Delayed-setting concrete

Abstract

The invention relates to a delayed-setting concrete based on blast furnace slag. The invention further relates to a method of initiating the setting of said concrete.

What is claimed is:  
     
         1 . A delayed-setting concrete based on blast furnace slag.  
     
     
         2 . A concrete according to  claim 1  which consists of a mixture essentially comprising a blast furnace slag, aggregates and water.  
     
     
         3 . A concrete according to  claim 1  or  2  in which the blast furnace slag represents from about 10% to about 35% by weight of the concrete composition.  
     
     
         4 . A concrete according to one of  claims 1  to  3  in which the blast furnace slag has a grain size below about 200 μm, preferably below about 100 μm.  
     
     
         5 . A method of initiating the setting of the concrete as defined in one of  claims 1  to  4 , which consists in activating the blast furnace slag.  
     
     
         6 . The method according to  claim 5  in which activation is effected by means of an alkaline agent such as sodium hydroxide, potassium hydroxide or sodium or potassium carbonate.  
     
     
         7 . The method according to  claim 6  in which the amount of alkaline agent used is such that the final pH of the concrete is between about 12 and about 13.5.  
     
     
         8 . The method according to  claim 5  in which activation is effected by means of a lime-based compound, a sulfate-based compound or a mixture of a lime-based compound and a sulfate-based compound.  
     
     
         9 . The method according to  claim 8  in which activation is effected by means of a mixture of a lime-based compound and a sulfate-based compound in a weight ratio of between about 0.5 and about 1.5.  
     
     
         10 . The method according to  claim 8  or  9  in which the amount of activating agent used is between about 2% and about 15% by weight, based on the weight of the blast furnace slag.  
     
     
         11 . The method according to one of  claims 5  to  10  in which the activating agent is enclosed in an envelope which degrades over time.