Patent GB-1371908-A (GB)
Title: Apparatus and method for forming a cavitied cementitious slab
IPC: B28B7/42
Filed: 1971-09-17
Abstract: 1371908 Moulding a cavitied concrete member J J DUES 17 Sept 1971 43522/71 Heading B5A [Also in Divisions B7 and E1] A cavitied concrete slab is made by depositing layers of concrete 140, 246 (Fig. 8) in a mould by means of a carriage that travels along the length of the mould and simultaneously pulls adjustable weight mandrels 162 through the concrete. Carriage.-The carriage 16 (Fig. 3) runs by wheels 50, 54 along the upper surfaces of a mould 12. The carriage is propelled at variable speeds by electric and hydraulic motors (see Fig. 6, not reproduced) and supports a control panel 220, cement hoppers 138 and 236, a reel 230 of wire mesh and a plurality of variable speed vibrators 210 and 264. Brackets 172 support a plurality of hollow metal mandrels 162. Mandrels.-Each mandrel 162 comprises a hollow metal shell 208 (Fig. 8) filled or partially filled with water and alcohol 176 surrounding a core 168 and immersion heaters 178. The cores 168 of groups of mandrels 180 (Fig. 4) are connected to levers 184 pivoted to a common member 188. Member 188 is reciprocatable by an hydraulic cylinder 190 to oscillate the mandrels 162 for trowelling the concrete, the cylinder 190 being controlled by limit switches 202, 204 and a solenoid valve 206.  Mould.-The mould comprises side and end walls that are adjustable by hydraulic jacks to allow removal of the completed concrete member, and transverse sawing into lengths. The mould bed 20 (Fig. 8) includes hot oil conduits, and catwalks are provided. Operation.-Intersecting reinforcements 266, 268 are placed on the mould bed 20, those parallel to the required cavities being tensioned by hydraulic jacks. Additionally, junctionboxes, window frames and conduits are positioned. The carriage 16 (Fig. 3) is positioned at one end of the mould, and the mandrels 162 supported by the brackets 172. Concrete is laid by hand in the mould to the level of the upper surfaces of the mandrels, from said one end of the mould up to the hopper 138. Mesh 222 from the reel 230 is guided around a roller 234, along the laid concrete, and secured to the end wall of the mould. Concrete is laid by hand above the mesh 222, up to the hopper 236. The carriage 16 is moved in the direction 18, the hoppers 138 and 236 being fed continuously with concrete by a moving readymix truck; an auger 254 and trough 256 direct the concrete to hopper 236. An auger feeds concrete from hopper 138 to complete the layer 140 (Fig. 8) which is spread and vibrated by the vibrators 210 (Fig. 3). The mesh 222 and other inserts are laid on the concrete and covered with a further concrete layer 246 (Fig. 8) by hopper 236 (Fig. 3), compacting being effected by the vibrator 264. Simultaneously, the mandrels 162 float in and are pulled through the laid concrete and are oscillated, until the carriage 16 reaches the other end of the mould. Heated covers (276) (Fig. 7, not reproduced) are placed over the mould to cure the concrete member, which is then sawn into lengths (not further disclosed) and removed. The mandrels 162 are disconnected from the brackets 172, the carriage 16 turned through 180 degrees, the opposite ends of the mandrels connected to the brackets, and the process repeated.  Examples are described for concrete having a slump (1-2) inches.