Fly ash is a byproduct of coal combustion in thermal power plants. It is a fine, powdery material that is carried away in the flue gas during the combustion process. Instead of being released into the atmosphere, fly ash is captured and collected for beneficial use in various industries, particularly in the construction sector.

What is fly ash also known as?

Fly ash, also referred to as flue ash, coal ash, or pulverized fuel ash (in the UK), is a byproduct of coal combustion in coal-fired power plants. It is composed of fine particles that are expelled from the boilers along with the flue gases during the burning of coal. These particles are collectively known as fly ash. It is important to note that fly ash is considered a type of coal combustion residual (CCR) and is commonly used in various industries, particularly in construction and cement production, due to its beneficial properties.

What is the difference between fly ash and cement?

The main difference between fly ash and cement lies in their composition and role in concrete.u003cbru003eu003cstrongu003eComposition:u003c/strongu003e Fly ash is a byproduct of coal combustion and primarily consists of fine particles that are carried away with the flue gases. It contains mostly silicon dioxide (SiO2), aluminum oxide (Al2O3), and iron oxide (Fe2O3), along with other elements. On the other hand, cement is a binding material made primarily of calcium, silicon, aluminum, and iron.u003cbru003eSize and Shape: Fly ash particles are spherical and generally smaller in size compared to cement particles. This finer particle size contributes to improved workability and increased surface area for chemical reactions.u003cbru003eu003cbru003eu003cstrongu003eActivation:u003c/strongu003e Fly ash requires the presence of cement for activation. When cement and water are mixed, a reaction occurs called hydration, which forms calcium silicate hydrates (CSH), the main cementing product. The lime produced during cement hydration reacts with the fly ash particles, resulting in the formation of additional CSH. This reaction between cement and fly ash enhances the strength and durability of the concrete.u003cbru003eu003cstrongu003eCementing Properties:u003c/strongu003e The CSH formed from the reaction of cement and fly ash has similar cementing properties to the CSH formed by Portland cement. It contributes to the binding and hardening of the concrete, providing strength and structural integrity.

Is fly ash a waste material?

Yes, fly ash is considered a waste material as it is a byproduct of coal combustion in power plants. It is generated in large quantities and needs to be properly managed and disposed of. Due to its fine particle size and potential environmental impact, fly ash disposal requires careful consideration and adherence to regulatory guidelines. However, it is important to note that fly ash can also be beneficially used as a supplementary cementitious material in various industries, including construction, thereby reducing waste and promoting sustainable practices.

What is the source of fly ash?

The primary source of fly ash is coal-fired power plants. When coal is burned to generate electricity, the combustion process produces fly ash as a byproduct. Fly ash is carried away from the combustion chamber by exhaust gases and collected using filtration systems, such as electrostatic precipitators or baghouses. This collected fly ash is then stored and can be utilized in various applications, including concrete production, as a supplementary cementitious material.

What is fly ash in concrete?

In concrete, fly ash is a supplementary cementitious material that is added to the mix in combination with cement and aggregates. It is used to improve the performance and properties of concrete. When fly ash is incorporated into concrete, it reacts with the calcium hydroxide produced during cement hydration to form additional cementitious compounds. This reaction, known as the pozzolanic reaction, results in the formation of calcium silicate hydrates (CSH), which contribute to the strength and durability of the concrete.

What are fly ash u003cstrongu003euses?u003c/strongu003e

Fly ash is commonly used in concrete production as a supplementary cementitious material. It is also utilized in cement manufacturing, road construction, embankments, landfills, soil stabilization, brick manufacturing, and agriculture.

What are effects u003cstrongu003eof coalu003c/strongu003e ash u003cstrongu003eon humansu003c/strongu003e?

Exposure to coal ash can potentially lead to respiratory issues, skin irritation, contamination from toxic substances, water pollution, and occupational hazards for workers handling coal ash.

What is fly ash formula?

