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Fly Ash: Types, Uses and Role of 3D printing in Preparation of Fly Ash Bricks

 |  pallavi mahajan

Fly Ash: Types, functions, and Role of 3D Printing in Creating Fly Ash Bricks

What is Fly Ash?

It is the residue from the combustion of powdered coal collected by electrostatic precipitators or separators from the gases of thermal power plants.

As Per ACI, Fly ash is defined as, "a very small amount of slag obtained from the burning of ground or powdered coal. This slag is transported from the furnace through the boiler by flue gases." Fly ash is the residue from the pulverized coal-fired electricity generating power plants.”

Fly ash is made up of very small powdered particles that are mostly spherical, either solid or hollow, and is mainly glassy or amorphous. Fineness is one of the important physical properties of fly ash that contributes to the pozzolanic reactivity.

3D printing in construction

        Fly Ash powder. Image source: Linkedin

The size of the fly ash particles ranges from 0.5 μm to 100 μm. The average size of the fly ash is 20 μm, which is similar to that of the average particle size of Portland cement.

Fly ash is used in concrete as a supplementary cementing material that generally acts as a water reducer in concrete, like a chemical water reducer.

When fly ash is combined with lime and water, the mixture formed is similar to Portland cement.

Fly ash is very beneficial from an environmental point of view. Fly ash upgrades the performance and quality of concrete.

Fly ash improves the plastic properties of concrete, increasing the workability of concrete, decreasing the water demand and also decreasing the segregation and bleeding while lowering the heat of hydration.

Using fly ash in concrete increases the strength of concrete, decreases the permeability and corrosion of reinforcing steel. It also increases the sulphate resistance and decreases the alkali-aggregate reaction.

Fly ash manifests its strength very slowly as compared to concrete made by only Portland cement.

It is economical and environmentally friendly.

Classification of Fly Ash:

ASTM broadly classify fly ash into two classes based on the type of coals:

  • Class F
  • Class C

Class F:

Fly ash normally produced by burning anthracite or bituminous coal is classified as a Class F fly ash.

Features of Class F fly ash

  1. It has less than 5% CaO. (Calcium oxide)
  2. It has pozzolanic properties only.


Class C:

Fly ash normally produced by burning lignite or sub-bituminous coal is classified as a Class C fly ash.

Features of Class C fly ash

  1. It has more than 10% CaO.
  2. It possesses pozzolanic and cementitious properties.

Physical and chemical properties of Fly Ash:

Chemical properties according to (IS: 3812 - Part -1: 2003)




Characterestic Requirement
            1.                                                         Silicon Dioxide (SiO2) plus Aluminium Oxide (Al2O3) plus Iron Oxide (Fe2O3) percent by mass, Min 70.0
2 Silicon Dioxide (SiO2), percent by mass, Min 35.0
3 Reactive Silica in percent by mass, Min 20.0
4 Magnesium oxide (MgO), percent by mass, Max 5.0
5 Total Sulphur as Sulphur Trioxide (SO3), percent by mass, Max 3.0
6 Available Alkalis, as Sodium Oxide (Na2O3), percent by mass, Max 1.5
7 Total Chloride in percent by mass, Max 0.05
8 Loss on Ignition in percent by mass, Max 5.0

Table1: Chemical properties of fly ash.

Advantages of Fly Ash:

  1. Fly ash is inexpensive and environmentally friendly.
  2. The waste material from industries is used to build quality building material.
  3. Fly ash is a very fine particle that builds a denser product, hence the size of pores are reduced.
  4. Fly ash improves the workability of concrete for the same water-cement ratio.
  5. It reduces the permeability to water and aggressive chemicals.
  6. It enhances the strength of concrete.
  7. It reduces the heat of hydration.
  8. The fine particles in fly ash reduce bleeding and segregation and improve the pumpability and finishing.
  9. Using fly ash concrete gives good workability, finishing and durability.

Disadvantages of fly ash:

  1. The quality of fly ash affects the quality of concrete and its strength.
  2. Bad quality fly ash increases the permeability of concrete and hence causes damages in the building.

Uses of Fly Ash:

  1. It is used in the construction of mass concreting, such as retaining walls, dams, pavements, etc.
  2. It is also used in the manufacturing process of bricks, asbestos sheets, asbestos pressure pipes, blocks, etc.
  3. It is used in the construction of high performance concrete.
  4. It is used in the construction of cold weather concreting.
  5. It is usually used in the construction of roads and pavements.
  6. It is used in the formation of geopolymer concrete.

