Grindability of some additions and its significance in the production of mixed cements

Grinding tests were conducted in a laboratory steel ball mill, to investigate the grindability of some natural and artificial materials as "additions" for incorporation in portland cement. Strength tests were performed on mixed cements composed of 71% portland cement clinker, 25% addition and 4% gypsum. In one series of experiments, the components of the mixed cement were separately ground and in another one they were simultaneously ground. It was found from surface production curves and from compressive strength data that when materials which are harder to grind than clinker such as sand are interground with clinker, the resulting cement develops higher early strength than a corresponding cement in which the pozzolanic addition is softer than clinker. For materials which are softer to grind than clinker, separate grinding of the cement components is better than combined grinding, particularly for the development of early strength. /Author/TRRL/