Utilization of Coal Ash in Sustainable Concrete Systems

Coal ash, a by-product of coal‐fired power generation, comprises fine fly ash and coarser bottom ash. Both fractions possess cementitious and pozzolanic properties that can be harnessed to replace a proportion of Portland cement or natural aggregates in concrete, thereby reducing carbon emissions and landfill disposal. When ground to suitable fineness, bottom ash contributes to long‐term strength gain through secondary hydration reactions, refines pore structure and enhances durability against sulphate attack and abrasion. As a fine or coarse aggregate replacement, bottom ash can lower material costs and conserve natural sand and gravel, though its angular shape and high water absorption demand careful mix design and possible use of water‐reducing admixtures. Global research efforts have demonstrated practical applications in structural members, road paving blocks and lightweight cellular concrete, with typical cement replacements of up to 20 % by mass and aggregate substitutions ranging from 25 % to 100 %. Key challenges include ensuring consistent ash quality, mitigating alkali–silica reaction and optimising water demand to maintain workability and mechanical performance.

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Utilization of Coal Ash in Sustainable Concrete Systems publication trend

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Technical terms

Coal bottom ash (CBA): The heavier, coarser fraction of coal combustion residue, often used as aggregate or cement substitute.

Coal fly ash (CFA): The fine particles carried from boilers by flue gases, commonly employed as a supplementary cementitious material.

Pozzolanic reaction: A secondary hydration process in which silica-rich materials react with calcium hydroxide to form additional cementitious phases.

Alkali–silica reaction (ASR): A deleterious reaction between alkalis in cement and reactive silica in aggregates, causing expansion and cracking.

Compressive strength: The maximum axial load per unit area a concrete specimen can sustain before failure.

References

1. Influence of Bottom Ash Replacements as Fine Aggregate on the Property of Cellular Concrete with Various Foam Contents. Advances in Materials Science and Engineering (2015).
2. Assessment of concrete road paving blocks with coal bottom ash: Physical and mechanical characterization. Case Studies in Construction Materials (2023).
3. Recycling Untreated Coal Bottom Ash with Added Value for Mitigating Alkali–Silica Reaction in Concrete: A Sustainable Approach. Sustainability (2020).