Use of locked-cycle protocol to assess Cement fineness and properties in laboratory grinding mills

Laboratory grinding mills operated for a given time interval 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 normally obtained from real-scale mills. The main objective of this paper is 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 protocol consisted of 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. For given Blaine fineness, test results have shown that cement ground in the laboratory for a fixed time interval possesses wide PSD curves characterized by spread factor n less than 0.96. Conversely, the locked-cycled protocol led to narrower PSD, with n varying from 1.025 to 1.175. Cement ground using the lockedcycle protocol was found to require increased water demand as compared to that ground for afixed time interval. Also, this protocol was found to generate a reducedfraction of particles finer than 1 μ/m, which led to relatively delayed setting times and reduced 1-day compressive strength. The locked-cycle approach led to higher 28-day compressive strength, given the reduced fraction of particles larger than 50 μ/m.PublishedN/