Reconstruction of Coral Runway
Palmyra Atoll, United States Minor Outlaying Island
Palmyra Atoll, located about 1,600 kilometres due south of the Hawaiian Islands, is a preserve owned by The Nature Conservancy (TNC) and one of the most pristine marine ecosystems on earth. Palmyra also hosts a mix of non-permanent residents (average year-round population of 20) to conduct conservation studies and preserve the thriving ecosystem.
Palmyra was not always so pristine. It was once a 2,400-man U.S. Naval Air Station in World War II. During the Pacific campaign, coral-derived aggregates were common building materials for roads and runways. Coral is comprised primarily of calcium carbonate and with the proper gradation and addition of water and compaction, has often been described as “self-cementing”. Coral can abrade significantly during compaction and pulverise to sand and silt-sized fractions. When correctly processed, coral aggregates can be extremely durable and serve as both a base course and wearing surface.
The enduring and resilient quality of coral as a construction material is apparent. Although original unmaintained runways at Palmyra have now been consumed by jungle, one 1,524 x 46 metre runway remains and now serves as a vital asset for the quickest and most economical access for the transfer of people, supplies, and equipment.
Maintenance works were completed on the runway in 2012 but weather-related issues caused construction complications of the cement-treated material. As a result, the runway would soften during rain and render the surface unusable. Without a safe place to land, aircraft would be prevented from departing Honolulu. To rectify the problem, TNC planned the rehabilitation of the central section (975 x 15 metre) of the strip using the most readily available and proven material - coral.
The specification called for the removal of the upper 127 mm layer and replacement with a new screened, graded, and processed layer. The resulting aggregate formation was then be heavily rolled producing additional fine material under the pulverisation process resulting in a dense interlocked aggregate formation suitable for use as a wearing course.
However, the contractor was limited by the equipment shipped from Hawaii to screen the coral and could not produce the specified maximum aggregate. As a result, coral larger than specification was introduced to the surface layer. The initial result was a product that yielded a failed gradation, a poor finish, and a product that would not last.
We adjusted the screening operation, the method of compaction, and assumed extensive hand work to effectively screen the larger coral and create a product and finish that yielded a solid, uniform, monolithic coral repair.
Vogt CE guided the contractor to meet all specifications for coral gradation, compaction, and surface tolerance. Well-written specifications guide the quality and durability of a product, and Vogt CE’s standards of quality and pragmatic solutions even in remote locations yield lasting results.