Role of the filler on Portland cement hydration at very early ages: Rheological behaviour of their fresh cement pastes

The rheological behaviour of fresh Portland cement (PC) pastes with different chemical and potential mineralogical compositions was analysed when were blended with crystalline mineral additions (fillers). These two fillers were very different: a siliceous, Q, α-quartz type, and another limestone, C. Trials were conducted during latent hydration at 25 °C. The findings showed that apparent viscosity was higher in the PC with low C3A and high C3S content, consequently, the Na2Oeq.(%) content of everyone also contributed very significantly. Moreover, it was also observed that the incorporation of each filler affects differently the rheological behaviour of fresh cement pastes. The different influence is due to the different physical and chemical properties of each filler (nature, chemical composition and character and texture intimate of the particles), and also of the type of PC to interact. Finally and at these very early ages, both fillers stimulated the hydration of the PC which they were mixed by direct and non-direct way, and in the case of C filler by indirect way as well, but without any pozzolanic activity. Despite the fact that blended cement P1/Q 60/40 has proved to be a “false positive” in Frattini test.