Effect of ultrafine slag dosage on chloride and sulfate resistance of blended cement

Abstract

To investigate the effect of ultrafine ground granulated blast furnace slag (GGBS) on the corrosion resistance of blended cement, in this study, the mechanical properties, chloride resistance, sulfate resistance, hydration products and pore structure of a fly ash–gypsum blended cement system were evaluated. The fly ash and gypsum contents were fixed at 10 wt% and 5 wt%, respectively, while the ultrafine GGBS replacement level was varied from 0 to 40 wt%. X-ray diffraction analysis, scanning electron microscopy and low-field nuclear magnetic resonance spectroscopy were used to analyse the hydration products and pore structure under different curing environments. The results showed that ultrafine GGBS improved the chloride and sulfate resistance of the cement system. Within the investigated range, 30 wt% ultrafine GGBS gave the highest 28 days compressive strength of 89.7 MPa, whereas 40 wt% ultrafine GGBS showed the best durability performance, with a chloride ion diffusion coefficient of 1.38 × 10−12 m2/s and a sulfate resistance coefficient of 1.20. The improvement in durability was mainly attributed to the formation of additional C-(A)-S-H gels, pore refinement, chloride binding by Friedel’s salt, and enhanced AFt formation under sulfate exposure.