The following are the effects of Fly Ash on the Properties of Concrete:

  1. Good quality fly ash decreases the water demand for the desired slump.
  2. With the reduction of unit water content, bleeding and drying shrinkage will also be reduced.
  3. Since fly ash is not highly reactive, the heat of hydration can be reduced by replacing part of the cement with fly ash.


Effect of fly ash on hardened concrete :

  1. Since the pozzolanic reaction proceeds slowly, the fly ash concrete tends to be lower than concrete without fly ash.
  2. Due to continued pozzolanic reactivity, concrete develops strength at a later age, which may exceed the strength of concrete without fly ash.
  3. It also produces dense concrete which reduces water and gas permeability.
  4. The pozzolanic reaction occurs in the presence of moisture, therefore fly ash concrete should be cured for a long period.

Tests on Fly Ash:

The following tests are conducted on fly ash:                         

Using 3D printing Technology in Building construction

3D printing technology

3D printing in construction. Image source: Designbuildings

3D modeling is the process of creating 3 dimensional objects based on the computer using a special software called 3D modeling software. 3D printing is where a digital object created in a 3D modeling software is turned into a physical model through the help of a 3D printer. Nowadays most constructions make use of 3D printing technology to aid in the construction process. 3D printing has many uses in the construction industry. For example, architectural designers use 3D modeling to draw plans of the houses and even generate the entire 3D design of the building in a CAD software and thereafter a 3D printer is used to print the model.

Also, 3D printing has been used in the construction of an entire building through the help of large format 3D printers

The material used for 3D printing usually depends on the type of 3D printer being used and the type of design being created. Water and aggregate, along with additive admixture are used in proportion to modern concrete cement, to improve the properties of mortar. Generally, additive admixtures have modified the properties of fresh and hardened concrete. Additives used for producing the concrete are fly ash, blast-furnace slag, silica fume, etc. They are treated as a chemically passive component.

Fly ash is a widely used admixture in concrete because of its fineness, chemical and phase constitution and pozzolanic activity. Fly ash improves the properties of mortar or hardened concrete. At the time of mixing, fly ash of 5% the total cement mass is added. 

Using 3D Design in the Preparation of Fly Ash Bricks

In addition to the above uses, Fly ash is also greatly used in making bricks used for masonry structures. Fly ash bricks are a great alternative to red clay bricks. 3D designing can be helpful in the preparation of customized Fly ash bricks. 

3D printing technology

Fly ash bricks. Image source: Azuko

You can use a 3D modeling software like SelfCAD to prepare the design of your brick, specify sizes, add textures, and do many other things like adding texts and then use your 3D printer to print the 3D design or you can export it as a realistic render. Preparing the prototypes of the bricks using a 3D modeling program and a 3D printer is helpful as it's cheaper and time saving. This is because corrections can easily be identified and rectified before starting to produce your bricks.You can also make adjustments as many times as you would like as it's easier to do so in a 3D design software.

Also, 3D printing can be used in printing mortar that has been mixed with Fly ash using specialized 3D printers. When doing this, it is essential to pay attention to the effect of modification caused by admixtures, which can upgrade one  thing and worsen another. While printing consecutive layers of the object, the initial mortar strength is very essential to stop the stratification and printed structure demoralization. 

During the 3D printing process, retarding admixtures are used because the transport of mixture takes a long time and because it is required to achieve proper bonding between specific mortar layers. Concrete with retarder admixture displays lower initial strength and generally slower hardening.

When using the 3D printing technology for the construction of building structure, it is essential to determine the composition of the mortar mixture and its required properties. When 3D designing a mortar mixture for 3D printing technology, it is important to note the mixture meets the accepted criteria and design assumption. 

The materials being fed into the 3D printer during construction mostly depends upon the raw materials used, method of production and its application. At the time of designing and forming 3D printed objects from mortar mixtures, it is essential to pay attention to properties that affect the ability and quality of the printed object. Specific attention should be paid to such parameters as stability of the printed shape, shrinkage concrete, flow of the mixture, extrudability, bonding time and strength. 

Benefits of 3D printing technology in construction:

The following are the benefits of 3D printing technology in building construction:

  1. Increased safety of the building.
  2. Highly effective automation in the building process.
  3. The workforce demand is reduced.
  4. The cost of construction required is less as compared to any traditional methods.
  5. Increases the potential of the construction sector.
  6. Using 3D printing technology, you can achieve greater accuracy, efficiency, and reduced resource cost. 
  7. Save the time and cost of construction.
  8. It produces versatile designs with great representation.
  9. Easy and safe optimization.

Enjoy powerful modeling, rendering, and 3D printing tools without the steep learning curve.

3D printing technology

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