Chapter 9: Manufactured Lightweight Aggregates from Coal Combustion Products


Peter Heeley, Heeley's Consulting
Roy Butcher, Engineered Material Solutions
Stefan Bernard, Engineered Material Solutions


The concrete industry is one of the largest users of raw construction materials in Australia. Fly ash is currently used to replace a portion of the cement (cement is the binder component of a concrete mix), and given that cement comprises only a relatively small proportion of the total constituents of concrete, the total market potential for fly ash as a cement replacement is inherently limited. A much larger proportion of concrete is represented by coarse and fine aggregates, and hence the potential for ash utilisation would be much greater if an aggregate could be produced from fly ash.

One of the major barriers to the introduction of a manufactured aggregate is the vertical integration of the quarrying, cement and concrete industries. Quarry companies own cement and concrete producers, to ensure captive markets for their own products. These industries are extremely protective of their markets; therefore introduction of a new product from outside the industry may be expected to meet strong opposition.

Opportunities for producing artificial aggregates for use in concrete are nevertheless increasing, due especially to the depletion of natural aggregate resources in major metropolitan areas such as Sydney. Sydney is expected to suffer a deficit of as much as 60% of current fine aggregate production once quarries at Kurnell and Penrith Lakes cease production. This corresponds to a deficit of some 3 million tonnes per annum, and will require the quarrying and transportation of aggregate from adjoining regions to increase substantially which will in turn increase production costs. Therefore, there is a real opportunity to cost-effectively and efficiently use manufactured aggregate as a partial substitute for natural aggregates in the concrete market.


  1. 9.1 Introduction
    1. 9.1.1 Fly ash in concrete aggregate
  2. 9.2 Technology Status
    1. 9.2.1 Principles of aggregate production
    2. 9.2.2 Ownership of production technologies
    3. 9.2.3 Commercial processes currently available
      • Lytag process
      • Consol process
      • Minergy process
      • Kobe process
      • Aardelite process
      • Processes not using fly ash
      • Non-commercial fly ash processes
  3. 9.3 Producing Aggregates from CCPs
    1. 9.3.1 Sintering
    2. 9.3.2 Cement bonding
    3. 9.3.3 Geopolymer binding
  4. 9.4 Properties of Lightweight Aggregates
    1. 9.4.1 Size distribution
    2. 9.4.2 Density
    3. 9.4.3 Compressive strength
    4. 9.4.4 Chemical stability and leaching from aggregates
    5. 9.4.5 Strength of products made with lightweight aggregates
      • Offshore gravity tank, North Sea oilfields
      • Canada Square Building, London
  5. 9.5 Markets
    1. 9.5.1 Characteristics of the Australian aggregate market
    2. 9.5.2 Competing with conventional aggregate materials
    3. 9.5.3 Other applications for lightweight aggregates
      • Lightweight screeds
      • Granular fill for drainage applications
      • Vehicle arrestor beds
      • Refractory materials
    4. 9.5.4 Potential markets in Australia
  6. 9.6 References

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