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New Approach to Fly Ash Processing and Applications to Minimise Wastage to Landfill - WR0401

Cement and concrete will remain the pre-eminent construction materials for the 21st century both in the UK and overseas. Indeed, with increasing demands for these materials internationally, in particular with the development of the giant Asian economies, and recent developments in the global organisation of the companies producing and supplying them, there is a growing need for a larger selection of materials to meet this. The use of fly ash as a cement component is well established and its application to enhance concrete properties, exploited worldwide. Of contemporary importance is the enhanced environmental sustainability that the use of fly ash to replace Portland cement brings to concrete construction.

At odds with this, fly ash remains one of the largest waste streams, with only about half of the 8Mt produced annually in the UK used, mainly in construction, and around 300 Mt put into long-term storage in lagoons or stockpiles, since the 1950s. This surprisingly low level of use is due mainly to the historical commercial drivers, rather than resistance by potential end users. In this respect the UK fairs poorly against countries that have developed the use of fly ash. For example, the Netherlands use 100% fly ash and even the USA has strong Federal funding for research to support strategies to minimise fly ash wastage.

Therefore, in the UK the situation is being reached where the practice of storing material long-term at power stations is no longer sustainable, as space is running out. Furthermore, it is likely that coal-fired generation of electricity will continue in the UK at least in the medium term. The implication of this is that either new areas will need to be established, or else for new material produced, disposed of at landfill sites. This is wasteful and there is, therefore, an urgent need to develop technology to recover and treat the stored material and to demonstrate its suitability as a valuable resource in a range of applications.

Given the high volumes involved, a low cost, low energy and low CO2 footprint technology is required, that can divide highly variable stock material into homogeneous phases, optimised for different end uses. The approach used in this project was to develop technologies (to pilot-scale), based on fluid separation systems for fly ash processing, followed by a series of scoping studies to demonstrate that the recovered material is a technically sound option for the various applications, including use as (i) a cement component in concrete and mortar; (ii) a filler component in concrete masonry units and cementitious grouts; (iii) a component of cement bound material in road construction; (iv) raw feed in cement manufacture and (v) fuel through carbon recovery.

The project combined the scientific / technical base of CTU and of key construction materials associations (British Cement Association, Precast Concrete Rederation, Quarry Products Association - BRMCA, UK Quality Ash Association) to enable full stakeholder input and the ownership of the technical outputs by UK-based companies (Castle Cement Ltd, Cemex Operations and ScotAsh) and international collaborators with expertise in this area from South Africa (Ash Resources), United States of America (University of Kentucky) and Europe (ECOBA).

It is believed that the outcomes of the project will enable recovery strategies to be developed and provide a solution to the problem of long-term storage, and offer an alternative and complementary resource to Portland cement for a range of construction applications, at a time where this is required in the UK and beyond, while providing benefits to the environment, in terms of reduced consumption of energy and natural resources. Technical benefits normally found with fly ash in the range of applications are also anticipated.
The general objective of the project is to recover and process coal combustion residues, either those recently produced, or stored in lagoons at or near power stations, where they have been stored for many years, for use as valuable resources in a range of construction applications and thereby establish an integrated approach to the use of the material and eliminate associated wastage.

Thus, the specific technical and scientific aims of the project are,

1. Identify, by examining international best practice, the elements of plant necessary to process combustion residues in order to produce material (mainly fly ash) with a range of qualities, suitable for use in various construction applications. Design and develop a pilot-scale plant.

2. Carry out trials with the pilot-scale plant to evaluate the system and identify optimum controlling parameters to obtain the different fly ash fractions for the various end uses.

3. Sample and test material from a lagoon at a power station to establish the quantities and qualities of materials available for recovery over the site. Thereafter, carry out processing with the pilot plant at the power station to produce sufficient quantities of materials for use in various scoping studies.

4. Carry out scoping studies for a range of applications of low, medium and high value with the processed fly ash, including (i) a cement and sans component in concrete and mortar, (ii) fine aggregate in concrete masonry units (iii) cement-based grouts and (iv) as a component of road bases (mixed with lime), (v) raw feed in cement manufacture and (vi) recovered carbon as a fuel.

5. Develop guidelines, both for (i) processing and (ii) using the recovered material in different construction applications.
Project Documents
• Final Report : New Approach to Fly Ash Processing and Applications to Minimise Wastage to Landfill   (11350k)
• Summary Report : New Approach to Fly Ash Processing and Applications to Minimise Wastage to Landfill   (1378k)
Time-Scale and Cost
From: 2006

To: 2008

Cost: £284,467
Contractor / Funded Organisations
University - Dundee
Advances in product design & development              
Carbon Dioxide              
Encourage change in resource use/waste generation              
Environmental Protection              
Greenhouse Effect              
Manufacturing Efficiency              
Market Development and Intervention              
Materials Science              
Natural Resource Use              
Products and Processes              
Residual Wastes Management              
Systems for Resource Recovery              
Uncover market opportunities outside WRAP's remit              
Waste Management              
Fields of Study
Waste Management