VIDEO: Investigators are working to determine the cause of a four-alarm fire at a Burlington concrete factory. The fire did a lot of damage -- but didn't stop employees from going to work. Investigators don't know when the fire at Gleason Redi-Mix started -- because no one had been in the building for hours. By the time firefighters got the call around 5:30 a.m. Wednesday, Aug. 22, the fire had taken over a company warehouse. "It looks like it had been going for a while. To gain access and get water on the fire took a little time," said Assistant Chief Eric Kurth, Burlington Fire Department. Burlington fire officials quickly called for backup -- and 13 departments responded to help.