TEXTURE AND GRINDABILITY OF THE DUST COMPONENT IN PORTLAND-CEMENT CLINKER

The dust component of portland cement clinker from the rotary kiln is generally less than 250 mum in size and consists of clinker fragments of various sizes, inclusive of separated alite and belite crystals with some interstitial material. In view of the close similarity in chemical composition and microscopic texture, dust grains are supposed to be separated mechanically from the outermost part of clinker nodules weak in adhesion and further fractured into small pieces during percolating toward the core of the moving mass. This process should occur after the complete crystallization of the interstitial liquid that acts as a medium of clinker nodulization. With the dust particles flying in the atmosphere of higher temperature the interstitial material remelts and, on quenching, is transformed into the glassy state; the alite and belite crystals undergo a concomitant texture change on the surface, too. The generation of dust can be depressed if clinkers are fully nodulized and sintered prior to the crystallization of the interstitial liquid in the kiln. The dust component is inferior in grindability to the outer part of clinker nodules. This is due presumably to the difference in grinding hysteresis.