Effects of incorporating large quantities of nickel slag with various particle sizes on the strength and pore structure of cement-based materials

Abstract

Firstly, nickel slag sand with a concentrated particle size distribution in the range of 2.36–0.60 mm was used to replace the mechanism sand in the ratio of 0%, 25%, 30%, 50%, 70% and 100%. Second, partial particle size substitution was used to partially replace nickel slag sand with particle sizes of 2.36–1.18 mm and 1.18–0.60 mm in proportions of 0%, 30%, 50%, 60%, 70% and 100%, respectively, to optimize particle gradation of mixed sand. Cement mortar specimens were prepared using different mixed sands composed of the above two substitution methods and at a water-cement ratio of 0.5. Then, the effects of nickel slag sand with varying substitution methods on the strength and pore structure of cement-based materials were investigated by mechanical tests, mercury intrusion porosimetry (MIP) and scanning electron microscopy (SEM). Standard sand was also used as an experimental control group. The experimental results revealed that the maximum flexural and compressive strength of nickel slag sand using a full-size substitution group corresponded to an optimal dosage of 30%, while the optimal dosage of nickel-slag sand using a specific-size substitution group was 60%. The water absorption of the two particle sizes replaced the specimens decreased and then increased with the inclusion of nickel slag sand. The results showed a consistent trend with the variations in electrical resistivity and total porosity of MIP. From the SEM photographic results of the SS, MS, NF30 and NP60 specimens, the cement paste can be more tightly wrapped around the round spherical nickel slag particles. NF30 and NP60 specimens showed a denser internal structure, multi-dimensional hydration products and a lack of pores and microcracks, which is fully consistent with experimental results of mechanical properties and microstructures.