Fresh state properties of spongilite blended cement pastes

In this paper, the behaviour of fresh cement pastes modified by two types of spongilite in various addition is assessed with the purpose of exploring a new application of this natural pozzolans as cement mortar additives. The rheological parameters (relative yield stress, plastic viscosity, thixotropy, and fluidity index) were correlated with flow table tests, initial and final setting time of cement pastes supplemented by calorimetric measurements. The fresh pastes behave generally as Hershel–Bulkley fluids with an evolution of the rheological parameters with admixture content. Both spongilites used had a thickening influence on cement pastes despite their different mineralogical composition. They caused an increase in viscosity and yield stress, and a decrease in the thixotropy of the pastes. The spongilites extends the initial and final setting times of cement pastes. As the spongilite content in the cement paste increased, the amount of hydration heat release decreased accordingly. In the pastes with the highest replacement of cement by spongilite (40%), the time of formation of AFm phase from C₃A and ettringite was slightly prolonged.