Method and plant for the manufacture of building products

Abstract

A plant and method for the manufacture of cementitious products, viz. cast concrete roof tiles (T), the plant comprising a mixing station where the constituents of a cementitious composition, less an air entraining agent, are admixed under atmospheric pressure and further mixed under a partial vacuum of 200 to 340 mBar after the addition of an air entraining agent, the plant also comprising a moulding station where the tiles (T) are cast in a gang-mould before being cured in a conventional autoclave for up to 10 hours at 45° C. The cured concrete roof tiles (T) are de-moulded after curing and conveyed to a surface preparation zone where a primer coat of a water based epoxy and a surface coating of a water based emulsion paint are applied to at least an upper surface (in use) of the cast concrete roof tiles (T). The admixed cementitious composition has a Ford Cup flow of between 40 and 60 seconds and a slump test of between 180 and 220 mm. In an alternative method, instead of applying a primer coat, the upper surfaces, in use, of the roof tiles T are subjected to abrasion by grit-blasting to remove a thin layer from the upper surfaces thereby facilitating the subsequent application thereto of a surface coating.

1 . A plant for the manufacture of a concrete roof tile, the plant comprising:
 a) a mixing station for admixing a cementitious composition comprising water, sand, pigment, reactive fine filler, cement, a super-plasticiser and additives;   characterized in that the mixing station comprises   a1) means for mixing the water, sand, pigment, reactive fine filler, cement and an air entraining agent under atmospheric pressure;   a2) means for adding the super-plasticiser to the cementitious composition; and   a3) means for thereafter subjecting the cementitious composition to a partial vacuum;   b) a molding station where the admixed cementitious composition is fed into a re-usable mold to form a green-state roof tile;   c) a curing station where the green-state roof tile is cured;   d) a de-molding station where the cured roof tile is de-molded,   e) a surface preparation zone including conveying means for conveying the cured roof tile through the surface preparation zone, and means for preparing the upper surface, in use, of the cured roof tile to facilitate subsequent application thereto of a surface coating, wherein the surface preparation zone comprises a first coating zone for the application of a primer coat to said upper surface; and,   f) a second coating zone where the cured roof tile is provided with a surface coating on its prepared upper surface   
     
     
         2 . A plant according to  claim 1 , wherein the surface preparation zone includes a first curing zone for heating and drying the primer coat to cause cross-linking thereof and to reinforce said surface to provide a more receptive surface for said surface coating. 
     
     
         3 . A plant according to  claim 1 , wherein the second coating zone also comprises a curing zone for the application of heat to dry the surface coating applied to said prepared upper surface. 
     
     
         4 . A plant according to  claim 1 , wherein the partial vacuum is between 240 and 320 mBar. 
     
     
         5 . A plant according to  claim 1 , wherein the feeding station comprises means selected from means to feed the cementitious composition into the reusable mold under pressure and means to feed the cementitious composition into the reusable mold by gravity. 
     
     
         6 . A plant according to  claim 1 , wherein the feeding station comprises a funnel device through which the cementitious composition is fed into the re-usable mold. 
     
     
         7 . A plant according to  claim 1 , wherein a plurality of half molds, arranged in a gang mold, are provided for the simultaneous molding of a plurality of roof tiles between respective pairs of said of adjacent half molds of the gang mold. 
     
     
         8 . A plant according to  claim 7 , the arrangement being such that, when molding the roof tiles, the half molds are oriented on end within the gang mold. 
     
     
         9 . A plant according to  claim 8 , wherein the de-molding station includes means to rotate the gang mold to orient the half molds and the cured roof tiles in a substantially horizontal condition for de-molding. 
     
     
         10 . A plant according to  claim 9 , wherein the de-molding station includes means to de-mold each cured roof tile together with a next inline below half mold, and separation means for separating the cured roof tiles from their respective half molds. 
     
     
         11 . A plant according to  claim 10 , wherein conveyor means are also provided for conveying the separated cured roof tiles to the coating station and the separated half molds to a cleaning station whereat the half molds are prepared for a subsequent molding operation. 
     
     
         12 . A plant according to  claim 1 , wherein the surface preparation zone further comprises abrasion means, whereby said upper surface of the cured roof tile is subjected to abrasion to remove surface detritus to thereby further facilitate a subsequent application thereto of said surface coating. 
     
     
         13 . A plant according to  claim 12 , wherein said abrasion means comprises a grit blaster.