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

5C2. Effective Use of Ash in Cement/Concrete
Technology overview

1. Technology overview
Research has been conducted on utilizing fly ash in the cement

early in the 1950’s, standards were established for fly ash in 1958

sector as an alternative for pozzolana. Enhanced research on theand then for fly ash cement in 1960, encouraging its widespreaduse of fly ash as a good-quality alternative to pozzolana led to its

application in general concrete structures.

first application as a concrete admixture in the late-1940’s, whenIn the meantime, fly ash came to be used as a clay-alternative

it was used for structures like dams in the United States. Thisraw material in cement in 1978 and by 2003, 70.1% of all theprocess was subsequently disseminated to other countries. In

effectively used fly ash was used in this manner.

Japan, following its commercialization as a cement admixture

2. Utilization in the cement sector1) Utilization as a clay-alternative raw material in cement

constitute approximately 5% of the raw materials for cement but

The raw materials for cement are limestone, clay, silica, and ferrictheoretically its use could be as high as around 10%.

oxide, with clay accounting for 15% of the total composition. Coal2) Utilization as cement mixture

ash containing silica (SiO2) and alumina (Al2O3) is also used as

Japanese Industrial Standards (JIS) specify standards for fly ash

an alternative to clay. However, coal ash contains less SiO2 andcement2, allowing the mixture to range from 5-30%. In general, flymore Al2O3 than clay, which requires that more silica be used toash can also be used as a Portland cement mixture, blended atoffset the shortage of SiO2. This deficiency limits the5% or less.

substitutability of coal ash for clay. At present, coal ash can

3. Utilization in the concrete sector
1) Utilization as a concrete admixture

2. Pre-packed concrete

1. Dam concrete

Pre-packed concrete is a concrete product fabricated by casting

In Japan, research on fly ash as a concrete admixture started

coarse aggregate of a designated grain size into a mold or placearound 1950, with favorable results and economics through theof application beforehand and injecting mortar into voids at an

first commercial use at a dam site in 1953.

appropriate pressure. The mortar used must be one of highRoller compacted dam-concrete (RCD) is a concrete productfluidity, with little material separation, and of moderate

finished by compacting concrete of ultra-thick consistency with aexpansibility. For this purpose, fly ash is generally mixed at a rate

vibration roller. The then Ministry of Construction led independentof 25-50%.

technology development to utilize this in a concrete dam,Applications include underwater concrete, mass concrete, andsuccessfully systematizing the trial into the RCD construction

the repair/reinforcement of existing concrete work. Themethod, which was commercialized for dam construction in 1978.

substructure work for the Honshu-Shikoku Bridge also employed

In order to prevent cracks, dam concrete is generally not allowed

this construction method.

to reach high temperatures.

3. High-fluidity concreteDue to this restriction for RCD, only a portion of the cement can

Fly ash enriched concrete (FEC) is a two component-type, high-be replaced by fly ash in order to limit temperature increases.

fluidity concrete product using cement and fly ash as powder

Generally, the replacement ratio is 20-30%. As many as some 30materials. It can contain 40% or more fly ash, providing suchdams have thus far been built employing this construction

characteristics as excellent self-filling capability requiring nomethod, making it a well-established engineering method,compaction after casting, minimal cracking due to heat ofjustifying the development efforts.

hydration, which increases its long-term strength, as well as higher
durability against alkali aggregate reactions and salt/acid damage.

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Clean Coal Technologies in Japan

Fly ash and slag concrete (FS), using steel slag and coal ash as

In addition, items with higher-performance qualities, or qualities

aggregates, is a plain concrete product developed for wave-

likely to prove effective as admixture despite their substandard

breaker superstructure works and fixation blocks/tetrapods thatstate, were added to the JIS standards3 and classified as grade 4

do not require great strength.

materials, thereby designating them with a quality suitable for

4. Industrial standards for concrete-purpose fly ashutilization. Grade 1 fine fly ash is used as an admixture for

After evaluating fly ash as a concrete admixture it wasconcrete products used as water/moisture barriers. It must be

determined that it performed well due to its ultra-fineness and thedurable, among other characteristics. Uses include ocean

limited quantity of unburned carbon. Subsequently, ultra-fineconcrete and specially-reinforced shielding material used foritems produced by an advanced analyzer were commercialized.

long-distanced pumping.

Table 1 Quality of fly ash (JIS-A 6201)

ClassClass I
fly ash3.0 or lessDensity (g/cm3)
Residue on 45 m sieve (screen sieve method) 3 (%)
Specific surface area (Blaine method) (cm2/g)

5.0 or less

8.0 or less

5.0 or less40 or less70 or less1.95 or higher
10 or less40 or less5000 or higher 2500 or higher 2500 or higher 1500 or higher
105 or higher

95 or higher

85 or higher

75 or higher

Material age: 28 days

90 or higher

80 or higher

80 or higher

60 or higher

Material age: 91 days

100 or higher

90 or higher90 or higher

70 or higher

Flow value ratio (%)
Activity index (%)

Class IV
fly ash1.0 or less

Moisture content (%)

Fineness2

Class III
fly ash45.0 or higher

Silica dioxide (%)

Ignition loss1(%)

Class IIfly ash1. In place of ignition loss, the unburned carbon content ratio may be measured by the method specified in JIS M 8819 or JIS R 1603 to apply tothe result a stipulated value of ignition loss.
2. Fineness based on the screen sieve method or the Blaine method.
3. Regarding fineness, the results of the Blaine method are provided as a reference value for the screen sieve method.

Application for dams

Application for buildings

References

1) The Japan Cement Association: Common Cement Practices, 2000.
2) JIS R 5213-1997, 1997.
3) JIS A 6201-1999, 1999.

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