Improved 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 portland cement with a carbonatable substance;   b. mixing the blended portland cement and carbonatable substance with water to form a damp blended portland cement and carbonatable substance mixture; and   c. carbonating the damp blended portland cement and carbonatable substance mixture in the presence of carbon dioxide,   
       wherein the carbonatable substance is air pollution control residue, cement bypass dust, or biomass ash. 
     
     
         2 . A process according to  claim 1 , further comprising initially sieving the portland cement and/or the carbonatable substance before blending. 
     
     
         3 . A process according to  claim 2 , wherein the portland cement and/or the carbonatable substance are initially sieved to obtain a particle size of less than around 0.1 mm before blending. 
     
     
         4 . A process according to  claim 1 , wherein a weight ratio between the portland cement and the carbonatable substance is approximately 1:2 to approximately 2:1. 
     
     
         5 . A process according to  claim 1 , wherein the blended portland cement and carbonatable substance is mixed with around 15-30% w/w of water to form the damp blended portland cement and carbonatable substance mixture. 
     
     
         6 . A process according to  claim 5 , wherein the process further comprises mixing the damp blended portland cement and carbonatable substance mixture. 
     
     
         7 . A process according to  claim 5 , wherein the process further comprises sieving the damp blended portland cement and carbonatable substance mixture. 
     
     
         8 . A process according to  claim 1 , further comprising pressing the damp blended portland cement and carbonatable substance mixture into a form or shape that resembles the shape of aggregate used in concrete. 
     
     
         9 . A process according to  claim 8 , wherein a force of around 100N is used to cast each form or shape. 
     
     
         10 . A process according to  claim 1 , wherein the damp blended portland cement and carbonatable substance mixture is carbonated in a carbon dioxide-rich gaseous environment. 
     
     
         11 . A process according to  claim 1 , wherein the carbonating takes place in a fully or partially enclosed carbonation chamber.