In the quest for sustainable construction materials, researchers have turned their attention to an unlikely candidate: ammonia-contaminated fly ash. This by-product of coal-fired power plants, often laden with residual ammonia from Selective Catalytic Reduction (SCR) systems, has long been a challenge for the industry. However, new research led by Teewara Suwan from Chiang Mai University’s Excellence Center in Infrastructure Technology and Transportation Engineering, suggests that this contaminated fly ash could find a valuable second life in the cement and concrete industry.
Fly ash, a by-product of coal combustion, has long been valued for its pozzolanic properties, which make it an excellent supplementary cementitious material. However, the introduction of SCR systems to reduce nitrogen oxide emissions has left fly ash contaminated with residual ammonia, raising concerns about its suitability for use in construction materials.
Suwan’s study, published in Case Studies in Construction Materials, investigates the characteristics and suitability of this ammonia-contaminated fly ash, known as SCR-fly ash, in Portland cement and geopolymer cement composites. The findings are promising, yet nuanced. “We found that Portland-fly ash blended cement mixtures containing 20% SCR-fly ash achieve comparable engineering properties to those with high-calcium fly ash,” Suwan explains. “However, there is a slight reduction in compressive strength of about 3.4% at 28 days.”
The story takes a different turn when it comes to geopolymers. Here, SCR-fly ash exhibits a significantly lower compressive strength—around 52.8% less than that of high-calcium fly ash at 28 days. This discrepancy is attributed to the larger particle size and presence of residual ammonia in SCR-fly ash, which can react to form detrimental gypsum or ammonium salts, leading to reduced strength.
But there’s hope yet for SCR-fly ash in geopolymer composites. Suwan suggests that a resting period of at least 20 days can help reduce the ammonia content, making it more suitable for use. Moreover, chemical treatment could further enhance its properties, opening up new possibilities for its application.
The implications of this research are significant for both the energy and construction sectors. As coal-fired power plants continue to operate in many parts of the world, finding a viable use for SCR-fly ash could promote resource recovery and environmental sustainability. It could also reduce the demand for virgin materials in the construction industry, contributing to a more circular economy.
Looking ahead, this work provides crucial insights into the potential utilization of SCR-fly ash in the cement and concrete industry. As Suwan puts it, “This research is a step towards promoting resource recovery and environmental sustainability in the construction industry.” The findings could shape future developments in the field, encouraging further research into the treatment and application of SCR-fly ash. As the world continues to grapple with the challenges of climate change and resource depletion, such innovations will be increasingly valuable.