Logan International Airport will repave one of its runways with a new asphalt mix that is said to require less energy to produce and cut down on greenhouse gas emissions. The Massachusetts Port Authority board voted recently to approve the $6.3-million project that will begin sometime this fall. Massport officials say the so-called “warm mix” asphalt takes less energy to heat than traditional asphalt, saving some 200,000 gallons of diesel fuel. The new mix is expected to produce about 20 percent fewer greenhouse gasses when applied. The mixture will also contain up to 20 percent recycled asphalt.