asphalt vs viaduct

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. 

viaduct

noun
  • A bridge with several spans that carries road or rail traffic over a valley or other obstacles. 

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