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Epoxy Asphalt

New Pingsheng Bridge  
 
 

Nanjing, China Project

Frequently Asked Questions

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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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