Mechanical properties and hydration process of steel slag-cement binder containing nano-SiO2

Research on low-heat cement (LHC) was significant for the preparation of mass concrete. However, the low early strength was one of the difficulties during the engineering applications. In present study, steel slag (SS) was used to produce LHC, and nano-SiO2 (NS) was added to promote the early strength development. Cement was replaced by SS, and NS was further added into the cement-SS binder. Setting time, fluidity, and compressive strength were researched; hydration process and hydrates were also studied by hydration heat, hydration temperature, XRD, TGA, and NMR; microstructure was characterized by MIP and SEM. Results showed that SS reduced the early hydration heat of cement significantly, and meanwhile the compressive strength was reduced and the porosity was increased obviously. However, the addition of NS into cement-SS binder promoted the early strength, which was equivalent to that of single cement, and more importantly the increase on hydration heat and hydration temperature was few. The use of SS reduced the Ca(OH)2 content of cement due to the dilution effect; the addition of NS decreased the Ca(OH)2 content of cement-SS binder owing to the pozzolanic reaction. Indeed, the hydration degree between cement and cement-SS-NS binder was very close. Furthermore, the harmless pore volume of cement-SS binder was increased evidently because of the addition of NS. This research proved that reactive nano materials was efficient to promote the early strength of LHC.