Low Energy Cements Prepared from Modified SO3 Doped Clinkers

Clinkers doped with optimized combinations of SO3 and Li2O or CuO or MgO were synthetized in laboratory furnace at 1350 °C. Clinkers were characterized by light and scanning electron microscopy. Chemical and phase composition of clinkers is discussed with respect to early hydration properties of cements. Hydration of cement pastes was monitored by isothermal calorimetry and reaction kinetics correlated with early strengths. Flexural and compressive strengths of cements were determined after 2, 7, 28, 90 and 365 days of hydration according to EN 196 on mortars. At high CuO contents, Cu-rich phases form inclusions in C2S. The limited incorporation of MgO into the structure of clinker phases is represented in the form of inclusions in C3S. Due to formation of Cu(OH)2, hydration slows down significantly, while Li salts accelerate early hydration. For the studied modified SO3 doped cements, there is a good correlation between heat development during the first 2 days and strength development during 1 year. Proposed four low-energy cements based on SO3 doped clinkers burned at 100 °C lower temperature meet the requirement for CEM I strengths.