What is fly ash brick?
Fly ash brick is a lightweight building unit made up of fly ash, sand, stone dust, gypsum, lime, cement. Fly ash brick has self-cementing properties. There is a number of compositions by which fly ash brick can be made. Some mix fly ash with sand and cement, and other mix fly ash with lime and gypsum.
Fly ash is residue obtained after combustion of pulverized coal. Fly ash consists of oxides of silicon, aluminum, iron, magnesium, potassium, sodium, titanium and sulfur are present in small amount. Further fly ash can be divided as class c and class F.
Sand is naturally occurring aggregate, finer than 4.75 mm in size. Silica present in sand helps to retain the shape of brick by preventing shrinkage, cracking and wrapping od brick. Also, high percentage of silica may lead the brick to be brittle.
Gypsum is hydrated calcium sulphate (CaSo4.2H2o). Gypsum is added in about 5%. Gypsum is added as a strength gainer in the brick.
Lime (CaCo3) is used as binder to join building units. Lime with water possess adhesive property. Lime mixes with fly ash in an ordinary temperature to have binding property. Sludge lime or hydrated lime are used to stick the material into a place.
Cement, ordinary Portland cement of about 5-10% is used in the brick.
Advantages of Fly ash brick
- Fly ash brick is light in a weight-reducing dead load of the superstructure.
- Fly ash brick has strength ranging from 7.5-10MPa
- Masonry from fly ash brick gives a plain surface reducing the cost of plastering.
- One fly ash brick can replace a few numbers of local bricks reducing the number of joints and mortar.
- These bricks have high fire insulation.
Disadvantages of Fly Ash Brick
- Fly ash brick does not absorb heat due to which not use of the cold climate.
- It has low mechanical strength.
- They are only available in the modular size.
What is red brick?
Redbrick is a building unit, made up of clay, sand, lime, and other ingredients in proportion.
1) Alumina (Al2O3): Alumina, Clay is a major constituent of the Brick. Clay acts as a cementing material in the Brick. The plasticity of the brick is due to the presence of Clay. An excessive amount of clay also tends to shrink the brick, deforming the shape of the brick.
2) Silica (SiO2): These are oxides of silicon; sand is used to adjust the percentage of silica in brick. The main purpose of the silica is to prevent the raw brick from wrapping, cracking, and shrinking.
The strength and durability of the brick depend upon the proportion of alumina and silica present in the brick. But the excess amount of silica reduces the cohesive property of brick material making it weak and brittle.
3) Lime (CaCO3): Lime is used in powder form, in small amounts only as a catalyst to fuse the silica at kiln temperature. For a good brick, a slight fuse of silica is preferred.
4) Iron oxides: Metal oxides are used to color the material. They are used in small amounts to give red color to the brick after burning. Besides, iron oxides make brick impermeable.
Advantages of Red Brick
- The compressive strength of red brick is up to 10.3 MPa.
- All the constituents are locally available.
- They provide thermal and sound insulation to the structure.
- They can be used in load-bearing structures.
- Red bricks are highly fire-resistant and easily reusable and recyclable.
Fly ash brick Vs red brick
|Fly Ash Brick
|The major constituents are, fly ash, sand, lime, and gypsum.
|The major constituents are clay, sand, lime.
|The density of fly ash brick is 1700-1850 kg/m3.
|Density of Red brick is 1600-1750 kg/m3.
|Waste product fly ash is used thus is environmentally friendly.
|Clay is used which is obtained by removing fertile top soil.
|They absorb about 6-12% of water,
|They absorb more than 15-25% of water.
|They are comparatively lighter.
|They area comparatively heavier,
|No plaster is required as it gives smooth surface.
|Plaster is required to obtain smooth surfaces.
|Availability of materials
|Fly ash can be obtained only from the industries where coal consumption is high.
|All the components are locally available.
|Consumption of mortar.
|Use of fly ash brick reduces mortar consumption.
|Use of red brick requires more mortar in compare to.
|There is only about 2% of breakage during transportation.
|Wastages during the transportation is about 10% for red brick.
|They do not absorb heat, so could not be used in a cold climate.
|They provide both sound and thermal insulation.
|The compressive strength of fly ash brick might vary within 10-12 N/mm2.
|The compressive strength of red brick might vary within 10.3 N/mm2.
|Effloresces is unlikely in the fly ash brick
|Effloresce is one of the major problems for red brick.
|Gaps between roofs and walls cannot be filled and hard to remodel.
|They are easy and handy to work with also changes can be made easily.
I hope this article on “Fly ash brick Vs red brick” remains helpful for you.
Happy Learning – Civil Concept
Civil Engineer – Rukshana Shrestha