Q. How long will it take my new driveway to harden (or
cure)?
A. Usually 6-12 months. You may walk on your new driveway
immediately, but you should keep automobile traffic off it for
at least three full days (and longer in hotter temperatures).
Even after your asphalt driveway is fully cured, do not expect
it to be as hard as concrete.
Q. Why are most roadways made of asphalt?
A. Over 90% of our nations paved roads utilize hot mix asphalt.
Asphalt tends to be the pavement of choice by most designers
and specifiers because of its lower construction cost, reduced
time of construction, ease of maintenance, and benefits related
to improved smoothness, reduced pavement noise, and ability to
resist deformation in colder climates and higher elevations.
Q. What materials are used to produce asphalt
pavement?
A. Hot mix asphalt can be simplified into two major components;
liquid asphalt cement and aggregates. The liquid asphalt cement
(often called asphalt "binder") is material that coats the
aggregate particles and acts as the glue that holds the mix
together. The aggregates may consist of natural aggregate
(river gravel and sands) or processed aggregates (from quarry
and blasting operations). The aggregates provide the structure
and framework that gives an asphalt mixture its stability and
strength. Another vital component to a well constructed asphalt
pavement is the presence of air voids in the mixture. The
amount of air voids in the asphalt is controlled through the
aggregate gradation and the quantity of liquid asphalt. The
proper blend of asphalt and aggregates is determined prior to
construction (during the mix design phase) in order for the
mixture to have the desired properties.
Q. Are all asphalt mixtures the same?
A. No, it is a common misconception that asphalt is asphalt and
that the asphalt used on the interstate roadways is the same
asphalt used in residential driveways. An asphalt mixture that
is designed for use on a heavily traveled highway has very
different characteristics than those used in low volume
residential applications. Those differences may include
different aggregate types, sizes and proportions as well as
different grades of liquid asphalt. Feel free to contact the
APAO office or your local APAO producer member to assist you in
determining which mix is appropriate for your application.
Q. What is Perpetual Pavement?
A. "Perpetual Pavement" is the name coined to describe a
three-layer, flexible pavement design and construction concept.
Application of the concept produces a deep-strength asphalt
pavement that can resist structural fatigue distress
indefinitely (more than 50 years) and, thus, results in a
long-lived pavement. These long-lasting structural bases can be
economically maintained by replacing just the surface, never
needing total removal and replacement. For more information on
Perpetual Pavements, see the concept paper prepared by the
Asphalt Pavement Alliance.
Q. What is this Superpave I keep hearing about?
A. Superpave is a system of material specifications
and laboratory mix design methods based on performance criteria
developed under the Strategic Highway Research Program (SHRP).
Using the Superpave system, materials and mixes can be designed
to reliably perform under any loading or environmental
conditions. The Superpave system is under- going continuing
development nationally. The Oregon DOT is fully implementing
Superpave in 2002 on all state projects. In general, Superpave
designed asphalt mixtures rely more on stone-to-stone contact,
they are generally more durable and last longer.
Q. What product is recycled the most in the United
States?
A. Americans who recycle their aluminum cans, newspapers,
plastics and glass are helping to preserve our nation's
resources. But daily and quietly, the Hot Mix Asphalt industry
is recycling asphalt pavement to a substantially larger extent.
Asphalt pavement is unquestionably the nation's most widely
recycled product. The Federal Highway Administration reports
that 73 million metric tons of the 91 million metric tons (or
80.3 million of the 100.1 million tons) of asphalt pavement
that is removed each year during resurfacing and widening
projects is reused as part of new roads, roadbeds, shoulders
and embankments. That's a recycling rate of 80 percent. In
terms of tonnage, only scrap metal comes close at 70 million
tons, which represents a recycling rate of 64 percent for
steel. A possible misconception is the extent to which the
recycling of consumer goods occurs. The EPA says Americans
recycle only 28 percent of the materials in the municipal solid
waste stream. The EPA says that of the 217 million tons of
solid waste generated in 1997, the latest year for which
figures are available, we recycled 60.7 million tons of paper
and paperboard, yard trimmings, glass, metal, plastic and other
materials. Thus, the 80.3 million ton volume of recycled
asphalt pavement is approximately one-third higher than the
total volume of 60.7 million tons of post-consumer recycling.
And it's double the volume of paper, glass, plastic and
aluminum combined.
Q. What impact does the production and use of HMA have
on the environment?
A. In many respects Hot Mix Asphalt (HMA) is the
environmentally friendly paving material. First, HMA materials
are 100% recyclable. Virtually all of the Reclaimed Asphalt
Pavement (RAP) that is removed from existing streets and
highways is recycled into new HMA. Because this recycling of
HMA is economical it occurs without the need for government
mandates or subsidies. HMA also has been shown to consume less
energy than other materials and systems. A study done by the
Asphalt Institute indicated that a comparably designed HMA
pavement required only about half the total energy to construct
as a comparable Portland cement concrete pavement. Improvements
in technology have been steadily reducing the airborne
emissions from the production and placement of HMA. Dust from
the drying of aggregates is the major emission and is now
almost totally captured and recycled. Other emissions are
primarily combustion products from the burning of fuel to heat
the aggregates and fumes from hot asphalt itself. Fuel burners
are now much more efficient, resulting in very complete
combustion. Studies to date by the government and industry have
shown emissions levels to be very low and have not identified
any health hazard associated with exposure to asphalt fumes.
Nevertheless, the industry continues to develop improved
technology for reducing emissions and minimizing exposure.
CCB#140837
