Development of new grinding method to assess fineness of cement in laboratory conditions

Abstract

Laboratory-grinding mills are widely used in the cement processing industry to assess the various parameters affecting comminution of clinker. Nevertheless, such mills are normally operated for given time interval and do not consider the effect of circulating load (CL), thus generating excessively wide cement particle size distribution (PSD) curves that are not representative of what is obtained from real-scale industrial grinding mills. This paper is part of a comprehensive research project undertaken to develop a locked-cycle protocol that takes CL into account and mimics the clinker grinding operations encountered in closed-circuit industrial ball mills. The approach developed was inspired from the well-known Bond grindability test used in the mineral industry to express the ores resistance to crushing. The protocol consisted on screening the laboratory mill content after each grinding run to remove undersize, which is then replenished with an equal mass of new clinker until CL becomes constant. As shown in Fig. 1, test results determined for given Blaine fineness have shown that cement ground in laboratory for fixed time interval possesses wide PSD curve characterized by spread factor (n) less than 0.96. Conversely, the locked-cycled protocol led to narrower PSD with n varying from 1.092 to 1.176 for cement mixtures possessing Blaine fineness of 3425 and 2880 cm2/g, respectively. Cement ground using the locked-cycle protocol was found to require increased water demand, as compared to the one ground for fixed time interval. Also, this protocol was found to generate reduced fraction of particles finer than 1 µm, which led to relatively delayed setting times and reduced 1-day compressive strength. The locked-cycle approach led to higher 28-days compressive strength, given the reduced fraction of particles larger than 50 µm. Particular emphasis and discussion was placed to assess and validate the effect of amine-based grinding aids on the proposed protocol. (PDF).