THE Conti Group of New York are currently using a Rapid Mix 400, manufactured by Northern Ireland-based Rapid International Ltd, to perform rehabilitation work on runways at JFK Airport in New York.
Econocrete is a lean concrete made with low-cost, locally available aggregates that do not meet conventional specifications. Interest in the use of the material has developed in the last few years owing to the high cost and dwindling supplies of high-quality aggregates in some areas of the US.
In the past, substantial quantities of natural aggregates and other crushed rock sources were discarded or rejected because of restrictive specifications, much of which could have been used in concrete structural elements had proper attention had been given to developing mix designs to meet the structural requirements and environmental conditions to which it would be exposed.
Today, however, the Federal Highway Administration and local governmental agencies are supporting the transition of the econocrete concept from the laboratory into the field. Mixes based on laboratory tests are being designed for specific strength and durability levels in accordance with their intended use.
The possible applications of econocrete are many and varied; it is a durable concrete with a well-distributed air void system, and water-reducing admixtures are often included in the mix to improve workability in the lower slump ranges that result in higher strengths.
The Conti Group’s JFK project is the largest runway surfacing contract at the airport in the past 20 years, and has been developed to accommodate the new Airbus 380 – the world’s largest airliner with a wingspan of 262ft. By using econocrete, the Conti Group have managed to reduce the total cost of the scheme.
A Rapid Mix 400 continuous mixing plant is being used for the project. The plant comprises a totally mobile and completely self-contained unit, capable of mixing up to 400 tonnes/h, depending on the application. Utilizing its hydraulic system to change from its travel mode into a fully operational plant in a matter of minutes, it features a 50-tonne capacity self-erecting cement silo and is equipped with a twin-shaft continuous mixer.
The Conti Group are producing the econocrete at JFK by milling material recovered from the demolition of old runways, screening it, and then mixing it with cement and water in the Rapid Mix 400. Because the econocrete reuses 70–80% of the material from the old runway, it is providing the airport with significant economic benefits as well as being a more environmentally friendly solution.
Although the project is still ongoing at JFK Airport, and at several other airports around the US, it is hoped that the success of econocrete and its benefits to both the customer and the environment will prompt even more US airports to consider using the material.