15 Sept 99
(2) CRD-C 256 & ASTM C 311 - Standard Test Methods for Sampling and Testing
Fly Ash or Natural Pozzolans for Use as a Mineral Admixture in Portland Cement
B-7. Environmental Considerations. One basic consideration involving the use of
waste materials, aside from cost, is the environmental affect of using the waste material
in a pavement application. There have been at least some initial investigations into the
environmental effects in pavement applications of many of the waste materials described
in this text. Many waste materials require special consideration for the same reason most
of them are considered as hazardous materials when used or stockpiled in non-pavement
applications. The possible environmental effects of the use of waste materials must be
considered during material preparation, during construction, and during pavement use.
Within most state DOT's and other agencies the use of most waste materials is handled
on a case-by-case basis; therefore, without the benefit of an established approval
procedures it is often difficult to utilize the waste materials.
B-8. Cost Considerations (Economic Factors)
a. The economics of using waste materials in pavement applications must be
favorable for their widespread use to become a reality. The economic benefit can come
either from improved pavement performance with the added waste material or from
consideration of other treatment or landfill costs concerning the waste material if not used
productively. One consideration that is rarely adequately addressed, is the effect that
waste materials may have on the pavement once it has deteriorated to the point where it
requires rehabilitation. What effect will the current use of waste materials have on the
future use of the pavement materials? Will it be possible to recycle or will the material
still be considered a hazardous or controlled material?
b. Accurate life-cycle cost analysis for most waste materials is difficult due to the
limited number of applications of a particular material. Some waste materials possess
pozzolanic properties that would allow them to replace or reduce the amount of portland
cement used in some applications. Some types of incinerator ash possess this property,
which could provide substantial savings in liner and other applications (Goodwin 1992).
Economically, waste glass should be used only to make more glass; however, limits on
the type and quality of the glass result in a sub stantial amount of waste glass being
available for use in pavement applications (Ahmed 1991). A limited study of paving
mixtures using roofing shingles and other waste showed cost savings of up to 20 percent
(Epps and Paulson 1986). Crumb rubber is one waste material with a substantial amount
of previous usage. One study found that the dry process was economically unfavorable,
while the wet process showed promise of being economically favorable (Emery 1995).
The life-cycle costs of using rubber in paving applications is not well defined. The use of
this material will increase the initial cost by 40 to 100 percent; however, it has been
shown to provide an increase in performance (Thirumalai 1992).
c. The use of RAP and RCP are additional waste materials with a substantial
history of usage in pavement construction. Especially for RAP, cost savings of 20 to 50