Pavement may not seem complicated, but it is. Concrete is made of aggregate, tiny bits of sand, crushed stone, and gravel. Asphalt is composed of sand, gravel, and bitumen, a byproduct of oil petroleum production. Both can go into pavement. How much does just obtaining these materials tax the Earth? A lot. Fortunately, with the federal government purportedly inching toward a trillion dollar injection into American infrastructure, now may be the perfect time to make the gray stuff just a shade more green.