Fly ash in concrete and other construction materials

The history of utilising fly ash in concrete

The exploration of fly ash in concrete dates back to the early 20th century, marking the beginning of a significant evolution in construction materials. Initially, the use of fly ash was limited due to a lack of understanding of its properties and potential benefits. However, this changed dramatically in the mid-20th century.

The pivotal moment came with the groundbreaking research conducted at the University of California, Berkeley. This research was crucial in demonstrating the practical and technical advantages of incorporating fly ash in concrete mixtures. It was found that fly ash, a byproduct of coal combustion in power plants, could enhance the durability and strength of concrete while also addressing environmental concerns.

From the 1950s onwards, the construction industry began to recognise the dual benefits of using fly ash for concrete production: improving material properties and reducing waste from coal power generation. Fly ash was found to act as a pozzolan – a material that forms a cementitious compound when mixed with lime and water. This property helps in enhancing the strength and workability of concrete.

In the following decades, the use of fly ash in concrete became more widespread. Various studies and experiments were conducted to optimise its use, improving the quality and sustainability of concrete. Engineers and researchers discovered that fly ash could partially replace Portland cement in concrete mixtures, reducing the overall carbon footprint of construction activities. This was significant, as the production of Portland cement is a major contributor to CO2 emissions worldwide.

By the late 20th and early 21st centuries, the use of fly ash for concrete production had become a standard practice in many parts of the world. It was recognised not just as a cost-effective alternative to traditional cement, but also as a means to improve the long-term performance and sustainability of concrete structures. Incorporating fly ash in concrete has led to advancements in construction techniques, allowing for building more durable, resilient, and environmentally friendly structures.

Using CDFA as a catalysis and cement replacement

Primarily, coal-derived fly ash (CDFA) is used as a substitute for traditional materials in construction, notably as a raw material or additive in cement production. CDFA containing metal oxides like iron oxides has proven effective in catalysis, offering a cost-effective and environmentally friendly method for recycling waste. Its stability due to aluminosilicates makes it suitable for various chemical reactions. For instance, CDFA with calcium oxide has been used as a recyclable catalyst in different chemical processes. Moreover, replacing up to 40% of cement with CDFA in concrete production not only reduces CO2 emissions by 35% but also improves the durability and strength of the concrete.

Evaluating the performance and feasibility of using harvested fly ash in concrete

As the demand for fly ash, the most widely used Supplementary Cementitious Material (SCM), and other similar pozzolans increases, the availability of high-quality, specification-compliant fly ash is decreasing. To sustain and grow its market presence and ensure the longevity of concrete products and structures, it’s essential to have a consistent supply of high-quality and cost-effective fly ash and other SCMs. This necessitates exploring alternative sources and methods, such as recovering and recycling previously stored fly ash.

A Pennsylvania study investigated the viability, effectiveness, and improvement of two plentiful alternative fly ash sources: reclaimed landfilled fly ash and fluidized bed combustion (FBC) fly ash. These samples were analysed for their composition, physical attributes, and performance against the standards of ASTM C618 (US regulatory requirements for the use of fly ash in concrete). A statistical plan was also developed to assess the variability of fly ash found in landfills.

The study revealed that landfill-derived fly ash could be classified as ASTM C618 Class F ash. After processes like drying and reducing particle size, this ash can be used in concrete. By replacing 20% of cement with this fly ash, concrete suitable for paving with favourable fresh and hardened properties can be produced.

However, fly ash sourced from landfills requires individual evaluation to understand its variability and suitability as a concrete pozzolan. Additionally, measures for its enhancement, such as reducing carbon content and removing harmful substances, might be necessary.

Other applications for CDFA in the Construction Industry

Understanding the diverse applications of CDFA is key to its efficient management and in minimising environmental pollution. Aside from the use of fly ash in cement production, other applications in the construction industry include:

• Soil Replacement and Stabilisation
  Adding CDFA to soil enhances its bulk density, structure, and texture. For example, adding 20% CDFA to expansive soils reduces their plasticity significantly. This improvement in soil properties is vital for construction projects, especially for building the base and sub-base layers of pavements and creating embankments in compressed soils. CDFA is also more cost-effective and environmentally friendly compared to traditional materials like lime for soil stabilisation.
• Innovations in Brick Making and Embankments
  The Central Fuel Research Institute in Dhanbad, India, has developed a method for making building bricks with CDFA. These bricks, tested for durability under various environmental conditions, have shown to be eco-friendly, sustainable, and cost-effective. In embankment construction, CDFA is preferred over traditional soil due to its uniformity, ease of handling, and compactness, which reduces construction time and costs. Typically, Class F CDFA is used in these applications, highlighting its versatility and effectiveness.
• Dams and Road Construction
  In dam construction, CDFA is valuable for reducing hydration heat, and facilitating the creation of thicker placements, as evidenced in the Ghatghar Dam Project in India. In road and pavement construction, studies have shown that incorporating CDFA with materials like crumb rubber and nano-silica enhances the mechanical properties of roller-compacted concrete, improving its strength and durability.

Overall, the use of CDFA in construction demonstrates a sustainable approach, balancing economic and environmental considerations while advancing the industry’s capabilities.

Our role in the fly ash industry

Here at Atritor, we are experts in the processing of fly ash that has been harvested from landfill and delivering a high quality output that meets European EN450 standards. In June 2023, Atritor and ST Equipment and Technology displayed their expertise in tailored solutions for fly ash processing in Coventry, showcasing how the Atritor Dryer Pulveriser and the STET separator effectively process fly ash.

Our equipment for fly ash treatment

The Atritor Dryer Pulveriser is capable of drying, deagglomerating, and sizing of materials all at once. It can handle up to 20 tonnes per hour and can evaporate up to 4,000 kilograms per hour, working with drying temperatures up to 550 degrees Celsius.

Collaborative testing and customisation

We work closely with clients at our Pilot Plant, where we test wet fly ash under various conditions to get the right quality for specific uses. This process, along with our extensive knowledge of fly ash, helps us provide guidance on the financial aspects of projects. We consider the characteristics of the fly ash, which can vary based on its source and the time of year it is collected. 

Bespoke design and manufacturing

Our in-house design and manufacturing capabilities allow us to create tailored solutions. We handle everything from installation and commissioning to training plant operators, ensuring our clients produce a profitable product.

Experience and expertise

With 90 years in the business, Atritor specialises in converting waste products into valuable materials. We manage the entire process of fly ash treatment – from testing and design to manufacturing, installation, and training. Our extensive experience and data help streamline feasibility studies, saving time and costs in decision-making. Reach out to our team with any questions regarding processing fly ash for concrete.