The chemical formula for fly ash can vary depending on the composition and source of the coal used. However, in general, fly ash is primarily composed of silicon dioxide (SiO2), aluminum oxide (Al2O3), iron oxide (Fe2O3), and calcium oxide (CaO). Other elements and compounds may also be present in smaller quantities depending on the specific coal and combustion process.

What are properties of fly ash?

Fly ash possesses properties such as pozzolanic activity, fineness, reactive silica and alumina content, reduced heat of hydration, improved durability, reduced carbon footprint, improved workability, and enhanced strength development.

Fly Ash Effects on Durability of Concrete - PDFYAR - Engineering Notes, Documents & Lectures

Fly ash, commonly used as an admixture in concrete and cement, has a significant impact on the durability of concrete structures. The growing use of concrete in harsh and potentially corrosive environments has led to an increased demand for its application. Concrete structures are relied upon to support various equipment, personnel, and products in the oil and gas industry. They are also employed in the construction of nuclear reactors, where they must effectively contain gases and vapors released under high temperatures and pressures during emergencies. In all these scenarios, the utilization of fly ash as a cementitious material plays a crucial role. Therefore, it is of utmost importance to study and comprehend the influence of fly ash on the durability of concrete. This article aims to explore and analyze the effects of fly ash on concrete durability.

How Fly Ash effects on Durability of Concrete

Ground Granulated Blast Furnace Slag (GGBFS) offers benefits to both fresh and hardened concrete due to its physical properties. In terms of fresh concrete, GGBFS is highly recommended for mix designs aiming to achieve a denser concrete mass, eliminating voids and ensuring solidity. This is crucial for enhancing the overall quality of the structure. Additionally, GGBFS plays a significant role in reducing permeability, making the concrete mass void-free and increasing its resistance to the passage of liquids or gases.

How Fly Ash Effects on Permeability of Concrete

Concrete permeability is closely tied to the amount of hydrated cementitious materials present at any given time. It has been observed that the permeability of fly ash concrete is lower than that of regular concrete after a curing period of 28 days. However, an interesting reversal occurs after six months, where the fly ash concrete becomes even less permeable and attains a significant level of impermeability. This change in the permeability of fly ash concrete over time can be attributed to the pozzolanic activity of fly ash. Initially, the pozzolanic reaction is relatively low in the early stages of concrete curing, but it gradually increases as the fly ash concrete ages. As a result, fly ash can contribute to improved concrete durability and enhanced imperviousness. Figure 2, provided by the US Department of Transportation, visually represents the impact of fly ash on concrete permeability.

Fly Ash Effects on Durability of Concrete — **Fig.2: Effect of Fly Ash on Concrete Permeability**

How Fly Ash Effects on Carbonation of Concrete

Carbonation is the reaction between carbon dioxide in the air and calcium hydroxide, as well as calcium silicates and aluminates in hydrates cement. This reaction produces calcium carbonate. It primarily takes place in moist environments and is influenced by concrete permeability, saturation degree, and the presence of available calcium hydroxide. Carbonation can potentially reduce the resistance of steel to corrosion. Therefore, it is important to consider the concrete mixture proportions, concrete cover, and duration of moist curing, particularly when using a significant amount of fly ash in the concrete.

Influence of fly ash on durability of concrete subjected to repeated cycles of freezing and thawing

Air entrainment in concrete is a commonly used method to enhance its resistance to frost, provided that all other requirements are fulfilled. The presence of fly ash in the concrete mixture can sometimes necessitate an increase in the amount of admixtures needed to achieve the desired level of entrained air. Additionally, fly ash may occasionally affect the stability of entrained air in fresh concrete. However, numerous research studies investigating the impact of fly ash on the durability of concrete subjected to repeated freezing and thawing cycles support the assertion made by Larson that fly ash does not appear to have any detrimental effects on the air voids in hardened concrete. When an appropriate volume of air is entrained, the characteristics of the void system in the concrete generally meet widely accepted criteria.

