"We needed only 1 month to teach our staff how to produce aggregates with the crushers and screen", says Isun. Crushing and Screening Process Fifteen persons work in the quarry, from 8 am to 5 pm, 6 days a week. The machines are processing ballast from 63 to 25 mm size and concrete aggregates in fractions of 25 to 10 mm and 10 to 0 mm.