What is Ashcrete?

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Ashcrete is an environmentally friendly material that is considered a substitute for traditional concrete. 

The invention of ashcrete is the result of efforts toward the production of sustainable construction materials. Not only does ashcrete reduce carbon emissions, but it also utilizes fly ash, which is a by-product of coal combustion that was previously disposed of in landfills. 

However, ashcrete is being used as a replacement for cement to increase concrete durability and strength, decrease shrinkage, reduce cement utilization, and subsequently reduce CO₂ emissions. The use of fly ash in ashcrete enhances the strength, durability, and resistance of the overall mixture.  

What is Ashcrete?

Ashcrete is an environmentally friendly construction material produced from a mixture of fly ash, borate, bottom ash, and chlorine compound. 

Around 93% of all materials used to produce ashcrete are recycled materials, making it a viable, sustainable construction material. 

The main component of ashcrete is Class C fly ash, which has high calcium content and less than 2% carbon. The hardened ashcrete is dense with an average weight of 1.8092 g/cm³, and it has low permeability with compressive strength of greater than 21 MPa.   

Advantages

Durability  

Fine particles of fly ash and their pozzolanic properties reduce the cracking and bleeding of fresh ashcrete, resulting in low permeability. This makes it stronger and more durable than conventional concrete. Fly ash increases the resistance of ashcrete against temperature fluctuations and corrosion.

Resistance to Aggressive Elements

The resistance of ashcrete to acid and fire is higher than traditional concrete.

Cost

Ashcrete is a cost-effective material because it is mainly produced from fly ash. Hence, the overall cost of ashcrete is less than conventional concrete.

Environmentally Friendly

Ashcrete has low embodied energy compared to normal cement, which needs a very energy-intensive manufacturing process. Embodied energy measures how much energy is used to produce and transport material. It has been shown that ashcrete can trap CO₂ from the air, reducing carbon emissions.

Workability

Spherical particles of fly ash improve the workability and pumpability of the ashcrete mixture. So, either water can be reduced in the mixture or the workability of the mixture can be increased for the same water-cementitious material ratio.

Save Water

Ashcrete requires smaller amounts of water to initiate the hardening process than traditional cement concrete; ashcrete helps conserve water.

Disadvantages

Slow Strength Development

Strength development in ashcrete is slower than in normal concrete due to the presence of fly ash in the mixture. This could prolong the construction period of a project.

Seasonal Limitations

Ashcrete is susceptible to low temperatures during pouring, significantly increasing the setting time and strength gain. So, using fly ash in the winter is not desirable. Fly ash requires greater air content than conventional concrete.

Sustainability

Ashcrete contains chlorine compound, which is hazardous. So, if a replacement for chlorine is found, ashcrete characteristics will be improved hugely. Additionally, fly ash is produced through coal combustion, which releases carbon, but the amount is still much less than that of the concrete production process.

Nonetheless, if the demand for fly ash increases, more coal must be combusted, resulting in unsustainable ways of producing fly ash. 

From a health point of view, fly ash is detrimental to human health when inhaled.  

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