizing high-calcium fly ash expansion during hydration. The object of the study was the fly ash of Berezovskaya GRES, which is capable of independent setting and hardening. The test in the Le Chatelier molds showed that the divergence of indicator arms was 90–100 mm 1 day after mixing with water. The …
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Investigating the role of reactive silica in the hydration mechanisms
During the 80s, several workers highlighted the distinct behavior of Class C fly ashes during hydration. Marsh and Day [14] for example, compared the hydration of a Class C fly ash to a low lime fly ash, indicating that the combined CH 2 per unit weight of fly ash was substantially higher for the high lime one. Diamond [15] tested two high calcium fly ashes, the …
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GEOPOLYMER MORTAR INCORPORATING HIGH …
The present study has High Calcium Fly Ash (HCFA) and silica fume as the source material for the geopolymer mortar. In this experiment, it is proposed to mix HCFA with silica fume …
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Fly Ash
1.2.7 Chemical Composition. Chemical composition of fly ashes include silica (SiO 2), alumina (Al 2 O 3), and oxides of calcium (CaO), iron (Fe 2 O 3), magnesium (MgO), titanium (TiO 2), sulfur (SO 3), sodium (Na 2 O), and potassium (K 2 O), and unburned carbon (LOI). Amongst these SiO 2 and Al 2 O 3 together make up about 45–80% of the total ash. The sub …
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Effect of chemical admixtures on properties of high-calcium fly ash
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 …
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Characteristics of High Calcium Fly Ash Geopolymer Mortar
2.1 Materials and Equipment. The brown coal fly ash was supplied from Germany; it was treated with water, homogenized and ground by the manufacturer. The chemical composition of the ash, as determined by Bruker Axs S4 Pioneer X-ray fluorescence instrument, is given in Table 1.The ash does not comply with either Class F or class C according to ASTM …
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Pervious high-calcium fly ash geopolymer concrete
The high strength geopolymer paste could also be obtained with the use of fine fly ash [32]. In this study, the fly ash used was an as-received one and was rather coarse with the Blaine fineness of 2250 cm 2 /g. However, it was illustrated that the rather coarse high-calcium fly ash geopolymer could be used to produce pervious concrete with ...
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A Cementless Binder Based on High-Calcium Fly Ash, Silica …
This study aimed to comprehensively investigate the properties of a binder based on high-calcium fly ash and silica fume with a complex additive consisting of calcium nitrate and magnesium chloride. The strength characteristics, the characteristics of the hydration process, and the phase composition of the hydration products of the binder were investigated. Silica …
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Compressive strength and chloride resistance of self-compacting
The influence of high-calcium fly ash and silica fume as a binary and ternary blended cement on compressive strength and chloride resistance of self-compacting concrete (SCC) were investigated in this study. High-calcium fly ash (40–70%) and silica fume (0–10%) were used to replace part of cement at 50, 60 and 70 wt.%. Compressive strength ...
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THE HYDRAULIC ACTIVITY OF HIGH CALCIUM FLY ASH
The so-called pozzolanic activity is the feature of high active silica containing fly ash while the hydraulic activity is related to the high calcium ones. However, the chemical and phase composition is variable and related to the particle size. ... Table 1 Chemical composition of high calcium fly ash Component Content in mass/% power station ...
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Rice husk ash (RHA) effectiveness in cement and
This behaviour is better than low-calcium fly ash (FL where k = 0.5–0.7) and almost equivalent to high-calcium fly ash, but much worse compared to silica fume (SF, where k = 2.5–3). RHA exhibits these k-values due to high silica content, higher than FL, and lower than SF; whereas in addition with the later, RHA is much coarser than SF ...
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Compressive strength development and durability properties of high
This research investigated fresh and hardened properties, and long term durability performance in extremely cold weather of concretes incorporated with three mineralogically different high-calcium fly ashes. The following conclusions were drawn for 20 wt% replacement of total cementitious content by fly ash. 1.
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Mineralogy and Chemical Composition of High-Calcium Fly …
On the basis of chemical composition, high-calcium fly ashes can be classified into four groups namely: calcium oxide, calcium sulfates, Ca−Al−Si compounds, and Ca−S−X (X: Fe, Al, Si, …
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Fly ash for sustainable construction: A review of fly ash concrete …
Fly ash for sustainable construction: A review of fly ash concrete and its beneficial use case studies ... The class F FA is a byproduct of bituminous coal combustion. The iron, silica, and alumina content of class F FA is high, but the calcium content is low. ... the improvement in CS becomes less significant. A high alkali content in FA can ...
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The effects of calcium content of fly ash on hydration and
According to the difference in calcium content, fly ash is divided into high-calcium fly ash (C-class FA, abbreviated to HFA) and low-calcium fly ash (F-class FA, abbreviated to LFA) during actual engineering practice (Du et al., 2022). In general, HFA possessed higher reactivity than LFA in the hydration process of cement, which was widely ...
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Using Class C Fly Ash to Mitigate Alkali Silica Reactions in …
High-calcium fly ashes, classified as Cla ss C by ASTM International (ASTM) C618 definition, are often excluded as a means to mitigate alkali silica reactions (ASR) in concrete. This is because a relationshi p between high-calcium content and expansion was often documented when Class C fly ash was used at a 10% to 15% replacement
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Strength and resistance to sulfate and sulfuric acid of ground
The compressive strengths of composite with 3.75% silica fume immersed in 5% magnesium sulfate solution and 3% sulfuric acid solutions were substantially higher than the control. The strength loss was from the high calcium content of FBC fly ash and incorporation of silica fume thus increased the durability of the composite.
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Structure formation of slag ash concrete on the basis of high-calcium
Cementless slag ash concrete may be manufactured using high-calcium fly ash and silica fume as replacements for a binder and a microfiller, and incorporating slag sand from thermal power plants (TPP) as an aggregate. This concrete consists of waste products from TPP (fly ash and slag) and ferro-alloy plants (silica fume) and contains neither natural nor artificial aggregates for …
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Recycled aggregate high calcium fly ash geopolymer concrete …
High calcium fly ash (HCF), OPC and nS were used as the raw starting materials. ... The increase in nS resulted in the increase in silica content and mole ratio of SiO 2 /Al 2 O 3 in the system. The SiO 2 /Al 2 O 3 ratio of geopolymer mixtures with 0%, 1%, 2%, and 3% nS were 4.02, 4.10, 4.19, ...
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(PDF) A Cementless Binder Based on High-Calcium …
A Cementless Binder Based on High-Calcium Fly Ash, Silica Fume, and the Complex Additive Ca(NO3)2 + MgCl2: Phase Composition, Hydration, and Strength
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CLASS C FLY ASH
Class C fly ash must replace at least 25% of the portland cement to mitigate the effects of alkali silica reaction. If using any organic admixtures such as air entrainment, the amount added must be modified since the carbon (LOI) in the fly ash adsorbs organic compounds. Finally, if the fly ash has a high calcium content, it should not be used ...
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High-calcium fly ash recovery from wet-stored condition and its
The reactivity of silica in the hydration of fly ash-cement blends was found to hold a ... (>20%) class C fly ash was found to be more reactive to water than that in the low-calcium (<8%) class F fly ash . The calcium content has been found as an ... CaO in the high calcium fly ash could participate in producing cementitious ...
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Desert sand-high calcium fly ash-based alkali-activated mortar
High calcium fly ash (HCFA) is a by-product of lignite or sub-bituminous coal combustion in power plants. ... DS has a high content of silica-alumina substances and also contains some alkali metal oxides. The mineral phases of the HCFA, GGBS and DS were identified by XRD, ...
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