Effect of nucleation seeding and triisopropanolamine on the compressive strength, chloride binding capacity and microstructure of cement paste

Free chloride ions in concrete can lead to serious corrosion of steel and properties deterioration of reinforced concrete structures. A successful control of free chloride ions is significant to the service life of concrete structures. In this work, the combination of triisopropanolamine (TIPA) and C–S–H seeds is used to improve the chloride binding capacity of cement paste as well as its compressive strength. Results show that the compressive strength was enhanced due to the early nuclei effect of C–S–H seeds and promotion of TIPA to hydration. The mineralogical composition and microstructure analyses demonstrated the improved chloride binding capacity of the cement paste to free chloride ions is mainly due to the formation of Friedel's salts phase and the physical adsorption behavior of gels. TIPA promotes the hydration of aluminum-containing minerals, indirectly contributing to the formation of Friedel's salts. The compactness of microstructure of cement pastes is improved by using TIPA and C–S–H seeds, contributing to the physical adsorption of free chloride and inhibiting its migration. This work provides a feasible approach for the effective control of free chloride in cement/concrete.