Part 2 CCT Overview
Environmental Protection Technologies (Technologies to Effectively Use Coal Ash)

5C3. Effective Use of Ash in Civil Engineering/Construction and Other Applications
Technology overview

1. Technology overview
Outside of its application in concrete, coal ash is widely used in

ash in the future due to such factors as the construction of new

the civil engineering sector for road construction, foundation

coal-fired power plants, utilization technologies are now underimprovements, back-filling, or for use in other earthwork and inactive development out of the necessity to expand the utilization

the construction sector as an artificial light-weight aggregate. Onof coal ash in the above-mentioned sectors. In order tothe other hand, in the agriculture/forestry/fisheries sector, it isaccomplish this, several challenges, including the diffusion ofused as a fertilizer or soil conditioner.

technology, the exploitation of demand, and the improvement ofTo cope with the anticipated increase in the generation of coal

the distribution mechanism, must be addressed.

2. Utilization for civil engineering
1. Road construction material

2. Earthwork material

The "Outline of Asphalt Pavement"1 allows fly ash to be used as

Fly ash can be effectively used for an embankment or

an asphalt filler material, and clinker ash as a lower subbase

reinforcement material since it is lighter than common earthwork

material, frost heave depressant, and barrier material.

materials. In recent years, therefore, various technology

Fly ash can be used for the upper/lower subbase and subgrade.

development efforts6,7,8 have been made, resulting in a number

A cement stabilization treatment construction method adds flyof applications. Among these is an application using fly ash in its

ash to cement to be treated under moderate moisture content fororiginal powder state with cement added as a solidifier to coalapplication. This construction method strengthens quickly and isash, as well as fly ash’s utilization as a stabilizing material. It isstable over the long-term. Another technology2,3,4,5 has also

also granulated or processed in other ways for different

been developed to process coal ash for use as a roadapplications. Review is also underway for the intended

construction material.

commercialization of fly ash as a soil stabilizer or a construction
sludge conditioner due to its pozzolanic activation as well as its
self-hardening9 property.
Meanwhile, basic research of the elution10 of coal ash’s traceelements is continuing since fly ash’s use in earthwork must be inharmony with the environment.

Photo 1 Application for road construction99

Clean Coal Technologies in Japan

3. Utilization in the construction sector

4. Utilization in the agricultural/forestry/fisheries sector

1. Artificial light-weight aggregate

1. Fertilizer

Development efforts11,12 have successfully produced technology toFly ash, from pulverized coal-combustion ash, was designated aspelletize/calcine coal ash and cement or the like into artificial light-

a special fertilizer in 1960, as was clinker ash in 1992. Several

weight aggregate. Demand, driven by urban development and high-thousands of tons a year of potassium silicate fertilizer,

rises, is expected to grow, making it important to further thecontaining hard-to-dissolve silicic acid contained in coal ash, istechnological development of artificial light-weight aggregate as

also produced.

well as to reduce production costs.

2. Soil conditioner

2. Others

Clinker ash, whose chief components, SiO2 and Al2O3, are

The resemblance of coal ash’s elements to the chemicalalmost the same as those of ordinary soil, is suitable for thecomposition of existing construction materials also allows it to be

growth of vegetables. Moreover, it is used to grow sod for golf

used as a clay-alternative raw material for ceramic products, suchcourses or to improve the soil of poor-drainage areas or arable

as clay roofing, bricks, and tiles, or as a cement mixture for boards

land since its countless spores retain water well, enabling(interior/exterior wall material for construction).

fertilizers to be effective for a longer duration and, at the sametime, its similarity in shape to sand provides comparable waterpermeability.
3. Utilization in the fisheries sector
There are long-established cases where coal ash has been used
for fish breeding reefs and seaweed beds. A recent effort aims touse coal ash as a mounding material for a man-made undersea
mountain range to cause artificial upwelling currents.13

Photo 2 Artificial aggregate fabricated from coal ash (Toughlite)

Photo 3 Application as fertilizerReferences

1) The Japan Road Association: Outline of Asphalt Pavement, 1992.
2) Environmental Technology Association/The Japan Fly Ash Association: Coal Ash Handbook 2000 Edition, 2000.
3) Public Works Research Institute: Public Works-Related Material Technology/Technical Review Certification Report "Ash-Roban," 1997.
4) Public Works Research Institute: Public Works-Related Material Technology/Technical Review Certification Report "Pozzotech," 1997.
5) Ohwada et al., 11th Annual Conference on Clean Coal Technology lecture collection, 2001.
6) Shintani et al., CCUJ, Civil Engineering 54th Annual Academic Lecture Meeting, collection of summaries, 1999.
7) Public Works Research Center: Public Works-Related Material Technology/Technical Review Certification Report "Hard Soil-Break Material," 2000.
8) Akira Onaka: The Clean Japan Center’s 11th Resources Recycle Technology Research Presentation Meeting, collection of lecture papers, 2003.
9) Ozasa et al., CCUJ, 11th Annual Conference on Clean Coal Technology lecture collection, 2001.
10) The Japanese Geotechnical Society: Research Committee Report on Utilization of Wastes as Foundations Material, 2000.
11) Ishii et al., The "Bulletin of the Chemical Society of Japan," 5, 431, 1992.
12) Ozasa et al., CCUJ, 10th Annual Conference on Clean Coal Technology lecture collection, 2000.
13) Tatsuo Suzuki, 14th ACAA International Symposium lecture collection, 2001.

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