asphalt vs concrete (over)

asphalt

noun
  • A sticky, black and highly viscous liquid or semi-solid, composed almost entirely of bitumen, that is present in most crude petroleums and in some natural deposits. 

verb
  • To pave with asphalt. 

concrete (over)

How often have the words asphalt and concrete (over) occurred in a corpus of books? (source: Google Ngram Viewer )