How does Epoxy Asphalt concrete differ from conventional asphalt concrete?
Epoxy Asphalt is a concrete made with a binder that, unlike conventional asphalt, does not become brittle at low temperature and does not melt at high temperature. Epoxy Asphalt pavements have much higher stability, much less susceptibility to cracking, are less permeable and maintain skid resistance much longer than conventional asphalt pavements.
How does Epoxy Asphalt perform?
Excellent fatigue resistance at low temperature and high
temperature prevents cracking even after millions of load cycles. Skid
resistance of Epoxy Asphalt pavements remains very good after nearly
40 years of service. High stability, even at high deck temperature,
permits no rutting or shoving. Long term performance has been equally
as good in wet as in dry climates and in sub-freezing exposure as well
as tropical climates.
What are the advantages of epoxy asphalt concrete for an orthotropic steel deck?
Epoxy Asphalt pavement has excellent resistance to fatigue
cracking and it also helps stiffen the orthotropic deck system. This
high performance pavement reduces (dampens) deflection of the deck plate
and extends the life of the deck plate. It does not rut or shove even
at high deck temperatures. Depending on the design of the deck system
it can be applied at any thickness from 25mm to 75 mm or as an overlay
at 19 mm. Unlike other special polymer and asphalt materials that are
poured and often placed by hand in a slow process, Epoxy Asphalt is
mixed by in a conventional asphalt pug mill and rapidly applied with
conventional asphalt paving and rolling equipment.
Can local asphalts be used as the asphalt in Epoxy Asphalt?
Epoxy Asphalt is formulated using a blend of materials
from a particular domestic oil field. The asphalt derived from this
crude has unique properties that make it compatible with the epoxy resins
and curing agents that make up the total binder and balance the working
life, cure time, strength and flexibility of the system. Other asphalts
do not provide all these properties and most are not compatible with
the epoxy resin and curing agents.
What are requirements of the time and temperature when mixing epoxy asphalt concrete?
The epoxy resin component is maintained at 80-85°C
prior to mixing. The asphalt/curing agent component is maintained at
150-155°C prior to mixing. The aggregate temperature is controlled
to be about 113-124°C. The mixed batch as it leaves the pug-mill
(asphalt plant mixing chamber) is controlled to be between 110 and 121°
C.
Are there special requirements for the mixing method and unique equipment?
ChemCo Systems supplies a metering-mixing machine and valve assembly to proportion and mix the two reactive components of the Epoxy Asphalt binder and inject the proper amount for each batch into the pug mill. A secondary spray bar is fitted into the pug mill to bypass the regular liquid asphalt delivery system. This allows the plant to be used for regular asphalt concrete production when it is not being used to produce Epoxy Asphalt.
What are the optimum aggregate properties for Epoxy Asphalt?
Since the aggregates make up about 94% of the paving
mix it is essential to use the best available aggregate to obtain a
durable pavement with good flexural life. Aggregate should be hard,
tough, resistant to wear and polishing and have 100% crushed faces.
Elongated particles with an aspect ratio of greater than 1 to 3 should
be no more than 5 % of all aggregate particles by weight.
A typical gradation for a paving course 25 mm thick is:
| Sieve Size |
Percent Passing |
| inches |
mm |
|
| 3/4 |
19.0 |
100 |
| 1/2 |
12.5 |
95-100 |
| 3/8 |
9.5 |
80-95 |
| No. 4 |
4.75 |
58-75 |
| No. 30 |
.0006 |
20-35 |
| No. 200 |
.000075 |
7-14 |
Adhesion loss to the substrate is usually an important cause
for the deterioration of the wearing surface. What is ChemCo's solution
to this problem?
Epoxy Asphalt concrete uses a bond coat of Epoxy Asphalt
that is sprayed onto the deck with special equipment (provided by ChemCo
Systems). This bond coat provides tensile pull-off bond strength to
the corrosion protection coating on the steel deck of at least 2.5 MPa.
Unlike thermoplastic material based bonds, the Epoxy Asphalt bondcoat
maintains its high performance even when the deck reaches temperatures
over 70 °C.
What are the key points to successful placement of epoxy asphalt concrete pavement?
The key elements are maintaining temperature control of the Epoxy Asphalt concrete at the batch plant and completing roller compaction of the Epoxy Asphalt concrete before the Epoxy Asphalt on the deck has cooled too much. The breakdown rolling must be complete before the temperature drops below 82°C and the finish rolling before the temperature drops below 65°C.
What are the material requirements of the adhesion layer and
waterproofing layer?
No waterproof membrane layer is required. The low void
Epoxy Asphalt pavement and bond coat are impervious to water. The steel
deck is initially protected from corrosion with inorganic zinc coating
or a zinc rich paint coating.
What information have past projects shown about rutting resistance of Epoxy Asphalt?
Properly mixed and installed Epoxy Asphalt does not rut,
even with overloads at 70°C. Only one Epoxy Asphalt pavement in
the US has reported rutting. The rutting occurred because the Epoxy
Asphalt binder content was too high ( at 7%). Marshall stability of
Epoxy Asphalt pavements at 60° C is usually between 12,000 and 17,000
pounds. Marshall stability at 204° C is over 4,000 pounds (above
the common value of ordinary asphalt at room temperatures).
What is the main cause of failures in epoxy asphalt concrete?
When properly designed and applied, Epoxy Asphalt has
not failed. The few decks that have had the surfacing replaced exhibited
fatigue cracking long after the design life of the pavement and after
the pavement had been subjected to many years of truck traffic (fatigue
cracks that occur after the design life of the pavement can be filled
with a thermo-set polymer to extend the life of the surfacing). Insufficient
compaction of the surfacing can result in a void content higher than
the required 3% max. High void content can result in premature wear
and/or fatigue cracking. An excessively high binder content can result
in reduced stability and displacement under heavy loads. Early replacement
of surfacing showing displacements can prevent progressive failure.
Can the life of an Epoxy Asphalt pavement on an orthotropic steel bridge deck be predicted?
Dynamic flexural load testing of a specimen plate that simulates the
deck system has been very effective in predicting the suitability of
the paving system. The test program takes into consideration the range
of deck temperatures the deck will be exposed to, the magnitude and
number of wheel loads (including and differentiating truck loads). The
test is carefully designed to produce the same radius of curvature in
the test specimen as will exist in the pavement over the longitudinal
stiffeners on the actual bridge deck.
How do traffic volume and overload influence performance of Epoxy Asphalt?
A properly designed Epoxy Asphalt surfacing with excellent
aggregates on a steel deck plate 16 mm or thicker should withstand about
15 to 25 million cycles of U. S. legal-limit wheel load without cracking.
However, wheel overloads can significantly reduce fatigue life. One
very heavily overloaded truck can cause a comparable loss in fatigue
life to many legal trucks.
For new projects or existing deck rehabilitation, fatigue
tests should be made with the mix design and actual aggregates that
will be used in the pavement.
On the San Francisco Bay Bridge, each lane
carries in excess of 1 million vehicles per year and the bridge has
carried over 250 million vehicles since paving was completed in 1976.
Can Epoxy Asphalt be installed over conventional asphalt pavement?
Epoxy Asphalt can be placed on conventional asphalt. However, a sound base is required. Any deficiencies in the underlying asphalt pavement, such as cracks or instability will sooner or later reflect through the Epoxy Asphalt pavement.
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