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• Workability of concrete can be improved by using magnesium slag. • Compressive strength of concrete was not reduced with magnesium slag content up to 30%. • Use of magnesium slag can improve the long-term properties of the concrete. Magnesium slag is a byproduct of the magnesium industry. It has not been commonly used in the construction industry due to the poor hydration reactivity and soundness risk induced by a high content of MgO. However, magnesium slag has hydraulic potential for similar mineral compositions to Portland cement. This study aims to investigate the potential use of magnesium slag as a mineral admixture in cement concrete. The influence of magnesium slag content and fineness on the workability, mechanical properties and durability of concrete was discussed. Results showed that the concrete fluidity increased with increasing magnesium slag content. The fineness of magnesium slag in this study showed a slight influence on the fluidity. Magnesium slag was not beneficial to the early strength development of the concrete due to the retarding effect on hydration, but it had a positive effect on the later strength. It could also optimize the long-term properties of concrete with reduced drying shrinkage and an improvement of sulfate- and frost- resistant properties. Finally, as a mineral admixture in concrete, magnesium slag with an optimum content of 30% and a specific surface area of 485 m2/kg was suggested. [ABSTRACT FROM AUTHOR]

• The inhibited mechanism of the nano-SiO 2 on the efflorescence of geopolymer was analyzed. • A negative effect of the efflorescence on compressive strength of geopolymer was found. • The nano-SiO 2 could improve the transport property of geopolymer. To inhibit the efflorescence of geopolymers, nano-SiO 2 particles were used as an additive to modify an alkali-activated metakaolin mortar. In this work, the effect of the nano-SiO 2 on the compressive strength, pore structure and ion leaching of geopolymers was investigated. Based on these results, the inhibitory mechanism of the nano-SiO 2 on the efflorescence of the geopolymer mortar was analyzed. The results showed that the nano-SiO 2 improved the compressive strength and inhibited the efflorescence of the geopolymer mortar. The nano-SiO 2 decreased the efflorescence by consuming excessive alkali ions in the pore solution to form an amorphous gel phase, and the negative effect of the efflorescence on the compressive strength was also verified. Moreover, the pore structure and transport properties of the geopolymer were also improved by the addition of the nano-SiO 2 , which reduced the diffusion rate and leaching of the ions. [ABSTRACT FROM AUTHOR]