Production of aggregates

Abstract

An improved process for the preparation of aggregates for use with mixtures of various carbonatable substances, in particular mixtures comprising pulverised fuel ash and/or steel slag. The mixtures also comprise a carbonatable binder. The process comprises the steps of a. blending a combination of two carbonatable wastes, b. mixing the blended carbonatable waste with a carbonatable binder, c. mixing the blended carbonatable waste and binder with water, and d. carbonating the damp blended carbonatable waste in the presence of carbon dioxide.

1 . A process for the preparation of aggregates, the process comprising:
 a. blending a first carbonatable waste with a second carbonatable waste to form a blended carbonatable waste;   b. mixing the blended carbonatable waste with water to form a damp blended carbonatable waste mixture; and   c. carbonating the damp blended carbonatable waste mixture in the presence of carbon dioxide;   
       wherein the process further comprises mixing the blended carbonatable waste with a carbonatable binder; and wherein the first carbonatable waste is steel slag or pulverised fuel ash and/or the second carbonatable waste is steel slag or pulverised fuel ash. 
     
     
         2 . A process according to  claim 1 , wherein the first carbonatable waste is air pollution control residue, cement bypass dust, or biomass ash and/or wherein the second carbonatable waste is air pollution control residue, cement bypass dust, or biomass ash. 
     
     
         3 . A process according to  claim 1 , further comprising initially sieving the first carbonatable waste and/or the second carbonatable waste before blending. 
     
     
         4 . A process according to  claim 3 , wherein the first carbonatable waste and/or the second carbonatable waste are initially sieved to obtain an average particle size of less than around 0.1 mm before blending. 
     
     
         5 . A process according to  claim 1 , wherein the carbonatable binder is cement kiln dust or ordinary portland cement. 
     
     
         6 . A process according to  claim 5 , further comprising initially sieving the carbonatable binder before blending with the first and second carbonatable wastes. 
     
     
         7 . A process according to  claim 1 , wherein a weight ratio between the first carbonatable waste and the second carbonatable waste is approximately 1:2 to approximately 2:1. 
     
     
         8 . A process according to  claim 1 , wherein a weight ratio between the first carbonatable waste, second carbonatable waste, and carbonatable binder is approximately 1:2:2 to approximately 2:1:2. 
     
     
         9 . A process according to  claim 1 , wherein the blended carbonatable waste is mixed with around 15-30% w/w of water to form the damp blended carbonatable waste. 
     
     
         10 . A process according to  claim 9 , further comprising mixing the damp blended carbonatable waste mixture. 
     
     
         11 . A process according to  claim 1 , further comprising sieving the damp blended carbonatable waste mixture. 
     
     
         12 . A process according to  claim 11 , wherein the damp blended carbonatable waste mixture is sieved to obtain an average particle size of less than around 0.1 mm. 
     
     
         13 . A process according to  claim 11 , wherein the blended carbonatable waste comprises any number of additional carbonatable wastes blended into the mixture. 
     
     
         14 . A process according to  claim 1 , wherein the process further comprises mixing the blended carbonatable waste with a third carbonatable waste. 
     
     
         15 . A process according to  claim 14 , wherein the third carbonatable waste is pulverised fuel ash or steel slag. 
     
     
         16 . A process according to  claim 1 , further comprising pressing the damp blended carbonatable waste mixture into a form or shape that resembles the shape of aggregate used in concrete. 
     
     
         17 . A process according to  claim 16 , wherein a force of around 100 N is used to cast each form or shape. 
     
     
         18 . A process according to  claim 1 , wherein the damp blended carbonatable waste mixture is carbonated in a carbon dioxide-rich gaseous environment. 
     
     
         19 . A process according to  claim 1 , wherein the carbonating takes place in a fully or partially enclosed carbonation chamber.