How prevalent is hearing loss amongst construction workers?

It’s very prevalent.

Answer Extra: 

In a study of construction workers in Washington state, results showed that construction workers were exposed to 85 dBA or higher in about 70% of their work shifts, yet wore their hearing protectors less than 20% of the time.

Seixas, Noah and Neitzel, Rick. "Noise Exposure and Hearing Protection Use Among Construction Workers in Washington State," September 2004.