Effect of particle size and slag content on the early hydration of interground blended cements

Three blended cements prepared by intergrinding 6–35% slag with clinker and gypsum, and a control portland cement, were sieved to yield 0–10 μm, 10–30 μm, 30–50 μm, and >50 μm subgroups. Clinker/slag/gypsum contents, and oxide compositions of the subgroups differed significantly from the unsieved cements. Fine subgroups always contained more gypsum and had lower slag-to-clinker ratios than coarse subgroups. Heat evolution was investigated up to 48 h using isothermal calorimetry. Contribution of slag to early heat evolution was limited. 0–10 μm particles evolved up to 5–10% of their heat in the first 30 min. Particle size affected the peak rate of heat evolution but not its timing. A linear relationship was observed between heat evolved from 0 to 24 h and from 24 h to 48 h. Median size or slag content of subgroups affected the positions of data points on this line. Heat evolved up to 24 h (or 48 h) was found to be closely related to particle size. Rate of heat development does not appear to be strongly influenced by particle size above ∼30 μm.