PERFORMANCE OF THIN BONDED PORTLAND CEMENT CONCRETE OVERLAYS ON MILITARY AIRFIELDS

The United States Air Force has more than 20 years of experience with thin bonded Portland cement concrete overlays--5 ,1 to 10.2 Gil\ (2 to 4 in.) in thickness. The construction history and performance of 14 features (a feature being defined as a pavement cross-section of like construction) involving thin bonded overlays at four Air Force bases are discussed in this paper. The features range in age from 13 to 21 years and include both runways and aprons. Traffic on the thin bonded overlays ranged from high volume, lightweight fighter aircraft to moderate volume, very heavy cargo, tanker and bomber aircraft. The construction procedure followed for each of the thin bonded overlays was similar. The surface of the original pavement was scarified to a depth of not less than .6 cm (1/4 in.) and all loose material was removed. When necessary, the pavement was cleaned with a detergent, flushed, and then etched with muriatic acid. The surface was again flushed, and a grout .15 to .3 cm (1/16 to 1/8 in.) thick was applied to provide a bond. The overlay was then applied quickly before the grout could dry. In general, the overlays have performed quite satisfactorily. Condition surveys indicate that after 17 years most features are in VERY GOOD condition, and the remaining are in GOOD condition. Problems encountered with the overlays can be traced to faulty construction procedures. Most notably, allowing the grout to dry prior to overlay placement and failure to match joints in the overlay with the underlying pavement have resulted in loss of bond and reflection cracking, respectively.