ETL 1110-3-503
15 Sept 99
2 percent were ground into crumb rubber for use in asphalt rubber (Collins and Ciesielski
1994 and Epps 1994). There are an estimated 2 to 3 billion tons of used tires stockpiled
across the country. Nearly half of the states have enacted legislation that prohibits
continued placement of used tires in landfills. Recent estimates indicate that more than
69 percent of all used tires were being used for some type of application. By 1996, there
had been over 70 roadbeds constructed using tire chips nationwide (Nightingale and
Green 1997).
Pavement uses of whole, chopped, or shredded used tires have included: fills and
embankments, retaining walls, drainage structures, and specialized pavement hardware
(Ahmed and Lovell 1992). The literature shows that one advantage, and often a reason
for selection, of the used tires in fill or embankment applications is the lightweight (low
unit weight) of the in-place material (Ahmed 1991). Alternative fill materials such as
wood chips are not as durable and lightweight aggregates or have relatively high unit
weights and are more expensive. The use of shredded used tires requires a design
allowance for the relative compressibility during construction and high deflections under
load in relation to most other construction materials (Ahmed and Lovell 1992, Newcomb
and Drescher 1994, and Bernal et al. 1997). One study found improved results when the
shredded tire layer roadway pavements were overlaid with a 3-foot thick versus a 1-foot
thick soil cap (Bosscher et al. 1992). Studies using shredded tires as an aggregate or soil
replacement for subbase construction and other uses have found that the addition of the
tire chips reduces the unit weight, CBR values, and resilient modulus values (Papp et al.
1997 and Tatlisoz et al. 1997). A study of the pullout resistance of a geogrid in shredded
tire and a shredded tire - sand mixture, determined that the use of geogrids could decrease
deformations for shredded tires with or without added sand (Bernal et al. 1997). One
study found that the addition of silty soils could provide increased compressive strength
of shredded tire fills similar to those provided by adding sand. However, clay materials
had a detrimental effect on strength. Compressive strength values increased for tire
contents up to about 25 percent (Tatlisoz et al. 1997). When shredded tires are used as
replacement for aggregate, the change in properties of the conventional subbase must be
considered in design. Early in 1996 two roadbeds constructed with shredded tires self-
heated and caught fire. These sites contained thick sections of tire chips of 7.9 m (26 ft)
and 15 m (45 ft) thick. The exact cause of these fires is not known, but thick app lications
using tire chips need further investigation in this regard (Nightingale and Green 1997).
In 1997, the Maine DOT used tire chips to stabilize a riverbank and an embankment
backfill during construction of a bridge. They took steps to prevent and monitor possible
self-heating, the project appeared to be successful and after more than one year
temperatures were decreasing after a slight initial increase (Humphrey et al. 1998).
Studies of the effects of shredded tires on water quality found that there were negligible
effects on the groundwater (Bosscher et al. 1992 and Humphrey et al. 1997). However,
some researchers recommend using shredded tire only in unsaturated zones (Shelburne
and Degroot 1998).
A number of states and other agencies have utilized waste tires for miscellaneous, site
specific pavement applications or as research projects, not as standard practice. The use
of the rubber from used tires is generally known as crumb rubber modifier (CRM). CRM
has been used, at least to some extent in most other developed countries. Australia has
B-8
Previous Page
