Binder admixture, kaolin product and their manufacture

Abstract

A binder mix containing a hydraulic binding agent and an admixture mixed therewith, a process for preparing a hydraulically hardened binder mass, a calcinated kaolin product and a process for preparing the same. A paste-like composition is formed from the hydraulically hardening binding agent, a pozzolanically reacting admixture and water, which, when so desired, contains stone aggregate or similar filler, the paste-like composition is worked and the worked composition is allowed to harden to form the binder mass. The admixture comprises spherical, porous metakaolin agglomerates, the size of which is 2-200 microns and which have an open pore structure. The invention can be used to improve the manufacturing methods of cast concrete products and shorten the manufacturing times, and to provide concrete with better mechanical and chemical properties, as well as improve the fire and frost resistance of concrete.

1 . Metakaolin agglomerates, the size of which is 2-100 micrometres and which are generally spherical and have an open pore structure, whereby the density of the surface part of the metakaolin agglomerates is lower than that of the inner part, and their pore structure in the surface part and the inner part is essentially the same, the agglomerates being produced by first preparing kaolin agglomerates from kaolin, said agglomerates having an average particle size of about 2-100 micrometres, and the kaolin agglomerates being calcinated into metakaolin. 
     
     
         2 . A process for preparing metakaolin agglomerates, according to which kaolin is treated at a higher temperature to prepare a product having a desired crystal structure, comprising the steps of:
 preparing kaolin agglomerates first from kaolin, the particles being generally spherical having an average size between about 2-100 micrometres, and   calcinating the kaolin agglomerates into metakaolin, whereby agglomerates are achieved which have an open pore structure, surface part density lower than that of the inner part, and essentially the same pore structure in the surface part and the inner part.   
     
     
         3 . The process according to  claim 2 , wherein the kaolin agglomerates are calcinated into the metakaolin phase in a fluid state at least mainly by means of radiation heat. 
     
     
         4 . The process according to  claim 2 , wherein the heat treatment is carried out in a radiation calcinator. 
     
     
         5 . The process according to  claim 2 , wherein the kaolin agglomerates are formed from kaolin slurry, the solids content of which is over 50% by weight, preferably about 60-75% by weight. 
     
     
         6 . The process according to  claim 5 , wherein the kaolin agglomerates are formed by spray drying kaolin slurry. 
     
     
         7 . The process according to  claim 6 , wherein the agglomerates are spray dried in a tower drier. 
     
     
         8 . The process according to  claim 7 , wherein the agglomerates are spray dried in a tower drier, using thermal energy provided by radiation. 
     
     
         9 . The process according to  claim 2 , wherein the agglomerates are classified and agglomerates of different sizes are separately brought to thermal treatment. 
     
     
         10 . The process according to  claim 9 , wherein ionic wind classification is used for classifying the agglomerates. 
     
     
         11 . The process according to  claim 2 , wherein the solids content of the kaolin slurry is adjusted using a method for increasing the solids content, which method is based on an electric field.