Effect of Large Amounts of Supplementary Cementitious Material on the Hydration of Blended Cement

Abstract

The influence of high-volume supplementary cementitious materials (SCM) on the hydration of portland cement was investigated. Usually, the application of SCM in portland cement systems is motivated by a sustainable consumption of raw materials and energy resources. Therefore, two types of zeolites have been used as SCMs: a natural zeolite and synthetic zeolitic waste. Moreover, 4% by weight of inorganic cement accelerators (either Na2SO4 or NaCl) was included. The influence of high-volume zeolites (50% by weight) and accelerators on the main hydration properties of portland cement pastes, hydration temperature, compressive strength, mineral composition, and microstructure of hardened cement paste, was investigated. The incorporation of zeolites as SCMs led to an abrupt 45% decrease in the strength of the early hydration stage (7 days) of the hardened specimens, while after 28 days it was only 18%. In all cases, the natural zeolite resulted in significantly higher compressive strengths than the synthetic zeolite after 28 days of hydration. The lower strength of the specimens containing synthetic zeolite seems to be related to the formation of large hexagonal stratlingite crystals, whereas in the specimens including natural zeolite these crystals were not observed. On the other hand, the accelerators improved the 7-day compressive strength. Hence, the usage of zeolite as high-volume SCM brings both ecological and economic benefits, while maintaining satisfactory mechanical performance of the specimens.