Not only were the runways not paved, neither were most roads 100 years ago, especially in rural areas where fighter airfields were situated. If you pore over the photos from that era you don't see too many airplanes parked on pavement. Still, maybe in a factory setting or at a field like Boistrancourt (where there was a large chateau adjacent to the flying field and even a factory nearby) -- maybe there was a paved surface here or there...