Each year about 250 million tires in the U.S.A. and
about 1,000 million in the world are scrapped. Current
trends indicate that less than 18 percent of these tires
are being recycled as products and 42 percent are being
burned for energy, and 5 percent are being exported
to third world countries for reuse (E.P.A., 1998).
Over 35 percent of scrap tires wind up in overcrowded
landfills, and millions more are left in empty lots
and illegal tire dumps. These dumps are potentially
causing serious fire and environmental hazards. Because
rubber tires do not easily decompose, economically feasible
and environmentally sound alternatives for scrap tire
disposal must be found.
In recent years, civil (geotechnical) engineering
applications of tire shreds, which are pieces of whole
tires cut into 50 - 300 mm pieces, has increased. The
use of tire shreds as fill material in geotechnical
applications has several potential benefits. In areas
where the underlying soil is compressible or weak, tire
shreds, with their unit weight about one-third of the
conventional backfill, would apply a smaller overburden
stress than conventional granular backfill, resulting
in lower settlement and increased global stability.
Moreover, the horizontal stress induced on retaining
structural systems would be about one-half lower than
conventional backfill, leading to a less expensive retaining
structure design.
However, the existing civil engineering applications
of tire shreds are facing with following technical difficulties:
i)
The quality control of
the in-situ compaction process of tire shreds is
subjected to many variables and uncertainties. The
performance of the compacted tire shreds is highly
workmanship dependent (Humphrey, 1996).
ii)
Another potential problem of the use
of tire shreds as a backfill material, however,
is the considerable amount of settlements that may
be used by surcharge loading (Tweedie et al., 1998;
Lee et al., 1999). Although the degree of settlement
can be reduced by appropriate mixture of soil-tire
chips, the vibration loads induced on the mixture
would easily causing segregation of soil from the
tire chips. The overall settlement of the fill will
eventually develop under long-term conditions (Lee
et al., 1999). Furthermore, the overall unit weight
of the tire chips-soil mixture is significantly
increased. This will result in the increase of construction
costs of the filling process.
iii)
The use of tire shreds as fill material
may potentially subject to pyrolysis process. The
moisture in the ground caused the steel contained
in the tire shreds to corrode. Since corrosion is
basically an exothermic process, this lead to a
steady heat buildup, which inadvertently ended up
as an uncontrolled pyrolysis process. The emitted
gases may cause fire hazard and hydrocarbon oils
may cause soil contamination (Humphrey, 1996; Scrap
Tire Management Counsel, 1997).
Recent years, there are a number of inventions have been
proposed to make use of recycled rubber tires into construction/building
materials. Nevertheless, all the inventions are known
to suffer from a number of disadvantages:
i)
The bonding agents are basically involved
with relatively expansive adhesive or latex compound.
The production costs of the resulting products are
inevitably very high.
ii)
The molding processes are generally
involved with heating and pressing on the mold for
substantial period of time. Thus, the product and
energy costs are increased substantially.
iii)
In a general sense, all the inventions
are resulted in the production of closely packed
products for building, construction, and outdoor
applications. The products, thus, require to resisting
relatively large structural loads, impact loads,
and normal wear and tear as expected in most of
the outdoor applications. However, the lightweight
and granular natures of ground rubber crumbs are,
generally, not fully utilized in these inventions.
Rubber Soil™
Rubber Soil™ is a new lightweight and porous construction
material is created, the material mainly comprises of
rubber crumbs/chips, cementitious materials such as
Portland and/or slag cement, fly ash or pulverized fly
ash (PFA), rubber powder or polymer fibers (filaments)
and water. The rubber crumbs/chips are, typically, derived
from scarp rubber tires with steel wires/belts removed.
Alternatively, the rubber crumbs/chips can be generated
from other means, such as recycled rubber crumbs derived
from other rubber products. The rubber crumbs/chips
are mixed with cementitious materials, rubber powder,
and water to form slurry. The slurry can be placed as
cast-in-place lightweight and porous construction material.
Alternatively, the material when it still in slurry
stage can be molded into lightweight construction blocks.
The construction material/blocks can be applied to various
civil and geotechnical works in replace with conventional
fill or backfill soils, the applicability of the construction
material/blocks includes, but not limited to, the following
earthworks: embankments, retaining structures, fill
slopes, backfill underground works, road fills and land
reclamation.
Objects and Advantages of Rubber
Soil™
i)
to provide a technology for massive
and permanent solutions for the utilization of scrap
rubber tires
ii)
to provide with a technology for the
development of a new rubberized lightweight and
porous construction material. The construction material
is mainly composed of rubber crumbs/chips and cementitious
materials such as Portland and/or slag cement. Bonding
developed between rubber crumbs/chips is mainly
achieved by hardened cement gel. The rubber crumbs/chips
used in the making of the construction material
are, typically, but not exclusively, derived from
scrap rubber tires
iii)
to provide with a technology to improve
the strain compatibility and flexibility of the
hardened cement gel with rubber crumbs/chips by
the use of rubber powders or polymer fibers (filaments)
as additive. The rubber powders are, typically,
but not exclusively, ground from rubber tire crumbs
iv)
to provide a way to reduce the cost
of the bonding agent for rubber crumbs/chips by
substituting a portion of the Portland cement with
pulverized fly ash (PFA) or fly ash
v)
to provide a molding process for casting
of uncured rubber crumbs/cement mixture into lightweight
construction blocks. The molding process can be
conducted in manufacturing plant or in-situ conditions
under specific and controlled environments. The
construction blocks, thus, are formed under well
quality-controlled processes, the resulting density,
void-ratio, and mechanical behaviors can be consistently
achieved. This manufacturing process can completely
eliminate the variability and uncertainties of the
mechanical qualities of in-situ compaction of fill
or backfill soils
vi)
to provide application technology
of the rubberized lightweight construction material/blocks
in projects relating to civil and geotechnical engineering
such as retaining structures, fill slopes, road
fills, embankments, reclamation works, etc.
