RockTron develops new process that enables more than 50% substitution by pulverised fuel ash

Recycling technology firm RockTron has developed a process whereby pulverised fuel ash (PFA) can be used to replace more than half the cement content in concrete, cutting its embodied energy.

The amount of cement that can be substituted by PFA is restricted under BS EN 450, but the firm has developed a special “benefication” process that takes out the materials that are detrimental to concrete and allows the substitution to exceed 50%. Independent testing at Kirton Concrete and research elsewhere is under way to assess substitutions greater than 60%.

The firm has opened a plant in Fiddlers Ferry, Cheshire, that has the capacity to process 800,000 tonnes of PFA a year. Lord Wade, chairman of RockTron, said the firm is in talks to develop further plants in the US, Russia and Malaysia.

Substituting 50% of traditional cement could save 400,000 tonnes of CO2 in the UK a year, says RockTron

Concrete made with RockTron's cement substitute has early strength development, claims the company, which means that formwork can be struck early and could reduce production times by 14-16 hours when it comes to manufacturing precast units.

The process developed by RockTron can be applied to fresh or stockpiled PFA. It turns the waste material into five “eco minerals”:

  • Two types of alumino-silicates, which can be used as a cement substitute. The company claims that using this to replace 50% of traditional cement could save 400,000 tonnes of CO2 in the UK a year.
  • Cenospheres, which are hollow glass spheres that can be used as a lightweight material in the aviation and automotive industries.
  • Carbon that can be reburned in power stations – RockTron recover three times the energy it consumes, claims the company.
  • Spherical magnetite, which is used in applications to shield people from radio frequency and electromagnetic interference.