Fly Ash Concrete Abrasion & Erosion

Concrete is often subjected to wear from scraping, attrition, sliding of cars, ice, and other objects. It is believed that the ability of concrete to resist abrasion is directly related to its compressive strength. When using fly ash in concrete, which has low abrasion resistance, it is important to ensure thorough curing to prevent issues. Research has shown that concrete containing ASTM class F fly ash generally offers better resistance to abrasion compared to those containing ASTM class C fly ash or no fly ash at all. Water flowing over concrete surfaces can lead to erosion. By increasing the strength and cement content of the concrete at a fixed slump value, its resistance to erosion can be improved.

How Fly ash effect on sulfate resistance of concrete?

Dikeou’s research revealed that fly ash has a significant positive impact on the sulfate resistance of concrete. According to the U.S. Bureau of Reclamation’s Concrete Manual, various cementitious materials can be used to produce sulfate-resistant concretes.

How fly ash effects on alkali aggregate reactions in concrete

Fly ash has been found to significantly reduce the harmful effects of alkali aggregate reactions (AARs), particularly when siliceous aggregates are involved. However, the beneficial impact of fly ash is not observed in the case of alkali aggregate carbonation, which is another type of AAR. Nevertheless, the expansion resulting from alkali aggregate reactions can be effectively reduced by incorporating low calcium fly ash as a replacement for approximately 25-30 percent of the concrete, as long as the alkali content is below four percent. The utilization of high calcium fly ash has not received much attention, and there is limited information regarding its effectiveness. However, there are indications that the effective replacement level of high calcium fly ash may be higher compared to low calcium fly ash. Figure-3 provides a visual representation of the development of alkali aggregate reactions.

**Fig.3: Progresses of Alkali Aggregate Reactions in Concrete**

Effect of fly ash on the corrosion of steel reinforcement in concrete

Corrosion of steel reinforcement in fly ash concrete can occur due to the presence of chloride ions from seawater or deicing. When the carbonation depth reaches the steel reinforcement, it can reduce the passivity of the reinforcement, leading to corrosion if sufficient oxygen and moisture are present. However, corrosion can be prevented if the fly ash concrete cover is thick enough and impermeable, providing adequate protection against the ingress of oxygen and moisture to the reinforcement surface.

Fly ash effect on concrete exposed to seawater

Concrete exposed to marine environments faces various aggressive factors such as wetting and drying cycles, wave action, abrasion from debris and sand, freezing and thawing cycles, and the corrosion of reinforcement, all of which occur in a chemical medium. However, concrete that is fully submerged is less susceptible to these factors. Research indicates that fly ash concrete, with 25 percent replacement by mass, and when the water-to-cementitious materials ratio is below 0.50, demonstrates satisfactory performance when subjected to freezing and thawing as well as wetting and drying conditions.

One major concern regarding fly ash concrete is the corrosion of steel reinforcement caused by chloride ions present in seawater or deicing agents. When the carbonation depth within the concrete reaches the steel reinforcement, the passivity of the steel can be diminished. Consequently, if sufficient oxygen and moisture reach the surface of the reinforcements, the steel bars can corrode. However, it is possible to achieve adequate protection against corrosion by ensuring that the cover of fly ash concrete is sufficiently thick and impermeable.

FAQs about Effects of Fly Ash.

What is fly ash?

Fly ash is a byproduct of coal combustion in thermal power plants. It is a fine, powdery material that is carried away in the flue gas during the combustion process. Instead of being released into the atmosphere, fly ash is captured and collected for beneficial use in various industries, particularly in the construction sector.
What is fly ash also known as?

Fly ash, also referred to as flue ash, coal ash, or pulverized fuel ash (in the UK), is a byproduct of coal combustion in coal-fired power plants. It is composed of fine particles that are expelled from the boilers along with the flue gases during the burning of coal. These particles are collectively known as fly ash. It is important to note that fly ash is considered a type of coal combustion residual (CCR) and is commonly used in various industries, particularly in construction and cement production, due to its beneficial properties.
What is the difference between fly ash and cement?

