Fly ash processing and manufacture of articles incorporating fly ash compositions

Abstract

A fly ash composition including fly ash and a plasticizing agent and being in a powder form is disclosed. The plasticizing agent is capable of binding the fly ash particles in the fly ash composition together on pressing of the fly ash composition. Processes of forming shaped articles containing fly ash may utilize the fly ash composition and/or mixtures containing fly ash and have low water content and may exhibit sufficient green strength to be handled by industrial equipment.

1 . A fly ash composition comprising fly ash and a plasticising agent, the composition being in a powder form, and wherein the fly ash composition includes greater than 70% fly ash by dry weight of the composition, and wherein the plasticising agent being capable of binding the fly ash particles in the fly ash composition together on pressing of the fly ash composition. 
     
     
         2 . A fly ash composition according to  claim 1 , wherein the average particle size of composition is less than 50 micron. 
     
     
         3 . A fly ash composition according to  claim 1 , wherein the plasticising agent is at least partially coated on the fly ash particles. 
     
     
         4 . A fly ash composition according to  claim 1 , wherein the fly ash composition includes from 70 to 95% fly ash by dry weight of the composition. 
     
     
         5 . A fly ash composition according to  claim 1 , wherein the plasticising agent comprises aluminium silicate with substantial rheological properties. 
     
     
         6 . A fly ash composition according to any preceding claim, wherein the fly ash has a LOI value of less than 2%. 
     
     
         7 . A fly ash composition according to  claim 1 , wherein the water content in the fly ash composition is less than 3 wt % of the total weight of the composition. 
     
     
         8 . A fly ash composition according to  claim 1 , wherein the plasticising agent is capable of binding the fly ash particles in the composition together on pressing of the composition when the water content in the composition is at least 4 wt %. 
     
     
         9 . A fly ash composition according to  claim 1 , wherein the composition further comprising one or more ceramic additive in a total amount of from 5 to 15% of the dry weight of the composition. 
     
     
         10 . A method of forming a shaped article having a matrix containing sintered fly ash, the method comprising the steps of:
 providing a mixture containing a fly ash composition comprising fly ash and a plasticising agent, and water, the mixture being in a particulate flowable state, and wherein the fly ash composition includes greater than 70% fly ash by dry weight of the composition;   applying pressure to the particulate mixture so as to temporarily bind the mixture so as to form a green article having a modulus of rupture of greater than 1.5 kg/cm2; and   firing the green article so as to sinter the fly ash.   
     
     
         11 . A method according to  claim 10 , wherein the mixture contains additional water to that contained in the fly ash composition. 
     
     
         12 . A method according to  claim 10 , wherein the water content in the mixture and/or the green article is less than 6%. 
     
     
         13 . A method according to  claim 23 , wherein the modulus of rupture of the green article is greater than 1.5 kg/cm 2 . 
     
     
         14 . A method according to  claim 10 , wherein the mixture comprises from 80 to 98 wt % of the fly ash composition by dry weight of the mixture. 
     
     
         15 . A method according to  claim 10 , wherein the thickness of the shaped article is less than 40 mm. 
     
     
         16 . A method according to  claim 10 , further comprising the step of firing the green article containing substantially the same water content present at forming of that green article. 
     
     
         17 . A method according to  claim 10 , wherein the plasticising agent includes a superplasticiser. 
     
     
         18 . A method according to  claim 10 , wherein the green article is fired without any substantial curing of the green article. 
     
     
         19 . A method according to  claim 10 , wherein the firing of the article includes a fly ash sintering phase where the fly ash in the green article is sintered at a temperature of from 1000° C. to 1300° C. 
     
     
         20 . A method according to  claim 10 , wherein the article is cooled at a rate greater than or equal to 200° C./minute after firing. 
     
     
         21 . A method according to  claim 10 , wherein plasticising agent comprises aluminium silicate with substantial rheological properties. 
     
     
         22 . A method according to  10 , wherein the plasticising agent comprises silicate mineral clay. 
     
     
         23 . A method of forming a shaped article having a matrix containing sintered fly ash, the method comprising the steps of:
 providing in a mould a mixture containing a fly ash composition comprising fly ash and a plasticising agent, the mixture being in a particulate flowable state, and wherein the fly ash composition includes greater than 70% fly ash by dry weight of the composition, and wherein the plasticising agent being capable of binding the fly ash particles in the fly ash composition together on pressing of the fly ash composition;   pressing the particulate fly ash mixture by uniaxial pressing at a pressure of greater than 200 kg/cm 2  in the mould to temporarily bind the mixture to form a green article shaped by the mould, wherein the water content in the green article is less than 12 wt % of the total weight of the green article; and   firing the green article to sinter the fly ash.