What Are The Pros And Cons Of Fly Ash Cement?

Fly Ash

Fly ash is a fine gray powder that consists of round, glassy particles produced as a result of combustion in coal-fired or thermal power stations. It is by far one of the largest wastes generated today. It contains harmful substances like arsenic, lead, mercury, etc. Therefore, releasing it into the environment will have detrimental effects. Thankfully, instead of going into landfills, it is put to highly productive use. Fly ash has pozzolanic properties. This means it reacts with lime and forms cementitious compounds, also known as Supplementary Cementitious Material. When the fly ash is blended with the cement constituents, like sand and aggregates, it fills tiny spaces within the mixture and forms an extremely cohesive and consistent substance.

Uses Of Fly Ash

  • Fly ash improves the performance of concrete significantly due to its water-resistant properties. Also, it fills the gaps in the cement, making the construction strong and giving it an even and smoother finish.
  • Fly ash works as a catalyst when treated with sodium hydroxide and aids in pyrolysis. It is the process where polyethylene is converted into a crude oil-like substance by heating it at very high temperatures.

Pros Of Fly Ash

  • A Cost-Effective Substitute Of Portland Cement – If we make a cost comparison, Portland cement is any day costlier than fly ash. By adding fly ash to the cement, one can not only reduce the content of Portland cement and gain the advantage of enhanced concrete performance. Substituting a portion of Portland cement with fly ash brings down the cost factor and makes it one of the most sought-after additives. 
  • It Prevents Cracking – Moisture particles trapped inside the cement mixture cause it to expand and contract with temperature changes. It causes the finished structure to develop cracks. Adding fly ash to Portland cement makes the concrete highly water-resistant. Typically, the grains of cement are bigger in comparison to fly ash. When the two are mixed, the smaller grains of fly ash and other supplementary cementitious materials adequately fill the gaps between the cement grains, thereby preventing water permeability and ensuring the finished structure does not develop cracks.
  • Makes For A Robust Construction – Higher density of fly ash in the cement mixture contributes to its improved strength. As the fly ash fills in the tiny gaps within the cement mixture, the residue adheres more thoroughly to components than an equivalent alternative, like Portland cement. Due to this, the concrete mixture’s final strength after drying and hardening is considerably better than that of the other cement mixture types.
  • Produces Different Set Times – Every construction has its unique peculiarities. Some require quick setting times, some longer, and others range somewhere in-between. Using fly ash in varying quantities with cement or mortar, one can easily achieve varying set times to suit their purpose. The simple rule of thumb is the less the fly ash, the quicker the set time and vice-versa. However, do remember that slower set times give the concrete or mortar mixture substantive time to settle into position and fill in the crevices better, leading to robust constructions. Critical, here is the knowledge of the cement user to know the proper proportions.
  • Easy To Use Even In Cold Weather – Fly ash is water-resistant, so its need for water, when mixed with other components, is less. The advantage that derives from this property is that it makes it easier to work with fly ash even in cold regions or under low-temperature conditions.

Other Benefits Of Fly Ash Cement

  • Fly ash cement is considered to be non-shrinkable.
  • It makes for dense concrete, which gives a smooth and sharp finish every time.
  • It is easy to work with.
  • It reduces the heat of hydration.
  • Using fly ash cement in constructions reduces carbon dioxide emissions.

Cons Of Fly Ash

  • Slow Setting Time – If you were thinking of fast curing times, it’s time to rethink your options. Adding fly ash to cement will increase the setting time. Nevertheless, if you think of it as a drawback, do ponder over the fact that the slow setting time gives your project more strength. So it is actually a matter of deciding what is important – making a strong and durable structure or finishing it quickly. 
  • Lack Of Knowledge May Lead To Improper Mixes – Small builders generally lack adequate knowledge that allows them to mix cement and fly ash in the right proportions. Getting the mix right is critical to every construction. Therefore, some may consider the lack of this knowledge a critical drawback.
  • Poor Quality Fly Ash Gives Questionable Results – The quality of fly ash can affect the quality and strength of the concrete. Fly ash that has not burnt sufficiently tends to have bigger particles. These big particles do not fit well within the tiny constituent crevices of the concrete. Instead, they create new voids or gaps where water molecules can easily permeate and cause cracking later. Hence, until the builder can gauge the quality of the fly ash, they cannot be considered good candidates to make or prescribe the concrete mix.

Disposing And Recycling Of Fly Ash

The environmental impact of coal ash or fly ash is significant. Some thermal power plants dispose it off in landfills or surface impoundments. Others put it into abandoned mines. Nevertheless, the best course of action is to recycle it. For a long time now, due to its cementitious properties, fly ash has been used in concrete, grout, etc. Another widespread use of fly ash has been as fill material to stabilize roadbeds. Even bottom ash is used for the same purpose and also to control the snow on roads. Recycling fly ash reduces greenhouse gas emissions. Consequently, it is better to repurpose it and put it to good use.

Summing Up

Due to its cementitious properties, fly ash makes for a suitable building additive. Left alone, discarding this by-product will only harm the environment. Nevertheless, using it as an SCM (Supplementary Cementitious Material) makes for stronger and sharper roads, buildings, dams, etc. Hence, learning the alternative uses of fly ash is to everybody’s advantage.