ETL 1110-3-503
15 Sept 99
Fly ash has been used successfully in various ways in embankments (Ahmed 1991). Fly
ash seldom provides desired properties by itself, but when combined with other
aggregates or other solid wastes it can be an excellent construction material (Lee and
Fishman 1993). A laboratory study of fly ashes from various sources showed their
suitability for stabilizing various soils for low volume roads (Turner 1997). Another
study showed that a sand mixture stabilized with the addition of 20 percent Class C fly
ash resulted in reduced permeability, increased compressive strength, and improved
weathering resistance (Taha and Pradeep 1997). The suitability of a particular fly ash -
soil combination should be evaluated prior to use. Fly ash has also been used by several
states as an additive to hot-mix asphalt. The CE has successfully used fly ash as a
stabilizing material in a stone matrix asphalt (SMA) mixture (Shoenberger 1997). A
laboratory evaluation, in the Netherlands, showed that combinations of two different fly
ash materials could be combined to produce a satisfactory stabilized material for base
course applications (Mulder 1996).
Bottom ash and boiler slag have been used as embankment materials, aggregate base
course (both stabilized and unstabilized) and aggregate in hot-mix asphalt by several state
agencies (Collins and Ciesielski 1994 and Roads and Bridges 1998). Two states permit
the use of bottom ash as a sand replacement in flowable fill mixtures. The use of these
materials, when there is no previous experience, should be thoroughly investigated to
determine their effect on performance.
Another coal ash is available as a by-product from "clean" coal-burning technologies.
These clean-burning ash materials are available from technologies including: fluidized
bed combustion, spray drying, and dry limestone or sodium furnace injection (Collins and
Ciesielski 1994). These technologies use a dry chemical reagent to react with the flue gas
from the burning coal to remove the sulfur dioxide from the emissions. Both bottom ash
and a lesser amount of fly ash are produced in these processes. The resultant ashes are
often high in sulfate and may contain unreacted lime that gives them an expansive
tendency.
c. Construction and demolition waste. It is estimated that anywhere from 20 to 30
million tons of construction and demolition (C&D) waste are generated every year in the
U.S. (Collins and Ciesielski 1994). A large percentage of this material, specifically wood
and plaster, is not suitable for most pavement applications. The remaining materials
include: glass, metal, concrete, brick, asphalt concrete, shingles, plastic and other
miscellaneous materials. When the quantity of any of these individual materials is
sufficient, they can be used individually in pavement construction (see the appropriate
sections of this report). All organic material or any other hazardous material such as
asbestos, should be kept separate from the C&D wastes. One location after removing
concrete, metal, paper products, and most wood and other organic material; generates a
soil product that is suitable as a top soil in pavement projects (McMahon 1997).
Several states have used or investigated the use of C&D waste materials, either as
embankment material, base course material, or as an aggregate in asphalt concrete. The
limited use has generally provided acceptable results. Of course the benefit derived from
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