Airplanes took off from Portland International Airport’s south runway Wednesday, marking a return to normal after three years of construction at PDX. The 11,000-foot south runway, worn by years of use, had closed for a complete rebuild that shifted flights to the airport’s north and crosswind runways. Construction led to increased flights over neighborhoods that had not been accustomed to frequent airplane noise. The south runway used an estimated 180,000 square yards of concrete — enough to pave a two-lane road for about 26 miles. Its rehabilitation was the final phase of a three-year effort that began with refurbishing and expanding of the north runway in 2009 and 2010.