Re-hydration of Thermally Treated Cement Pastes Containing Limestone and Metakaolin

The notable environmental impact of Portland cement concrete manufacture is of great concern, driving the efforts towards the design of sustainable binders with reduced cement component. Here, information about the dehydration of cement pastes containing limestone and metakaolin, and the hydration characteristics of the materials obtained after heat treatment (1 h at 800 ºC), are reported. The analytical techniques used include X-ray diffraction, infrared spectroscopy, scanning electron microscopy, and isothermal conductive calorimetry. The results showed that the dehydration of the studied cement paste fines led to the formation of clinker phases and CaO, with C₂S being dominant. The increase of limestone content in cement resulted in the formation of lower amounts of clinker phases, while less CaO formed in the thermally treated paste containing metakaolin. The re-hydration process was accelerated with the increasing limestone content in cements, but it was considerably delayed in the case of the thermally treated blend with metakaolin. Re-hydration of the thermally treated fines resulted in the recovery of the hydrated phases, and it was characterized by increased formation of Ca(OH)₂ and adsorption of water, as well as by the formation of C-S-H with less polymerized silicate chains, compared to the original cement paste fines.