hollowcore slabs 9slipforming and extrusion0
 

hollowcore slabs (slipforming and extrusion)
hello everyone
i would like to know if someone can explain me the differenece between slipforming and extrusion production of precast hollowcore slabs.
thank you

slipforming, i believe, involves the concrete placed in bulk in front of a moving vibrator/screed that maneouvers the concrete into place. in this method, the hollow cores are simply formed in place prior to depositing the concrete. the concrete stays in place and the form moves over it.
extruded - the concrete is pressure injected through a non-moving form pattern that replicates the cross section of the hollow core plank. the concrete is mixed to a low enough slump to maintain its shape. the form stays in place and the concrete moves along a guide conveyor.
the hollowcore guy i talked to last week called their process "extrusion" but then described it like jae mentioned above. it's really more of a slipforming than a true extrusion. they place a very very stiff mix over a rotating auger which tapers down into a solid mandrel. the mandrel od matches the core id. the machine travels along the 400' long bed and lays the finished slab behind it as it goes. after a surprisingly short cure time, they saw the 400' pieces into custom lengths and, viola, a slab is born.