What is Epoxy Asphalt?
|Laying the levelling course
The two-component Epoxy Asphalt binder, when cured, becomes a two-phase epoxy polymer that contains an asphalt extender. The continuous phase is an acid cured epoxy and the discontinuous phase is a mixture of asphaltic materials. It is a thermoset polymer (it will not melt). This binder, combined with high quality standard asphalt paving aggregates, forms a tough polymer concrete called Epoxy Asphalt Concrete. A hot spray application of an Epoxy Asphalt bond (tack) coat precedes the laying of the Epoxy Asphalt Concrete to provide a very high strength bond to the substrate (concrete, steel or asphalt) that won’t melt.
The excellent fatigue resistance of Epoxy Asphalt enables it to maintain its integrity on orthotropic steel bridge decks without cracking even after the deflections caused by millions of wheel loads. The fatigue resistance is 3-4 orders of magnitude (of fatigue load cycles) higher than polymer modified asphalt binders. The composite action of the epoxy asphalt, unlike that of more flexible pavements, increases the fatigue life of the steel deck and structure by reducing deflection, and thus strain, in the steel.
Epoxy Asphalt provides another layer of corrosion protection for the steel deck in addition to the primary corrosion protection coating because of its low void content of less than 3%. The voids that exist are not interconnected. The result is an impervious (non-porous) pavement with extreme resistance to penetration of water and chloride ions.
Resistance to Rutting and Shoving
Because Epoxy Asphalt binder is a thermoset polymer (as opposed to a thermoplastic polymer such as conventional and rubber-modified asphalt), it provides excellent resistance to rutting and shoving even under high wheel loads in hot and cold climates
Epoxy Asphalt pavements include high quality, polish resistant aggregates that provide outstanding skid resistance throughout their life. The Epoxy Asphalt binder does not “bleed” as do thermoplastic bituminous paving materials when the pavement gets hot. As soon as the binder on the aggregate exposed to traffic wears off, vehicle tires see only the aggregate.
Epoxy Asphalt binders exhibit extremely low rates of oxidation and loss of resiliancy unlike standard and polymer modifed binders. Pavements and overlays constructed with Epoxy Asphalt maintain their properties and do not become more rigid (more brittle) with time. These properties have been validated by several OECD research studies seeking a long-lived pavement for busy roads conducted by the International Transport Forum. In addition, New Zealand is using Epoxy Asphalt as a extended life binder for open-graded porous pavements (with ~20% voids), in an application where the binder is exposed to more air and water by design.
Epoxy Asphalt pavements include a separate, high strength, temperature resistant (non-melting) bond coat. Unlike regular or polymer modified asphalts, the Epoxy Asphalt bond coat provides a high strength bond to the underlying substrate (concrete or steel) even at elevated temperatures of 158°F (70°C). In some cases, where delamination has been identified previously as a primary cause of failure, the Epoxy Asphalt bond coat has been successfully employed with polymer modified SMA pavements on steel decks.
Minimum Traffic Delays
|Epoxy Asphalt bond coat is sprayed onto the inorganic zinc-coated deck plates. The bond coat is about 0.03 inches (0.68mm) thick.
Epoxy Asphalt provides the absolute minimum delays for re-paving existing bridges under traffic. An Epoxy Asphalt pavement is ready for traffic in its partially cured state once it has cooled to ambient temperature. The I-day-old uncured Marshall stability of type IX Epoxy Asphalt (measured at 60°C) is generally > 2000 lb (9.4 kN). It develops full strength over two to four weeks depending on average daily temperatures
Local Paving Crews
Local paving crews using conventional asphalt paving equipment install Epoxy Asphalt. ChemCo Systems engineers provide training and technical support during the project. ChemCo supplies the special blending equipment (meter-mix machine) for the two Epoxy Asphalt components. This special equipment is operated by local labor. There is no need to import specialized labor.
|2nd Yangtze River Bridge, bridge deck side view
Epoxy Asphalt technology helps meet the challenge of replacing old concrete bridge decks with orthotropic steel decks while minimizing traffic interruption. Shop applied Epoxy Asphalt Chip Seal provides a durable skid resistant surfacing that protects each steel plate from wear and corrosion until all plates are in place and welded together. This technique will be employed on the Macdonald Bridge in Halifax, Nova Scotia during a deck replacement project in the next several years and the bridge will remain open during the project during daytime. Epoxy Asphalt concrete provides the long term wearing surface when it is installed after all deck plates are in place. Both the Golden Gate Bridge and the Lions Gate Bridge used this system for their deck replacement projects. The Macdonald Bridge in Halifax Nova Scotia is undergoing deck replacement currently and also uses Epoxy Asphalt chip seal on the replacement deck sections.
The concrete deck of the heavily traveled Golden Gate Bridge was replaced and paved with no daytime lane closures. Lane shutdown began at 8 PM, paving began at 10 PM and all lanes were opened at 5 AM the next morning. Throughout the night at least one lane was always open in each direction for traffic.