Coral as an aircraft pavement material: case histories

A discussion is presented by D Newill, G Austin, RD Nutt, GR Woodman and B Dolton of the paper by C Stevens and BG Verrall on the field testing of coral at Bonriki Airport, Tarawa (see IRRD 813514). The use of coral as aggregate in aircraft pavement construction is discussed using examples from various remote parts of the world including Barbados, the Ellis Islands, Papua New Guinea and Vanuata. Several points are examined including the equipment which can be transported, the physical characteristics of coralline materials, tyre damage, surface dressing methods, aircraft type and traffic, causes of rutting, compaction, bearing capacity and the availability of material. The difficulties of accommodating airstrips on small islands are also examined. Grading and filler qualities are particular problems of soft corals and although some pavements laid in the 1940s appear self-cementing samples were found to disintegrate in water. Some corals are extremely hard and will never form a smooth stone. When kept in a closed container, lagoon mud grows a fungus and degrades indicating a high organic content. Conventional northern European and northern American criteria for soil testing are found to be inadequate for corals as with other tropical materials.