MECHANOCHEMICAL ACTIVATION OF MATERIALS IN CEMENT MANUFACTURE

Abstract

Mechanochemical activation has been reported for a number of materials being subjected to jet grinding, such as sand, limesand mixes, slag portland cement, straight cement, bellte slurry, end high alumina cement. Jet grinding has been revealed to improve compressive strength ratings of the cement by 5 to 10 MPa on average. The reason for this increase lies in a more uniform grain size distribution of cement and the modified surface morphology of cement grains which include reentrant angles /1, 2/. This report is devoted to the mechano-chemical activation of cement raw materials and clinkers in jet mills (table 1) operating with two counter streams of material whose particles are accelerated to supersonic speeds by gaseous fluids, air and water steam, carrying them. The grinding of certain raw materials and their mixes in a model MSP-0.5 jet mill provided an almost 100 % yield in the 1-40µm fraction range (table 2). As a result a 100 °C lower temperature can be afforded in the calcination zone of pilot rotary kilns, as compared with the temperatures needed to calcine the ball-mill ground mixes, the respective c linkering rate constant being also increased 2 to 7 times (table 3). The resultant clinkers exhibited an increased dislocation density on the chippings (table 4) which led to a 28-day compressive strength of this cement being increased by 5 to 15 MPa. The largest increment of strength was exhibited by cements prepared from the raw mixes in which one component was jet-grinded (carbonaceous or agrillacious) and the other component was ball-mill grinded, the specific surfaae of the cements being about 3000 cm2/g (table 5). For higher specific surface figures of 4000 and 5000 cm2/g, a certain decrease was noted of the positive effect of jet grinding on cement strength ratings. Moreover, a further grinding of clinkers manufactured from jet milled raw materials, performed in a laboratory jet mill, to a fineness of 4000 cm /g failed to result in an additional increment of strength as compared with the ball milling of the same clinkers (table 5).