The main difference between fly ash and cement lies in their composition and role in concrete.u003cbru003eu003cstrongu003eComposition:u003c/strongu003e Fly ash is a byproduct of coal combustion and primarily consists of fine particles that are carried away with the flue gases. It contains mostly silicon dioxide (SiO2), aluminum oxide (Al2O3), and iron oxide (Fe2O3), along with other elements. On the other hand, cement is a binding material made primarily of calcium, silicon, aluminum, and iron.u003cbru003eSize and Shape: Fly ash particles are spherical and generally smaller in size compared to cement particles. This finer particle size contributes to improved workability and increased surface area for chemical reactions.u003cbru003eu003cbru003eu003cstrongu003eActivation:u003c/strongu003e Fly ash requires the presence of cement for activation. When cement and water are mixed, a reaction occurs called hydration, which forms calcium silicate hydrates (CSH), the main cementing product. The lime produced during cement hydration reacts with the fly ash particles, resulting in the formation of additional CSH. This reaction between cement and fly ash enhances the strength and durability of the concrete.u003cbru003eu003cstrongu003eCementing Properties:u003c/strongu003e The CSH formed from the reaction of cement and fly ash has similar cementing properties to the CSH formed by Portland cement. It contributes to the binding and hardening of the concrete, providing strength and structural integrity.
Is fly ash a waste material?

Yes, fly ash is considered a waste material as it is a byproduct of coal combustion in power plants. It is generated in large quantities and needs to be properly managed and disposed of. Due to its fine particle size and potential environmental impact, fly ash disposal requires careful consideration and adherence to regulatory guidelines. However, it is important to note that fly ash can also be beneficially used as a supplementary cementitious material in various industries, including construction, thereby reducing waste and promoting sustainable practices.
What is the source of fly ash?

The primary source of fly ash is coal-fired power plants. When coal is burned to generate electricity, the combustion process produces fly ash as a byproduct. Fly ash is carried away from the combustion chamber by exhaust gases and collected using filtration systems, such as electrostatic precipitators or baghouses. This collected fly ash is then stored and can be utilized in various applications, including concrete production, as a supplementary cementitious material.
What is fly ash in concrete?

In concrete, fly ash is a supplementary cementitious material that is added to the mix in combination with cement and aggregates. It is used to improve the performance and properties of concrete. When fly ash is incorporated into concrete, it reacts with the calcium hydroxide produced during cement hydration to form additional cementitious compounds. This reaction, known as the pozzolanic reaction, results in the formation of calcium silicate hydrates (CSH), which contribute to the strength and durability of the concrete.
What are fly ash u003cstrongu003euses?u003c/strongu003e

Fly ash is commonly used in concrete production as a supplementary cementitious material. It is also utilized in cement manufacturing, road construction, embankments, landfills, soil stabilization, brick manufacturing, and agriculture.
What are effects u003cstrongu003eof coalu003c/strongu003e ash u003cstrongu003eon humansu003c/strongu003e?

Exposure to coal ash can potentially lead to respiratory issues, skin irritation, contamination from toxic substances, water pollution, and occupational hazards for workers handling coal ash.
What is fly ash formula?

The chemical formula for fly ash can vary depending on the composition and source of the coal used. However, in general, fly ash is primarily composed of silicon dioxide (SiO2), aluminum oxide (Al2O3), iron oxide (Fe2O3), and calcium oxide (CaO). Other elements and compounds may also be present in smaller quantities depending on the specific coal and combustion process.
What are properties of fly ash?

Fly ash possesses properties such as pozzolanic activity, fineness, reactive silica and alumina content, reduced heat of hydration, improved durability, reduced carbon footprint, improved workability, and enhanced strength development.

Fly Ash Effects on Durability of Concrete