Posted 7/11/2019 13:43 (#7608916 - in reply to #7608820) Subject: RE: Concrete under silage pit help please
Re-bar in this type of flat work is for temperature and shrinkage control. Our standard for this type of work had 1/2 inch re-bar at 18 inch spacings each direction unless the distance exceeds 50 feet. Bar was placed on 3 inch chairs with 1.5 inches end clearance to the form work. !/2 inch on 18 inch centers is equivalent to 3/8 inch on 12 inch centers, but over weight concrete workers in big yellow boots can stand between the re-bar and not on it. This standard was used to build concrete floors under liquid fertilizer tanks that were 30 to 36 feet tall, they place roughly 2950 pounds per square foot on the concrete and the base. Most decent soils in their original unmolested state will support 3000 pounds or more per square ft. Good base preparation is the first step in good concrete.
I designed an approach apron for a bunk silo that was designed to capture and direct leachate from the silage to an existing in ground manure tank and keep it out of a roadside ditch. It was about 120 feet square and was cut into 4 nearly equal panels of 60 feet square. The concrete contractor insisted on dowelling the panels without being able to do it correctly (they need to be able to slide back and forth on one side of the dowel) finally the concrete design engineer said to propose to the landowner and contractor that we eliminate the steel all together, pour the 4 panels 1 inch thicker or 7 inches. Winner, winner, everybody was happy. It is still in place, Michigan loads of silage (remember we load our trucks up to 160,000 pounds gross weight) are regularly back up into the bunk silo. The advantage this site had was the base was already compacted from years of use without the concrete.