Piarco Airport - Trinidad , West Indies

Piarco International Airport in Trinidad , West Indies , was overlaid with 100mm of TLA modified mix in 1983. The PIA runway which is 45 m wide by 3, 000 m long is located on a mixed sandy clay deposit with a high (1 m) and sometimes perched water table. The average subgrade conditions can be considered as fair to poor (CBR 4.0 %) and the climate is rainy (150 cm per year). Prior to the overlay in 1983 , runway dislevelment and extensive structural degradation were major obstructions to landing aircraft and annual maintenance costs averaged US$ 40, 000 per year.

The overlay was placed in two layers, a 50 mm binder course and a 50 mm wearing course. The mix used was a dense graded aggregate with 25 mm top size aggregate for the binder course and 12.5 mm top size aggregate for the wearing course. The binder was a TLA modified 60/70 pen grade cement made up of 33 % TLA and 67 % of a 180/200 pen bitumen. The average asphalt cement for the binder course was 5.5% and the wearing course had an average of 5.7 % asphalt content. Marshall stabilities ranged from 10.7 KN (2,400 lbs.) to 14.3 KN (3,200 lbs.) and air voids content from 3.5 % to 3.7 %

Overall the overlay is performing remarkably well, having services in excess of 50,000 equivalent departures of a Boeing 747 at 3,482 KN (780,000 lbs.) without any expenditure on pavement repairs over the fourteen year period since 1983.

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